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6
0 30 60 90
SULPHATE Loading to Lake Water (Kg/ha/yrl
Figure 28. Effects of various sulphate loading rates on lake pH for lakes in
very sensitive (1) and somewhat less sensitive (2) surroundings in
Sweden. Added points are for: (•) Florida (Crisman and Brezonik,
1980); (o) Como Creek (Lewis and Grant, 1979); (&) Hubbard Brook
(Likens et al., 1977); and (x) Norway (Wright and Snekvik, 1978).
(modified from Aimer et al., 1978).
Figure 15. From Anon. (1981).
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Sulfur Ofagenesis
George R. Holdren
Until I came on this trip, I felt that there were a number of elements
for which there was some hope of getting a reasonable deposition rate from
a sediment core, of learning something about their deposltlonal history.
Now, having watched Merrill HIte and Richard Carlgnan, and from what I've
understood talking to Steve Elsenrelch, the trace metals, the transition
metals, and trace organIcs are moving around a lot. So there are fewer
things you could really attack for Information. My Interests Involve
looking at chemical dlagenesis, that Is, at those things for which you
cannot just take a dated core, and obtain a concentration at a given depth
to learn something about either the timing or the magnitude of Increased
deposltonal fluxes because of post-deposit tonal changes In the distribution
of that particular element. All of the changes that I am talking about are
lumped into a category which we can call chemical dlagenesis. Chemical
dlagenesis can be put into one of two categories. First, we can change the
chemical form of a substance, for example, changing iron oxide to an iron
sulfide or changing an amI no acid into ammonium ion. These reactions
change the chemical form, but may not necessarily affect the distribution
of the element. The other part of chemical dlagenesis, and the part that
I'm going to concentrate on, Is the redistribution of the element within
the sediment column. It Is really this aspect of diagenesis which, for
certain elements, can make time reconstructions very difficult.
If we look at the mobilization and redistribution we can categories
the reactions into several types of processes. There are the physical
processes such as the resuspension which Dr. Jerome Nriagu was talking
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178
about, and bioturbatlon, Involving organisms mixing the top part of the
sediment column, In which they are living. These processes can be
understood by comparing the distributions of elements with things like
Cs or Pb. We can have some Insight Into what the magnltlde
of these physical redistributions are by using these short living time
tracers.
The chemical aspect of remoblIIzatlon is something which Is a more
complex. It Involves the transport of an element through the pore water.
The process may result In significant redistribution of the element within
the sediment column. Now what two things drive the chemical mobilization
and redistribution? We need activity gradients In the sediment pore waters
to get transport. Other things being equal, you need changes in pore water
gradients as a function of depth within the sediment column to get net mass
accumulation or mass depletion from the sediment solids. The larger the
gradients and the greater the changes In the gradients, the greater the
mass redistribution Is going to be.
There are some common examples of the types of dlagenetic changes
which occur. In marine systems, suI fates have been studied extensively
(Figure I). On the left hand side of Figure I Is the pore water
Information. These profiles then generate the corresponding sediment
solids profiles. We can get these profiles In different forms. I have
generalized them, however. Into three categories here. We can get new mass
added to the system, as In the case of sulfur in marine systems. Here, we
have sulfate coming Into the sediment where It Is mlcroblally reduced to
hydrogen sulflde. This, consequently Is turned into acid volatile sulfides
and pyrlte. These species Increase In the sediment solids as a function of
depth.
A depletion or net loss of mass from the sediment column occurs In the
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179
case of silica. Here, we normally have low overlying water concentrations
of dissolved silica which Increase to several hundred mlcromoles within the
pore water over an 8-10 cm depth before leveling off. This Is a result of
the dissolution of biogenlc silica. As It dissolves, dissolved silica Is
transferred down the gradient and out of the sediment. This results In
mass lost from the sediment.
There Is a third broad classification of dlagenetlc redistribution.
There Is no net change In the total Integrated mass In the sediment column.
This Is Illustrated by a species such as where there Is dissolution of the
solid below the oxlc zone, and repreclpltatlon In the surface zone, and/or
at depth. This produces a profile with relatively large concentration of
dissolved manganese at some depth, and lower concentrations at the surface
and below the concentration maximum. The solid profile is a mirror Image
of that of the dissolved species. With this process, there Is no net gain
or loss of mass from the system, Just a redistribution of that mass within
the sediment column.
To summarize, there are two main points to figure I. The solid phase
gradients are passive actors. They are a reflection of what Is going on
or has gone on. Second, the solid phase gradients mask changes In
historical Inputs which we are trying to get, either directly or
Indirectly, from the study. All of the action Is happening In the pore
water, as reflected by the pore water gradients. These gradients are the
things that drive the mass transfer processes. So, by studying these
gradients, you can gain an Idea about the rates of those reactions which
are affecting the distribution processes.
If a species is chemically active this should be reflected In pore
water gradients of the species. For obtaining historical Information from
lake sediments In regions which are receiving acidic Inputs, the big
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180
question Is: are chemical dIagenesis and redistribution significant enough
to warrant studies? Are there enough dIagenetic changes to suspect that
these might be having a significant impact on the shapes of the sedimentary
profiles? Or. Richard Carigan suggested that this was the case with the
trace metals. However, until now, there have not been many studies which
have addressed this question directly, and, in most literature, one finds
that the presumption has been that the concentrations and the concentration
activity gradients are too small to drive significant redistribution.
If, as I maintain, post-deposittonal redistribution Is significant,
the next question Is how do we deal with it? Because pore water
redistributes species over many centimeters, we get a smearing of the
historical record over that zone where you see the gradient. Under these
conditions, we need some way to unsmear the record or, otherwise, deal with
that problem. One way to approach this Is through the use of the
dIagenetic equation (Figure 2). For pore waters, this describes the
concentration of the species as a function of time and depth. The equation
Includes terms for dlffusional transport, for burial plus other advective
processes (e.g.. In seepage lakes, it would be the groundwater influx into
a lake), for removal of a species from the pore waters by precipitation or
microbial uptake reactions and for production of the dissolved species from
the sediment solids. For any particular element we need to know what each
of these terms are to solve the dlagenetic equation.
For sulfate, In most systems which have been studied, the production
term, P, can be assumed to be smalI and thus it can be ignored, and the
removal terms are used to describe observed changes In the profile. Here
removal rates are proportional to the dissolved sulfate concentration in
the pore waters (Cook and Schindler, 1983). If we solve the dlagenetic
equation using a first-order removal term, we can calculate a profile for
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181
sulfate under steady-state contIons (I.e., assuming no time dependent
changes In the concentration of sulfate as a function of depth). The
result Is Illustrated In Figure 3.
If all the action Is happening In the pore water, and changes In these
gradients give us the changes In mass accumulation as a function of depth
In the sediments, we can match these changes In the pore waters with
changes In the solids. The dlagenetlc equation which describes the solids
profile Is somewhat analagous to the previous equation (see Figure 2). In
this equation, the first term describes the biological mixing, I.e.,
bioturbatlon. The second term describes burial, but, unlike the situation
with the pore waters, this does not Include evectlve processes like
seepage. Presumably, the solids are not mobile In this fashion. The
reaction term, which Is taken from the change In the sulfate gradient, plus
time dependent changes which occur with the detrltal component. Solving
this under steady conditions, we end up with the solid sulfur
concentrations as a function of depth. For any given time or depth, the
sulfur concentration Is equal to the detrltal plus the dlagenetlc
contribution from the dissolved sulfate (Figure 4).
If everything is being driven by reactions In the pore waters, how do
we get at the pore water Information? There are three ways that have been
used to obtain pore water data. Squeezing and centrlfugatlon are two
techniques which have been used a fair amount In the past In various
sediment pore water studies. There are certain advantages to these
techniques. You can extract large volumes of pore water; in fact, you can.
In many cases, extract as much as your patience allows. Secondly, you
retain the mud from which that water was extracted.
There are some disadvantages of these two techniques. Both methods
are prone to significant oxygen and temperature effects. Anything that Is
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182
oxygen sensitive (Iron, manganese, phosphorous, hydrogen sulflde, sulfate,
and silica) respond to changes In or exposure to atmospheric oxygen. To
minimize these effects requires extensive glove bags, or boxes for sampling
handling. The temperature effect results In essentially an Ion exchange
effect. As one Increases the temperature, Ions desorb or dissolve from the
solids. For certain things like silica, changing the temperature from
8°C to 18°C results In a doubling of the amounts of dissolved
silica In the pore waters (Matlsoff, 1978). The set-ups to minimize both
temperature and oxygen effects are large and costly. Sampling is
relatively slow for the squeezing, requiring 60-90 minutes per sample
unless you have a huge bank of squeezers. Sampling time Is a little bit
faster for the centrtfugatlon, but still a time consuming process. These
methods become increasingly cumbersome If you're trying to prepare samples
In the field. It's very difficult to get the equipment to a remote lake.
A third approach, and one that Is becoming quite popular, is a method
called peepers or pore water equiIIbrators. These devices have several
advantages. They are very easy to work with. Essentially, they consist of
a dialysis bag In a rigid frame. When you retrieve it, you only have water
present, so you won't have to worry about the temperature effect. Also,
these devices can be sampled quickly. Typically, In our set up, which
consists of 24 or 26 samples, complete sampling can be done from start to
finish In about 12 minutes. Still, the oxygen effect Is evident, but the
approach Is better than squeezing because we have some control over it.
There are some disadvantages, too. Once you put these in the field. It
requires several weeks for the water to equilibrate. The exact amount of
time depends upon the length of the diffusion path. For example, If you
have a 1 cm long diffusion path in a cell, the device needs about 3-4 weeks
to equilibrate to within 95% of the actual composition. Also, If you
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183
require sediment solids, a core must be obtained separately, and this can
raise reasonable questions as to whether the mud Intervals are equivalent
to what the peeper Intervals were looking at. That Issue Is something
that's difficult to answer. The cost of a peeper Is about $500 per peeper
frame, making It comparable to or cheaper then the other two methods. Now,
back to the main topic.
How does the sediment dIagenesis apply to estimating the timing or
magnitude of Increased deposltlonal fluxes to remote lakes. If we look at
sulfate, the major an Ion In modern precipitation, we can study dissolved
sulfate profiles In the pore water to estimate Its mobility. Typically we
have high concentrations In the overlying water, which decrease with depth
In the sediments. Based on these gradients and changes In the gradients
with depth, we can calculate the transfer of the sulfur from the lake water
phase Into the sediment solids. The factors controllng this transfer
Include the concentration of the SO " In the lake water, the rate
of sediment deposition, the activity, diversity, and density of Infaunal
organisms, and several general chemical factors.
To calculate a mass balance using the dlagenetlc equations we need the
rate of sulfate uptake by the sediment micro-organisms regardless of the
details of the specific reaction. We can get this directly from the
dissolved sulfate profile In the pore water. Second, we need the sediment
deposition rate. Third, we need the dissolved sulfate profile (absolute
concentrations, as well as the gradients.) Fourth, we need the detrltal
sulfur Input to the sediments, and finally, we need Information about the
biological mixing coefficient of the surflclal sediments.
We need to know these things as function of time. Here we are stuck,
because there Is no good historical Information on any of these parameters.
For example, what was the lake water sulfate concentration In 1920? How
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184
was the mlcroblal activity different then from what It Is now? How does
the detrltal sulfur Input differ between 1920 and now? Because there Is no
really good way to obtain these data, the best that we can probably do Is
study sediments at a lake In an area receiving acidic precipitation but not
suffering drastically from those acidic Inputs. That Is, we should study a
lake In which the pH of the water Is still 6-7. In doing this, we can
hope, at least, that the micro-organisms haven't been severely stressed by
reductions In pH, and that they are responding to their environment in
about the same way as they did prior to acidic deposition. Under these
conditions the two remaining significant unknowns are the detrital Inputs
and the lake water sulfate concentrations as functions of time.
Before presenting the detailed results of the calculations, let's
first describe, in general, the types of profiles which might be expected
from 1) a normal, steady-state sulfate Input and 2) how perturbations of
this input affect the solids' chemistry (Figure 5). If we stimulate the
bacterial incorporation rate, Increase the lake water sulfate
concentration, or decrease the sedimentation rate, we get an Increase in
the total sedimentary sulfur concentration. With time, this would lead to
some new steady state profile as it gradually gets buried in the sediment.
On the other hand. If we Introduce a lot of acid to suppress mlcroblal
processes. If the sedimentation rates are Increased Cas might happen
through logging and Increased erosion], or if we decrease lake water
sulfate concentrations, the result is a decrease In the total sedimentary
sulfur In the surface sediments. We can also get combinations of these two
situations (Figure 6). We could hypothesize a situation where there Is an
Increase in the sulfate loading prior to a substantial depression of the
pH. In this case, we might expect to find an Initial Increase in
sedimentary sulfur followed be a decrease In surflcial sediments as the
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185
mlcroblal activities become depressed.
Consider Grass Pond, In the Adirondack Mount tans of New York, a lake
that has a near neutral pH, ca. 6.5, and look at the total sedimentary
sulfur profile (Figure 7). In the deep sediments, sulfur contents are
about 0.25%. This value Increases up to about 0.6, the maximum being at a
depth of about 5 cm. The concentration, then, declines to the surface.
This profile Is something you would expect to observe with an Increased
sulfate loading.
The dissolved sulfur profile for Grass Pond Is Illustrated on figure
8. The heavy line Indicates the sulfate profile, the lighter line
Indicates the hydrogen sulflde profile. We can use these data to derive
-9
the first order rate constant for sulfate asslmiltlon (k = 3 x 10 ).
In contract, the sulflde gradient Implies that mass Is moving up through
the sediments. However, this transport Is less than about \5% of the
downward sulfate transport, so we can Ignore this reverse flux.
The next problem Is to evaluate the sulfate boundary condition. We
assume the lake water sulfate concentration to be constant through time.
One thus obtains the expected steady-state profile. Then, we can envision
various sorts of Increases In the loading rates (figure 9). For example,
there could be a long gradual Increase, followed by a more rapid Increase.
We could attempt to model responces (figure 9) to WW1 and WW11. From this,
you can see that the boundary condition Is really the great unknown.
Clearly, we don't know what the actual boundary condition Is. However, the
way we've decided to model It Is to assume some steady sulfur Input through
time to some point at which loadings begin to Increase. Then, In 1965,
when we start having some good trend analyses available, (loadings have
been constant to within 2Q% since 1965) have it stabilize at present day
conditions. We can vary the time of onset of increase and use these
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186
various boundary conditions to calculate total sedimentary sulfur profiles.
I have assumed that the the detrltal sulfur Inputs have been constant
through time. The last figure shows some typical examples of the results.
The data points are shown. Line 2 is the steady state profile, and the
other lines were calculated using the boundary condition shown In the
previous figure. Assuming that the increase of SO/" started In
1950 results In curve b; curve c assumes an Increase starting In 1935, and
curve d corresponds to an Increase starting In 1920. Clearly, the 1935
onset date fits the data best. Remember all that has been done here Is a
mass balance calculation. We've taken the gradients that were found In the
pore waters to calculate the mass transfer of sulfur Into the sediment.
Finally, we compared those profiles with the actual distributions In the
sediment. We can also use modelling and balancing approach to estimate
pre-anthropogenic sulfate concentrations In the lake. Our current
estimates are somewhere In the neighborhood of 10 mlcromolar. In other
words„ we think that there as been about an 8-fold Increase in the rate of
sulfur delivery to the lake.
(tow, if the sulfur mobility had been Ignored, and we had just compared
210
the excess sulfur directly to the Pb, then we would have estimated
an onset of about 1880-1890. That's based on depth where we first observe
the rise above base level for the total sulfur concentration. If we
consider sulfur mobility however which allows that essentially modern
sulfur diffuse Into older, deeper sediments, the estimate for the time
since onset Is cut about In half, or to about 1930.
This is just one example of an approach that can be used to unravel
depositional histories In complicated, chemically reactive sediment
systems.
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Trace metal diffusion across the sediment-water Interface:
Implications In the chronological Interpretation of
dated trace metal sediment profiles.
Richard Cartgnan
Dated sediment profiles are often used to recontruct the deposition
history of anthropogenic pollutants. For example, the rapid increase in
concentration of several trace metals (Pb, Zn, Cu, Ni, Cd, Ag, and others)
observed in the more recent (100 y or less) sediments of many lakes has
generally been attributed to the Increased atmospheric emission and subsequent
deposition of these trace metals. While trace metal profiles collected in
circumneutral lakes generally show a maximum at the surface, the most recent
sediments of acid lakes typically show a concentration maximum located one to
several cm below the sediment-water Interface. In acid lakes, this superficial
decrease in trace metals has usually been interpreted as a result of their
recent acidification. According to this interpretation, subsurface maxima
could be explained either by the leaching of superficial sediments by acidic
overlying waters, or by a decreased sedimentation of some trace metals due to
their increased solubility in acidic waters. The objective of this
presentation is to show that at least another mechanism, which Is independent
of hypothetical past changes in acidity, can lead to the formation of trace
metal profiles having subsurface maxima.
Recent observations on porewater trace metals In acid lakes of the
Sudbury (Ontario) and Quebec (Quebec) regions show that the downward diffusive
flux of trace metals across the sediment-water Interface can account for a
major part of trace metal accumulation by the sediments. Moreover, trace
metals can be diffusively transported several (2-5) centimeters below the
sediment-water Interface. Such a mechanism is Illustrated in fig. 1, where
profiles of porewater and total Ni collected at a depth of 15 m in Clearwater
-------
199
Lake (Sudbury) are presented. At this site, a steep porewater Ni concentration
gradient (2.0 x 10 umol.cm .cm ) is present between I and 4 cm below the
sediment-water interface. Assuming steady state conditions and using Pick's
first law, as applied to the sedimentary environment (at 10 °C), it is
calculated that such a concentration gradient should support a downward
—2 —1
diffusive flux of 16.3 ug.cm ,y . At the same site, the recent accumulation
2 10
rate of Ni in the sediments, estimated from Pb sedimentation rate and total
—2 —1
Ni amounts to approximately 17 ug Ni.cm .y . In this lake, similar
calculations for Zn and Cu yield similar results. Diffusion is therefore a
major mechanism by which these sediments accumulate trace metals. The
porewater Ni profile also shows that the Ni concentration gradient is linear
between 1 and 4 cm and vanishes around 4 cm, where the Ni++ presumably
precipitates as millerite (NiS). The linear gradient indicates that most of
the diffusing Ni is transported down to 4 cm below the interface (Pick's
second law), where it accumulates and forms the observed peak in total Ni.
Chronological reconstructions of trace metal deposition in lake
sediments are usually based on the assumption that diffusive transport is
negligible within the sediment column. The above results show that diffusion
should not be ignored in acid lakes. Chronological reconstructions, and their
interpretation in a recent acidification context, should therefore be
considered with caution in the absence of a good knowledge of trace metal
diagenesis in recent sediments.
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30
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POREWATER Ni (pm)
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1000 2000
TOTAL Ni(ppm)
Figure 1: Total ( O K and porewater ( • )
Ni in the sediments of Clearwater lake.
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201
Stable Isotopes
Gerald Matisoff
Stable isotopes are perhaps the ideal tracer for geochemical processes. The
reason is that, in order to trace a particular element, the best thing to use is a
tracer of that element itself (i.e., a different isotope of that element). In
essence, stable isotopes have tremendous potential for use for just about any kind
of tracing process. In fact, carbon, oxygen and hydrogen isotopes have been used
extensively to study many geochemical, biogeochemical and biological processes.
The sketch in Figure 1 illustrates a situation of particular interest to
paleolimnologic studies in remote lake regions. Lead, nitrogen and sulfur are
released from industrial sources, undergo long range transport, and are deposited
in a remote watershed. The record preserved in the lake sediments also reflects
contributions from within the watershed and all processes which occur within the
watershed and lake prior to and after deposition. Of particular interest are the
isotopes of sulfur, nitrogen and lead which may be used to identify the sources of
these materials. It is hoped that these isotopes can also be used to determine if
the source material is from automobile exhaust or a particular coal burning unit,
and the percentage of the lead sourced from within the watershed and from the at-
mosphere. There is essentially no work at all on nitrogen isotopes in paleolimnologic
studies, although there is an increasing amount of literature about nitrogen isotopes
in the marine environment. Here, I will present a review of lead and sulfur isotopes
in paleolimnology.
Lead isotopes are derived from the uranium and thorium decay series. U-238
q
undergoes a decay to lead-206 with a half-life of 4.5 x 10 yrs. Lead-206 comprises
0
about 23.6% of all lead. U-235 has a half-life of 7.1 x 10 yrs and undergoes decay
to lead-207. Lead-207 comprises about 22.6% of all lead. Thorium-232 has a half-life
of about 1.4 x 10 yrs and undergoes decay to lead-208. Lead-208 comprises about
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202
Figure 1. Cartoon illustrating the sources and long range transport (LRT)
of sulfur, nitrogen, and lead to remote lakes.
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203
52.3% of all lead. Finally, lead-204 makes up about 1.5% of all lead. It has a
half-life of about 10 yrs, so for most purposes it is constant. Natural geological
variations in the uranium to thorium ratio and the different half-lives of the
parents of the lead isotopes have resulted in significant variations in the lead
isotope ratios in different geological materials. The half-lives are sufficiently
long, so that for paleolimnologic work lead isotope ratios can be used as conser-
vative tracers of the source materials. Lead-208 represents about half of the lead
and would be particularly valuable to study. Since it's derived from thorium as
opposed to uranium, there is the additional problem in that any difference in lead-208/
lead-204 ratios might also reflect differences in the uranium to thorium ratios in
the starting materials.
Figure 2 shows the lead-208/lead-204 and lead-207/lead-204 ratios versus the
lead-206/lead-204 ratio in surficial sediments. The data are about 10-15 years old
and are from a variety of sources. Note that the data tend to fall on a straight
line in both tri-isotope plots. The reason is fairly straightforward. As U-238
in the starting material increases, U-235 in the starting material also increases
because the uranium proportions remain approximately the same. Similarly, the decay
products of those will also increase. However, in terms of geological materials,
such as basement rocks, the data may not necessarily follow a straight line because
the materials consist of a very large age range. Data of interest in Figure 2 are
those surficial grab samples from Lake Superior, the Canadian Shield, Hudson Bay,
Great Bear Lake, and Great Slave Lake. Note that these samples exhibit very high
lead-206/lead-204, lead-207/lead-204 and lead-208/lead-204 ratios. The lead
isotopic composition is more a function of age of source areas for the sediment
than of rock type because the source rocks contain significant quantities of U
and Th relative to lead. As a result, these sediments from Precambrian terranes
exhibit the high isotope ratios.
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Fig. 2 207Pb/204Pb and 20BPb/2<)4Pb versus 2nf> Ph/204 Pb for sediments ol
Cenozoic age from various localities rprom rjoe 1970)
Area or
Symbol
Description
A Pelagic sediments of the Red Sea and basins of the Atlantic,
Antarctic, and Indian Oceans except for the Gulf of Aqaba,
HCI soluble lead
A Sediment from the Gulf of Aqaba. HCI soluble lead
P Pelagic sediments from the Pacific Ocean basin, HCI soluble lead
ST-GC Calcareous clastic sediments from the Salton Trough and a
manganese nodule from the Gulf of California:
o HCI soluble lead
• residue lead
B Sediments from the Baltic Sea:
x HCI soluble lead
Sediments from Lake Superior in the Canadian Shield:
D HCI and water soluble lead
• residue lead
HB Sediments from Hudsons Bay in the Canadian Shield, HCI
soluble lead
GSL-GBL Sediments from Great Bear Lake and Great Slave Lake in the
Canadian Shield:
+ HCI soluble lead
V Sediments from the Mediterranian Sea, HCI soluble lead
ro
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205
The lead isotopic composition of ores from the Mississippi Valley district are
shown in Figure 3. Note that the lead isotope data exhibit considerable overlap
with some of the Precambrian rocks from North America and Cenozoic sediments from
Precambrian terranes, but are significantly more radiogenic (higher ratios) than
Cenozoic and Mesozoic igneous rocks anywhere in the world.
A literature search reveals that the vast majority of lead isotope studies
in recent sediments has been performed by Patterson and his co-workers. They report
that the lead-206/lead-207 ratio in most lead ores is in the range of 1.19 to 1.25
(Table 1). In Missouri lead ores the ratio is much higher, 1.28 to 1.33 They
note that the proportion of U.S. lead ore consumption provided by the use of Missouri
lead ores has increased from 9% of the lead in the U.S. in 1962 to 82% in 1976.
The question with respect to paleolimnologic work is whether or not this change
in the source material will cause a change in the isotopic composition of atmospheric
lead, and consequently result in downcore changes in the lead isotopic composition
in remote lakes. There is very limited data for the isotopic composition of atmos-
pheric lead. Chow et_ al. (1975) report an atmospheric lead-206/lead-207 ratio
~1.15 before 1967 which closely reflects the lead from outside the Missouri district.
They report that the ratio increased to ~1.20 by 1974 and to ~1.23 by 1977.
Shirahata et^ al. (1980) examined the isotopic composition of lead in sediments
from a remote lake from the High Sierras. Figure 4 is their plot of the lead-206/
lead-207 ratio leached from pond sediment humus as a function of the date of deposi-
tion. Superimposed is the atmospheric lead data previously discussed (Table 1).
Note that prior to about 1960 the lead isotopic ratio was around 1.15, reflecting
a source that certainly was not Missouri lead. After 1960 there seems to be an
increase in the lead-206/lead-207 ratio in the most recent sediments. A better
defined increase in that ratio was observed in coastal California sediments. This
indicates that the change in source lead is recorded in remote lake sediments.
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whole-rocks
from north america
Cenozoic sedi-
ments from pre-
cambrian terranes
of the world
Cenozoic and mesozolc
igneous rocks of the world
Cenozoic sediments from precambrian
terranes of the worldv
Precambrian whole-rocks
from north america
Cenozoic and mesozoic igneous
rocks of the world
18/3
20.0
24.0
Fig.3 207Pb/204Pb and 208Pb/20*Pb versus J06Pb/JO*Pb for extremes and means
of four Mississippi Valley districts: 1 Illinois-Kentucky fluorspar district;
2 Southeast Missouri lead belt; 3 Tri-State zinc
district; 4 Wisconsin-Illinois-Iowa lead-zinc district,
For comparison, enclosed areas include the kinds of
data as labeled (from Doe, 1970).
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207
Table 1. Pb/ Pb ratio in lead ores and atmospheric lead.
Data from Shirahata et al. (1980).
206Pb/207Pb JL Year
Most Lead Ores: -1.19 - 1.25
Missouri Lead Ores: -1.28 - 1.33
U.S. Ore Use: 95? 1962
21% 1968
57% 1971
825? 1976
Atmospheric Trend: -1.15 < 1962
(California)
-1.20 1974
-1.23 1977
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208
1.280 -
1.260 -
1.240 -
1.220
1.180
1.160
1.140
NATURAL LEAD IN POND SEDIMENT
SILICATES AND NATURAL LEAD LEACHED
FROM PONO SEDIMENT HUMUS
\\\\\\\\\\\\\\\\\
ZONE OF EXTRAPOLATED VALUES FROM OLD SEDIMENT
\\\\\V\\
ANTHROPOGENIC
ATMOSPHERIC
LEAD
_ EXCESS LEAD LEACHED FROM
PONO SEDIMENT HUMUS
1900 1920 1940 I960 1980
DATES OF DEPOSITION IN THOMPSON CANYON
Fig. 4 Pbio*/Ptr07 ratios in excess leads leached from pond sediment humus, natural lead in pond
sediment silicates, natural lead leached from pond sediment humus, and atmospheric lead deposited in
Thompson Canyon correlated with dates of collection in Thompson Canyon.
From Shirahata et al. (1980).
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209
Another interesting point is that if the lead in the most recent sediment was derived
strictly from atmospheric lead then it would not be possible to use lead isotope
ratios to distinguish between old silicate material and the current anthropogenic
component because there is an overlap of the values. The old silicate material has
very high lead-206/lead-207 values C-L'25), while current atmospheric values are
also very high (~1.24).
Here I'd like to present preliminary data that Dr. Holdren and I have collected
from Grass Pond (Herkimer Co., NY). Figure 5 is a plot of total lead versus sediment
depth. It is a 'typical1 profile of lead in recent remote lake sediments, where
high values (MOO ppm) are observed at the surface and much lower values (<10 ppm)
occur at depth. This type of profile is discussed in detail elsewhere in these
proceedings. Figure 6 presents lead-206/lead-207 ratios from Grass Pond sediment
sections. Superimposed is the atmospheric trend in the lead isotope ratio observed
in California and presented earlier (Table 1; Fig. 4). Note that old sediments have
very high lead-206/lead-207 ratios. Presumably they reflect contributions from
pre-industrialization atmospheric lead plus country rock lead. Higher
up the core (more recent sediments) the lead-206/lead-207 ratio decreases reflecting
an increased input of anthropogenic, atmospheric lead. In the most recent sediment
there appears to be a leveling off of the lead-206/lead-207 ratio and perhaps even
a slight increase in the ratio in the topmost sediments. This may be a reflection
of increased U.S. usage of Missouri Valley lead since 1962 (Table 1).
Of fundamental importance is whether or not it is possible to determine if
there is more than one source of lead and, if so, what the proportions are of those
sources. One way of determining the number of sources of lead is to use a tri-isotope
plot (Fig. 7). In this type of diagram any one source may not necessarily have a
distinct value of one of the ratios but it is unlikely that two sources will have
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210
f=» m >
O
O
1 SO
£
u
I
h-
Q.
UJ
Q
50
Figure 5. Total lead concentration versus sediment depth
from a core collected in Grass Pond (Herkimer
Co., NY).
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211
a o
T1 S O
1 . 3 O
D
rx 0.
N \
D
Q_
1 Z
50
Figure 6. Pb/ Pb ratios from Grass Pond sediment sections (horizontal
bars). Superimposed ('X') is the atmospheric trend in the lead
isotope ratio reported for California (Table 1; Fig. 4).
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212
s . ~
Q_
rv.
o
CM
1 5 . S
1 1 1 1 1 1
-
2 6
.31
i i i i i i
-
11
:
-
i i i i i i i i i
1 S . 5
2 O S
2O-4
Figure 7. Lead tri-isotope plot of Grass Pond sediment sections. Higher
sample numbers indicate greater burial depth (see Fig. 6). Note
expanded ordinate.
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213
the same values for both isotope ratios. Thus, by using two isotope ratios it is
possible to distinguish between two sources. Mixing of two sources would be repre-
sented as a straight line on a lead-207/lead-204, lead-206/lead-204 plot. The data
in Figure 7 do seem to lie along a straight line. Note that the vertical axis is
very expanded. We don't really know how precise the data are at this point so we
can't say for sure if sample number 2 might actually be off the line.
In order to test the two component source hypothesis, the data may be compared
to a very simple mixing model (Fig. 8). In the model, lead is contributed to the
sediment from two sources: 1) background lead with a lead-206/lead-207 ratio of 1.265
and a steady-state flux yielding a lead concentration in the sediment of about 9 ppm,
and 2) varying amounts of atmospherically derived anthropogenic lead of unknown
isotopic composition. Prior to the introduction of industrial lead the sediment
concentrations of lead would be 9 ppm and the lead-206/lead-207 isotopic ratio would
be 1.265. Addition of increasing amounts of atmospheric lead with an isotopic ratio
much smaller than the background lead value of 1.265 will generate a curve that has
smaller isotopic ratios with increasing lead concentrations. Since there is always
a contribution of both sources of lead which are isotopically different from each
other, the curve will asymptotically approach both end members. Here, I have
selected two values for the lead-206/lead-207 ratio in the atmospheric component.
First, a value of 1.175 was chosen because that approximates the value measured
in California in 1971. Second, a value of 1.23 was chosen because that is the
current (1977) value in California. Clearly the data fall off the lines. There
are several possible interpretations. First, extra lead might be leached from
the watershed by acidic precipitation. Thus, more lead would be deposited without
really changing its isotopic composition. This would cause the data to lie above
the mixing curve. Two, the estimated value of the lead isotope ratio in the at-
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214
2 O O
R t>—
O
1.18
206
1 . 2
Figure 8. Two lead-spurce-mixing model compared to Grass Pond sediments,
Assumed Pb/ Pb ratios of the atmospheric component are
1.175 and 1.23.
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215
mospheric component could be different from the true value. Since there are no
measurements for the lead value in the Adirondacks, it is possible to try to fit the
data by arbitrarily selecting a lead isotope ratio in the atmospheric component.
However, there is no single value for that ratio which will permit the mixing
curve to go through all the data points. Another possibility is that the data
reflect transients in the lead isotopic composition of the atmospheric lead. The
model assumes steady-state inputs and does not address this possibility. Finally,
the model doesn't account for any post-depositional remobilization of lead in the
system by upward diffusion due to recent acidification if such an effect does
exist. These preliminary results indicate that it is possible to use lead isotope
ratios to determine the sources of the lead and the proportions of the lead from
each of those sources. However, they also indicate that there are some additional,
unexplained phenomena.
Several suggestions for future research are listed in Table 2. At the present
there are too few case studies to highlight the full utility of this technique.
Additional case studies are needed. That research must include accurate measure-
ments of the downcore values of lead isotopes in various fractions of lake sediments.
It is also important to determine the isotopic composition of both wet and dry
fallout. At the moment there is little or no data of this type for anywhere in the
northeast U.S., and especially in remote locations. The isotopic compositions of
various watershed materials also needs to be measured. At the moment, there are
no background studies. The geographical and temporal variation of industrial and
atmospheric lead has been measured in some places, but to my knowledge very little
background work in the northeast U.S. is available. Certainly the temporal data
has not been monitored. It is not possible to go back in time and get it, so that
the historical record must be reconstructed from paleolimnologic studies. The
leaching of lead from watersheds will increase with increasing atmospheric acidic
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216
TABLE 2. SUGGESTIONS FOR FUTURE WORK
1) Case Studies
2) Isotopic Composition of Wet and Dry Fallout
3) Isotopic Composition of Watershed Materials
4) Geographical and Temporal Variation of
Industrial and Atmospheric Lead
5) Effects of Acidification on Leaching of
Lead Isotopes
6) Model of Transient Flux with Bioturbation
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217
deposition. It is unknown if this enhanced weathering will preferentially leach
certain isotopes. Furthermore, it is also unknown if the acidification of the lake
water will affect the deposition and accumulation of lead in the sediments.
Finally, it is essential to unify this information by including transient depo-
sitional flux and bioturbation in a comprehensive model of the depositional and
post-depositional processes.
Sulfur is the other element that has stable isotopes of interest in the system.
It has four isotopes that are known: S-32, S-33, S-34 and S-36. About 95% of the
total sulfur consists of S-32 while S-34 is about 4.2% of the total sulfur. There
are large fractionations between S-32 and S-34, so that they are the two isotopes
normally examined. The standard notation is del S-34 in parts per thousand. It
is the ratio of S-34 to S-32 in the sample to S-34 to S-32 in the standard Canyon
Diablo troilite, minus 1 times 1,000:
^s\
634S(%0) =
32_
S-
sample
-1
x 1000 (1)
CDT
The major mechanism for the isotopic fractionation of sulfur is the reduction
of sulfate to sulfide:
32s04(aq) + H234S(g) = 34SO=(aq) + ^Sg) <2>
This reaction has a theoretical fractionation factor of 1.075, although observed
values for 6S-34 are on the neighborhood of 30-50 parts per thousand. Isotope
exchange reactions can also be important fractionation mechanisms. This is par-
ticularly important when attempting to identify the source of industrial sulfur.
In Figure 9 the sulfur isotope fractionation can be seen to be a function of various
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218
a
i
<3
18
16
14
12
10
8
6
4
2
100 200
300 400 500
Temperature, °C
600
700 800
Fig. 9 Theoretical sulfur isotope fractionation curves for pvrite-ealena, pyrite-
sphalerite, and sphalerite-galena . From Hoefs (1973).
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219
mineral pairs. With increasing temperature the fractionation of sulfur isotopes
between the two mineral pairs decreases, but at lower temperatures the fractionation
can be quite large. There is also a fractionation between dissolved aqueous sulfur
species. Figure 10 shows that the fractionation factor for the sulfate-sulfide
pair is very high at low temperatures and decreases with increasing temperature.
There is also a pH effect. H-S-sulfide and HS"-sulfide have fractionation factors
of about 1.01 at lower temperatures which decrease with increasing temperature.
This pH effect is much smaller than the oxidation/reduction fractionation displayed
by the sulfate-sulfide couple.
Typical values of natural variations in sulfur isotopes are presented in Figure
11 and Table 3. Extraterrestrial material are similar to the isotope standard
and therefore yield 5S-34 values near 0. Basaltic and granitic rocks also show
very little fractionation. Metamorphic rocks show a range of fractionation factors
depending on whether or not the sulfur mineral component is sulfide or sulfate, since
sulfides have large negative fractionations and sulfates have large negative fractiona-
tions. Similarly, sedimentary rocks yield 5S-34 values over the entire range.
Sulfate SS-34 has varied in sea water from +9 to +35%0 throughout geologic history.
It is currently about +20%0. This has occurred as a result of significant pre-
cipitation of sulfate evaporites (gypsum and anhydrite) or sulfides (pyrite), so
that the sea water sulfur reservoir was affected. $S-34 in marine pore water
sulfide ranges from very large negative numbers near the sediment surface to positive
values at depth. The SS-34 value in petroleum depends on the original source of the
sulfur. If it was sulfate that was reduced to sulfide, then the «S-34 value will
be negative, but if it was from anhydrite, then large positive «S-34 values-would be
expected. Similarly, coal exhibits a wide range of values. «S-34 values in native
sulfur are very slightly positive. Sulfide ores are highly variable and reflect the
source of the sulfur as well as the ore forming process. Finally, primary igneous
rocks tend to have KS-34 values on the order of 0.
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220
1000 In a = 534Sj-534Ss-2
3 8 S § S
FIGURE 10 Fractionation of sulfur isotopes
among S(V2. H,S (aq), HS'. and S': af.• a
function of the temperature. Note that SOi"2 is
stronglj' enriched in 3iS relative to S~2 and that
the enrichment increases with decreasing tem-
perature. Fractionation of sulfur isotopes among
H:S (aq) and HS" is less pronounced but these
ions clearly prefer JaS over 35S compared to the
sulfide ion. From Hoefs (1973) .
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221
Evaporite sulfate
| Ocean water
imentary.
ic rocks
Granitic rocks
Basaltic rocks
Extraterrestrial matter
(meteorites and lunar rocks)
I I I i
50 40 30 20 10 0 -10 -20 -30 -40
4 *S in V.
Fig. 11MS/32S distribution in some naturally occurring sulfur compounds (^-varia-
tions in '/»relative to Canyon Diablo troilite)
From Hoefs (1973).
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222
Table 3. .Typical values of natural variations in sulfur isotopes,
6J
rioucj.J.aJ.
Seawater SO^ +20 (9 to 35 Geologic History)
S.W. Porewater HgS, N -32 to + 4
Petroleum -8 to +32 ( -15%o < S0jj)
Coal -30 to +32
Native Sulfur +2 to +6
Sulfide Ores variable
Primary Igneous -0
Sedimentary Rocks
Sulfates -+17
Sulfides —15
Igneous & Metamorphic Rocks -2.5
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223
Consider a sediment system in which there is an initial pool of sulfate which
is reduced and/or incorporated into the biological material (Fig. 12). In an open
system like the ocean, the sulfate maintains the same isotopic composition it started
with. In Figure 12, the 6S-34 in the sulfate would remain at +10%0. Since the
fractionation factor doesn't change (here equal to 1.025), the sulfide produced by
reduction of the sulfate would always have a 6S-34 of -15%0. The situation is
different in a closed system. Sediments aren't exactly a closed system, but they
are not exactly an open system, either. Sulfate diffuses into the sediment and is
reduced and/or incorporated into the solid fraction. In sufficiently organic rich
sediments, the concentration of sulfate goes to 0 as in a closed system. However,
sediments also have the property of an open system because sulfur is exchanged across
the sediment-water interface. In a completely closed system sulfate reduction
preferentially removes the light isotope from the remaining sulfate pool, making
the pool of sulfate heavier. However, the fractionation factor remains the same
so that the 6S-34 in the sulfide also continuously increases. After all the sul-
fate has been reduced to sulfide the 6S-34 of the total sulfur is exactly the same
as the initial sulfate (+10%0), except that originally it was sulfate and now it's
all sulfide. Therefore, it is essential to account for sulfur diagenesis when
examining downcore isotopic changes.
Jtfrgensen (1979) attempted to quantify this sulfur diagenesis in a steady-state,
diffusion, reaction model. His model (Fig. 13) incorporates sulfate diffusion across
the sediment-interface, bioturbation inhibiting sulfate reduction of the top 15 cm of
the sediment column, sulfate reduction to H_S, sulfide diffusion and precipitation as
pyrite, and sulfide oxidation to sulfate in the top 15 cm. One of J0rgensen's (1979)
simulations is also presented in Figure 13. Here he has assumed that open system
conditions prevail for sulfide (10% is precipitated as pyrite) and he has assumed a
fractionation factor of 1.025 for sulfate reduction. Note that the sulfate concentration
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224
-10 -20
60 50 40 30 20 10
Fig • 1- Variations of ^fS values of sulfide produced and of residual sulfate in a
closed system. Assumed fractionation factor: 1.025; assumed starting composition
of sulfate: +10; assumed starting composition of sulfide: -15
Frora.Hoefs (1973).
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225
The sulfur cycle in marine sediments. All processes incorporated into the model are shown.
SO?*.
I
a
1
100
150
10
)nnet S cm
« 20 0
4*51.
•10 *20 «30 •AC
FtS,
30
10 20
F»Sj pmol S on'1
Calculated concentrations (A) and isotopic compositions (B) of SOJ~. H2S, and FeSj in the
model sediment. Concentrations are stated per cm3 fresh sediment. Open system conditions prevailing
for sulfide (/ = O.I) and sulfate. a =» 1.022.
Figure 13. Steady-state, diffusion, reaction, sulfur isotope
fractionation model for marine sediments (from
J0rgensen, 1979).
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226
is constant down to (15 cm) and then decreases. Reduction of the sulfate increases
the sulfate pool in S-34 so that the $S-34 increases from +20 to +45 per mil.
Because very little sulfide gets precipitated and a large fraction is recycled,
fractionation increases the SS-34 of the pyrite only about 4 or 5 per mil.
Nriagu and Coker (1976) examined sulfur isotopes in Cake Ontario sediments?" They
found that sulfate disappeared from the pore waters by about 6 cm (Fig. 14). The
total sulfur profile shows a subsurface maximum, which probably represents recent
increased sulfate concentrations in the lake water (see Holdren, this volume).
Nriagu and Coker examined the sulfur isotopes in two fractions. First, the acid
volatile sulfur (essentially FeS) profile shows the exact shape that would be
interpreted in terms of sulfur diagenesis; fairly low $S-34 values at the surface
which increase downcore as sulfate is reduced. This interpretation implies a
fractionation factor of about 30 per mil which is consistent with known values.
However, the lake value is currently about 7%0 so that the SS-34 of the total
sulfur should not exceed that value. Both the acid volatile sulfur and the residual
sulfur (fixed sulfur) are heavier than 7 per rail. Nriagu and Coker (1976) inter-
preted this as loss of reduced, light H-S sulfur by emission from the sediment.
That would enrich the sediment in the heavy isotope to SS-34 values above the
starting (lake) value. There is no other reasonable interpretation in a steady-state
system. Another possibility is that the lake once had a SS-34 of about 24%0 and
recent loading of very light sulfur by industrial sources has lowered the value
to its current level. A diagenetic interpretation is also consistent with 'the
data except, that the diagenetic model needs to include a heavier sulfur component
in the lake water originally and transient conditions for the <£S-34 in the lake
water. My interpretation is that both processes are probably important. Diagenesis
clearly changes the isotopic ratios in the sediment, and there is mounting
evidence for historical changes in the concentrations (and consequently the
isotopic ratios) in lake water.
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227
CS] mg/gds
0 .2 .4 .6 .8 1.0 1.2 l.l) 1.61.8 2.0:.2 2.1
I I I I i I i i I l i I
-15 -10 -5 0 5 10 15 20 I-, 30
i i i i i i i i i i
10 -
1
20 _
30
Total S
From Nriaeu and Coker
197C
Acid
Volatile
Sulfur
I I \ i i i i i i i
0 2 4 6 8 10 12 14 16 18 20 22 24
[SOT] mg/1
Figure 14. Sulfur fractions and isotopic composition of Lake Ontario
sediments. Data from Nriagu and Coker (1976).
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228
Nriagu and Coker (1983) also examined six lakes in northern Ontario. Their
data from one of the lakes is redrawn in Figure 15. The total sulfur profile is
similar to that observed in many lakes. Sulfur concentrations exceed 1% dry weight
at the surface and decrease rapidly to .l-.2% dry weight below about 10 cm. The
SS-34 shows about a 15 per mil increase downcore from about -8%0 to a more or less
constant value of 5-7%0. Note that many of the cores exhibit a subsurface maximum
in
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229
[S] (dry wtl)
0 .1 .2 .3 .'i .5 .6 .7 .8 .9 1.0 -15 -10 -5
i i I I i I i i i
63ftS ',c
10
10-
I
u
a
20 -
30
From Nrlagu and Coker
1983 . ..
Figure 15. Sulfur and SS-34 from McFarlane Lake sediments (northern
Ontario). Data from Nriagu and Coker (1983).
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230
-1
10-
20.
"e
^ 30-
x
0.
w
'40"
50-
60.
7n _
/ U
0-5 0 5 10 15 -10 -5 0 5 10 15 2v
1 i i i i / i i i i i
*
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231
TABLE 4. . SUGGESTIONS FOR FUTURE WORK
1) Case Studies
2) Isotopic Composition of Wet and Dry Fallout
3) Isotopic Composition of Watershed and Lake Materials
4) Sulfur Diagenesis in Soft-water Lakes
5) Effects of Acidification and Eutrophication on
Sulfur Diagenesis
6) Model of Transient Flux with Bioturbation
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232
sulfur fractions are emerging. However, in order to understand their meaning,
we need to understand sulfur diagenesis in particular. Isotopic compositions of
wet and dry fallout in watershed and lake materials need to be measured to help us
understand sulfur diagenesis and an understanding of sulfur diagenesis can help us
understand the isotopes. The effects of acidification also need to be addressed.
These reactions are microbially mediated so that acidification would be expected
to have a profound effect on the nature and extent of the reactions. At present,
we have no idea how acidification will affect either the diagenesis of sulfur or,
for that matter, the isotopes. Finally, it is necessary to put this all together
in a comprehensive transient diagenetic model where bioturbation and mixing of
new and old materials are included with all the post-depositional reactions.
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233
REFERENCES CITED
Doe, B.R. (1970). Lead Isotopes. Springer-Verlag, New York, 137 pp.
Hoefs, J. (1973). Stable Isotope Geochemistry. Springer-Verlag, New York, 140 pp.
J^rgensen, B.B. (1979). A theoretical model of the stable sulfur isotope dis-
tribution in marine sediments. Geochim. Cosmochim. Acta, V. 54, 363-374.
Nriagu, J.O. and R.D. Coker (1976). Emission of sulfur from Lake Ontario sediments,
Limnol. Oceanogr., 485-489.
Nriagu, J.O. and R.D. Coker (1983). Sulphur in sediment chronicles past changes
in lake acidification. Nature, V. 303, 692-694.
Shirahata, H., R.W. Elias, C.C. Patterson, and M. Koide (1980). Chronological
variations in concentrations and isotopic compositions of anthropogenic
atmospheric lead in sediments of a remote subalpine pond. Geochim.
Cosmochim. Acta, V. 44, 149-162.
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234
Paleolimnological approaches to the study of acid deposition:
metal partitioning in lacustrine sediments
Peter G.C. Campbell and Andre Tessier
Universite du Quebec
INRS-Eau, C.P. 7500
Sainte-Foy, Quebec
Canada G1V 4C7
Presented at the U.S. EPA Workshop on
"Progress and problems in the paleolimnological
analysis of the impact of acidic precipitation
and related pollutants on lake ecosystems"
Held at Rockport, Maine, 22-26 May, 1984.
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235
Introduction
Metals introduced into the aquatic environment, whether from
atmospheric or terrestrial sources, are distributed among a variety of
physico-chemical forms. As these different metal forms will generally
exhibit different chemical reactivities, the measurement of the total
concentration of a particular metal provides little indication of the
metal's potential interactions with the abiotic or biotic components present
in the environment. The corollary, of course, is that knowledge of the
speciation of a metal is useful for determining its origins and for
understanding its geochemical behavior (mobility/transport) and biological
availability.
Metal species exist along a size spectrum ranging from dissolved
through colloidal to particulate phases; in the context of this workshop on
paleolimnology and its application to acidic precipitation research, we
shall emphasize the right-hand end of spectrum, i.e. those settleable forms
likely to be found in lacustrine sediments before/after diagenesis. Metals
in such sediments may be:
1. adsorbed at particle surfaces (e.g.: clays; humic acids; iron
oxyhydroxides);
2. carbonate-bound (e.g.: discrete carbonate minerals; co-precipitated
with major carbonate phases);
3. occluded in iron and/or manganese oxyhydroxides (e.g.: discrete
nodules; cement between particles; coatings on particles);
4. organic-bound (e.g.: bound up with organic matter, in either living or
detrital form);
5. sulfide-bound (e.g.: amorphous sulfides, formed in s i tu; more
crystalline forms);
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236
6. matrix-bound (e.g.: bound in lattice positions in alumnosilicates, in
resistant oxides or in resistant sulfides).
Intuitively, it might be expected that chemical reactivity, geochemical
mobility, and biological availability will decrease in the order 1 > 2, 3,
4, 5 > 6; the relative ranking of forms 2, 3, 4 and 5 is, however, more
difficult to predict.
In principle, the speciation of sediment-bound metals could be
determined both by thermodynamic calculations (provided equilibrium
conditions prevail) and by experimental techniques (Table 1). The modelling
of sediment-bound metals is far less advanced than is that of dissolved
species, primarily because the thermodynamic data needed for handling
sediment-interstitial water systems are not yet available. Thus, the only
realistic means of studying metal partitioning in sediments at the present
time is to fractionate the sediment physically and/or chemically.
Conceptually, the solid material can be partitioned into specific fractions;
sequential extractions with appropriate reagents can then be devised to
leach successive fractions "selectively" from the sediment sample.
Alternatively, the sediment may be fractionated physically, according to
grain size or by density gradient separation, and the individual fractions
analysed separately. Many such experimental procedures have been proposed
and applied to a wide variety of suspended or surficial sediments from
streams and lakes; a limited number of sectioned sediment cores have also
been studied in this manner.
In this contribution to the workshop, the increasingly prolific
literature pertaining to metal partitioning in sediments is summarized
briefly and several important methodological problems are discussed.
Applications of partitioning procedures in paleol imnological studies are
reviewed, with particular emphasis on those bearing on the acid
precipitation phenomenon, and specific research objectives are formulated.
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237
1. Metal partitioning as determined by selective chemical extractions
Choieof
To extract sediment-bound metals selectively from a particular form or
phase, one may choose among a variety of different reagents (see Table 2 for
a partial list). The reagents fall naturally into classes of similar
chemical behavior, for example:
* concentrated inert electrolytes (desorption of electrostatically
adsorbed metals);
» weak acids (dissolution of carbonate phases, desorption of specifically
adsorbed metals);
» reducing agents (reduction of amorphous iron and/or manganese oxides);
« complexing agents (competition for metals complexed with organic
functional groups, dissolution of precipitates);
o oxidizing agents (oxidation of organic matter and sul fides);
» strong mineral acids (dissolution of resistant oxides, sulfides,
aluminosilicates).
If the extractants are chosen in order of increasing strength, they can be
used in sequential fashion; representative examples of this type of approach
are shown in Table 3, as used for pollution studies in the freshwater
(Tessier et a!., 1979; Forstner, 1982) and marine environments (Engler £t
al. , 1977), or for geochemical exploration (Chao and Theobald, 1976). Note
that each of these procedures was designed for use with oxic (surface)
sediments; this same comment applies to all other published sequences.
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238
A number of points should be mentioned in this context. First of all,
it would be unrealistic to think that one could select a sequence of
reagents that would extract the individual fractions in order without
influencing the other sediment constituents. As must be chemically obvious
from inspection of Tables 2 and 3, available reagents are inherently
unselective and any sequential extraction procedure will unavoidably suffer
from a certain lack of selectivity. There is a related potential problem
with readsorption in that if you liberate a metal with a given reagent then
it may readsorb onto the remaining solid phases, i.e. the extraction
procedure itself may cause a shift in the metal distribution pattern.
Precipitation reactions may also be a problem, particularly if sodium
hydroxide is used to remove the organic fraction (i.e., metal hydroxide
formation).
Once the reagents have been selected, there remains a decision as to
the order in which they are to be employed. As is evident in Table 3, the
precise sequence of extractants may vary considerably, particularly with
respect to the oxidation of the organic matter present in the sediment; this
step may follow the reduction procedure (methods 1 and 2), may be introduced
between two reduction steps (method 3) or may even be discarded completely
(method 4)! In addition, the exact experimental conditions employed to
conserve the sediment sample, and subsequently to extract the different
metal fractions, may influence the metal distribution. For example, the
ratio of extractant to sediment may be important, particularly if the
sediment is consuming some of the reagents, as is the contact time between
the sediment and the extractant. It follows that the distribution of a
metal among various fractions is operationally defined. I would like to
dwell a little longer on two points in particular: extraction selectivity
and sample conservation.
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a Extraction selectivity
How can you go about evaluating extraction selectivity? As indicated
in Table 4, one can use pure solids or known geochemical phases, alone or in
model sediments built up from various solid phases or in natural sediments;
these samples are then subjected to the extraction procedure under
evaluation and one notes in which fraction(s) the added metals appear. One
could also analyze extracts and/or the residual sediment remaining after the
various extractions, and determine various complementary parameters. For
example, if you were using a procedure that included a step designed to
remove organic matter, then you could follow the fate of the organic matter
and note when it actually disappeared from your sediment. You could also
perform successive extractions with the same reagent and determine to what
extent the first extraction removes the phase of interest; ideally the metal
concentrations in the second and subsequent extractions with a particular
reagent should be much lower than those in the first extraction.
Rapin & Forstner (1983) used a number of these approaches to evaluate
the selectivity of an extraction procedure comprising five steps (cf.
Tessier et al.. 1979):
step I NH^OAc, pH 7
step II NaOAc / HOAc, pH 5
step III NH2OH.HC1 /HOAc, 96°
step IV H202 / HN03, 85°, pH 2; NH^OAc
step V concentrated HN03, 120°
Using both a freshwater and a marine sediment, they measured the
concentration of organic carbon and total sulfur in the residual solid phase
remaining after each extraction (Table b). For both sediments the
selectivity of the procedure for organic matter proved satisfactory, almost
all of the organic carbon remaining intact until the oxidation step (IV).
Similarly, for the marine sample most of the sulfur remained with the
residual sediment until extraction with acidic hydrogen peroxide. In the
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freshwater sediment, however, the selectivity for sulfur was poor and
appreciable quantities were extracted in each fraction (Table 5).
In a parallel study the same authors (Rapin & Forstner, 1983) subjected
a number of solid phases to the extraction procedure, notably several pure
carbonates (Ca, Cd, Mn, Pb), two amorphous iron/manganese oxides from deep-
sea nodules, two more crystalline iron oxide minerals (hematite, goethite),
an amorphous iron sulfide and a crystalline lead sulfide (galena); in each
case they determined the fate during extraction of both the major metal and
any metals present as impurities. Selectivity proved to be good for the
carbonate phases (>85% extraction in fraction II), acceptable for most
metals associated with the amorphous iron/manganese oxides (>80% extraction
in fraction III, except for Cd and Pb), but poor for those metals present as
impurities in the technical grade iron sulfide. In this latter case
appreciable solubilization of Fe, Mn and Cu was noted in fractions I, II and
III, i.e. before the oxidation step (IV) that is nominally designed to
liberate metal sulfides. Note that the results from both the analysis of
residual sediment after extraction (see above) and the use of sulfide phases
of known composition indicate that selectivity for metal sulfides is
unsatisfactory.
» Sample conservation
Let us now consider a second methodological point, namely the need to
preserve sample integrity between sampling and analysis. I have gleaned
several perspicacious quotes from the literature.
- "drying, grinding and contact with atmospheric oxygen are
undesirable" - Engler et_al_. (1977);
- "effects of temperature changes during sample collection and
preparation are very important and should be considered" - Engler ^t
al. (1977);
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- "sample handling and pre-treatments may noticeably affect extraction
results" - Jenne & Luoma (1977).
Experimental data to support these contentions were not presented in the
original publications, but recent results from our laboratory have served to
emphasize their relevance and demonstrate how important the effects of
sample pre-treatment may be.
Conscious that there are often unavoidable delays between sample
collection and the subsequent analyses, we experimented with various
preservation techniques: wet storage (1-4°C), freezing, freeze-dry ing,
drying under a nitrogen stream (20°C), drying under air in a convection oven
(105°C). Using the familiar sequence of extractants (Table 6), we studied
several natural sediments, both oxic and anoxic. In all cases the fresh
sediment was subjected to the extraction procedure within 48 h of sampling
and the resulting metal distribution was used as a reference for comparison
with the distributions obtained after different sample pre-treatments.
Representative results are shown in Figures l(a) and (b) for fractions I and
II extracted from an anoxic sediment (lake Magog, Quebec). The dashed
horizontal line corresponds to the fresh sample (100%); values above/below
this line indicate an increased/decreased extractability. Clearly sample
pre-treatment influenced the distribution of metals among the various
fractions; of the preservation methods tested, those involving the drying of
the sediment (air-drying; N2-drying; freeze-dry ing) had especially marked
effects. Among the different metals studied, copper and zinc were
particularly sensitive to sample pre-treatment, extractions I-II being the
fractions most affected.
Similar results were obtained for oxic sediments, but as expected the
changes were somewhat less dramatic than those observed with anoxic samples.
In the light of these results we would strongly urge that drying of the
sediments be avoided; acceptable preservation techniques would include
short-term wet storage (dark; 1-2°C) or freezing.
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In a related study (Table 7) we have also evaluated the importance of
maintaining an oxygen-free atmosphere during the manipulation of anoxic
sediments, a point of obvious importance when dealing with sediment cores.
Two anoxic sediments were subjected to the usual extraction procedure: in
one experiment the manipulations were carried out in a glove box under a
nitrogen atmosphere and the reagents used for the first three extractions
were deoxygenated prior to use, whereas in the second experiment no such
precautions were taken. The acid-volatile sulfide (AVS) content of the
sediments was measured on the fresh sediment (100%) and after each of the
first three extraction steps (Table 8). If oxygen was not rigorously
excluded, AVS concentrations dropped markedly during the first two
extractions; 11-38% remained after treatment with MgCl2, 1-20% after
reaction with the NaOAc/HOAc (pH 5) buffer. If a working atmosphere of
nitrogen was maintained, the AVS levels were preserved through the first two
extractions (87-97%) but were reduced to < 5% of the initial concentrations
after treatment with the NH2OH»HCl/HOAc reagent. Note that even in this
most favorable case the acid-volatile (amorphous) sulfides are removed not
in the oxidation step (IV) but rather during the extraction designed to
solubilize the Fe/Mn oxides present in the sample. This lack of selectivity
of the extraction procedure with respect to sulfide phases was mentioned
earlier.
Consider now the influence of adventitious oxygen, not on acid-volatile
sulfides but rather on metal partitioning in the sediment. In the absence
of precautions taken to exclude oxygen, several general trends were
observed:
fraction I: increase Cd Co Cr Cu.Ni Pb Zn
decrease Fe Mn
III: increase Co Cu Ni Fe Mn
IV: decrease Cd Cr Cu Ni Zn Fe
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Representative results are shown in Table 9 (Fe) and Tables 10-11 (Pb). In
the former case, for the lake Nepahwin sediment, the decrease in fractions I
and II was accompanied by an increase in fraction III, as would be expected
if oxidation of ferrous to ferric ion had occurred during sample handling;
indentical results were observed for the lake Aylmer sediment. For lead,
fractions II and III were also very sensitive to the introduction of oxygen,
but in this case the two samples exhibited contrasting behavior: for the
lake Nepahwin sediment a marked increase in fraction II was accompanied by a
corresponding decrease in fraction III, whereas for the lake Aylmer sample
an equally important but opposite shift occurred (F II +; F III t). These
latter results illustrate the fact that it generally will not be possible to
predict the consequences of not having prevented the introduction of
adventitious oxygen, i.e. it will be impossible to "correct" retroactively
data that have been obtained without adequate precautions. As will become
evident in part 2 of this presentation (see below); this is an exceedingly
unfortunate conclusion since virtually all the available paleolimnological
data have been generated either from dried sediments or from wet sediments
that have been allowed to come in contact with adventitious oxygen.
In summary, our evaluation of the effects of sample pre-treatment on
metal partitioning in sediments leads to the following conclusions:
- no storage method tested completely preserves the initial chemical
and physical characteristics of the sediments;
- if a variety of extractants are to be used (e.g. sequentially),
there is no choice but to perform the extractions as soon as
possible after collection;
- drying of the sediment (air-dry ing, N2-dry ing, freeze-dry ing) should
be avoided at all costs;
- possible preservation techniques include wet storage (dark, 1-2°C)
or freezing;
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244
- for anoxic sediments the maintenance of oxygen- free conditions is of
critical importance during the extraction procedures.
Finally, several lines of evidence suggest that for sul fide- rich (anoxic)
sediments the various extraction procedures currently in use in the
environmental field (cf. Table 1, methods 1-3) will be compromised by the
tendency of the metal -containing sul fide phases to be progressively (rather
than selectively) extracted from the host sediment.
******
2. Paleolimnological applications
In this section we shall consider how the determination of metal
partitioning in sediment cores might be helpful in the study of acid
deposition, e.g. in determining the chronology of environmental
acidification, or in evaluating geochemical responses to acidification.
Three questions merit our attention, namely the effects of (i) sediment
diagenesis, (ii) atmospheric inputs of metals and (iii) environmental
acidification on the partitioning of metals in sediments.
Effects
To identify down-core changes in metal partitioning that are related to
environmental acidification, it will first be necessary to account for any
changes due to sediment diagenesis. Chemical reactions occurring after
sediment deposition will include:
- the breakdown of organic matter;
- the removal of dissolved 02;
- the reduction of N03-, SO^- HC03-;
- the production of C02, NH,/, HP01+2-} HS~, CH^ ;
- the reduction of Fe, Mn oxy hydroxides;
- the formation of metal sul fides, carbonates.
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245
Down-core changes in the concentrations of such parameters as 02, pe, pH,
SO^, S2~, and dissolved organic carbon (DOC) may thus be anticipated.
Concomitant changes in the chemical nature of the dissolved and particulate
organic carbon may also be expected. Similarly, sediment compaction at
depth will lead to a decrease in the surface area available for adsorption.
Integrating these changes in a qualitative conceptual model, one can
identify the possible effects of sediment di agenesis on metal partitioning
in sediments; in effect, on analyzing successively older sediment strata one
might anticipate:
- a decrease in the adsorbed fraction (F I);
- a decrease in the easily/moderately reducible fraction (F III);
- a decrease in metals formerly adsorbed to this fraction (F II);
- an increase in the sulfidic fraction (F III in recent sediments,
F IV as crystallinity increases);
- an increase in the carbonate fraction (F II).
Clearly there is no evident trend on going down the core. This can best be
attributed to the previously demonstrated inadequacy of the common
extraction procedures when applied to anoxic sediments. As mentioned
earlier, these procedures were developed for surficial (oxic) sediments but
subsequently have been used rather indiscriminately in the study of sediment
cores.
lf!e£t.s_ 2f_i£C£6jiS£d_ata£S£h£ri_c_l2ajli£gs- of _metal_s_ (at constant pH)
Once again, to identify down-core changes in metal partitioning that
are related to environmental acidification, it will first be necessary to
consider any changes brought about by increased atmospheric loadings of
metals (i.e., direct deposition). If the metal input is in dissolved or
acid-leachable form, then one would anticipate increases in the relative
proportions of one or more of the non-detrital metal fractions in the
sediments (e.g., Fe/Mn oxides, F III); such changes have indeed been
observed in surface sediments affected by mine drainage (Tessier etal . ,
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246
1980; 1982) and by air-borne smelter emissions (Campbell & Tessier,
unpublished data from the Rouyn-Noranda area, Quebec). Alternatively, if
the metal input is in particulate, non-leachable and settleable form, then
one might anticipate an increase in the relative contribution of the
residual fraction (F V). This latter suggestion was first advanced by
Patchineelam and Forstner (1977), who observed an increase in the
concentration and relative proportion of residual metal in the upper or
intermediate strata of a sediment core taken from the German Bight. They
attributed these increases to inputs of metal -containing atmospheric
particulate material that passed through the water column unchanged,
resisted diagenetic change and thus was preserved within the sediment
without transformation. This intriguing observation does not appear to have
been followed up.
Effects
Finally, adding the third element to our conceptual model, we might
anticipate that environmental acidification would lead to a lower efficiency
of metal capture by suspended solids in the lake water column (Dillon, 1982;
Dillon & Smith, 1982); total concentrations of certain metals in the lake
sediments might thus be expected to decrease. With respect to metal
partitioning in these sediments, based on laboratory studies of metal
adsorption on well -character!' zed hydrous metal oxides (Fe, Mn, Al ) as a
function of pH (Kinniburgh & Jackson, 1981), environmental acidification
would be expected to cause a decrease in the relative proportion of
specifically adsorbed metals (i.e., fraction F II in our sequential
extraction procedure: Table 3, method I). Similarly, a decrease in pH might
be expected to lead to the dissolution of any carbonate phases present in
the sediment (also fraction F II). Other more subtle effects of
acidification can be envisaged; for example, increased sulfate reduction
(Kelly et al ., 1982) might lead to an increase in metal sulfide formation.
However, as mentioned earlier, these sulfide-bound metals tend not to appear
in a particulate fraction but rather to be extracted progressively from the
sediment, appearing in several fractions.
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Experimental data relating to these predicted changes have been
provided by both Gambrell and Khalid (Gambrell et al., 1980; Khalid et al.,
1981), who determined the effect of pH changes on metal partitioning in
river sediments. In their laboratory incubations of sediments in closed
containers, a decrease in pH from 8 to 5 led to an increase in the levels of
dissolved and exchangeable cadmium and zinc, i.e. to an increase in the
geochemical mobility of these metals. In a natural (i.e., open) system,
such an increase in mobility would result in a net loss of the metal from
the sediment. In contact, lead and mercury were little affected by pH
changes in this range. As indicated in Table 12, the increase in dissolved
and exchangeable cadmium occurred at the expense of the "organic fraction"
(H202/HN03 extraction, F IV), whereas in the case of zinc there was a
corresponding decrease in the relative contribution of the reducible
fraction (NH2OH.HCl/HOAc extraction, F III).
Having considered how sediment di agenesis, increased metal inputs and
environmental acidification may affect metal partitioning in sediments, let
us now examine the available data for metal partitioning in sediment cores.
We have identified some 21 such studies: 10 in the marine environment, the
earliest dating from 1972, and 11 from freshwater systems, starting somewhat
later, in 1979. Given the purpose of this workshop, we have considered only
those investigations carried out in lacustrine (freshwater) environments.
The relevant data have been summarized in two tables*, for circumneutral
(Table 13) and acid lakes (Table 14).
For studies performed on sediments from circumneutral lakes, in all but
one case the sediment sample was preserved by freeze- dry ing; the only
exception is the study of Baiker, as cited by Forstner (1982), for which no
* N.B.: The present authors would appreciate learning of any freshwater
studies that may have been omitted from this compilation.
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248
perservation technique is indicated. As has been mentioned earlier, freeze-
drying affects metal partitioning in sediments. Note also that in no cases
were precautions taken to exclude oxygen from the lower (anoxic) sediment
strata. Clearly the metal distributions reported in these studies cannot be
considered representative of the metal partitioning in the different
sediment strata in situ at time of sampling. Even with this caveat,
however, some potentially useful information can be derived from these
studies. For example, Dominik and co-workers (1983) determined the
distribution of copper and zinc in two cores from lake Geneva (0-1, 31-33,
75-80 cm strata), using an extraction scheme identical to that described
earlier and used by Rapin and Forstner (1983). Total metal concentrations
were higher in the upper sediment strata, this increased concentration being
associated with non-detrital fractions (F II for Zn, F IV for Cu). Similar
observations have been made by Baiker (1982), who noted Zn accumulation in
the carbonate fraction F II in lake Constance sediments, as well as by
Manning and co-workers (1983), who reported Cu, Pb and Zn accumulation in
the reducible fraction F III in lake Ontario sediments. As mentioned
earlier, this type of distribution pattern is indicative of an increased
anthropogenic input of metal (not necessarily of atmospheric origin) in
dissolved or Teachable particulate form. Dominik et al. also noted that the
partitioning of 210Pb in their cores differed from that of stable lead
(Figure 2): for 210Pb the reducible fraction dominated (NH2OH-HCl/HOAc
extraction, F III) whereas for stable lead the most important contribution
was that of fraction II (NaOAc/HOAc extraction). These authors suggested
that there were at least two distinct sources of lead, lead speciation being
different for each source and exchange among the different species being
slow. In view of their potential implications in the development of 210Pb
dating models, these results clearly merit further study in properly
preserved sediment cores for which artifacts due to sample handling may be
discounted.
For studies performed on cores from acid lakes (Table 14), it should be
noted that in 3 of 6 instances the sediment was air-dried; in the remaining
studies the sediments were stored wet, but in 2 of these 3 cases no
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249
precautions were taken to exclude oxygen from the anoxic sub-samples during
the extraction procedure. Once again it is clear that the metal
distribution patterns observed in all but one of these studies have been
altered by sample pre-treatment and cannot be considered representative of
the metal partitioning that existed in the original intact cores.
Despite these problems, it is intructive to consider the results of
Reuther and co-workers (1981), who determined the partitioning of several
metals in sediment cores from lakes Hovvatn (pH 4.4) and Langtern (pH 4.95)
in Norway. For the lake of lower pH they noted a decrease in the total
concentrations of cadmium and zinc (but not lead) in the upper sediment
strata. This decrease was attributed to the remobilization of Cd and Zn
from the sediment, mainly from the organic and easily reducible fractions,
respectively. That this apparent remobilization was noted in lake Hovvatn
but not in lake Langtern suggested to the authors the concept of a
"threshold pH", a value below which the pH must drop before mobilization is
observed (c.f. Norton et al., 1981). Similar results were subsequently
reported by the same authors (Reuther et al., 1983) for lake Gardsjon
(pH 4.7) in Sweden. For Clearwater lake (pH 4.65) located near Sudbury,
Ontario, total zinc concentrations also decreased in the upper sediment
strata, this decrease again occurring predominantly in the reducible
fraction (Rapin et al., 1984). However, data for Dart lake (pH 5.2) in New
York showed no evidence of zinc mobilization as concentrations increased
monotonically towards the sediment-water interface (White, 1984).
f
The^Te is a certain seductive consistency among all the results obtained
at pH values less than ~ 4.8, notably for Zn - see Figures 3a, b, c. Note
also that this apparent mobilization of Zn from the reducible fraction
agrees with the laboratory simulations reported by Gambrell et al. (1980) -
see Table 12. However, Reuther and his co-workers did not consider the
potential effects of sediment diagenesis on zinc partitioning in their
sediment cores. That such diagenetic effects may indeed be important is
suggested by the results obtained by Viel et al. (1983) for a core from
circumneutral lago Maggiore, situated on the Switzerland-Italy border
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250
(Figure 3d). The authors attributed the increase in zinc concentration at
intermediate depth (notably in the reducible fraction) to the diagenetic
formation of vivianite (FePO^) and the co-precipitation of zinc. Th'is
result underlines the danger inherent in interpreting decreased metal
concentrations near the sediment-water interface solely in terms of metal
mobilization upward towards the overlying water column (Reuther et al.,
1981; 1983). It is imperative to consider the possible effects of sediment
diagenesis on total metal concentrations and on metal partitioning; one of
the best ways to follow such diagenetic processes is to sample the
interstitial water (e.g., with in situ dialysis chambers) and determine
down-core gradients of the parameters of interest not only in the solid
phase, but also in the associated interstitial water.
In summary, our analysis of published applications of selective
extraction procedures to the paleolimnological study of lake sediments leads
to two principal conclusions:
.?-•'•''"''"'"/
- metal ^distribution patterns reported in the literature for sediment
cores (Tables 13, 14) have been influenced by sample pre-treatment
and cannot be considered representative of the metal partitioning
that existed in the original lake sediment;
- to identify down-core changes in metal partitioning that are related
to environmental acidification, it will be necessary to "correct"
for any down-core changes due to sediment diagenesis or to changes
in the direct atmospheric deposition of metals.
3. Recommendations
In light of the various methodological considerations developed earlier
in this presentation (part 1), and taking into account our conclusions with
respect to the potential application of selective extraction procedures in
paleolimnological studies (part 2), we offer the following research
recommendations:
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251
- develop selective extraction procedures better adapted to anoxic
(sulfide-rich) sediments (i.e., more selective for sulfidic phases);
- determine the speciation of the atmospheric inputs of certain key
metals (e.g., the relative importance of leachable-particulate and
insoluble-particulate forms of Cd, Zn and Pb) in order to evaluate
whether particulate atmospheric inputs can persist unchanged in lake
sediments and thus directly influence metal partitioning in these
sediments (cf. Patchineelan & Forstner, 1977);
- compare the partitioning of 210Pb with that of stable Pb, in
properly preserved/handled sediments, in order to determine the
generality of the apparent disequilibrium reported for lake Geneva
sediments by Dominik et al. (1983);
- for those metals reported to be mobilized from lake sediments below
a certain threshold pH value (e.g., Cd, Mn, Zn), determine down-core
changes in metal partitioning in properly preserved/handled
sediments collected from lakes selected along a pH gradient, and
combine these measurements with the appropriate analysis of down-
core changes in interstitial water chemistry ... in order to
distinguish between changes attributable to "normal" diagenetic
processes and those induced by acidification of the overlying water
column. These same measurements could also be performed within the
framework of an experimental lake acidification programme.
Acknowledgements
Unpublished data were graciously furnished by R.D. Evans (Trent
University), M.S. (Jesse) Ford (Ecosystems Research Centre, Cornell
University), J.R. White (Indiana University), as well as by R. Carignan and
F. Rapin of our research center. Discussions with the latter two colleages
were invaluable in the preparation of this report.
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252
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Effect of pH-changes on the distribution and chemical forms of heavy metals
in sediment cores from Swedish lakes. 4th Int. Conf. on Heavy Metals in the
Environment, Heidelberg, Proceedings p. 868-871.
Reuther, R., R.F. Wright and U. Forstner (1981).
Distribution and chemical forms of heavy metals in sediment cores from two
Norwegian lakes affected by acid precipitation. 3rd Int. Conf. on Heavy
Metals in the Environment, Amsterdam, Proceedings p. 318-321.
Schwertmann, U. (1964).
Differenzierung der Eisenoxide des Bodens durch photochemische Extraktion
mit sauerer Ammoniumoxalat-Losung. Z. Pflanzenernahr. Dung. Bodenkde,
105: 194-202.
Stover, R.C., L.E. Sommers and D.J. Silviera (1976).
Evaluation of metals in wastewater sludges. J. Water Pollut. Cont. Fed. 48:
2165-2175.
Tessier, A., P.G.C. Campbell, J.C. Auclair, M. Bisson and H. Boucher (1982).
Evaluation de 1'impact de rejets miniers sur des organismes biologiques.
Universite du Quebec, INRS-Eau, rapport scientifique No 146, 257 p.
Tessier, A., P.G.C. Campbell and M. Bisson (1980).
Trace metal speciation in the Yamaska and St. Francois Rivers (Quebec).
Can. J. Earth Sci. 17: 90-105.
Tessier, A., P.G.C. Campbell and M. Bisson (1979).
Sequential extraction procedure for the speciation of particulate trace
metals. Anal. Chem. 51_: 844-851.
Viel, M., G.P. Nembrini, J. Dominik and J.P. Vernet (1983).
Vertical distribution and chemical speciation of heavy metals in Lago
Maggiore sediments (North Italy). 4th Int. Conf. on Heavy Metals in the
Environment, Heidelberg, Proceedings p. 793-796.
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257
Volkov, I.I. and L.S. Fomina (1974).
Influence of organic material and processes of sulfide formation on
distribution of some trace elements in deep-water sediments of the Black
Sea. Am. Ass. Pet. Geol. Mem. 20: 456-476.
White, J.R. (1984).
Trace metal cycling in a dilute acidic lake system. PhD Thesis, Dept.
Civil Engineering, Syracuse University, 261 pp.
-------
258
MO
4*0.
MO
y
•o
Q
©
1 -
/L^tT-.
c»
III
VIO
I 310
6
®
TI
FIGURE 1. Effects of sample pre-treatment on metal partitioning in an
anoxic sediment (a) fraction I (exchangeable at pH 7, MgCK);
(b) fraction II (carbonate and exchangeable at pH 5, NaOAc/HOAc)
Sample treatments: fresh; wet storage, 4°C, 20 d; freezing;
dried under N,
20 C; dried in air,
4'
105°C
20
freeze-dried.
-------
259
210
Pb
8.6
1.9
2.1
Pb
32
21
130
20
Zn
145
60
410
65
Cu
62
20
185
32
625 0-1 cm
<
>
UJ 625 75-80 cm
527 2-3cm
UJ
O
UJ
** 527 31-33 cm
m nr
I- adsorbed and exchangeable at pH 7; II-carbonate
and exchangeable at pll 5; I 1 I - reducib le; IV-orqanic
matter and sulphides; V-residual
FIGURE 2. Partitioning of Cu, Zn, Pb and 2l°Pb in two sediment cores from
circumneutral lake Geneva. (From Dominik et al.. 1983).
-------
JO 00
—^-XvX-X-X-X-l i • IV.',:; : t'f-
.. Jx-XvX-XvX-x-x-x-x-^/
•x-x-x-xvXvx-Xx-x-x^
Zn
•*-.-.•.-.•.'.•.'.'I '**•*'
0
zoo IppmJ
MOO
100 200 300 PPB
Zinc
(0-20)
Exchangeable pH 7
I JZ2 Carbonates •*• exchangeable pH 5
Fe-Mn oxides
Organic matter + sulfides
Residual fraction
FIGURE 3. Partitioning of Zn in sediment cores from (a) lake Hovvatn (pH 4.6) - from Reuther et
al. (1981); (b) lake Gardsjon (pH 4.7) - from Reuther et al. (1983); (c) Clear-water
Take (pH 4.65) - from Rapin et al. (1984); (d) lago MaggTore (circumneutral) - from
Viel et al. (1983).
ro
en
o
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261
Table 1: Possible approaches for the determination of metal
partitioning in sediments.
o mathematical modelling
thermodynamic equilibrium calculations
• experimental manipulation
physical separation: grain size
specific gravity
magnetic properties
chemical separation: selective extractions
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262
Table 2: Methods for the extraction of metals from major chemical
phases in sediments (examples). After Forstner (1982), with
modification.
BaCl2-triethanolamine (pH 8.1)
MgCl2
ammonium acetate (pH 7)
£ajrbonate jahases
C02-treatment of suspension
acidic cation exchanger
NaOAc/HOAc-buffer (pH 5)
redii£ib]e_ j>hases (in approximate order
of release of iron)
acidified hydroxylamine (+ 0.01 M HN03)
ammonium oxalate buffer
hydroxylamine-acetic acid
dithionite-citrate buffer
or£aji i£ f_ra_ct i on (i nc 1. s u 1 f i de s)
H202-NH1+OAc (pH 2.5)
H202-HN03
organic solvents
0.1 M NaOH/H2S01+
Na-hypochlorite
Na-pyrophosphate
diethylenetriaminepentaacetic acid
(DTPA) - NaOAc (pH 7)
Jackson (1958)
Gibbs (1973)
Engler et al. (1977)
Patchineelam (1975)
Deurer et al. (1978)
Tessier et al. (1979)
Chao (1972)
Schwertmann (1964)
Chester & Hughes (1967)
Holmgren (1967)
Engler et al. (1977)
Gupta & Chen (197b)
Cooper & Harris (1974)
Volkov & Fomina (1974)
Gibbs (1973)
Stover et al. (1976)
Khalid et al. (1981)
-------
Table 3: Examples of sequential extraction procedures .
263
step method # 1
method # 2
method # 3 method # 4
MgCl
NH^OAc
NH..OAC NH2OH.HC1/HN03
II
NaOAc/HOAc
III NH2OH.HCl/HOAc
NH2OH.HC1/HN03 NH2OH.HC1 NH2OH.HCl/HOAc
H202/HN03
IV H202/HN03
H202/HN03
f/HCl/HN03
HF/HCIO
HN0
HF/HN03 HF/HN03
(a) method 1 = Tessier et al. (1979); method 2 = Forstner (1982); method 3
= Engler etal. (1977); method 4 = Chao & Theobald (1976).
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264
Table 4: Possible approaches for the evaluation of extraction
selectivity
use of pure solids
o alone
• in model sediments
o spiked into natural sediments
analysis of extracts and/or residual sediment for
various "complementary" parameters
• organic C
* inorganic C
o total S
» acid volatile sulfide
o Al, Si
successive extractions with same reagent
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265
Table 5: Extraction of sulfur and organic carbon from marine (A) and
freshwater (B) sediments. After Rapin & Forstner (1983); see
text for description of steps I- V.
B
% in sed.
Step I
II
III
IV
V
S
0.09%
10%
—
90%
___
C org
4.3 %
—
—
77%
23%
% in sed.
Step I
II
III
IV
V
S
0.6 %
17%
13%
20%
42%
8%
C org
2.7 %
—
—
85%
15%
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266
Table 6: Evaluation of the effects of sample pre-treatment on
metal partitioning (INRS-1).
metals : Co Cu M1 Pb Zn; Fe Mn
extractants: MgCl2
NaOAc/HOAc
NH2OH-HCl/HOAc
H202/HN03
sediments: lake Aylmer (oxic)
lake Magog (anoxic)
preservation: wet storage, 4°C (20d)
methods freezing
freeze-drying
drying, N2, 20°C
drying, air, 105 °C
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267
Table 7: Evaluation of the effects of sample pre-treatment on
metal partitioning (INRS-2).
metals:
extractants:
sediments:
comparison:
Cd Co Cr Cu Ni Pb Zn; Fe Mn
MgCl2
NaOAc/HOAc
NH2OH-HCl/HOAc
H202/HN03
lake Aylmer (anoxic)
lake Nepahwin (anoxic)
with/without N2 atmosphere
for extractions 1 •»• 3
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268
Table 8: Fate of acid volatile sulfides during the extraction
procedure - influence of adventitious oxygen.
lake Aylmer lake Nepahwin
(1.8 x 10-6 mole/g) (29 x 1Q"6 mole/g)
fresh sediment (100%) (100%)
lyophilized 33 2
air-dried 11 1
with N2 atmosphere
step I 97% 89%
II 97 87
III < 5 1
without N2 atmosphere
step I 38% 11%
II 20 1
III < 5 0
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269
Table 9: Influence of adventitious oxygen on the partitioning of iron
in an anoxic sediment (lake Nepahwin).
iron concentration (10-6 mole/g)
fraction
I
II
III
IV
with N2
19.0 ± 0.6
123.6 ± 2.1
119.3 ± 0.6
13.1 ± 1.0
without Np
2.7 ± 0.2
47.3 ± 2.8
176.5 -t 3.2
10.3 ± 1.0
a
- 16.3
- 76.4
+ 57.1
- 2.8
246.5 ± 5.2 273.1 ± 4.0 + 29.7
521.5 ± 5.7 509.9 ± 5.8 - 11.6
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270
Table 10: Influence of adventitious oxygen on the partitioning of lead
in an anoxic sediment (lake Nepahwin).
lead concentration (10-9 mole/g)
fraction with N2
I 0.1 ± 0.01
II 99.9 ± 6.3
III 1071.5 ± 74.8
IV 419.9 ± 28.0
V 154.4 ± 8.2
without Np
2.7 ± 0.2
502.0 ± 17.4
656.4 ± 66.1
337.9 ± 18.3
173.8 ± 11.6
A
+ 2.6
+ 402.1
- 415.1
- 82.0
+ 19.4
1747.2 ± 82.1 1674.8 ± 72.4 - 72.4
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271
Table 11: Influence of adventitious oxygen on the partitioning of lead
in an anoxic sediment (lake Aylmer).
lead concentration (10~9 mole/g)
fraction with Np without Np A
I 1.9 ± 0.1 2.4 ±0.2 + 0.5
II 173.8 ± 12.1 117.3 ± 10.6 - 56.5
III 168.9 ± 5.8 214.8 ± 12.1 + 45.9
IV 43.9 ± 3.9 55.0 ± 6.3 + 11.1
V 97.0 ± 1.9 102.3 ± 2.9 + 5.3
Z 485.5 ± 14.0 491.8 ± 17.4 + 6.3
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272
Table 12: Influence of pH on the partitioning of sediment-bound metals.
metal A pH
Cd
effect
relatively mobile; organic forms decreased as
pH lowered; accompanying increase in dissolved
and exchangeable forms; no significant changes
in Cd associated with reducible fraction.
reference
Zn
relatively mobile; dissolved and exchangeable
Zn increased markedly as pH decreased;
concomitant decrease in Zn associated with
reducible fraction.
Pb
immobile; little or no dissolved Pb detected
at any pH; exchangeable forms increased under
moderately acid conditions (pH 5.0); no
significant changes in Pb associated with
reducible fraction.
Hg
immobile; little or no dissolved Hg detected at
any pH; exchangeable Hg increased slightly
under moderately acid, reduced (pH 5.0, -150mV)
and weakly alkaline, oxidized (pH 8.0, +500mV)
conditions.
-------
Table 13: Determination of metal partitioning in sediment cores (circumneutral lakes).
reference
Capobianco
& Mudroch
(1979)
Baiker, in
Forstner
(1982)
geographical
location
lake Ontario
lake Constance
dating preservation
no freeze-dried;
ground
yes ?
N2 strata
(cm)
no 1
(* 26)
? 2, 3
(+ 15)
metals
Fe Mn
Cr Cu
Ni Pb
Zn
Zn
extraction
procedure
0.5 N HC1, 20°
HC1/HN03, 90°
HF/HC1 0^03
BaCl2/EDTA
?
NH2OH»HC1
0.3 N HC1
Manning et al . lake Ontario
(1983)
Viel et al. lago Maggiore
(1983")
yes
yes
210pb
freeze-dried
freeze-dried
no 1
(* 10)
no 1,2
(+ 20)
Cd Co
Cr Cu
Ni Pb
Zn
Cd Cu
Pb Zn
MgCl,
NaOAc/HOAc
NH2OH»HCl/HOAc
H909/HNO,
HF/HC1
MgCl2
NaOAc/HOAc
NH2OH-HCl/HOAc
H262/HN03
HF/HC10U
Dominik
et al. (1983)
lake Geneva
yes
210pb
freeze-dried
no 0-1 Cu Zn NH^OAc
31-33 Pb NaOAc/HOAc
75-80 210Pb NH?OH»HCl/HOAc
21°Po H262/HN03
HNOo
CO
-------
Table 14: Determination of metal partitioning in sediment cores (acid lakes).
reference
Evans &
Parliament
(1983)
Reuther et al.
(1981)
Reuther et al.
(1983)
White (1984)
Ford (1984)
Rapin et al.
(1984)
geographical dating
location
Plastic lake yes
lake Hovvatn yes
lake Langtjern
lake Gardsjon ?
lake Stora Gal ten
lake Lysevatten
Dart lake yes
Cone Pond yes
South King Pond 210Pb
Clearwater lake
preservation N2
air- dried, no
80 °C; ground
air- dried; no
70 °C
air-dried; no
70 °c
wet storage, no
4°C (-> 6wk)
wet storage, no
?°C (3-12mo)
wet storage, yes
4°C (+ 7-lld)
strata metals
(cm)
2 Pb
(- 12)
1 Cd Co
(+ 20) Cu Ni
Pb Zn
1,2 Cd Pb
(- 20) Zn
Fe Mn
1,2,4 Pb Zn
(-- 20) Al
Fe Mn
1 Al
Fe Mn
1,2,4 Cd Cu
(> 20) Ni Pb
Zn
Fe Mn
extraction
procedure
MgCl,
NaOAc/HOAc
0?3l5 HC13
HC1/HN03
(non-sequential )
NH^OAc
NH,OH'HC1/HN03
(NH^ )oC2Oj.
H202/HN03
HR03
NH.OAc
NH.OH.HC1/HNO,
(NHJ-C-O,,
H202/RN03
HR03
MgCl2
NH2Ofl.HCl/HOAc
H202/HN03
HN03
H202/HC1
NaOH
LiB02
MgCl2
NaOAc.HOAc
NH2OH-HC1
NH9OH.RCl/HOAc
p
F/RC10
[\3
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275
DIATOM ANALYSIS
by
Richard W. Battarbee
Pa IaeoecoIogy Research Unit
Department of Geography
University College London
26 Bedford Way
London WCIH GAP
Introduction
I would like to start by thanking Steve for Inviting me and also by
thanking the EPA for funding the workshop and providing us with excellent
accommodatIons.
First, I want to Introduce you to diatoms because I think that a
number of people here are not particularly familiar with diatoms and diatom
analysis. I shall then talk about the history and some of the problems of
diatom pH reconstruction. Finally, I will suggest some other things that
we should be doing with diatom analysis.
Diatoms
Figure I shows SEM pictures of two common acid diatoms, label I aria
quadrIseptata and T. blnalIs. Diatoms are unicellular algae. They are
particularly Interesting to palaeolImnologlsts because they have slllclous
cell walls and therefore tend to be well preserved In lake sediments. In
the figure there are two complete cells. The features we are Interested In
for taxonomic purposes are the characteristics of the valves. These valves
are connected by a series of girdle bands of various kinds and quantity,
although In sediments It's likely that these various components of the
diatom cell will be separated. Diatoms grows In most wet or damp habitats.
They are, of course, particularly common In rivers, lakes, estuaries and
the oceans. In lacustrine environments many people think mainly In terms
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276
of plankton Ic diatoms, the ones that grow In the open water more or less
free floating and completing most of their life cycle In the water column.
However, especially In acid lakes, we are also concerned with pertphytlc
species, those that grow around the edges of a lake associated with various
kinds of substrates, on plants, the eplphyton, on sand, the eplpsammon, on
stones, the eplllthon, and on mud, the eplpelon. There Is a lot of overlap
between the species found In these habitats. We might expect that almost
all surfaces situated above the photic limits In a lake will have a fairly
dense cover of diatoms. These are the communities, as well as the plankton
communities, that contribute diatoms to the sediment. In addition we must
not forget that diatoms can come from outside the lake, from lakes
upstream, from streams, and In fact there may be diatoms associated with
soils in the catchment. All of these can come Into the sediment often
going completely unrecognized. It Is a possible source of error that has
to be considered in some situations.
pH Reconstruction
Diatoms respond very strongly to water quality. In fresh water,
especially mesotrophic and oligotrophic fresh waters, pH or hydrogen Ion
activity, or more probably factors correlated with hydrogen Ion activity,
have a strong influence on the composition of diatom communities. The
starting point in most diatom pH studies Is Hustedt's classic monograph on
the diatoms of Java, Ball and Sumatra (Hustedt 1937-39). He Introduced a
number of terms describing groups of diatoms In relation to pH
(I) AlkalIbiontic: occurring at pH values > 7;
(2) alkalIphilous: occurring at pH about 7 with widest distributions
at pH > 7;
(3) indifferent: equal occurrences on both sides of pH 7;
(4) acidophilous: occurring at pH about 7 with widest distribution
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277
at pH < 7;
(5) acldobiontlc: occurring at pH values < 1, optimum distribution
at pH = 5.5 and under.
That was the beginning and nothing much really happened for quite a
while until the Danish algologlst Nygaard In 1956 tried to quantify the
Hustedt scheme by producing three Indices:
Index a = (acid units)/(alkalIne units);
Index co = (acid unlts)/(number of acid species);
Index e = (alkaline unlts)/(number of alkaline species).
Indexu) and Index e have not really been used very much because they seem
to produce variable results. They are dependent on the number of species
Identified, taxonomtc conventions that vary between workers and the number
of Individuals that are counted In any sample. Consequently, they are not
very good. But Index a has been used and Is still being used by dlatomists
today as a way of reconstructing pH. The Index calculation produces a
number which can be correlated with measured pH and this can be used to
calculate a linear regression equation to predict pH (Fig. 2).
This Introduces the problem of which pH measurement we use In such a
regression, how we measure pH, and what time of year the pH Is measured.
Should we look for an average pH value, should we use a value for a
particular time of year, how many samples do we need for a lake that may
have fluctuating pH before we are happy that we can actually ascribe one pH
value to put Into our equation?
Jouko Merilainen has addressed this problem with respect to Finnish
lakes. By looking at the pH of 150 lakes through the seasons he showed how
in some cases the summer pH can be up to two units higher than the autumn
pH (Fig. 3). He suggested that only pH measurements that were taken after
the overturn In autumn should be used in calibration models. That may be
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278
fine in Scandinavia and may work well In dlmlctfc lakes but then many of
our lakes are holomlctic and there are seasonal variations In pH caused by
different factors, so It's still not entirely clear Just which pH value we
should use. If we go back to the regressions we can see that Merllalnen
produced a very good relationship using the pH measured In autumn against
the log of the Nygaard Index. However, ft has a certain deficiency, one
that Ingemar Renberg In particular was concerned with. In very acid
conditions It may be that there are no alkaline diatoms at all, so the
denominator of the equation Is 0, producing scores of infinity. To counter
this problem Renberg Included the percentages of the clrcumneutral taxa In
the equation and produced an index B:
%ind.+(5x
-------
279
get away from this classification system by using the occurrences of
selected taxa In the data set as individual predictors of pH. An example
Is shown In Fig. 6. It has a good r value but the relationship Is not
quite as good as that given by the other systems. There are ways of
Improving this by using various PCA methods which Involve the whole data
set.
Davis and Anderson compared the various techniques of pH
reconstruction on a sediment profile from Speck Pond In Maine (Fig. 7).
The diagram shows that whether we use the Index system, the multiple
regression analysis of groups or the multiple regression analysis of
Individual taxa the story Is similar although there seems to be more
variability with the latter.
These are the various ways being used at the present time to
reconstruct pH and they allow diatomlsts. If a good chronology Is
available, to address a number of questions. What I want to do very
briefly Is to show you an example of this In practice using some of our
work from Scotland. The site is called Round Loch of Glenhead and It has a
pH at the present time of about 4.7. Figure 8 shows a dated diatom
diagram. In the lower part of the diagram the percentages of the various
species are quite stable, but at about 1600 AD there Is a decline In the
plankton, a feature which seems to be very common In acidifying lakes at a
pH of about 5.5. In this particular case one can see that it Is quite
clearly a pre-Industrial Revolution feature, so the cause is not associated
with acid deposition. From about 1850 there Is very clear evidence of
acidification with strong declines In circumneutral species, Increases In
the percentages of the acidophilous species, and then strong Increases In
the acldobiontic species. The data can be summarized by grouping the
species Into the various pH categories and using a pH reconstruction
-------
280
method, here Index B, to show likely pH change through time (Fig. 9). It
appears that we have a drop of about I pH unit since about 1850. Our
predicted pH for the surface sediment Is about 4.7, agreeing very nicely
with the measured pH that we have for this site which ranges between 4.5
and 5.
DI atoms and the Cause of Lake Acidification
So we can begin to produce some Important Information about whether a
lake Is being acidified. We can. If necessary, calculate the rate of
acidification through time If we translate pH Into H concentrations
and by doing more and more of these sites In different areas we can begin
to assess the extent of acidification. However, by careful choice of sites
we can also begin to address the problem of the causes of acidification.
For example, in Britain one of the possible causes of aldlfication Is the
afforestation of our uplands. Afforestation is usually the planting of
conifers In the uplands on acid moorland soils. There are various ways
that such planting might cause acidification, we think, so to test the
hypothesis we chose sites that were afforested and compared them with
non-afforested sites. We found that our most extreme examples of
acidification occurred In catchments that had not been afforested and In
the two sites that had been afforested we found evidence of acidification
beginning a number of decades before the time of planting.
D i atoms and Acid If I cat I on HI story
Last year I reviewed the available literature to work out a chronology
of acidification (Table I). So far there are only about 30 or 40 sites
which have been worked on In this way so we do not have much to work with.
However, I suspect there are at least two or three times that many sites
actually being worked up at the present time and the situation is likely to
improve dramatically In two to three years time. The evidence presently
-------
281
available from America, Norway and the UK suggests that the present
acidification problem In those countries began In the nineteenth century
with the most rapid changes taking place since about 1930. This Is
apparently counter to the view that acidification Is a problem of the last
20 or 30 years. It Is clear from this that most documentary records, where
they exist at all, do not have the antiquity or reliability required to
determine the history of this problem.
ProbI ems of pH ReconstructI on - ExtrInsIc Factors
I. Good pH reconstruction needs very large modern data sets. These take a
long time to produce and they need to be of very high quality. But how
valid Is It to amalgamate regional data sets to produce the large files
necessary? Should we put all our data together to produce data sets that
are very useful statistically but by doing this we are bringing problems
associated with regional variations In ecology and distribution of the
various taxa. I think It Is better to try to work with smaller regional
data sets and only amalgamate after careful Inspection of the behavior of
the different species In the various regions.
2. Clearly a very important question In all this Is taxonomy and the
correct Identification of species. There are plenty of obvious examples In
the recent IIterature where mistakes have been made by poor taxonomy.
Correct identification Is especially important where species of very
different ecology have similar morphology as in TabelI aria. On a
different plane there are many very genuine taxonomlc difficulties, as with
all diatom analysis, mainly relating to the difficulty of the species
concept In diatoms and form variability within species.
3. Then again, there are problems relating to the lack of Information
about the ecology of many diatom species. Some species are reasonably well
understood, they occur frequently, In abundance, and we can see their
-------
282
distribution In relation to a range of water quality parameters. For many
species, however, especially the ones that are less common, we really don't
know which pH class to put them In or, If we look to the literature for
help,, we might find that the literature Is wrong or conflicting. In which
case we might arbitrarily choose the more conservative of two
posslblIItles.
4. Perhaps one of the most worrying problems Is the artificiality of the
pH classification Itself. Species ranges and optima are likely to follow a
continuum of values and many species may legitimately fall between classes.
Consequently models that move away from the pH classification system should
certainly be encouraged.
ProbI ems of pH Reconstruct Ion - Intrinsic Factors
We might expect to find some of variance associated with the
relationship between measured pH and predicted pH to be related to other
intrinsic factors i.e. beyond the control of the operator and the models
used. There are many and I have suggested five.
I. One problem Is using diatoms as Indicators of pH when their presence Is
due to another or a combination of other factors. I don't know of any
examples of this In acid system but It Is clear that the same species can
occur in different environments for different reasons. For example,
Cyclotella meneghInlana Is correctly thought of as a halophllous species
since it occurs In saline lakes and brackish estuarlne conditions. It also
occurs In eutrophic lakes but It would be wrong to use it as an indicator
of salinity in this environment. In an acid system It might be that
nutrient enrichment leads to the development of a flora that contains taxa
categorized at higher pHs although pH itself may not have changed.
2. Another question which we are working on at the moment is the
relationship between the diatom assemblage and the sources of the diatom
-------
283
assemblage. It must not be forgotten that what we are doing Is relating pH
to a fossil assemblage that, we assume, fairly represents the contemporary
living communities In each lake. In other words the relationship between
the point of accumulation, the point at which we take a core or surface
sediment sample, and the distribution of communities and micro-habitats Is
critical to the composition of the sediment assemblage and thereby to the
reconstructed pH within any particular lake system. Some of our
preliminary data Indicate that there Is considerable spatial variability In
diatom communities within a lake. pH reconstruction, for example, on a
range of II eplpsammlc and 17 eplllthlc habitats within the same lake and
at the same time gives values from 3.7 to 5.3 and 3.7 to 5.0 respectively.
The mean of these values Is close to the pH 4.7 value predicted from the
surface sediment assembalge so at this site our assumptions appear to be
fairly valid. However, there has been so little work of this kind we must
continue to question these assumptions In many other situations.
3. A related problem to this Is that of differential transport and
accumulation. This Is not just a problem of mlcrohabltat variability but
variability In the way In which the diatoms from those habitats are then
transported to the point of accumulation and the Influence of this on the
spatial pattern of accumulation of an Individual taxon. John Anderson, a
graduate student of mine, has looked at the spatial distribution of
planktonlc diatoms In the sediments of a eutrophic lake. Figure 10 shows
variations between cores of one species, Stephanadlscus tenuis. The trends
are very similar but the detailed patterns and the ranges of percentages
vary quite strongly and this would undoubtedly cause variations in pH
reconstruction.
4. Another factor that hasn't really been considered In acid lakes is the
problem of breakage and dissolution. While dissolution Is a very Important
-------
284
problem in many alkaline and saline sites I am not sure to what extent they
are a problem In acid lakes. Our data suggests that diatoms are preserved
reasonably well, but If dissolution does occur and If It Is differential
between taxa It will cause problems In pH reconstruction. What seems to be
more Important In our Scottish sites Is breakage. We have a lot of diatom
fragments and debris there that we cannot really Identify and we have to
hope that the diatoms that we count and Identify are In fact a
representative sample of the ones that we can't. But If there is
differential breakage, again there Is going to be a problem In
reconstruction.
5. The final point I would like to make Is about the Importance and
problems of allochthonous Inputs. It may not be a problem in many sites
but in some of our Scottish sites the catchments of the lakes have been
disturbed by afforestation processes involving deep ploughing to drain the
soil prior to planting. These operations have been followed by severe soil
erosion. We think considerable quantities of diatoms are comlnig In with
eroded material and causing problems In pH reconstruction.
Other Areas of Ignorance
There are some problems with pH reconstruction, but, perhaps
surprisingly, it seems to be a good technique and it does work quite well
In lots of situations. However, I want to suggest that In all this kind of
work we do not pay enough attention to understanding the dynamics of the
contemporary diatoms In these systems. There are all sorts of questions
that we need to address ourselves to. Not just what the pH of a lake was
and what are the error bars on that pH, but we need to know why these
changes have taken place, why do we lose the diatom plankton around the mid
5 pH, what happens to diatom productivity In acidifying lakes, what Is the
relationship between diatom and other primary producers, and can we, from
-------
285
dfatom accumulation rates fn the sedlmens Infer anything about changing
production? Also, does transparency Increase when lakes acidify and If so,
to what extent does that Influence habitats within the system, and could
some of the changes we observe be due to habitat change rather than changes
In water chemistry? Why do we get this very marked change In diatoms at
low pH? There has to be a very Important ecological mechanism operating
across these particular gradients and we are not sure what It Is. I would
like to see a lot more attention paid to these ecological questions as well
as to the statistical questions of pH reconstruction.
Recommendat1ons
I. Don't Ignore contemporary diatom populations.
2. Integrate palaeolImnologlcal research with llmnologlcal research.
3. Monitor populations over a wide range of lakes In relation to both
lake and catchment variables.
4. Take advantage of manipulation experiments e.g. liming, to assess
diatom responses.
5. Persuade ecophyslologlsts to consider core-derived hypotheses and
questions.
6. Choose sites very carefully to answer specific questions.
7. Assess within basin variability.
8. Evaluate hypotheses by comparison with parallel data.
9. Take taxonomy very seriously.
-------
286
-•z.C'S. llar-ia auzar-issztata Knuds.
ia b-inal'is (Hhr.) Grun.
Figure 1. Two acich'obiontic diatoms from Loch Enoch.
-------
a
index
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-------
150 Lakes in Eastern Finland
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Speck Pond
293
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(from Davis & Anderson, unpublished manuscript).
-------
Diatom diagram for Round Loch of Glenhead, Galloway
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-------
298
Chrysophyceae
John Smol
It has been well documented that fossil diatoms can be very useful In
reconstructing lake water pH. Nevertheless, a frequent complaint of
paleoltmnologlsts has always been that diatoms represent only one portion
of past algal communities, and that a clearer understanding of past lake
conditions could probably be achieved if different algal groups were used.
The Chrysophyceae represents such an algal group for a variety of reasons.
The Chrysophyeae are a very diverse group of algae with approximately 1,000
described species, the majority of which are flagellated and planktonlc.
They are found In a variety of habitats, but appear to be most abundant in
ollgotrophlc and acidic waters, where they may represent upwards of 90$ of
the primary production In some Canadian shield lakes.
When I discuss chrysophycen microfosslIs, I am referring to
chrysophycean cysts or statospores, and mallomonadacean scales.
All chrysophyte species produce cysts (=statospores), which Is a
resting and/or sexual stage. In fact the formation of the statospore Is a
characteristic feature of the Chrysophyceae, and the external morphology
appears to be species specific. Statospores are formed endogenously by all
chrysophytes, but relatively little is known about them at this time. What
we do know about statospores Is that a I I chrysophytes produce them, that
all statospores are siliceous and therefore are well preserved lake
sediments, and that the statospores themselves seem to be species specific.
However, only a small portion of statospores have been linked to the algae
that produce them. In fact, less than 5% of chrysophyte species have been
linked to their respective statospores. This situation hasn't changed much
-------
299
since 1956, when Nygaard, In his classic paper from Lake Gribso, recognized
the viability of chrysophycean statospores as a useful group of
mlcrofosslIs. He recorded and Illustrated a variety of statospores from
his diatom slides. Seventy seven morphotypes were described by Nygaard,
and he gave them temporary names under the genus Cysta and then a suitable
species name, usually of a descriptive nature. Although this was a very
practical approach, Nygaard recognized Its short comings, as evidenced by
the fact that he compared himself to an ornithologist who was trying to
describe a bird fauna of an unexplored region with only the eggs at his
disposal for identification. However, he did produce a stratigraphy and he
showed that there were changes In the statospore profiles. That was almost
30 years ago, and we haven't progressed very much since that time.
However, recently the International Statospore Working Group (I.S.W.G.) has
been formed. I would predict that In about 10 years most statospores will
be linked to the algae that produced them, as the I.S.W.G. is setting down
strict guidelines as to how to describe statospores.
There is still a large amount of work to be done here besides
statospore taxonomy. There is some evidence In the literature suggesting
that not all chrysophytes form a statospore every year and they may
overwinter In the vegetative state. Research should be done on the stimuli
triggering encystment and the physiology of resting stage formation. This
Is especially Important for acidification studies because very often
chrysohytes are abundant In acidified lakes.
Much more progress has been achieved with the scaled chrysophytes, the
Mailomonadaceae, a very Important family In the Chrysophyceae which
Includes such genera as Mailomonasp Synurar and Chrysosphaerella. The
characteristic feature of the Mailomonadaceae Is that they are covered by
siliceous, species specific scales. Until the 1950's, most taxonomlc work
-------
300
on this family was based on the size and shape of the cells. However, with
the advent of electronmicroscopy, it was demonstrated that this was an
inadequate way of describing the taxonomy of these organisms, and now the
entire taxonomy Is based on the morphology of the scales. Each scale is
species specific. Since these scales are siliceous, they have all the
necessary characteristics to be useful paleo indicators. They are well
preserved and abundant in lake sediments, In fact they are sometimes more
common than diatoms (In some lakes It's not uncommon to have 200 scales per
diatom). They can be prepared using the same techniques used for diatoms,
and they also appear to be ecologically diverse. These scales were almost
totally ignored in paleolimnological studies until I960 when three papers
were almost simultaneously published (Battarbee et a I., I960; Munce, 1980;
Smol, I960). However, these early studies largely addressed the problem of
eutrophicatlon (Smol et a I., 1983).
More recently, much of my research effort has been focussed on lake
acidification. All of this work has been done in "conjunction with Don
Charles and Don Whitehead at Indiana University. As has been discussed by
Rick Battarbee, diatoms are very useful for lake acidification studies, but
unfortunately planktonic diatoms tend to be excluded In acidic waters of a
pH < 5.5. Consequently, If only diatoms are used In paleo studies of
acidified lakes, one wouldn't be able to trace changes in the
phytoplankton. In contrast, chrysophytes are almost exclusively
planktonic. It would seem that if chrysophycean microfosslls could be
recorded in acidified lakes, we would get some Indication of changes In the
open water community.
In order to better understand the ecological preferences of
mallomonadacean species, we have recently completed a survey of the
mallomonadacean assemblages from the surficlal sediments of 38 well studied
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301
lakes In the Adirondack Mountains (N.Y.) (Smol et al., I984a). Reciprocal
averaging and cluster analyses Indicated that pH and factors correlated
with It (e.g., alkalinity) exerted the greatest Influence on
mallomonadacean assemblages. However, some of the most striking
relationships could be seen when the relative abundance of Individual taxa
were expressed relative to the summer pH levels of the surface waters of
the 38 study sites (Figs. I & 2). Certain taxa appeared to be quite
specific In their pH preferences. From this preliminary survey. It would
appear that taxa such as Mailomonas caudata and M. punctlfera , as we11 as
Synura splnosa appear to be circumnutral or even alkalI philous species,
whereas M. hamatar M^. hlndonlI. and S. macracantha appear to be
acldoblontlc.
The next stage was to see If these assemblages could be used to infer
past pH levels from stratigraphlc analyses. Deep Lake In the Adlrondacks
was chosen as an initial study site (Smol et al., I984b). Fossil
mallomomadacean assembalges shifted abruptly In the lakes recent sediments
from a clrcumneutral flora dominated by Mallomonas crass I squama, with
lesser amounts of M*. punctlferaf to one dominated by acidobiontlc species
(i.e., M. hIndon11 and M. hamata).
The results of the Deep Lake study have been confirmed by the study of
a variety of other lakes In the Adirondack Mountains (currently part of the
PIRLA project funded by the Electric Power Research Institute). As an
additional example, data from Big Moose Lake are presented here (Fig. 3).
Recently, Charles (1984) described the diatom stratigraphy from this core.
As In the Deep lake study, a marked shift In Mallomonadaceae occurred In
the mid-1940's with more acidobiontlc taxa Increasing In abundance. An
analysis of the accumulation rates of scales In the Big Moose core (Fig. 4)
Indicates that mallomonadacean populations Increased substantially during
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the proposed period of acidification. Quite possibly, the decreased
populations of planktonfc diatoms at this time (Charles, 1984) resulted In
a less competitive environment for the planktonlc chrysophytes.
Chrysophycean microfossils still represent a relatively unexplored
group of pa IeoIndicators; however, I believe that these preliminary studies
Indicate that future Investigations are clearly justified. Further studies
on the physiological ecology of chrysophytes will be required to refine the
predictive value of these microfossils. Continued surveys of
mallomonadacean distributions should elucidate these relationships, but
laboratory studies on chrysophyte physiology and the monitoring of
chrysophyte populations In manipulated lakes should be undertaken. In
addition, taxonomic research on statospores will eventually allow the
Inclusion of all chrysophyte species In the Interpretation of lake
hIstorIes.
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REFERENCES
Battarbee, R.W., G. Cronberg, and S. Lowry. I960. Observations on
the occurrence of scales and bristles of Mailomonas spp.
(Chrysophyceae) In the micro-laminated sediments of a small
lake In Finnish North Karelia. Hydroblologla 71: 225-232.
Charles 0. 1984. Recent pH history of Big Moose Lake (Adirondack
Mountains, New York, USA) Inferred from sediment diatom
assemblages. Verh. Internat. veretn Llmnol. 22: (In press).
Munch, C.S. I960. Fossil diatoms and scales of Chrysophyceae In the
recent history of Hall lake, Washington. Freshw. BIol. 10:
61-66.
Nygaard, G. 1985. Ancient and recent flora of diatoms and
Chrysophyceae in Lake Grlbso. Folia llmnol. scand. 8:
32-262.
Smol, J.P. 1980. fossil synuracean (Chrysophyceae) scales In lake
sediments: a new group of pa IeoIndicators. Can. J. Bot.
58: 458-465.
Smol, J.P. 1985 (In preparation). Chrysophycean mlcrofosslIs as
Indicators of lake water pH. To be published in Smol, J.P.
etal. (Eds.). Diatoms and Lake Acidity. Dr. J.V. Junk
Publishers, The Hague.
Smol, J.P., S.R. Brown, and R.N. McNeely. 1981. Cultural
disturbances and trophic history of a small meromlctlc lake
from central Canada. Hydrobiologla 103: 125-130.
Smol, J.P., D.F. Charles, and D.R. Whitehead. I984a. Mailomonadacean
(Chrysophyceae) assemblages and their relationships with
limnologlcal characteristics in 38 Adirondack (New York)
lakes. Can. J. Bot. 62: 911-923.
Smol, J.P., O.F. Charles, and D.R. Whitehead. I984b. Mailomonadacean
mlcrofosslIs provide evidence of recent lake acidification.
Nature 307: 628-630.
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1. The percentage contribution of selected Ivlallomonas scales plotted
relative to the summer pH values for the Adirondack study lakes
(from Smol 1985).
7.
100
50
0-
/
50-
o-
4
20-
1 100
M. crassisquama
& pseudocoronata
• •
•
.. ' V. 50
: •
• .
• • • .
.••
. .
»
M. acaroides
•
• •
•
• • *
>l ' 1 | 1 1 1 1 1 1 OT i***f« 1 i 1 T***T *~i
i 5 6 7 8 45678
P H pH
•
* 50 -
M.hamata M. hindonii
*
: . v. .
•:•
.... . • ." • * • * *'t:;.\. f. : o-
5678 4
PH
20-j
M. caudata .
• •.!•••• f*
» -••••
..r— :. r •••-. /• .
45678 4
pH
•
. *..
• 1 • «1-M .f . 1 . lf..M^..M, lf .1 t
5678
PH
M. punctifera
. •
. ••••
•»t*""V"-r « — i • •«• ..f >. ; ; ,
5678
nH
CO
o
-------
Figure 2. The percentage contribution of selected Gynura scales plotted
relative to the summer pH values for the Adirondack study lakes
(from Smol 1985).
50
V.
S. spinosa
0 i ••>••*!*»• .T • T—v
5 6
PH
8
% 50-
H
<
S. echinulata
•
• •
• • *•
• - *--T — *i 1 • ^ * — i* • V • i — *-{
5678
PH
V.
50-
• S. sphagnicolo
V.
PH
20-
S. macracantha
..^. •!«. • •_ _• . — _ . .
A 5 6 7
pH
8
co
o
en
-------
|A
IU
o
x 20
a.
Q
30
40
i
m
^
"^
*
*
*
*
*
»
—
"
•"•••^
"*
*
19/0
1 O£ A
i y\j v
| QC A
1 jOw
1O/ A
IrfHW
1 GOA
192U
1900
loarv
• lOOU
1820
1800
50 0 30
PERCENT OF SCALE SUM
(. = less than IV.)
20
Big Moose Lake
Figure 3- The relative frequency of mallomonadacean scales in the recent sediments of
Big Moose Lake. The Pb-210 dates were provided courtesy of Dr. S. Norton and
Ms. Geneva Blake of the University of Maine at Orono, Dept. of Geological
Sciences.
CO
o
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307
10
20
CL
LU
O
30-
40-
0 5 10 15
SCALES («106)/cm2/y
20
Figure 4-. The accumulation rates of mallomonadacean scales in
the recent sediments of Big Moose Lake.
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308
Cladocera
David F. Brakke
I thank Steve Norton for getting this workshop organized and for
putting me on the program at about the time that I would normally be
driving to work so that I'm at least half awake. Rick Battarbee
summarized many things that apply to most groups of organisms. In
addition to diatoms, his discussion applies to the Cladocera, and to
many of the other Invertebrates that I shall discuss. I will start
out with some slides to show you the kind of organisms I will talk
about, because more people know about diatoms, I think, than know
about cladocerans.
Here is one cladoceran. It Is a very large one, certainly large
enough to handle a few diatoms. It is a littoral zone cladoceran. It
lives in the shallow areas of the lake, in the weed beds and the mud.
This is an Intact organism. It Is not planktonic, so we are talking
about a totally different set of organisms, than is In the littoral
zone. Cladocerans reproduce mainly by parthenogenesis. They make
xerox copies of themselves. There Is a sexual phase, which usually
occurs in the fall, with males and gamogenetic females being produced.
They produce resting eggs, which are saddle shaped resting structures
called ephippia. These structures, for some of the cladocerans are
the only structures that remain in the sediments. For example, almost
all of the other parts of Daphnla will disappear. The parthogenetic
females do not leave any remains; the males may leave clasping hooks,
but the ephippia will remain In the sediments. These can be
Identified at least for certain species.
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In lake sediments, a cladoceran will be disarticulated. They are
not siliceous as are diatoms; they are made of chitln. Chit I nous
structures do preserve very well, but there Is differential
preservation. Not all groups of the cladocerans preserve equally
well. In fact, many of the cladocerans are completely eliminated
except for very small parts. This Is also true for other planktonlc
groups, such as the copepods.
This Is another of the littoral zone cladocerans. You can
determine very easily the species from Individual parts. A few little
pollen grains on the slide show the rough size of the parts. Other
parts of the organism that are preserved, In addition to the shell,
are the post-abdomen and the post-abdominal claw. These one can also
differentiate. One can tell the species by nearly any one of the
parts that are recovered from the sediments. This is the reverse side
of one of the cladocerans which live primarily In the mud. The parts
that preserve normally are the headshield, shell, the post-abdomen,
and post-abdominal claw. Most of the other parts disappear. To
reiterate, the parts are species specific.
A totally different kind of cladoceran would be these little
elephant-like forms. This Is Bosmlna. which Is normally a
euplanktonlc form. Most of Its population Is probably off shore In
the center of the lake; but there are also very large littoral
populations. It Is from a different family than the littoral chydorld
cladocera, but very Important In oligotrophic lakes. In contrast to
Daphnlar Bosmlna preserves very well. Wolfgang Hofmann Is one of the
few people In the world who can handle them taxonomlcally. They are
rather variable morphologically, and they are very common In
oligotrophic lakes and in acidic lakes.
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Returning to Daphlna. I will give you some examples where It may
be preserved. Sometimes the claws preserve very well and are very
useful; the ephlppla preserve well. Cladocerans have been used for
Inferring a variety of things about changes In lakes. They have been
used very successfully to reconstruct the eutrophlcatlon history of
lakes. For example, Saint Clair Lake in Northwestern Minnesota was
enriched when a sewage plant was hooked up to a series of lakes, and
started spilling phosphorous downstream. After 1870, with excessive
phosphorous loading, essentially the whole community became dominated
by one species, Chydorus sphaericus. The lake had a number of species
and ended up with many fewer, with the community essentially dominated
by Chydorus. There are very good relationships between primary
production In a lake and the species diversity of cladocerans. The
greater the production In the lake, the lower the species diversity of
cladocerans. The community becomes simpler and is dominated by a
single form or just a few forms, usually Chydorus sphaericus.
There have been some surface sediments that have been studied for
cladocerans in similar fashion to diatoms (Figure I). They show
variations with respect to a pH gradient, just as do the diatoms.
They are not as powerful, but if you put up some New England surface
sediment samples for cladocerans you would see these butterfly
diagrams of percent composition vs. depth. Some species occur at
higher pH's and never to any great abundance; some occur throughout a
profile and you cannot say very much about them at all. If you do a
cluster analysis of surface sediment samples, you do find some
groupings of lakes that tend to have lower pH's and groupings of those
that have generally higher pH's, although there are other important
variables (Figure 2).
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Elevation has an Influence on these cladoceran communities; they
may be much more complicated In terms of their response to pH than
diatoms. They are Influenced by many more factors. Some of the
cladocerans have a greater abundance at higher pH and their decline In
sediment Implies that the lake water pH may be going down.
Essentially, It Is confirmatory evidence for a pattern that might have
been Inferred on the basts of diatoms. There are some species that
seem to have constant relative abundance with pH and some like
Chydorus sphaerlcus that are either more abundant at higher pH's In
eutrophic lakes or more abundant In the acidic lakes. This species
group may be a rather Interesting one, because once It Increases with
either Increasing or decreasing pH It really does tell you something.
It may tell you that the lake has either moved into a eutrophic phase
or that It has been acidified. We have categorized these various
species In terms of pH group and also an altitude group (Figure 3).
There are still more than a few question marks, and In some cases an
Inadequacy of enough material to classify a taxon. Some very abundant
taxa occur but there are other taxa that you see at very low
frequencies.
Does this have any correlation with other data? From some work
in Norway by Hobaek and Raddum, which Includes some of the lakes that
Steve Norton and Ron Davis have sampled, there are differences between
so called acidic lakes, humic lakes, and less acidic lakes in terms of
the number of species present. The number of species may be something
that Is useful. If a lake moves from a pH of 5.5 to a lower value,
you might assume that some of the species are being lost. This Is
particularly true for the cladocerans, but apparently less true for
the copepods and the rotifers about which we know little. But species
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number looks like something that we might be able to use, at least for
the cladocerans. The copepods leave few resting structures so It Is
one part of the plankton that we really cannot say much about In terms
of changes related to acidification.
Will we ever get to these kinds of equations relating pH and taxa
for the cladocerans? I frankly doubt It. One of the main reasons Is
that there are many more factors,that begin to shape cladoceran
communities than Influence diatom communities. The cladocerans,
however, do respond to pH. The number of species and diversity for
New England surface sediments appears to decrease with a decrease In
lake water pH (Figure 4). There Is certainly variability, but there's
a general trend from more than 20 different species to less than 5 In
the more acidic lakes.
Some of the species of copepods occur across a transect of pH in
Norway. But some of the other species are only found In the more
acidic lakes and not In the higher pH lakes. With the cladocerans
there Is one group that occurs only In the higher pH lakes. As the pH
goes down, those organisms are eliminated. The Bosmlna complex which
Is a very diverse group, apparently occurs across the entire pH
gradient. There may be a lot of information to be gained from this
group and no one has really looked at it. I think there Is a lot of
controlled variability that might be expressed and quantified.
There are a number of other areas for which this pattern has also
been observed. If you look at the Sudbury area or the LaCloche
Mountain area in Ontario, In areas where the pH is greater than 5,
Daphnia occurs. When pH is less than 5, there are no Daphnia.
Daphnia at deeper levels In the sediments but not In surfIcla I
sediments may be an indication that the pH has gone down. This may
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not tell us exactly what that pH level was, but In most lakes with a
pH that Is 5.7 or 5.9 Daphnla will be present In the population. If
It disappears that may tell us something.
Let's get back to some of the variation that occurs In some of
these communities. Figure 5 shows the distribution of chydorld
cladocerans in a number of surface sediment samples In Norway against
elevation above sea level In meters. As elevation Increases, Chydorus
starts to dominate the community. That Is also evidenced by a plot of
diversity against relative abundance of Chydorus. When Chydorus Is
very abundant (>60$) the diversity Is very low. When Chydorus
abundance Is low, diversity Is much higher (Figure 6). And again this
can occur on either end of the pH gradient. There are also
Interactions between various species that you have to begin to tease
apart. For example, when Alonopsls elongata Is abundant, AI one I la
nanaf which Is another very common species. Is almost not there
(Figure 7).
What happens In terms of changes over time? This Is the history
of Speck Pond based on Ron Davis' diatom data; they Indicate when a
change in pH occurred. These are the metal increases based on Steve
Norton's data. The cladocerans did not give a clear pattern of
change, and In fact Indicated that other disturbances had occurred in
the lake (Figure 8). A cluster analysis of these same data Indicated
that there was a difference between the surfIcla I sediments and those
deeper in the core (Figure 9). The cladocerans seem to indicate that
the lake has changed. In this lake, also, Daphn ia did occur at depth
In the core in fair abundance. Daphinla did, however, disappear from
the lake, presumably as pH declined. The cluster analysis and
disappearance of Daphlnla confirm the Inference based on the diatoms
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(Figure 10).
Here Is another example from Ledge Pond In Maine. The littoral
zone cladocerans, Indicate that the lake water pH had decreased. They
showed the same pattern of surface sediments analyzed across a pH
gradient (Figure II). This Included a decrease In the number of
species In the upper-most sediments, perhaps related to acidification
or a decrease In pH.
In another lake In Norway this same patterns occurs. One of the
species occurs primarily In higher pH lakes; there Is a very clear and
marked decrease In that taxon towards the surface (Figure 12). Some
Individual taxa have a more direct relationship with pH than others.
Alonopsisf which we would have predicted on the basis of the surface
sediment relationships to be more abundant In the acid lakes,
Increases up core. What did the diatoms Indicate for this lake? The
acidibiontic taxa Increased to the surface, so It looks as though
there was a decrease In pH in this lake.
Disturbances In the watershed are reflected in the cladoceran
community. This small lake had some logging activity In It. It looks
as though the community Is relatively the same through a period of
time, and then there was a (sediment) Interval, here, when this more
alkaline-loving taxon Increased. The lake has returned to some kind
of condition that was similar to what It was before. Perhaps effects
of logging changed the community, and It has now rebounded to Its
former condition. It is important to keep In mind other watershed
perturbations.
Many of these cladocerans living In the littoral zone are
dependent on the kinds of aquatic plants and associated communities
that are found there. Kris Ken I an demonstrated that lake water pH has
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more of an Influence on the cladocerans than does the distribution of
the macrophytes. The pH-Is more important than the specific type of
macrophyte.
One of the major problems In trying to use cladocerans to assess
acidification In lakes Is that the kinds of lakes that have been
examined. In terms of being the most sensitive lakes, may be not very
good candidate lakes to take a core for cladoceran analyses. A lake
like this, which Is In Norway, may have very inorganic sediment; it
has very steep sides to ft, very little littoral zone development, and
there may be no way to get enough cladocerans, at least from the
littoral zone. In the sediment to count. There may be abundant
Bosmlnar but an Important part of the community may not be there.
Blavatn, a lake in the center of Norway, has only five or six species
present and In very low numbers. In this case, you would have to use
enormous quantities of sediment to get enough taxa and Individuals to
work with. There is a very practical limitation to doing cladoceran
analyses on some of lakes. For some of the lakes that you would want
biological Information In addition to diatoms, It will not be
available. In these cases, Bosmlna may be a very useful organism to
concentrate on. I have mentioned the taxonomlc difficulties with that
group. Bosmlna Is very abundant, even In some of the high altitude
lakes with very low sedimentation rates, little organic material, and
few chydorid cladocerans in the sediments. Whereas, Bosmina has not
been utilized In these cases, It may be something to work on.
In summary, there are a number of factors that Influence the
structure of cladoceran assemblages. I have reviewed a number of the
more important factors In this talk and list several here (Figure 13).
A final topic to mention Is the tremendous variation In terms of
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size of cladocerans. Cladocerans get eaten by vertebrate and
Invertebrate predators. The size structure and species composition of
a cladoceran assemblage can change due strictly to predatlon. For
example, If we look at a lake that you might call non-acidified there
Is a significant forcing relationship between fish populations and the
size structure of the zooplankton. Certainly, zooplankton graze
selectively, but they may not have as great an effect In terms of size
structure of diatoms. A species of cladoceran may be exposed to a
vertebrate-predator dominated system. But if fish are eliminated by
low pH/high Al, you may end up with only Invertebrate predators. Fish
select different sized cladocerans, so they may force a change
selectively In the community. Whether the cladocerans force some
significant change In the phytoplankton Is open to question. I do not
think that It Is Important enough to cause significant variability In
dlatom/pH relationships. And it may be In these acid lakes that as pH
goes down, as we get a change In the algal community, the cladoceran
community may also change, but there may be absolutely no causal
relationship between the two. However, If the euplanktonic diatoms
and other algae begin to change from diatoms to something like
Mai lomonas,. this may Influence the grazers. As far as I know no one
has really looked at that. We do know that if the grazer community
has been altered and we start putting phosphorous into the system, the
phytolankton undergo wild oscillations because this whole system Is
very unstable.
We have a problems In using the cladocerans In the same ways that
we can the diatoms to Infer pH changes. But they do give us a window
through which we can look at other kinds of communities. We need much
more experimental work aimed at understanding the dynamics of systems
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with different predatJon regimes. A disappearance of a key taxon may
tell us when fish were eliminated or when corIxIds became abundant,
but those Interactions are not well known. The key concern related to
aquatic acidification Is the success of fish populations; the
cladocerans may tell us something of the history of changes In fish
populations, but only If we understand the relationships much better.
This Is a major area for further research on cladocerans to
understand the acidification process.
Clearly additional sediment analyses are recommended. This
applies to both surface sediments and cores. The cladocerans do tell
a story that seems to be useful In Interpreting acidification
histories. The species relationships across pH gradients would
benefit greatly from more analyses than the relatively small number
that have been accomplished so far. Some additional sediments are
available from the Adirondack Mountains of New York and Norway; these
should be examined. Consideration should also be given to obtaining
larger cores from a few well-selected sites, where multiple parallel
measurements can be made, and where ancillary sediment data can be
gathered.
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ponds In western Canada. J. Fish. Res. Board Can. 28:311-321.
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Baker, J.P. 1982. Research priorities for assessment of impacts of acidic
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320
Norton, S.A., R.B. Davis and D.F. Brakke. 1981. Responses of Northern New
England Lakes to Atmospheric Inputs of Acids and Heavy Metals. Land
and Water Resources Center, University of Maine, Orono, Completion
Report, USD I OWRT A-048-Me.
Pennak, R.W. 1957. Species composition of limnetic zooplankton communities.
Limnol. Oceanog. 2:222-232.
Fatal as, K. 1964. The Crustacean plankton communities In 52 lakes of different
altltudinal zones of northern Colorado. Verh. Int. Ver. Limnol.
15:719-726.
Roff, J.C., and R.E. Kwlatkowski. 1977. Zooplankton and zoobenthos communities
of selected northern Ontario lakes of different acidities. Can. J.
Zool. 55:899-911.
Schindler, D.W. and M. Turner. 1982. Biological, chemical and physical
responses of lakes to experimental acidification. Water, Air, Soil
Poll. 18:259-271.
Smol, J.P. 1981. Problems associated with the use of 'Species Diversity' In
paleolimnologlcal studies. Quat. Res. 15:209-212.
Srnirnov, N.N. 1971. Chydorldae Fauny MIra. Rakoobraznye. Vol. I, Sec. 2,
101:1-529.
Sprules, W. 1975. Midsummer Crustacean zooplankton communities in acid
stressed lakes. J. Fish. Res. Board Can. 32:389-395.
Sprules, G.W. and L.B. Holtby. 1979. Body size and feeding ecology as
alternatives to taxonomy for the study of limnetic zooplankton
community structure. J. Fish. Res. Board Can. 36:1354-1363.
Synerholm, C.C. 1979. The Chydorld Cladocera from surface lake sediments In
Minnesota and North Dakota. Arch. Hydrobiol. 86:137-151.
Whiteside, M.C. 1970. Danish Chydorld Cladocera: Modern ecology and core
studies. Ecol. Monog. 40:79-118.
Van, N.D. and R. Strus. I960. Crustacean zooplankton communities of acidic,
metal contaminated lakes near Sudbury, Ontario. Can. J. Fish. Aquat.
Sci. 37:2282-2293.
Van, N.D., C.J. Lafrance and G.G. Hitchin. 1982. Planktonic fluctuations In a
fertilized, acidic a Ike: the role of Invertebrate predators, p.
137-152. la Lake and Reservoir Management. EPA 440/5-84-001.
-------
•*-,«'.!$•••.#• .#•
321
••1
T
Fimirp 1 Relative abundances of the chydorid cladoceran taxa vs lakewater pH [3].
9 (Brakke et al., 1984)
ELEV. pH
( M)
976
880
948
837
750
I 123
813
803
893
I 13
457
78
122
I 17
125
469
527
LAKE
NO.
4.65
e c
6.2
4 75
4.7
4.8
4.5
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1
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. II 1
4 1
: ^
m 1 1
09
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07 |
3 1
1
11 1
16
0 2 4 6 8 10 12 14
CHI-SQUARE DISTANCE
Figure 2
Cluster analysis of 18 lakes based on surface
sediment chydorid assemblages.
-------
322
Figure 3
Chydorid Cladoccra Recovered from New England Lake Surface Sediments*
Species
pH Group
Altitude Group
Acroperus cf. harpae
Alona affinis
A. barbulata
A. bicolor
A. circumfibriata
A. costata
A. quttata
A. intermedia
A. quadranqularii
A. rustica
A. spp.
Alonella excisa
A. exiqua
A. nana
A. pulchella
A. sp. #1
Alonopsis spp.
Anchistropus minor
Camptocercus ntc rectiroaris
Chydorus bicornutus
C. faviformis
C. gibbus
C. piger
C. sphaericus
C. spp.
Disparalona aaairostru
D. rostrata
Eurycercus (Bullatifrons) spp.
Graptoleberis tatudinaria
Kurzia latissima
Leydigia leydigi
Monospilus dispar
Pleuroxus denticulaius
P. procurvus
P. striatus
P. trigonellus
Pseudochydonu globosus
Rhynchotalona falcata
B?
B7
A?
BorD?
E?
B
B
B?
B
B?orC7
A?
A?
C?or B?
A
B
B
D
B?orC?
E?
A
A
A?
A?, B?. or C?
A
A?
C?
A
e
b?
bore
e
b
b
a
b
b?
c.'
b?
b?
b?
b
core
bore
b
c
b?
• A = grertest relative abundance at higher pH; B = uniform or variable relative abundance
re pH; C = less frequent at both high and low pH values; D = more frequent at both high and low
pH values; E = greatest relative abundance at lower pH; a = greatest relative abundance at lower
altitude; b = uniform or variable relative abundance re altitude; c = less frequent at both high and
low altitude; d = more frequent at both high and low altitude; e = greatest relative abundance at
higher altitude.
-------
DIVERSITY (H'J
2.0 2.8 3.6
i
a
4.5 -
6 10 14 18 22 26
NUMBER OF SPECIES (S)
60-
40-
20-
70
Chydorus sphaericus
* * *+ *
422 775
Elevation (m)
1128
Figure 4
Numbers of chydorid species and
Shannon-Weaver (H') diversity at each lake.
(Brakke et al,, 1984)
Figure 5
CO
ro
CO
-------
60-
8
-S40-
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324
Chydorus sphaericus
1.19
Figure 6
1.55
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1.90
2.25
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-------
325
SPECK PONO
»
O }0
_
l¥ I ! H » I
z 0
!
Figure 8 Relative abundances of chydorid cladoceran taxa vs sediment depth in Speck
Pond, Maine. The scale is in 10% intervals.
-------
326
co
LU
_i
CL
2
<
CO
LJ
5
Q
LJ
CO
0-0.5
2.0-2.5
8.0-8.5
6.0-6.5
4.0-4.5
5.0-5.5
18.0-18.5
24.0-25.0
20.0-21.0
12.0-12.5
14.0-14.5
10.0-10.5
02468
CHI-SQUARE DISTANCE
Figure 9 cluster analysis of chy-
dorid assemblages in 12 sediment lev-
els from Speck Pond, Maine.
Dophnio/cm3
10 20
E
o
CL
LU
O
30
Figure 10 Daphnia ephippia
in sediment levels from Speck
Pond.
both figures from Brakke et al., 1984
-------
DIVERSITY (H')
2.0 2.2 2.4 2.6 2.8
u
I
r-
Q-
UJ
Q
r-
Z
UJ
2
Q
in
10
15
25
15 17 19 21 23 25
^Figure 11 Numbers of chydorid species
NUMBER OF SPECIES (S) Ledge Pond core.
and Shannon-Weaver diversity (H') for the
Figure 13 Factors Influencing the Structure of Cladoceran Communities
General Factors Influencing Cladoceran Communities
I. Lake morphometry
2. Latitude and elevation
3. Water [2] chemistry, esp. Ca, alkalinity
4. Lake nutrient status and algal productivity
1. Littoral zone development and macrophyte communities
Changes over Time Caused by
I. Watershed disturbances
2. Climatic change
3. Shifts in predation
4. Change in nutrient regime
5. Atmospheric deposition of acids/metals
• Watershed and lake titration of alkalinity, pH change
• Elimination of fishes changing balance on invertebrate predation
• Structural changes in the littoral zone
• Alteration of food supply due to change in production/decomposition
• Effects of metals and acids/metals
6. Various other types of pollution
Figures 11-13 from Brakke et al., 1984
K)
20 23
SNSF 31
Nedre molmesvotn
0 2O
3O
20
Alonoptli alongat*
..... Aeropiruf fcorpat
Along off Inli
^— Alone f uillco
Alonalla ticlio
Alonallo nana
— Onrdorat iphatrlcui
Ctiydorwi »lg«r
Curfccrui lamtllalut
OJ
f\>
Figure 12
Chtngci in uleclcd chydorid Ctidoccri of Ncdre Mllm»vnn(SNSF .1.11. Norway. Chronology of pH chinir and heavy mrial
deposiiion ii given in Fig. 6. 2 cm = 1963; 6 cm = 1917; 10 cm = 1877.
-------
328
Invertebrates in Sediments
Wolfgang Hofmann
Ma ny thanks again for the invitation to this wo r k s h o p.
A drop of pH in lake water has various effects on the lake
ecosystem and one effect is a faunal succession due to a
shift towards predominance of species which are adapted to
low pH or which are selected by secondary effects of
acidification. This is one point.
Another point is if a strong correlation between low pH and
its faunal effects occurs for instance indicated by the
existence of indicator species. In this case the species com-
position of an assemblage may be indicative of a certain pH level
Such relationships provide the opportunity to follow faunal
changes by analysis of animal remains in the sediment and to
use faunal successions for reconstruction of former pH
conditions. An important point is to.check if such correlations
between the occurrence of certain species and pH really
exist.
I wi I I now have to discuss the use of "other
invertebrates" as indicators of pH conditions and the use of
their remains in lake sediments in order to track the
process of acidification."Other invertebrates" cover roughly
12 taxonomic groups (besides Cladocera) which are
represented by remains in the sediment (Rhizopoda,
Gastropoda, Bivalvia, Ostracoda, Acari, Ephemeroptera,
Odonata, Megaloptera, Heteroptera, Coteoptera,
Trichoptera,Diptera)(s. Frey 1964). A presentation
time of 35 minutes means 3 minutes for each.
In this situation, a concentration on a certain taxon
seems inevitable. The selection of organisms which are of
particular interest in this respect is based on three
criteria:
1.Abundance: The remains should occur in high abundance in
the sediment to get sufficient numbers of specimens to
characterize the composition of the assemblage. This is
particularly important as the effect of acidification occurs
very near the sediment surface, so sampling distances and
sample volumes are generally small.
2. Positive indication of low pH: that means that species
typical of low pH should be present in the taxonomic group.
Some groups (Mollusca, Ostracoda) do not occur if pH falls
below a certain threshold. However, it is very difficult to
prove the absence of a taxon and additionally it is
generally difficult to demonstrate the relationship between
the absence of a taxon and a certain ecological factor.
3. Pa IeoI imnoIogicaI studies should exist which provide a
basis for the discussion.
In most of the taxonomic groups mentioned above abundance
of remains in lake sediments is extremely low. Hence,
kilograms of material are needed and only single specimens
are found more or less occasionally. This is the case in
Mollusca, Acari, Ephemeroptera, Odonata, Megaloptera,
Heteroptera, Coleoptera, and Trichoptera. The remaining
Ostracoda avoid Iow pH conditions. Rhizopoda occur at t ow
-------
0.
RHIZOPOUA
GASTROPODA
«£" " """SfV^" v f
MEGALOPTERA
B1VALVIA
329
EPHEHEROPTERA
-sA
ODONATA
•i.- t~r-
"tffrgr
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TR1CHOPTERA
D1PTERA
I nvc'ft irlir.i ICK iiiiJ
rciiiiiins in lake so dime nis
-------
330
and high pH values (Grospietsch 1958) and their remains are
often abundant in lake sediments. But they have been
primarily used as indicators of changing moisture during bog
development (Tolonen 1979).
Due to this procedure of selection the Chironomidae among
the Diptera are the only taxon which left ov.er. Chironomids
are the predominating insects in lakes both in respect to
number of species and individuals. They occur in all types
of freshwater habitats and chironomid analysis is an
established method in paleolimnological research (Stahl
1969, Frey 1964, Hofmann 1971b, 1979).
In large lakes 100 to 200 species occur the head capsules
of which are preserved in the sediment. In respect to
identification of these remains there are some restrictions
because chironomid taxonomy is generally based on adult
males. However, we don't have adults and we even don't have
complete larva. The basis for identification is in most
cases a more or less incomplete head capsule.
In pa IeoI i mnological research chir onom ids have up to now
been primarily used to follow the process of eutrophication
in lakes. Recently, a few papers came out discussing the
influence of changing pH on chironomid assemblages.
This is to show you just one example of a core study of a
north German lake (Schoehsee). In the first phase of lake
development chironomid species occurred which are typical of
oligotrophic conditions. They disappeared during lake
history
in the postglacial period and occur today in oligotrophic
lakes of Scandinavia and the Alpine region. The occurrence
of such species is closely relateted to the oxygen
conditions in the hypoli mn ion which is on the other hand
related to the trophic conditons of the lake. So their
disappearance indicates oxygen depletion during summe r
stagnation and the establishment of an eutrophic lake
(Hofmann 1971b).
Relationships between pH conditions and the species
compos ition of the chir onom id fauna became evident by
observation of recent faunas. Brundins (1949) study on the
bottom fauna of Swedish lakes included some acid, polyhumic
lakes. Minimum pH was 5.7. Brundin listed an assemblage of
chir onom id species which are characteristic of low pH
e nv i r onmen t s:
Ab labesmyi a brevi tabiI is Tr issoctadi'us mucronatus
Ablabesmy/a long/palp/s Chironomus tenuistylus
Zalutsch/a za/utschicola Sergentia longi venfris.
, Even at lower pH values in Lake Trestickeln (Sweden) (pH
range 3.9 - 4.6) Wiederholm & Eriksson (1977) found a fairly
diverse chironomid fauna with Za Iu t schi a present and high
abundance of Chironomus in the littoral zone.
Mos sberg £» Nyberg (1979) summa r i z ed some trends in the
chir onom i d commun ities in relation to pH on the basis of
results f r om seven Swedish takes: 1. The chir onom id fauna of
these lakes, where pH ranged between 3.6 and 5.4, were again
characterized by the occurrence of Zatutschia. 2. A
succession from Sergentia longiventr/s (which was a
character species of Brundins (1949) polyhumic lakes with pH
-------
331
100
60
60
20-
= A28.9-85.6x
.0 4.2
4.4
4.6
4.8
5.0
pH
FIR. 2. Relative number of Chironomiis .»/>. in the
littoral zone (1 and 2 m) in relation to pH. (In per
cent of totn! fauna.)
60-
AO
20-
100 -i Chironomus sp JU Phaenopsectra sp.
ao
m
X
in
c.
:2.
in
o>
-j
a
m
o<
£
4.0
4.4
4.6
4.8
5.0 pH
Fig. 3. Relative importance (in percent of total fauna)
of Cli:rono»>ns sp. and Phacnoprccira ;p. at 6—10 m
depth in five of the lakes.
Mossberg and
(1979)
-------
332
values between 5 and 7) is replaced by Ch/ronomus at a pH
level of about 4.5. 3. Relative abundance (percentage) of
Ch /ronomus increased in the littoral zone with decreasing
pH.
The latter is in accordance with a list given by
Thienemann (1954) of chironomid taxa found in waters with pH
below 4 due to sulphuric acid. Under these conditions there
is a distinct predominance of the genus Chironomus.
The results of these observations may be summarized as
foilows:
1. The chironomid faunas at pH below 7 are positively
characterized by the occurrence of certain species
(indicator species).
2. Two pH ranges are obviously characterized by different
taxa: above 4.5 to 5 the typical taxa are Za Iu t sch/3,
Sergent/a longiventris, Ch/ronomus tenuistylus. Below 4.5 a
shift occurs to predominance of Ch/ronomus alone.
Hence, among the chironomids indicator species of
different pH conditions exist. The question arises if such
indicators can be used in pa IeoI imnoIogicaI studies to
demonstrate the effect of low pH on the chironomid community
and, furthermore, to reconstruct former pH conditions.
Walker & Paterson (1983) observed the chironomid
succession in long cores from two humic lakes in New
Brunswick, the recent pH values of which ranged between 5.2
- 6.7 and 4.0 - 4.8, respectively. The subfossil assemblages
were highly diverse and the indicator taxon Zatutsch/a was
present in both lakes. The last phase of development in the
more acid lake was characterized by a decrease in
Ta n y t a r sus
and an increase in Ch/ronom'js and Psec t roc i ad i us, which has
been explained by the establishment of peat-pool
e n v i r o nme n t .
Recently, Brodin (ms.) presented some interesting results
from Lake Flarken in Sweden. The author very carefully
discussed the changes of the environmental conditions
reflected by changes in the chironomid community. In this
case climate was an important factor governing the
development: Changes in temperature and humidity led to
falling and rising water level. The rise of the water level
led to the estabt i shmen.t of a hypol imnion as a low
temperature environment as an habitat of cold stenothermal
profundal species. So climate was one factor and the other
predominating factor was pH: A major phase of lake
deveIopment was very distinctly characterized by
predominance of two species one of them was Zalutsch/a and
its occurrence is explained as indicative of the existence
of a polyhumic and low pH environment. A mos t d r ama t i c
change in t.he chironomid fauna occurred in the surficial
sediment layer: The number of taxa decreased from 50-55 to
15-20 and a species succession led to predominance of two
Chironomus species.
This development was obviously related to a drop in pH
which was 6.5 in 1974 and between 5.0 and 5.5 in 1979/32.
Th i 5 clearly demonstrates the effect of a further drop of pH
on a " Iow-pH-commun i t y" .
The same process has been observed by Moss berg (ci ted
-------
333
C l> i r o n o m i d en a u s in i n e r a 1 s a u r e n (HiSOi) C e w a s s e r n
mil e i n c in pH < 4
Name
Cchict
Niedrigslci pll
Ccratopogonidac:
I^asioliclea aciilicola Japan
Dasyhelea lersa Sumatra
Ceratopogonidae vermiformes Europa
Tanypodinac:
Ablabcsmyia monilis japan
Ortliocladiinae: Japan
Corynoneura bifurcate Europa
Chironornariae:
Chironomus acerbiphilus Japan
Chironomus sp. sp Japan
Cliiroiiomus costatus opicatus Sumatra
Cliironomus sp Sumatra
Cliimnoiiius plumosus Japan
Chironomus tlorsalis Europa
Chironomus sp. t/mmnii-Cruppe .... Europa
Chironomus sp USA
PentopeJilum coiwexum ....... • Sumatra
Tanytarsariae:
Tanytorsus sp Japan
2,68
3,17
3-5
2.9
3,17
1.4
1.4
2,83
2,68
3.5
3,17
3.1
3.6
<4
2.9
-------
POHTEY POND CHIRONOMID DIAGRAM
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35
0 200400 600
0 20 40 60 60 100%
Fig. S. Porlcy Pond percentage chironomid diagram.
Walker and paterson (1983)
OJ
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WOOD'S POND PERCENTAGE CHIRONOMID DIAGRAM
0 20 40 60 SO 100%
Fig. 6. Wood's Pond percentage chironomid diagram.
Walker arid paterson( 1983 )
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Chronology
Corynocara amblgue
Polypediium nubveulosurn
Paratanylarcui »p.I
PtaclrocUdiut 7 tordldallut
Tanylarcut uimaentli
Abl»ba»myl* monlll*
Tanylariut ap. Q
Dlcrotandlpa* nar«o»u«
Chlionomui plumotui
Tanylartui 7 glibretcan*
Paactrocladlut "taptantrlonalla"
Tanylartut cf. gragarlut
Procladlut cf. chorau*
Dlcrolandlpai »p- Q
Chlronomu* gr. Ihumml I
Cladolanytaraut cf. mincut
Cladopalma 7 vlildula
Slampalllnalla cf. minor
Polypediium gr. icalaanum
Pageallalla orophlla
Zaluttchla i»lul»chicola
Tanytaraut gr. amlnului I
Cladotanytareua cf. atrldoraum
Tanyltrtut chlnyenila
CUdolanylaraua nlgrovlllatua
Cladotanytarau* ap.I
TaAnytaraui type m«dlua
Procladlui ap. II
Chlronomua gr. plumo»u» n
Slampallina bautal
Tanylaraua gr. eminulut II
Tanylanua lugani
Paaclrocladlua lypa •dwardtll
Chlronomu* >p. X
Chlronomut ap. VI
Php«jfOp»eclra 7 flerloei
Lake Flarken. Most abundant chironomid taxa at each sampling level of
the main core. For comparison, the most abundantly occurring taxa
in the lake at present, gained from live chironomid sampling in
1979-1982, is indicated in the right part of the figure.
Rink order of lii*
Q most abundant
Znd
O 3rd
• 5|h
(ms.)
GO
CO
en
-------
337
after Brodin) in Lake Grimsgoel where pH dropped from 6.2 in
1949 to 4.8 - 5.5 in 1977: As in Lake Flarken, 50 % of the
chironomid species disappeared. The low pH led to an
increase in faunal similarity between the two lakes. Before
acidification 15 % of the species were common in both lakes,
now they have 40 "*• of the taxa in common. Thus,
acidification led to characteristic and uniform chironomid
commun i t i es.
As the effects of cultural acidification occur very near
the sediment surface, there is the chance to observe this
process on the basis of short sediment cores.
In an Bavarian lake (West Germany) with a recent pH of
3.6 - 4.8 a 40 cm core has been analyzed (Erneis-Schwarz &
Kohmann 1984). There was a general trend of reduction of
number of taxa which began already at 40 cm sediment depth
and in the uppermost layer an increase in Ch/ronomus and
disappearance of Tanytarsus was attributed to acidification.
Some limitations in the interpretation of results from
such short cores are evident:
A main advantage of pa IeoI imnoIogicaI methods is that
they allow to characterize the "predisruptive conditions"
(Binford, Deevey & Crisman 1983). For the interpretation of
what was happening near the sediment surface we need
i n f o r ma tion on the "background variation" of species
abundance and occurrence due to successions under natural
conditions. This information can only be supported by the
analysis of long sedi men t cores. This lack of info rma tion
often leads to an overaccentuation of the variation observed
near the sediment surface.
Results from single cores neglect horizontal variation, so
Henriksson, Olofsson S. Oscar son (1982) based their results
on mean values from three short cores. They were from two
Swedish lakes with pH ranges between 4.3 and 4.7. In the
uppermost layer, a decrease in Tanytarsini and an increase
in Sergentia and Psec troclac/ius was observed which was
explained as a result of acidification. The mos t recent and
most dramatic change of the fauna is obviously not
documented in the sediment: In the cores from Lake Gardsjoen
869 head capsules have been examined and no specimen of the
genus Chironomus has been found. Today Ch/ronomus belongs to
the predominating taxa in the lake.
Again, the interpretation of the changes in subfossil
assemblages is difficult because the natural variation is
not known. And, as in the example by Erne i s-Schwa r z & Kohmann
(1984), in the diagrams there is no indication of the
influence of low pH, because no indicator species was
present. It is insufficient to discuss the influence of an
ecological factor such as pH on the basis of genera (with
some exceptions). Phaenopsectra obviously means
Sergent i a in
which only one species, S. longiventris, is typical of
polyhumic lakes (Brundin 1949). Chironomini includes taxa
such as Chironomus which increase with decreasing pH and
others which disappear.
The problem is that at a pH higher than about 4.5 a
relatively diverse chiron om id fauna ma y exist without
indicator species which indicates a pH below 7 and which can
-------
Orllwclodllnor
Tonypodlnot
CMionominaf
Chliononlnl Tonrlor|lnl
0-
l-»
1-10
11-10
lltlt
Abbildung 1:
Die relative Abundanz der Unterfami 1ien Orthocladiinae, fanypodi-
nae, Chironotinae (Chlronotini 4 Tanytars/niJ; alle Chirqnonmi-
den-Gattungen einer Sedimentschicht entsprechen 1007..
Emeis-schwarz and K°hm»nn
CO
CXI
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339
LAKE GARDSJON
0 10 20 30 40 SO 0 10 20 0 10 20 30 40 0 10 20 0 10 20
1-2
5-6
8-9
14-15
cm
|
Phaenopsectro
JL
IT
IJ
other
Chironomini
,1
1
Tanylarsini
j
I
1
I
Tanypodinae
1
Orlhocladinae
LAKE HARSEVATTEN
10 20 30 40 50
1 -2
5-6
8-9
14-15
cm
F
]
Phaeno-
psectra
V
J
.elht
Chiro
ni
r
nomi-
Tanylarsini
Tanypodinae
I
Orthocladinae
Fig. - Hercemuge distribution of head capsules of different chironomid subgroups at different sediment levels in Lake Clrdijbn an<<
Lake Harsevaucn.
Henriksson et al. (1982)
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340
Tahlf 3. Change* in »ome chirunomid subgroups reported as eltecls uf ucidificatiun ol oligohumic lake* with an
actual pH level below 5.
Lake* Tanytar*inii I'liui-nu/i.'n-cira Pneciriit'lailius Cliiri>iiiniiu.\
(iardijun. prulundal + +
llar^evaltcn. profundal + -r
Tre>iickcln(Wiederholm& Eriksson 1977) + +
l-'ive lakes, liloral (Mossberg 1979) + +
l-'ive lakes, profundal (Mossberg 1979) + +
Henriksson et al.
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341
be identified at the larval head capsule. In the list given
by Brundin (1949) 6 species are considered to be typical of
pH values above 5.5 and below 7, only one of them
(Za lutsch / Nyberg (1979) have shown that
below pH 4.5 Sergenf/a longiventris typical of polyhumic
lakes is replaced by Chironomus. The genus
Psectrocladius is
not typical of low pH. Similarly, the genus Chironomus does
not indi.cate acidification, as it is also abundant in
eutrophic and polluted sites (Thienemann 1954).
If pH drops distinctly below 4 as jt is the case in the
Reinbeker Tonteich in the vicinity of Hamburg (West Germany)
the effect of low pH can be read from the chironomid
community. The chironomid fauna has been sampled in 1933
when pH was 3.2 and in 1950 when pH was 3.3. In both cases,
the predominating taxa were Chironomus and
Corynoneura
(Thienemann 1954). The chironomid head capsules from a short
sediment core obviously reflect this extremely poor
chironomid assemblage: 76 % of the specimens belonged to two
Chironomus species, followed by Corynoneura. Four taxa of
three genera made up 97 % of the material (Hofmann, unpubl.
data ) .
Also in this case the effect of low pH is reflected by the
tow diversity of the assemblage rather than by the
occurrence of indicator species. It is known from adult
midges sampled at the pond that particular Chironomus
species were involved which are typical of acid
environments. However, they cannot be used as indicator
species if only subfossil ma terial is available because the
species cannot be identified at the larval head capsules.
In this point lies the most important restriction in the
use of chironomids as indicators of the pH conditions.
Relationships between the fauna and ecological factors can
in most cases only be deduced on the basis of species. So, a
prerequisite for the use of these organisms as indicators is
an accurate taxonomic differentiation of the subfossil
ma terial. Generally a refi nemen t of larval t axonomy i s
necessary.
Although some trends in the response of chironomid
assemblages to dropping pH became distinct by the material
published there is need for some more case studies based on
long sediment cores and of course including other
pa IeoI imnoIogicaI methods which provide information on what
-------
Reinbeker Tonteich, Naumann-Lot, 16.3.1983: Chironomiden
Sedimenttiefe (cm) 6-8 4-6 2-4
Frischsediment (g) 7.8 9.1 7.5
Chironomus p 37 55 4O
Chironomus a 23 17 12
Corynoneura 24 12 4
Tanytarsus 5 5 8
Polypedilum gr. sordens 1
Microtendipes 1
Cladotanytarsus 1
Glyptotendipes 1
Psectrocladius 1
Procladius
Pentaneurini indet.
y 69 92 66
0-2 y-
9.8
57 189
61 113
6 46
2O 38
1
1
1
1
4 5
1 1
1 1
150 397
Tanytarsus evtl. = Tanytarsus gr. pallidicornis (s. Probe 6-8 cm)
Abundance of chironomid head capsules in a short sediment core from the
Reinbeker Tonteich (y. Germany) (nofmann, unpubl. data)
00
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343
was going on in the lake ecosystem.
To come to the other invertebrates which have been
neglected: Of course they have to be included whenever
possible. The Rh i zopoda are of particu'lar interest in this
respect. But also the Ostracoda should be considered. The
consideration of these different groups gives the chance to
get information on the development of many representratives
of the fauna under the influence of decreasing pH.
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344
Re IPiences
Bintord. M. W., Deevey. E.S. 6. Ctisman, T. L. (15-63):
P a Ie oI imn ology: an historical perspective on lacustrine
ecosystems. Ann. Rev. Eeol. Syst., 14: 255-266.
Brodin, Y.: The postglacial history ot Lake Tiarten.
interpreted from subfossil insect remains, (ms.)
Brundin. L. (1949): Chironomiden und andere Bodentiere
der suedschwedischen Urgebirgsseen. Rep. Inst. Freshw. Res.
DrottninghoIm, 30: 1-914.
Erne i s-Schwar z . H. £. Kohmann, F. (19M): Die Chironomiden
(Diptera: Chironomidae) eines veisauerten Bergjees. Kleiner
Arbersee. Bayerischer WaId. in: Lenhart. B. el al. (ed.):
Vcrsauerung in der BRD, Verlag E. Schmidt (in press).
Frey, D. G. (1964): Remains ot animals in Quaternary lake
and bog sediments and their interpretation. Arch. Hydiobiol.
Beih. Ergebn. Limnol. 2: 1-114.
Grospietsch, T. (1968): WechseI t ierchen (Rhi?opoden ) .
F r anckh, St uIt gar t .
Henrikson. L.. Olafsson, J. B. f. Oscarson. H. G. (1982):
The impact of acidification on Chiron on-, idae (f>iptera) as
indicated by subtcssil stratification. HydrobioIogia 86:
223-229.
Hofmann. W. (1971a): 0 i e DOStgI aria Ie Entwicklung der
Chironomiden- und Chaoborus-Fauna (Dipt.) des Schoehsees.
Arch. Hydrobiol. Suppl. 40: 1-74.
Hofmann. W. (1971b): Zur Taxonomie und Paloekologie
jubfoisiler Chiron omiden (Dipt.) in Seesedimenten. Arch.
Hydrobiol. Beih. Ergebn. Limnol. G: 1-50.
Hofmann. W. (1979): Chitonomid analysis. >n: Berglund.
B. E. (ed.): Pa IaeohydroIogicaI changes in the temperate
zone in the last 15000 years. Subproject B. Lake and mire
environments. IGCP 158 B. Project guide, vol. 2. Lund:
259-270.
Mossberg. P. £. Nyberg. P. (1979): Bottom tauna ot small
acid forest lat.es. Rep. Inst. Fresr.w. Res. Or o t t n i ngho I m 56:
77-87.
Slahl. J, B. (1969): The uses ol chironomids and other
midges in interpreting lake histories. Mill. int. Ver.
Limnol. 17: 111-125.
Thienemann. A. (1954): Chir onomus. in: Die
C< i nriengewae:. i,e r . Stuttgart'. 20: 1-834.
Tolonen. K. (1979): Rhi;opod analysis, in: Berglund. B.
E . ( e d . ) : Palaeohsdrological changes in the temperate rone i
the last 15000 years. Subptoject f*. Lake arid m i i e
env i r onmen Is. IGCF 158 B. Project guide, v. o I . .. Lund:
Walker, I. R. & P a t e r «. o n . C. Ci. i i 9 J. 3 ) : Post-glacial
•r h i i o n crri i d f. u c c e r r i t*n in t *,,-> *-ma I I . h u'i-1 < I AI e- 5. in the IJ t- w
P- r ufi svw i ck - Nova Scotia « C a n a d a i border n r e 3 . r i r- =, hw.
I n v e r t r- ti I . 6 i O I . .'• : f. 1 - 7 > .
W i e cl e i h o I m . T . f. E r i k 11 o n . L . ( 1 ri 7 7 ) : benthos o t an acid
lake. • j i t o; 23: j 6 1 - r f. 7 .
n
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345
CONTRIBUTIONS OF PLANT PIGMENTS TO PALEOLIMNOLOGY
Seward R. Brown
The commonest and most widespread method of estimating phytoplanktonic
biomass in freshwaters and the oceans is by measurement of chlorophyll £
content. The approach is made possible because of the ubiquitous presence
of this pigment in the photosynthetic tissues of plants. Other chlorophylls,
phycobilins, and a wide variety of carotenoids are frequently associated
with it, but the suite of these pigments differs greatly among planktonic
taxa. Because the pigments are preserved in lake and marine sediments, a
similar approach can be taken in estimation of former planktonic populations
in existence at the time when the pigments were deposited. In fact, this
is the only approach that permits an estimate of the total planktonic assemb-
lage, since microfossils usually provide only evidence of silicified algae
such as the diatoms and chrysophytes. In living assemblages the presence
of blue-green algae, flagellates, and many non-silicified taxa may be readily
observed on microscopic examination of plankton samples, yet these forms
which are rarely preserved in fossil samples may have contributed very signif-
icantly to the planktonic biomass of their time. This becomes a matter of
considerable importance in paleolimnology if studies encounter periods of
eutrophic conditions when blue-green algae often dominate the algal assemblage,
as well as in other situations where flagellates and picoalgae are known to
contribute very substantially to primary productivity.
The main obstacle to the use of pigments and other organic fossils
relates to molecular stability of these compounds. As organic entities,
they are particularly vulnerable to degradative processes. Diagenesis begins
in senescent and non-living cells and is accelerated by photo-oxidative pro-
cesses, bacterial attack, and passage through the guts of grazing anitials.
The diagenetic pathways in chlorophyll are well known. A sequence of coloured
compounds is formed, beginning with the loss of magnesium from the molecule
to form pheophytin, or breakage of the ester linkage with phytol to form
chlorophyllide. Loss of both substituents produces pheophorbide, moreover
any of these derivatives may also be found in oxidized form. As a result,
lake sediments invariably contain a complex mixture of native chlorophylls
and various products of the diagenetic sequence in addition to the carotenoid
pigments associated with the photosynthetic apparatus of the algae that produced
them. Measurement of the chlorophyll of living planktonic assemblages is rel-
atively simple because only native chlorophylls and early derivatives need be
distinguished. The sedimentary mixture of fossil forms requires chromatographic
separation before measurement can be achieved, but methods for this separation
and identification have been developed and are routinely practised. Lability
of the pigments imposes a further inconvenience on paleolimnologists in that
sediment samples require somewhat more protective handling than is necessary
for samples to be analysed only for pollen and microfossils.
In this paper the emphasis on chlorophyll is placed on its use as an
estimate of total algal production where the objective is to reconstruct
paleoenvironmental conditions through interpretation of algal response to
change in them. Increases in populations of indicator taxa are seen as a
response to changes favourable to those taxa. Ecological success, however,
is the outcome of competition, and the competition is rarely to extinction,
thus the need for a measure of total productivity relative to that of any
specific producer or group of producers.
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346
Changes in environmental conditions are frequently associated with
change in the levels of nutrient input to lakes and with change in the
composition of those inputs. Some algal forms compete more successfully
than others for scarce nutrient resources. Upon enrichment of nutrients,
changes of dominance in the algal assemblage take place, productivity in-
creases, and competition for nutrients may become less important than that
for light - in which case low light-adapted forms are favoured. Change in
metals, associated with change in pH, undoubtedly affects various taxa
differently, although their toxic effects have been little studied and are
poorly understood. It is well known that biotic interactions occur and
that these too are important determinants in the outcome of competition.
Diatom populations may be inhibited by allelopathic interactions with
blue-green algae. Selective grazing by zooplankton may suppress those
algal species favoured by the grazer. Heterotrophy and disease are addit-
ional factors. Under some conditions, as yet most frequently observed in
meromictic lakes, the minute picoalgae contribute as much as 85% of total
algal productivity. Competition must be seen, therefore, as a very complex
process. From this it follows that where its outcome is to be used in the
interpretation of environmental change, some attention must be given to the
total planktonic community in addition to that focused on selected component
species. The chlorophyll derivatives preserved in sedimentary deposits have
the potential to supply that information, as well as to provide insights
into the intensity of grazing pressure exerted by herbivorous zooplankton.
While the ubiquity of chlorophyll
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347
extracts. Differences in their polarity make phase separation between
organic solvents a simple matter whereby the classes thus separated were
thought to distinguish between allochthonous and autochthonous inputs to
sediment deposits. Attempts were also made to estimate planktonic species
diversity based on numbers of carotenoid entities discovered in lake sed-
iments, however these results may be misleading because the studies did
not take into consideration the fact that diagenetic products may have
contributed to these numbers. The validity of the approach remains to be
tested through rigorous identification of the carotenoid fractions in the
pigment assemblage. A few readily distinguished members have been isolated
from carotenoid mixtures, and these have been used successfully to indicate
the presence of specific algal components of former planktonic communities
where no other evidence of their existence was preserved in the sediment
matrix.
The remarkable advances that have taken place in carotenoid chemistry
in the past quarter of a century have opened the way to much greater exploit-
ation of the ecological information provided by these pigments. It is not
suggested that routine fractionation and identification of all components
of sedimentary extracts is a practical measure for paleolimnologists, but
it is clear that some of these pigments can be readily used to identify
elements of the planktonic assemblage that otherwise cannot be recognized.
Thus far the best success in this endeavour has been achieved relative to
the blue-green algae and photosynthetic bacteria, but certainly present and
future use is not restricted to this limited application. Paleo-reconstruct-
ion depends upon the re-assembly of fragments of the fossil record, and its
validity is increased by the more such fragments that can be fitted together.
REFERENCE S
BROWN, S. R. 1969. Paleolimnological evidence from fossil pigments.
Mitt. Internat. Verein. Limnol., 12:95 - 103
BROWN, S. R., R. J. DALEY and R. N. McNEELY, 1977. Composition and stratig-
raphy of the fossil phorbin derivatives of Little Round Lake,
Ontario. Limnol. Oceanogr., 22: 336-348
BRUGAM, R. B., 1984. Holocene Paleolimnology in. H. E. Wright, Jr. ted.)
Late Quaternary Environments of the United States, Vol.2
University of Minnesota Press, Minneapolis
CARPENTER, S. R. and A. M. BERGQUIST, 1984. Experimental tests of grazing
indicators based on chlorophyll ja degradation products.
Archiv. Hydrobiol. (in press).
DALEY, R. J. 1973. Experimental characterization of lacustrine chlorophyll
diagenesis. 2. Bacterial, viral and herbivore grazing effects.
Arch. Hydrobiol., 72: 409-439
DALEY, R. J. and S. R. BROWN 1973. Experimental characterization of lacust-
rine chlorophyll diagenesis. 1. Physiological and environmental
effects. Arch. Hydrobiol., 72: 277-304
FOGG, G. E. and J. H. BELCHER 1961. Pigments from the bottom deposits of
an English lake. New Phytol., 60: 129-138
LIAAEN-JENSEN, S. 1978. Marine Carotenoids. pp. 1-73 jji P. J. Scheuer (ed.)
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348
Marine Natural Products, Vol. 2, Chemical and biological
perspectives. Academic Press, New York.
SANGER, J. E. and E. GORHAM 1972. Stratigraphy 'of fossil pigments as a
guide to the postglacial history of Kirchner Marsh, Minnesota.
Limnol. Oceanogr., 17.: 840-854
REPETA, D. J. and R. B. GAGOSTAN 1982. Carotenoid transformations in
costal marine waters. Nature 295_: 51-54
WATTS, C. D. and MAXWELL 1977. Carotenoid diagenesis in a marine sediment.
Geochim. Cosmochim. Acta, 41; 493-497
WATTS, C. D., J. R. MAXWELL and H. KJOSEN 1977. The potential of carotenoids
as environmental indicators, pp. 391-414 iji R. Compos and J. Goni
(eds.) Advances in Organic Geochemistry. Enadimsa Servicio
Publicaciones.
WHITEHEAD, D. R. and T. L. CRISMAN 1978. Paleolimnological studies of
small New England (U.S.A.) ponds: 1. Late-glacial and post-
glacial trophic oscillations. Polish Archiv. Hydrobiol., 25:
471-481 ~~
ZULLIG, H. 1982. Untersuchungen fiber die Stratigraphie von Carotinoiden
im geschichte^n Sediment von 10 Schweizer Seen zur Erkundung
frGherer Phytoplankton-Entfaltungen. Schweiz. Z. Hydro1., 44:
1-98
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34?
Sedimentary Humic Materials
Daniel R. Engstrom
Limnological Research Center
220 Pillsbury Hall
University of Minnesota
Minneapolis, MN 55455
The use of sedimentary humic substances in my work has been largely
restricted to "natural" lake acidification and has not been related
specifically to acid rain phenomena, although I think that it may have
important application to such problems. Those individuals working on water
chemistry in acidified lake regions have generally separated out lakes that
have high dissolved organic content from clear-water lakes, because it's been
observed and/or assumed that they behave differently in response to acid
inputs. In addition, it seems likely that humic materials in surface waters
could influence diatom communities, so that in reconstructions of pH from
diatom stratigraphy, water color (dissolved organics) may be one of those
"other factors" that affect transfer functions. Then finally, it appears from
some of the Scandinavian studies that there is an increase in water clarity,
that is a decrease in dissolved humics in surface waters, as lakes become
acidified. If we can somehow reconstruct the humic content of lake waters in
the past, we may then have an additional index to changes in lake acidity.
The results that follow are from ongoing paleoecological work in
Labrador, Canada, and most of the interpretations are from a series of surface
sediment samples and associated water chemistry data that were collected in
1979 as part of a regional survey of 70 lakes distributed throughout the
Province from the Strait of Belle Isle north to Okak Bay (Fig. 1). These
sites span a distance of 800 km across a pronounced vegetational gradient,
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350
from spruce-fir forest in the southeast, through spruce-lichen woodland,
forest tundra and finally open tundra in the north; there are also extensive
peatlands in some parts of southeastern Labrador. The lakes are clustered in
these different vegetational regions.
Water quality data front Labrador show extremely dilute lakes (Fig. 2);
mean alkalinity is around 2 mg/1, mean conductivity is about 10 uS/cm, and
most sulfate values are below 2 mg/1. On the other hand, pH values are
largely circumneutral. There is no indication from these water quality data
of acidification from anthropogenic sources, so we have a group of sensitive
yet pristine sites that could serve as an important reference for pH
reconstructions (from diatom spectra) in acidified lake districts.
I'll first discuss the relationship between the content of humics in
surface waters and the content of humic materials in the sediments of those
same lakes. I have used apparent color (in standard relative units of the Pt-
Co scale) as a simple estimate of humic content of lake water. While it might
be preferable to have a more direct measure of humic concentration such as
D.O.C., for field work in remote regions where laboratory analysis of samples
may take weeks, a more immediate determination using a field comparator is a
reasonable solution. The distribution of water color in relation to the
different vegetational zones is illustrated in Figure 4. A striking trend is
evident in that lakes in the tundra region have extremely clear water (Pt-Co
color generally 5 units or less), lakes in lichen-woodland and forest-tundra
areas are somewhat darker (10-20 Pt-Co units), while in forested regions water
color from dissolved humics is much higher, and the range of values is
greater. In those southeastern lakes surrounded by peatlands, the color is
darker yet. While vegetation and soils are obviously important controls on
lake water color, there are other factors that influence the level of
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351
dissolved humics in these lakes: the area of the catchment relative to lake
surface, the water residence time, and the sedimentation/degradation rate of
the humic materials themselves.
The content of humic materials in the sediments of these same lakes was
measured with a spectophotometric method for analysis of dissolved tannin and
lignin (Standard Methods) as modified for lake sediments by J.P. Bradbury.
20-25 mg of dried powdered sediment were extracted in 0.1 N KOH for 1 hr. at
o
100 C. A mixture of tungstophosphoric and molybdophosphoric acids (tannin-
lignin reagent) was then added to a diluted aliquot of the. hydroxide extract,
and the absorbance of the resultant blue complex was measured at 700 nm.
Spectrophotometric readings were calibrated against tannic acid standards to
provide a relative measure of humic content per gram dry sediment.
An important problem that should be mentioned at the onset is the
difficulty of comparing concentrations of a substance from a single sediment
sample from one lake to another. Because of density-dependent deposition of
materials in lake basins, the content of humics per gram dry sediment will
vary depending upon where in the lake the sample was taken. This situation
arises because organic materials, being less dense than clastic components,
are preferentially deposited in deep water, which results in a concentration
gradient across lake depth that also varies from lake to lake. One way to
circumvent this difficulty is to express the humic concentration relative to
sedimentary organic matter rather than total dry sediment. Organic matter,
including both humic and non-humic materials, being of more uniform density,
should be less subject to density-dependent sorting. This is indeed the case
for the Labrador data: humic content per gram organic matter in the sediments
is strongly correlated (r = 0.81) with water color (Fig. 4). A logarithmic
transformation of color improves the relationship slightly (r = 0.8S). As a
further test of this empirical relationship I obtained a second series of
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352
sediment samples from 35 lakes in the Boundary Maters Canoe Area of Minnesota
and again compared the humic content with lake color. As shown in Figure 5,
both the correlation coefficient (r = 0.81) and the slope of the line (m =
1.38) are the same as in the Labrador data set, although similarity of slopes
may be somewhat fortuitous.
These results imply a fairly robust relationship between humic materials
in lake water and surface sediments. However, it's seductive to think that we
can reconstruct paleo water color without some understanding of the mechanisms
of humic sedimentation. In relatively simple terms, humic content per gram of
organic sediment can be viewed as a ratio of allochthonous inputs to the sum
of autochthonous plus allochthonous inputs; it is a relative measure of
allochthonous to total organic productivity of the system. If we assume that
sedimentation of humic materials is somehow proportional to the amount of
dissolved humics in the surface waters, then an increase in water color from a
greater flux of humic materials to the lake, all other things being equal,
should increase humic concentrations in the sediments. We might also expect
the autTochthonous productivity of the lake to decrease, thereby increasing
humic concentrations in the sediments, because it is known that dissolved
humics can suppress phytoplankton productivity either through shading or
complexation of nutrients.
A preliminary application of sedimentary humics in a paleolimnological
reconstruction of water color is illustrated in Figure 6. This stratigraphic
diagram is from Lake Hope Simpson in southeastern Labrador, for which we have
assembled detailed geochemical and palynological data as well. The horizontal
lines demarcate vegetational zones from pollen analysis: the lowermost zone
represents a sedge-herb tundra, the next a shrub tundra of birch and alder,
then a zone representing the transition from trundra to a forested
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353
environment, and finally a zone covering the last 6000 years during which the
region was dominated by black spruce forest. I argue in some detail elsewhere
(Engstrom and Hansen, 1984) that the content of humics in the sediments (per
gram dry matter) accurately reflects changes in the soils and vegetation of
the catchment, which altered the input of humics and the erosion of clastic
materials to the lake. The major increase in humic content of the sediments
(per gram dry matter) corresponds exactly to the development of closed-crown
fir-forest (ca. 7500 yr B.P.) as determined by pollen analysis. In a
qualitative sense we might expect that water color would have increased
markedly at Lake Hope Simpson in response to this vegetational and pedological
change. However, if we want to reconstruct paleo water color quantitatively
from the surface sample data, the humic content of the sediments must be
normalized to the organic matter. This curve (humics/ g O.M.) is included in
Figure 6 along with a profile for water color as calculated from the transfer
function shown in Figure 4. Because water color in derived from a simple
linear relationship the two profiles are virtually parallelj an exception is
evident for basal sediments O9000 yr B.P.) for which water color was not
calculated. As expected, water color increases from about 10-20 Pt-Co units
during the tundra and woodland phases to about 60 Pt-Co units after the
transition to conifer forest at 7500 yr B.P. These values are reasonably
close to that found in corresponding Labrador environments today, including
the present-day value for Lake Hope Simpson (60 Pt-Co units). Water color was
not reconstructed for the oldest sediments because no modern analogue exists
with high humic concentration (per gram organic matter) in the tundra regions
of Labrador (Fig. 7). I hypothesize that the coagulation and deposition of
dissolved humics was much more efficient during the early postglacial
perhaps because of high levels of suspended clays that would aid sedimentation
— so that the deposition of humic materials relative to other organic matter
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354
was greater or, alternatively, that the internal productivity of the lake was
extremely low at this time, perhaps for climatic reasons. This period probably
represents a clear water phase of the lake, except for the aforementioned
clays inwashed from the newly deglaciated terrain.
The next step in humic studies would be the application of these
techniques to sediment cores from anthropogenically acidified lakes. However,
the interpretation of humic stratigraphy from such systems might be different
from that described above for the Labrador sites where the primary signal is
one of changing humic inputs to the lake. Instead, we would be looking for
changes in the efficiency of humic sedimentation. The trend resulting from
acidification should be an increase in sedimentary humic concentration
corresponding to a decrease in water color. Polymerization and sedimentation
of dissolved humics may be more rapid in acid lakes where high levels of
aluminum and other multivalent cations are available for complexation with
colloidal hutnates. In addition, the supression of phytopl ankton populations
in acid lakes might lower the deposition of autochthonous organics and thereby
indirectly increase sedimentary humic concentrtions (per gram organic matter).
The empirical relationship between water color and sedimentary humics in
present day lakes needs to be further tested in other regions, particularly
those presently receiving acid rain. If results from these initial
applications are promising, then refinements in the analytical procedures,
such as quantitive fractionation techniques, are in order.
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FI6URES
Figure 1. Map of Labrador showing location of surface-sample sites.
Figure 2. Selected Mater chemistry data from Labrador lakes.
Figure 3. Distribution of water color in Labrador lakes in relation to
catchment vegetation.
Figure 4. Relationship between water color and sedimentary humics (per gram
organic matter) in 70 Labrador lakes.
Figure 5. Relationship between water color and sedimentary humics (per gram
organic matter) in 35 lakes from the Boundary Waters Canoe Area,
Minnesota.
Figure 6. Stratigraphic profiles for 7. organic matter (from loss-on-ignition) ,
sedimentary humics (as mg tannic acid /g dry matter and /g organic
matter), and the reconstruction of water color from the regression
relationship in Figure 4. Vegetation zones defined by pollen
analysis: Zone 1 = sedge-herb tundra, Zone 2 = shrub tundra, Zone 3
= forest transition, Zone 4 = spruce forest.
Figure 7. Sedimentary humic concentrations (per gram organic matter) in
Labrador lakes in relation to catchment vegetation.
-------
356
LABRADOR SURFACE SAMPLE
SITES 1979
• Surface Samples
if Coring Sites
-------
357
HO '/.
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00
03
-------
358
80
70.
60
50
40
30
20
10
(N = 24)
TUNDRA
40
30
20
10
WOODLAND
(N = 19)
30 -
20 -
10 -
(N = 15)
FOREST
30 -
20 -
10 -
(N = 9)
PEATLAND
20 40 60 80 100
WATER COLOR (Pi-Co UNITS)
120
140
-------
LRBRRDDR LRKE5
359
Y -31.0 + 1.32 X
in
i
i-
CL
o:
a
HUMIC5 MG TflNNVB D.M.
-------
360
BWCR LRKE5
in
a
i
CL
a:
a
H0
Y -45.9 + I.36 X
R2 .HE
HH
B
HUMIC5 MB TflNN./B D.M.
-------
LflKE HOPE SIMPSON
LRBRRDOR: N52 27' N56 20'
YBP
1000-
2000-
3000-
4000-
5000
6000-
7000-
8000-
9000-
10000-
11000-
O.M.
HUMICS/D.M
HUMICS/O.M.
COLOR
M. MG/G D.M.
MG/G O.M.
f i i i i i
20 40 60
PT-CO UNITS
co
cr>
-------
en
•n-
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TUNDRR
FDRE5T-TUNDRR
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4+ •«• +-H-
PERTLRND
CDR5TRL-TUNDRR
20 H0 B0 B0 IBB
TRNN./E D.M.
-------
363
Polycyclic Aromatic Hydrocarbons
Ron Hites
Polycyclic aromatic hydrocarbons (PAH) are well preserved in sediments
(see Figure 1 for example structures), and as best as we can tell, they are
not mobile in a core. The compounds were first of interest because some of
them, particularly benzo[a]pyrene, will cause cancer in animals. Most PAH are
produced by combustion, and therefore, when we find them in sediments we know
that something, somewhere had to get burned and that the combustion effluent
got to the sediment. Logical ly it got to the sediment through the air, and
I'l 1 come back to that. There are two exceptions to this combustion source.
One is peryl ene. We know that it is formed in situ in sediments because its
concentration increases as we go down a core, but we don't know the identity
of its precursor. Retene is another compound which is of natural origin, and
it is formed from diterpenes.
The paradigm that we're using for the movement of polycyclic aromatic
hydrocarbons from combustion sources to aquatic sediments is as follows:
There are essentially two kinds of sources, one is stationary and one is
mobile. We're not particularly concerned about mobile sources. Stationary
sources can be 1 arge seal e burners of coal , for exampl e, a coal fired power
plant or small scale burners of coal, for example, home furnaces. The burning
of petroleum and the burning of natural gas under the wrong conditions also
wil 1 give PAH. The PAH leave the combustion source adsorbed on soot and are
injected into the atmosphere where they can do one of two things. They can
land near the source if the soot particles are large enough. For particles of
10 urn or more, they will land within a few kilometers and then be transported
into local sinks by run-off. This transport mode is not terribly efficient
-------
364
Pyrene
Chrysene
Fluoranthene
Benzo[a]pyrene
Perylene
100O
Benzo[a]pyrene emission rates
in tonnes/year
from NAS, 1972
C0100
2
a
o
10 ••
Ed
1
I
i
•
i
•
Mobile Coal big Gas Waste Oil ref.
Coal home Oil Wood Open burn Coke prod
Source type
-------
365
(except in cities which are paved). In remote lakes, this particular
mechanism is not applicable. The alternate mechansim is transport by the wind
for distances on the order of 1,000 kilometers. The particles with the
associated PAH will come out of the air either in the rain or as dry fall out
and then be transported through the water column to the sediment where they
will then accumulate in the sediment record. We can core the sediment and
read the record.
It is important to know something about the history of inputs of the PAH
into the environment. We would really like to know how many PAH went out into
the atmosphere, and presumably have come down into the sediments, as a
function of time. We can get some such information from emission surveys.
Although published by the National Academy of Sciences (1972), I must point
out that the data on which the inventory was based were measured during the
mid-1950's to mid-1960's with several different methods; some were good and
some were bad. Figure 2 shows the emission rate of benzo[a]pyrene in metric
tons per year on a logrithmic scale. There are three major sources. One is
coke production. The second is open burning of such things as coal trash near
a coal mine. Both of these two sources have been decreasing lately. The
other major source of PAH is coal used to heat homes. Hand stoked, home
burners of coal were very inefficient, producing large amounts of soot and
PAH. This source has gone down dramatically, and we'll come back to that. In
Figure 2, "coal big" means industrial scale coal burning such as coal fired
power plants. This is not a very large source. Oil and gas burning do not
produce much polycyclics either. Judging from thi s inventory, we conclude
that PAH came mostly from coal burned in homes, coal burned in refuge heaps
near coal mines, and from coke production (at least in the 1960's). Much of
this coal waste burning and coke production takes place in the United States'
-------
366
midwest.
Let's look now at how these things have changed as a function of time.
Figure 3 i s a hi story of energy use in the U.S. in quadr i 11 ions of BTU's, and
it shows energy produced from different fuels: coal, oil, gas, and wood. For
example, in 1850, most of the energy in the U.S. was coming from wood. The
history of coal use is particularly interesting. We note that coal use went
up dramatically around the turn of the century and then levelled off. Oil use
has been going up dramatically since about 1930 (see the black bar), and
natural gas use almost parallels that of oil. These historical patterns are
quite useful. For example, if we look at polycyclic profiles in a core over
time and we see an increase in the 1900's and stability ever since, we can
say: "The source is coal." On the other hand, if we see a dramatic rise
starting around 1930, we can say: "The source is oil". There is an obvious
connection to acid rain; presumably PAH from coal would track pH
reconstructions in cores.
Before showing our data, I thought it would be wise to use the scientific
method and to calculate what we might expect (see Figure 4). We can calculate
the fluxes of polycyclics based on either wet or dry depositional mechanisms.
If we use dry deposition mechanisms, we can talk in terms of an average
atmospheric concentration and a depositional velocity (which is how fast the
particles come down to the surface). Unfortunately, there is a wide range in
estimates of the depositional velocity: 0.01 to 0.5 cm/sec. By multiplying
the atmospheric concentration by the depositional velocity, we end up with a
flux of 0.3-15 ng cm~2 yr'l from a dry depositional effect. Wet deposition is
••nuch easier to calculate once we know the concentration of PAH in rain which
is in the range of 1-3 ng/1. Multiplying this by the average rainfall, which
for the northeastern U.S. is 80-100 cmyr"^, we get a wet flux of 0.08-0.3 ng
cm~2 yr"1. We add the dry and wet fluxes together and take a geometric
-------
S^^^v History of energy use
) in the United States
v.
4O-
36-
3O-
Td a,.
|20'
w
10-
-
o-
-^ (quadrillion BTU)
H- !« 10 llj
185O 187O 189O
JL
^
*fl
"fe
191O 193O
186O I860 19OO
1920
I
t
t
/
RI ;
n
^
J
^
}
. a
3
^
^
^
i
t
t
t
i
. g
Fuel
^^^ Coal
1^1 Oil
Z3 Gas
^^^ Wood
195O 197O
194O
I960
Year
367
Calculated fluxes
Dry deposition
Atms. cone, x Depositional velocity = Dry flux
1 ng/m3 x 0.01-0.5 cm/sec = 0.3-15 ng
Wet deposition
Rain cone,
1-3 ng/1
Emission basis
x Rainfall = Wet flux
x 80-100 cm/yr = 0.08-0.3 ng
Input rate
* Area
1300 x 106 g/yr * 7.8 x 1016
cm
= Flux
2 = 17 ng
-------
368
average of the ends of the range and come up with 2-3 ng cm~2 yr'l. Another
way we can get a flux estimate is to take the emission rate which was
estimated by the National Academy of Sciences (1972) to be 1300 x 106 g/yr and
divide that by the area of the U.S. One ends up with a flux of 17 ng cm"2 yr"
\ Comparing this to our other estimates, we are led to expect about 2-20 ng
cm~2 yr"''.
Let's compare these estimates to what we have measured. Figure 5 is a
table from a paper in which we reported PAH fluxes at several locations
(Gschwend and Hites, 1981). These sites include Lake Superior, Somes Sound
(which has a sill so it's somewhat separated from the Atlantic), Hadlock Lower
Pond (which is a fresh water pond on Mount Desert Island), and Coburn Mountain
Pond. We reported f 1 uxes for three di fferent periods: presentdayflux, a
flux corresponding to 1950, and a flux corresponding to the turn of the
century. At present, these fluxes average 0.8-3 ng cm~2 yr"^ which is in
reasonably good agreement with what we calculated. The flux in 1950 was
generally twice as high as at present and the flux at the turn of the century
was lower by a factor of 5-10 than at present. The data at the top of the
table are all from remote sites. As I mentioned, if one goes to urban sites,
like the Boston Harbor, one should find much higher fluxes. The numbers given
in the bottom of Figure 5 are averaged over the 20th century for three
locations: Boston Harbor, Buzzards Bay, and Pettaquamscutt River. The PAH
flux averages 25-55 ng cm"2 yr" ^. This is gratifying because Bates j^t al.
(1984) carried out measurements of PAH in a Puget Sound core and found a flux
similar to what we've measured at these urban areas.
I now want to show several PAH core profiles. Figure 6 shows data from
the first core that we ever did. This was a core from Buzzard's Bay which is
between Cape Cod and Rhode Is!and. We measured PAH in three sections which
-------
369
PAH fluxes (in ng cm yr~ ) to sediments from S remote sites In the Northeastern United States for 3 age
Intervals: present, approximately 1950, and 1900: and to sediments from 3 urban sites for 1940 to the present.
Buzzards Bay data from Httes et al. (1977), and 1n sHu density estimated from oater data of Rhoads and Young (1970).
Pettaauamscutt River PAH data from Hites et al. TTSSOb), sedimentation rate from Goldberg et al. (1977), and in situ
density estimated from data of Orr and Saints (1974).
Remote Sites
Lake Superior (IS)
0.02 cm/yr
Isle Royal e (IR)
0.09 cra/yr
Somes Sound (SS)
0.1 cm/yr
Had lock Lower Pond (HLP)
0.07 cm/yr
Coburn Htn. Pond (CMP)
0.3 cm/yr
AVERAGES
Urban Sites
Boston Outer Harbor
0.1 cm/yr
Buzzards Bay, Mass
0.3 cm/yr
Pettaquamscutt River
0.3 cm/yr
AVERAGES
•includes all CjgHjj 'son
Interval
1955-now
1930-1955
1870-1920
1974-nm
1951-1955
1960-no«
1940-1960
I860- 1940
1950-now
1920-1950
1975-no*
1943-1947
1898-1901
present
•» 1950
•* 1900
1900-non
1940-now
1940-now
in
situ
dens.
0.55
0.55 .
0.55
0.33
0.32
0.43
0.52
0.51
0.1?
0.11
0.036
0.057
0.057
.
.
-
0.93
0.3
0.16
-
Chen
0.3
0.2
0.06
0.4
1
2
4
0.4
2
0.3
2
8
0.8
1
3
0.4
24
18
46
30
anth
0.03
0.02
0.004
0.01
0.05
0.2
0.4
<0.02
0.1
0.04
0.2
0.5
0.07
0.1
0.2
0.03
5.6
2
5
4
ers except perylene
C,
phen
0.3
0.2
O.OB
0.5
2.5
1
4
•0.2
2
-
4
12
1
1.5
4.5
0.4
17
.
36
25
From:
fluo
i
0.9
0.2
0.4
1
5
8
0.4
4
0.3
4
11
0.5
3
4
0.4
37
53
93
55
pyr
0.6
0.5
0.1
0.3
0.7
4
5
0.4
3
0.2
3
8
0.3
2
3
0.3
39
48
93
55
Gschwend
b(a)a
0.3
0.3
0.07
0.2
0.2
2
3
<0.05
0.6
0.04
0.7
3
0.2
O.B
1.5
0.1
19
37
42
30
chry*
tri
1
1
0.3
0.8
0.7
2
4
<0.2
1
0.1
2
6
0.9
1.5
2.5
0.2
23
37
42
35
& Hites,
b(e)p
0.9
0.9
0.2
0.8
0.9
2
2
0.2
0.8
0.1
2
7
0.4
1.5
3
0.5
14
.
.
•v25
1981
b(a)p
0.4
0.3
0.07
0.2
0.2
2
2
0.2
0.6
0.06
0.7
4
0.1
0.8
1.5
0.1
17
140*
130«
•v30
Total relative un-
substitmed PAH abun-
dance observed in three
dated sections of a sedi-
ment core from Buzzards
Bay. Massachusetts (open
circles), and calculated
PAH production (closed
circles) as a function of
time.
-------
370
were dated by lead-210 so we knew to what year these sections corresponded.
In 1850, we found very 1 ow PAH concentrations (about 7% of the maximum). At
the turn of the century, we saw the maximum concentration, and in about 1972,
we found PAH were still near the maximum. Our probl em was to ex pi a in this
1 eve! ing off at 1900. From the coal use pattern, factoring in a 1 ittl e bit
due to oil, we calculated an estimated production of polycyclic aromatic
hydrocarbons. These calculated values are shown as the curve labeled
"Production" in Figure 6, and they agreed we! 1 with the PAH measurements of
the sedimentary record.
We did cores at other locations. Figure 7 is the PAH profile for a core
taken from the Pettaquamscutt River. We were able to do this location through
the good graces of Ed Goldberg at Scripps who had dated this core using lead-
210. One finds a low, but relatively constant level, of PAH up to 1900, a
rapid increase between 1890 and 1920, and a subsurface maximum corresponding
to 1950. This was a very good core because it is from an anoxic basin of the
Pettaquamscutt River. The water on the bottom of this basin is saline and has
been anoxic for some time, and thus, there is no bioturbation. The other data
plotted in Figure 7 as open circles are benzo[a]pyrene concentrations in a
core from the Grosser PI oner Sea in Europe. This core also shows a subsurface
maximum in 1950 and agrees well with our data from the Pettaquamscutt River.
Let's look at a few other locations. Figure 8, top left, shows data from
the Mountain Pond near Coburn Mountain in Maine. The date (time) scale was
based on lead-210. The core profiles of three compounds (benzo[a]pyrene, the
sum of chrysene and triphenylene, and pyrene) are plotted. These all parallel
one another. In fact, we almost always see that the concentration ratios of
the different PAH stay constant as one goes down a core. This convinces us
that there is no degradation. If there were some degradation, some of these
compounds would be changed relative to others. In all these cores (see Figure
-------
371
~ I3r
a 12'
O)
o
3
(A
E
o
=>
CJ
0
a
c
X
Q_
|
II
10
9
8
7
6
5
4
3
2
1
e
.' i '« -
'' 1 •
' i ' ^^~~
'
2.4
2.2 _
E
2.0 |
o
/ : • H'-e"
II, I 01
• i \ f -1
"~"-s-^ \ / -
1 ,' \ '
i i \ ,'
1 f+
i 6
/ ;'
/ •'
/ ? —
i '
i %•
-i- — T — ""^-i — — • : .,1,1.
1.6 ">
1.4 1
1.2 a
1.0 S
to
0.8 |
0.6 .E
ft
O
0.2 m
1820 1840 I860 I860 1900 1920 1940 I960 1980
Year o' Deposition
Total PAH abundance (see Table 11 in the various Pettaquamscutt River sediment core sections
vs date of deposition (horiponial bars, left scale): benzo[a]pyrene abundance in the Gosser Ploner Sea
(GRIMMER and BOHNKE. 197S) vs date of deposition (®. right scale).
From: Hites et al., 1980
Concentration Ing/pn dry scdnwnt)
n ZOO 400 600
t
&
20
30
Coburn Mountain Pond, Maine
Concentration (ng/gm
n TO 300 300 tOO 500
Concentration Ing/gm aVy c*dan»ntl
SO 100
Concjntroliuii Ing/gm *y Mdrantl
SO
H0 Lake Superior, Michigan
10
S ^.BB
Somes Sound, Maine
PAH profiles in four sediment cores. Symbols: A benzo(a)pyrene; O chrysene and triphenylene;
pyrcne From: Gschwend & Hites, 1981
-------
372
8), we see a subsurface maximum at 1950. Figure 8, lower right, presents PAH
data from the Somes Sound, Maine, core. There's a subsurface maximum at 1950,
and a raise from background at about the turn of the century. Figure 8,
bottom left, gives PAH core profiles-for a site in Lake Superior which is
interesting because this site is more upwind from the major midwestern sources
of combustion than is Maine. We see an indication of a subsurface plateau.
In this case, we don't see the surface concentrations drop off as much as
we've seen in other locations, but we do see an increase at the turn of the
century.
The only other PAH data from a dated sediment core are from a paper by
Prahl and Carpenter (1979) of the University of Washington. They analyzed a
core from Oabob Bay which is a bay on the southwestern side of Puget Sound.
These authors found profiles looking very much like what we've seen before.
Figure 9 shows their data for benzo[a]pyrene and fl uoranthene. There is an
increase at the turn of the century and also the 1950 maximum. Very recently,
Sates et_ _aj_. (1984) have published a PAH core profile from another location in
Puget Sound; it too looks similar to these profiles (Figures 7 to 9).
There are two features of polycyclic aromatic hydrocarbon profiles which
are constant. One is the increase at the turn of the century and the other is
the subsurface maximum at 1950. Why the increase in 1900? Because that's
when coal use increased dramatically. This has been discussed above. Let me
now address the maximum at 1950. Clearly coal use did not maximize in 1950.
Coal use for all practical purposes has been constant during the last 70
years. Factoring in petroleum doesn't help because that increases since 1950.
We need some way of causing PAH to go down starting in 1950; putting more
fuels into the equation doesn't help. Better emission controls on large scale
burners of coal don't help us either. Emission controls really didn't start
-------
373
P4H IN DAB(» 9A« SEDIMENTS
r: 4c co K we
Profiles of three PAH concentrations with depth in
a Dabob Bay sediment core. Approximate ages of the sub-
surface maxima and deepest sediments based on 2>0Pb
measurements are given on the diagram. Average porosity
for the sediment core is 83°0 (range: 92°cr 0-1 cm: 79°,.
29-30 cm I.
From: Prahl and Carpenter, 1979
Residential Heating by Fuel Type
8O--
OO--
4O--
3O--
ZO--
10--
193O 194O 195O I960 197O 198O
Year
-------
374
in 1950, and it's also hard for me to imagine them having that large an
effect.
The answer to thi s probl em begins by remembering Figure 2 which showed
there were a lot of polycyclics coming from the burning of coal in homes.
Figure 10 presents data on residential heating by fuel type. In 1930, about
35% of all the residential heating in the U.S. was from wood and about 65% was
from coal. Thus, only two fuels were used to heat homes in the 1930's. Let's
look at the other end of the time scale. Today, home heating is about 65%
from natural gas. Oil has been decreasing since 1960 as people converted to
other fuel types (mostly electricity). There is very little coal used today
for home heating. In fact, today wood is ahead of coal. Thus, one of the big
sources of polycycl ics has been el iminated since the 1930's. It had been a
1 arge source, not in terms of the amount of coal burned, but in the terms of
the inefficiency with which that coal has been burned. All of these badly
maintained, hand stoked, home coal burners emitted large amounts of PAH and
soot; that source has been completely turned off starting in 1930-1940. It's
been replaced by natural gas which produces almost no polycyclics, by oil
which produces some PAH but not nearly at the rate that coal does, and by
electricity which is the product of large coal fired power plants which
produce few polycyclics. We believe this trend away from coal as a home
heating fuel accounts for the PAH decrease since 1950.
Research Recommendations
We need more cores from more lakes. We could then develop a better and
more quantitative correlation between polycyclic fluxes and fuel usage. More
lakes would also allow us to expand the regional data base of fluxes. At the
moment, we only have fluxes for two regions: the upper Great Lakes and Maine.
We need to determine if these fluxes are correct for other remote regions.
-------
375
References
Bates, T. S.; Hamilton, S. E.; Cl ine, J. D. (1984) Vertical transport and
sedimentation of hydrocarbons in the central main basin of Puget Sound,
Washington. Environ. Sci. Technol. 18, 299-305.
Gschwend, P. M. and Hites, R. A. (1981) Fluxes of PAH to marine and lacustrine
sediments in the northeastern United States. Geochim. Cosmochim. Acta,
45, 2359-2363.
Hites, R. A. ei_ a 1. (1980) PAH in an anoxic sediment core from the
Pettaquamscutt River (Rhode Island, USA). Geochim. Cosmochim. Acta, 44_
873-878.
National Academy of Sciences (1972) Particulate polycyclic organic matter.
National Academy Press: Washington, D.C.
Prahl , F. G. and Carpenter, R. (1979) The role of zooplankton fecal pellets in
the sedimentation of PAH in Dabob Bay, Washington. Geochim. Cosmochim.
Acta. 43, 1959-1965.
-------
376
CARBONACEOUS PARTICLES (SOOT) FROM FOSSIL FUEL COMBUSTION
Ingemar Renberg, Department of Ecological Botany, Umea University,
S-901 87 UMEA, Sweden
Combustion of coal, oil, wood and other kinds of organic matter generates
particles containing elemental carbon. Several types of particles are
formed, both submicrometer sized and coarse particles. At least for
coarse particles their surface morphology and surface texture is indi-
cative of their origin. According to Griffin & Goldberg (1981) spheri-
city is a characteristic of particles from fossil fuel burning and the
fine surface structure makes it possible to distinguish between partic-
les derived from coal and oil. Wood and also coal burning produce
elongate particles which often display the fine details of plant cellu-
lar structure (Fig. 1).
No consistent nomenclature exists for carbonaceous particles and a
large number of terms have been used. In this paper they will be called
soot.
Soot particles are released into the atmosphere along with other pollu-
tants generated at fossil fuel combustion. The amount emitted depends on
several things, such as type of fuel, type of combustion system, cleaning
devices etc. In the atmosphere the lifetime of these particles are con-
trolled by several factors. The particle size is very important. The
residence time of fine particles is usually longer than of coarse par-
ticles. But all particles will sooner or later return back to the surface
of the earth, where they are deposited everywhere.
Rather few seem to have thought about what happens to all these soot
particles. Due to the elemental carbon in the particles, which is very
resistent to degradation, they are preserved in soils for a long time
and in lake sediments forever.
The soot particles in sediments form a stratigraphic record that shows
the history of the deposition of pollutants from fossil fuel combustion.
This was first shown by Griffin, Goldberg and co-workers in their study
of a sediment core from Lake Michigan (see e.g. Griffin & Goldberg 1983).
They prepared and analysed the sediment according to the scheme shown in
Fig. 2. In their charcoal (all kinds of elemental carbon particles were
included) content diagram from L. Michigan, Griffin & Goldberg (1981)
discerned four different sections (a-d), see Fig. 4, and drew the follow-
ing conclusions:
(d) prior to 1900 the majority of the particles were elongate-prismatic
in shape, with many showing woody cellular structures,
(c) chis is a transitional period with an increasing abundance of
spheroidal particles indicating a coal source,
(b) smaller amounts of elongate-prismatic particles and more porous
spheres from coal combustion, and from about 1950 also particles
derived from oil combustion,
-------
377
(a) after 1960 the charcoal concentration decreased probably due to
improved cleaning techniques.
We have made soot particle analysis of lake sediments from Sweden.
We have prepared the sediment in a similar way as Griffin & Goldberg
with H202, although usually not dissolved the silicates with HF, and
furthermore, actually counted the number of spheres with a stereomicro-
scope. The method is described by Renberg & Wik (1984a) and is schema-
tically shown in Fig. 3. When using this method it is possible to count
spheres (Fig. 6) larger than about 5-10 ym.
Results from Lake Granastjarn, N. Sweden, are shown in Fig. 5 (left).
A core of the varved sediment was sampled with the crust-freeze corer
and was sub-sampled quantitatively to allow calculation of annual net
accumulation values of soot spheres to the lake bottom (cf. the presen-
tations about freeze coring and varves in chronology). When comparing
the results from this lake with the results from L. Michigan (Fig. 4)
the shapes of the two figures turn out to be very similar.
Lake Granastjarn is situated in an area which was industrialized rather
late. Despite that, there was soot deposition during the 18th century.
At the middle of the 19th century there was a slight increase in the
soot deposition. This is the time for the so-called industrial revolu-
tion in N. Europe. A marked increase in the soot deposition took place
about 1950 due to the industrial upswing after the second world war when
oil combustion really increased in extend. There was a peak in soot de-
position around 1970, just before the "oil crisis".
The Swedish coal and oil consumption is also shown in Fig. 5 (right).
This curve is probably typical for many European countries. There are
similarities between the soot deposition in L. Granastjarn and the con-
sumption of coal and oil in Sweden.
Several things justify more research about soot in sediments.
1. The role of carbonaceous particles in the atmosphere. The history of
the elemental carbon pollution of the atmosphere, recorded in sedi-
ments, is worth studying because: elemental carbon has a significant
impact on visibility, it plays a role in atmospheric chemistry,and as
it absorbs light may have some potential for altering the climate
(Wolff 1981).
2. Soot - metal pollution. Heavy metals deposited from the atmosphere
derive from several different sources, of which fossil fuel combus-
tion is important for some metals (Pacyna 1984).
In a sediment core from L. Michigan, Goldberg et al. (1981) found
that concentrations of several metals covaried with the concentration
of charcoal from coal, oil and woodburning (Fig. 7). Of course, that
does not necessarily mean that soot and metals are closely related.
They might both be indications of the general increase of air pollu-
tants during this century.
3. Soot - PAH. See summary of presentation by Ron Hites.
-------
378
4. Soot - acidification. It is likely that the soot particle record to
some extent reflects the history of acid precipitation. The best
correlation must be expected between submicrometer sized particles
and acid substances. Ogren & Charlson (in print) have in fact been
able to demonstrate a significant correlation between wet deposition
fluxes of excess sulphate and elemental carbon in rain water samples
collected in Sweden. Coarse particles (>5 ym) were not included in
their analysis. But can we expect to find a correlation between
coarse soot particles like the ones we have analysed and acid depo-
sition? Probably, because there is likely to be a relationship bet-
ween the deposition of coarse and fine soot particles. In the acidi-
fied Lake Girdsjon in Southwestern Sweden we have made both a soot
particle and a diatom analysis (Fig. 8). The pH curve inferred from
the diatoms is more or less a mirror image of the soot particle dia-
gram. The pH value started to decrease concomitant to the marked
increase in the soot particle deposition.
5. Soot-paleomagnetism. See summary of presentation by Jan Bloemendal.
6. Soot as a dating tool. In Sweden (and Europe) the history of fossil
fuel combustion as recorded by statistical data,and hence the influx
of soot to lake sediments, shows some characteristic points;
a) the middle of the 19th century - the industrial revolution with
increased coal burning,
b) about 1950 - the industrial upswing after the war with increased
oil combustion, and
c) about 1970 - the peak in oil combustion before the oil crisis.
As pointed out earlier in this paper these three points are discern-
able in the varved sediment of L. Granastjarn. One model for "soot
dating" is to determine the soot content at different levels of a
non-varved sediment core and try to identify these points or other
local points of marked change of the soot curve (Renberg & Wik 1984b).
Of course, there are local and regional variations in the soot fall-
-out history. Therefore, it is recommendable, or necessary, to
establish local soot fall-out chronologies before trying to make any
detailed soot datings.
Fig. 9 shows the results of an attempt to show that soot dating really
works. Lake Koltjarn has a varved sediment and Lake Omnesjon not.
The soot concentration curves from the two lakes are rather similar
in shape and three points (about 1930, 1950 and 1970) can be identi-
fied rather easily.
Recommendations for research
Reliable methods for quantitative analysis of different size fractions
of soot particles should be developed.
The behaviour of soot particles in lake water, e.g. the pathways
from the lake water surface to the sediment should be studied.
The correlation between soot in sediments and sulphur, nitrogen, PAH,
magnetic parameters and certain heavy metals should be studied.
-------
379
References
Goldberg, E.D., Hodge, V.F., Griffin, J.J., Koide, M. & Edginton, D.N.
1981. Impact of fossil fuel combustion on the sediments of Lake
Michigan. - Environ. Sci. Technol. 15, 466-471.
Griffin, J.J. & Goldberg, E.D. 1975. The fluxes of elemental carbon in
coastal marine sediments. - Limnol. Oceanogr. 20, 456-463.
Griffin, J.J. & Goldberg, E.D. 1981. Sphericity as a characteristic of
solids from fossil fuel burning in a Lake Michigan sediment. -
Geochim. Cosmochim. Acta. 45, 763-769.
Griffin, J.J. & Goldberg, E.D. 1983. Impact of fossil fuel combustion
on sediments of Lake Michigan: a reprise. - Environ. Sci. Technol.
17, 244-245.
Ogren, J.A. & Charlson, R.J. Paper in print in Tellus.
Pacyna, J.M. 1984. Estimation of the atmospheric emissions of trace
elements from antropogenic sources in Europe. - Atmos. Environ. 18,
41-50.
Renberg, I. & Wik, M. !984a. Soot particle counting in recent sediments;
an indirect dating method. - Ecol. Bull, (in print).
Renberg, I. & Wik, M. 1984b. Dating recent lake sediments by soot par-
ticle counting. - Verb. Internat. Verein. Limnol. 22, xx-xx.
Smith, D.M., Griffin, J.J. & Goldberg, E.D. 1975. Spectrometric method
for the quantitative determination of elemental carbon. - Anal.
Chem. 47, 233-238.
Wolff, G.T. 1981. Particulate elemental carbon in the atmosphere. -
APCA Journal 31, 935-938.
-------
380
MICROSOPIC SURFACE TEXTURE
ETCHED,
CONVOLUTED,
LAYERED
Fig. Hal
MICROSCOPIC SURFACE TEXTURE
SMOOTH
ROUGH, IRREGULAR,
PITTED or CELLULAR
ETCHED,
CONVOLUTED,
LAYERED
ELONGATE
PRISMATIC
UJ
Q.
I
1/5
COAL
WOOD
WOOD
COAL
COAL
WOOD
COAL
WOOD
OIL
Fig. l(bL
u«n cff charcoal pjrticlc* According lo their shapes and surface icxlures. The "-hapci (\ernc3l u*i«.l arc \icwrd under 1000 x mj^nificjiion and the
surface icxlurn (hori/onial atisl arc oh».cr\rd under >HOO * m-j£nifn.~di»on.
Fig. 1. Figures from Griffin & Goldberg (1981).
-------
381
OVEN DRIED SEDIMENT
I
OXIDIZING WITH H2°2 + KOH
I
LEACHING WITH HCI
1
DIGESTION WITH HF
I
LEACHING WITH HCI
4
OXIDIZING WITH H2O2 + KOH
I
LEACHING WITH HCI
*
THE RESIDUE IS OVEN
DRIED AND THE CARBON
CONCENTRATION DETERMINED
BY INFRARED ASSAY
Fig. 2. Schematic description of a method for charcoal analysis in
sediments by Griffin & Goldberg (1975) and Smith et al. (1975)
This method has been slightly modyfied recently (Griffin &
Goldberg 1983).
OVEN DRIED SEDIMENT
I
OXIDIZED WITH »2°2
I
SUSPENDED IN H20
AFTER HOMOGENIZATION
A SUBSAMPLE IS POURED
INTO A GLASS PETRI DISH
I
EVAPORATION AT ROOM
TEMPERATURE
I
THE NUMBER OF SOOT
PARTICLES IS DETERMINED
BY COUNTING UNDER A
STEREOMICROSCOPE
Fig. 3. Schematic description of a method for counting soot spheres
in sediments by Renberg & Wik (1984a).
-------
382
cm
LAKE MICHIGAN BOX CORE LM-780914
See d
See b
Set c
o c : 020
•/. CARBON by WEIGHT >38^
5CV1"
Charcoal pnrticla in Core LM 780914 collected September 14. 1978 Tram southeastern Lake
Michigan a( 43 WN and H6J22'W. The scanning electron micrographs show the particle morphologies
common to four periods: (at The 0-8 cm interval is representative or the particles in the sediments ol' the
post I960 period; lb| 12-Ucm, 1930-1960: Id 27-28cm. IVOO-1930. and Idl 30-31 Drc-1900 ocriod.
Fig. 4. From Griffin & Goldberg (1981).
0)
e
o
o
4)
h»
fl
E
o
<0
®
Lake Granastjarn
soot particle deposition
no m"2yr1
1980
1970
1950
1930
1910
1890
1870
1850
1830
1810
1790
zoo ooo
coal & oil consumption
In Sweden
metric tons • 106
400 OOO 0 1O 20 30 4O
Fig 5 The annual net accumulation of soot spheres in the varved
sediment of L. Granastjarn (left) and the Swedish coal and
oil consumption (right).
-------
383
Fig. 6. A soot sphere from a lake sediment.
-------
384
The charcoal (soot) concentration in the
L. Michigan core. This figure is re-drawn
from Fig. 2 in Griffin & Goldberg (1981)
to make the comparison with the figures
below easier.
IK coee (.'**).
YEAR
I'JOO
JO «0 JO ?0 10
DEPTH IN CORE (cm)
50 «O SO 20 10
DEPTH IN CORE (cm)
60 50 40 30 ?0 10
DEPTH IN CORE (cm)
60 5Q 40 30 20 fQ
DEPTH IN CORE (cm)
60 JO «0 SO 20 IO
DEPTH IN CORE (cm)
50 40 50 !0 10
DEPTH N CORE (cm)
Metal concentrations (on a dry-weight basis) as a (unction of depth in the Lake Michigan core.
Fig. 7. Figures from Griffin & Goldberg (1981).
-------
385
inferred from diatom
/analyses (index B)
6 -
r
a
TO 5
5
0)
nj
4 -
r1800
- 10 ooo
1979
c
W Q)
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"'•5
- 20 000 w
a >,
o w
SE
CO
o o
c a.
Fig. 8. The soot particle concentration in a core from L. Gardsjon
and the pH history of the lake inferred from the subfossil
diatom record of the sediment.
-------
386
• GRANASTJARN
KOLTJARN &
LAKE KOLTJARN
SOOT SPHERULES (no. g'dry «ed.)
0 1 000 2 000
3 000
o .
10 ~ i
E , ... — ,
z
£ i. "...— ~...IZ
UJ
- 1982
- 1070
(• 1974
!- 1968
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|-1958
L1953
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1-1943
r 1938
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I . _
Q
Z
UJ
20 --
(-1928
-1900
a
UJ
o
LAKE OMNESJON
SOOT SPHERULES (no. g'dry sod.)
0 500 1 000
1 500
10 -1
1
30 -
-1858
1-1749
Fig. 9. The soot particle concentration in the varved lake sediment
of L. Koltjarn (left) and in the non-varved L. Omnesjon (right)
-------
387
Accumulation and Processing o-f Chlorinated Hydrocarbons in
Lake and Bog Sediments: Relationship to Atmospheric Deposition
by
S.J. Eisenreich, R. Rapaport, N. Urban, P. Capel, B. Looney, J. Baker
Environmental Engineering Program
Department of Civil and Mineral Engineering
University of Minnesota
Minneapolis, MN 55455
Contribution to the Workshop on
"Progress and Problems in the Paleolimnological
Analysis of the Impact of 'Acidic Precipitation'
and Related Pollutants on Lake Ecosystems"
Introduction
Atmospheric transport and deposition play an important role in
distributing trace organics of anthropogenic origin throughout the
aquatic and terrestrial environment. Trace organics of interest in
this presentation are chlorinated hydrocarbons such as PCBs, DDT-group
compounds, chlorinated hexanes (BHC's), hexachlorobenzene and
toxaphene. These compounds exhibit similar chemical/physical
properties of low aqueous solubility and vapor pressure, high
-------
388
partition coefficients with respect to octanol, solid and aqueous
organics and lipid phases of organisms., and long chemical residence
times in the environment (i.e., persistent and re-Fractory) . They are
transported through the atmosphere primarily as gases or attached to
•fine particles «2 urn mmd). The primary removal mechanisms are
unproven but thought to be scavenging o-f organic-laden aerosols by
precipitation and dry deposition, especially of the large particles.
The role o-f air-water transport o-f the gas phase organics is unclear,
although volatilisation is an important loss process for lakes and
oceans. Once deposited in a lake, the hydrophobic organics bind
preferrentially to organic detritus and ultimately are deposited in
bottom sediments. The proportion of trace organics in the dissolved
phase depends on the concentration and composition of particles. For
organics having log Kow > 3.0 and S3 in the range of 1 to 100 mg/1 , 75
to 1007. is apparently in the dissolved phase based on filtration.
Even so, small and large lakes exhibit fine particle residence times
less than one year, and trace organic residence times of 2 to 4 years.
Thus, sediment profiles may preserve, in the absence of major
bioturbation, the historical input pattern, although sediment focusing
probably alters the actual magnitude of inputs.
The objectives of this presentation are to present the historical
record of CH input to lake and bog sediments, and to provide
information how organic profiles may be useful in dating sediment
cores.
Discussion
Lake Sediments:
The historical record of CH deposition to lake sediments has been
obtained for a variety of trace organics. I will present information
-------
389
on cores taken -from Lake Ontario in a high sedimentation rate
environment and in Lake Superior having slow rates of sediment
accumulation. In this -first section, the Lake Ontario cores will
be discussed in some detail. Box cores taken in eastern Lake Ontario
were dated with both Pb-210 and Cs-137 by J.A. Robbins, and mixing
parameters and sedimentation rates determined -from the rapid steady-
state mixing model which adequately describes Pb-210 behavior (Table
1) .
The Pb-210 pro-files are consistent with mixing depths of 3 to 4
cm in E-30 and 5-6 cm in G-32, corresponding to an intrinsic
resolution
-------
Table 1. Lake Ontario Sed1ment_Core_Data
390
Long/Lat ? ,
R (gem *yr ')
W (on yr'1)
S (cm)
S (g/cm2)
*V(yr)
E-30
.0443 ± .0027
0.2
3-4
.50 ± ,08
11.3
6-32
.0795 ±
0.3
5-6
.92 ±
11.6
.0031
1.0
•V S/R
-------
391
TOTAL PCBs ng/g
400 800
10 A
DEPTH cm
15 -
20 ir
1981
1961 -
1941
1921 -
TOTAL PCB FLUX rig/cm yr
20 40
TOTAL PCB ng/g
400
1981
1961
1941
1921
Figure 1. t-PO3 concentrations and fluxes in dated
sediment cores from Lake Ontario.
-------
392
concentrations scale to the sedimentation rate. Figures 2 and 3 show
the depth profiles o-f PCB, t-DDT, mirex and HCB in the two Lake
Ontario cores. In these cores, mirex concentrations are about equal
and thus accumulation is proportional to sedimentation rate. This
behavior is consistent with the hypothesis that mirex enters the lake
on particles via riverine sources; potential PCB delivery to both
sites occurs via settling particles -followed by dilution with
uncontaminated, erosional sediment. The t-DDT peak occurs deeper in
both cores than the PCB or HCB peak, the age o-f which is probably
about I960 representing the period o-f peak usage in North America.
For persistent hydrophobic organics, transport and fate are
dominated by associations (sorption/partitioning) with the high
surface area, high organic content particles. Thus, the total
quantity of organics in sediment cores differing in sedimentation rate
should be directly related to the ratio of organic carbon fluxes.
Figure 4 shows the relationship of accumulated mass of several
different organics in the two cores. The data points cluster closely
along the line representing the ratio of the organic carbon fluxes,
and not the mass accumulation rate.
The penetration of PCBs to depths in both cores having ages prior
to the onset of production suggests downward migration in the sediment
cores. As a test of this hypothesis and searching for evidence of PCB
degradation, the ratio of tri-, tetra-, and pentachlorinated byphenyl
congeners to t-PCB versus depth was plotted. Initially, Figure 5
shows that the penta-substituted congeners are lost (degrade) at the
expense of the lighter congeners. A more plausible explanation is
that the lighter congeners are diffusing in the porewater away from
the sedimentary peak leaving the heavier species behind. This
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-------
395
Sedimentation Rat* • 1.89
Organic Carbon
Sedimentation Rat* • 1.44
Heplachlor Epoxld*
4-PCS
O
UJ
2000 t-
1000
4000
1250
5000
1500
6000
ACCUMULATED MASS (ug/m*) in LO-8J E-30
Figure 4. Relationship of accumulated mass of several organic
contaminants in two Lake Ontario cores to mass and
carbon accumulation rates.
-------
396
scenario necessitates that PCBs and perhaps other organics occur at
measureable concentrations in porewaters, These data have been
modeled assuming di-f-fusion is responsible -for the deep penetration
into the core by lower chlorinated species, yielding a tortuosity-
corrected di-f-fusion coe-f-ficient of about 10"* cmz/sec. Table 2
documents the occurence of t-PCB occurring at concentrations 10 to 500
times overlying water values. The cores -from Lake Ontario have
demonstrated the differential mixing of sediment components, the
potential application of organic input functions to date cores, and
the mobility of trace organics in sedimentary profiles.
Nine sediment cores collected in 1978 in the western and central
basins of Lake Superior were dated with Pb-210 and analysed for PCBs
and DDT. Surficial sediment concentrations (0.5 cm) of PCBs ranged
from 4 to 180 ng/g of dry dediment corresponding to estimated recent
fluxes of 2 to 70 ug/ma yr. Highest concentrations and fluxes of PCBs
occur in the western arm of the lake nearest the urban areas of
Dulnth/Superior and the major source of sediment to the lake - erosion
of red clay along the Wisconsin shoreline. Levels are also generally
elevated in the central region of the lake in the vicinity of Isle
Royale. We believe this area may be impacted by atmospheric transport
from the upwind urban/industrial center of Thunder Bay, Ontario.
Surficial FCB concentrations are higher than observed by Frank et al
(19SO), who reported values integrated over 3 cm, and generally lower
than observed for the other lakes. Figure 6 provides an example of
concentration-depth profiles for selected sediment cores taken in 1978
in Lake Superior. Fractionating the cores into ~ 0.25 cm segments in
the upper few cm corresponds to a time resolution of ~6 years for a
linear sedimentation rate of 0.04 cm/yr to 2.5 yrs for a sedimentation
-------
397
Loke Ontario - 1981
Core G-32
3-CB x 3
t-PC3 10
x»
1 - PCS
10 20 30
10 20 30 40 50
Figure 5.
m_i_T
Table
PCB congener ratios to t-PCBs in L081-G32:
evidence for diffusion of lower chlorinated congeners.
CB* In Pore Water of Great Lakes' Sediments
Pore Water
(ng/1)
Lake Superior
26
18
12
9-35
M
Lake Erie (HS-81)
72
35
1-5
Lake Huron (HS-81)
39
26
307
•\.l
Sediment
(ng/9)
5.0
7.9
7.8
9-19
M700
76
40
—
46
39
21
.»
KP
("9/9)P/
(ng/g/w
190
440
640
MO6
1060
1160
~
1180
1520
70
,106
Site
10
9BX-81
19BX-B1
31BX-81
2BX-81
Lake
0-2 em
2-4 on
Lake
0-2 cm
2-4 en
4-6 cm
Lake
-------
398
Depth
(cm)
Total PCB(ng g"1)
70 I40 2IO
0
t-
4
8
10
0
2
4
6
8
m
I
,, I
Site 1,1 Bx
1 i i
70 140 2!
, J 370
Site 2, 4Bx
i i
1CT7O
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-1961
-1951
-1942
1933
0
4 f*\ ^m9
-1963
•1931
•1901
70 140 210
0, . i 1QKQ
2
4
6
8
n
Site 5, 11 Bx
i i
'1938
'1874
Figure 6. PCBs in lake Superior Sediment Cores
-------
399
Total PCB (ng g"1)
7 14 21
Depth
(cm)
u
2
4
6
8
10
Site 4, 8 Bx
i i
7 14 2
w
2
4
6
8
10
Site 10, 24 Bx
i i
35 70 10
0
2
4
6
8
m
i
i •
d
Site 11, 26 Bx
i i
.1967
-1959
1939
1919
Figure 6 contd.
-------
400
Total PCB (ng g ')
35 70 105
0
2
4
fi
VJ
8
10
1 »
I
j
[
Site 6, 13 Bx
i i
4 c\-rr\
.1972
-1967
-1961
-1955
-1950
"1944
70 I40 2IO
!
2
4
Depth
(cm) 6
8
10
J
Site 7, 15 Bx
i i
h1972
"1965
-1949
-1934
"1919
35 70 I05
Q, • • locrt
p
L-
4
6
8
m
j
1
Site 9,21 Bx
i i
-1940
"1902
Figure 6 contd.
-------
401
rate of 0.1 cm/yr. Pb-210 analyses of these sediment cores show
mixing depths o-f 0 to 4 cm, with most cores having values o-f 0 to 2
cm. A mass accumulation rate of 0.04 cm/yr (lakewide average) with a
mixing depth o-f 1 cm yields a time resolution o-f 25 years.
Application of various biological mixing models using Pb-210 as a
tracer suggest a low rate of mixing. The detailed 'shape of the PCB
profile in the upper few cm argues against significant mixing. Figure
7 shows the historical profiles of PCBs in three sediment cores
differing in mass accumulation rates by > two times. In nearly, all
cores examined, the onset of elevated concentrations occurs near 1950,
peaks in 1972-73, and decreases in the last decade. The date at which
PCB levels increase most rapidly is about the same in all the Great
Lakes.
The sedimentary profiles of PCBs in Lake Superior are in close
agreement with the decrease in PCB residues measured in Lakes Michigan
and Superior coregonids and chubs and the U.S. sale of PCBs. The
decrease in PCB concentrations in major fish species demonstrates
clearly reduced loading to the lakes as a result of improved disposal
practices. The difference in time between the peak in PCB sales and
the peak in sedimentary concentrations corresponds (fortuitously) to
the average residence time of PCBs and DDT determined from mass
balance calculations - about 2 to 4 years. We conclude that the FCB
profiles in Lake Superior sediments record the historical input
pattern. Furthermore, the sedimentary burden responds rapidly to
decreased loading, on the order of the chemical residence, time of the
lake. Implicit in this discussion is the necessity to collect
undisturbed sediment cores and have the ability to segment the cores
with appropriate time resolution.
-------
1980
0
1970
1960
1950
1940
0
PCBs in Fish
g"1-)
4
PCB Sales
a L.Michigan Coregonids
o L. Michigan Chubs
+ L. Superior Coregonids
10
20
30
Domestic PCB Sales
(103 Kg yr"1)
8
40
PCBs in L.Superior Sediments
0
0
35
(ng g"1)
70
105
140
B
+ S-78-1
o S-78-6
• S-78-7
1 40
(ng
280
Figure 7. Historical PCB Profiles in Three Lake Superior Sediment Cores
Comparison to PCB Sales and Fish Concentrations.
O
PO
-------
403
Bog Sediments:
Ombrotrophic mires or wetlands are referred to as bogs and
receive their hydrologic input entirely from the atmosphere; i.e.,
little or no groundwater or sur-face runoff. Several peat cores -from
bogs in eastern North America have been collected and analyzed for
various chlorinated hydrocarbons. We have concluded that hydrophobic
trace organics behave conservatively in the core, mimic the tentative
input function and provide both the shape and magnitude of the
atmospheric flux to these sites. An example of particular interest to
us is the story evolving concerning purportedly new DDT inputs to
North America.
DDT is perhaps the most effective and notorious pesticide
developed to date. Its uses, benefits, and environmental hazards have
been documented. DDT was first introduced to the environment during
the latter stages of World War II to combat typhus and malaria in the
tropics. Peak use of DDT in the U.S. occurred in the late 1950's and
early 1960's, with peak U.S. production occurring in the early 1960's.
DDT was banned from use in North America in 1972, and concentrations
and fluxes of DDT and metabolites have decreased substantially since.
We believe that new DDT inputs continue and may be increasing.
When DDT is released to the environment after application to
fields usually by aerial spraying, or is allowed to migrate into
lakes, streams and coastal areas, it is transformed into metabolites,
most notable DDE and DD. DDT is transformed into DDE in aerobic
environments and ODD is the first product formed in anoxic systems.
DDE is a metabolic deadend in that it is stable to further
degradation. However, ODD can be transformed into other metabolites —
mostly hydroxylated and dechloroinated species. The halflife of DDT
-------
404
in the environment has been estimated to be about 10 years, with much
variabibi1ity depending on conditions.
As o-ften occurs in scientific endeavors, the discovery of this
potentially-injurious phenomenon occurred by serendipity. We are
investigating the biogeochemistry of Sphagnum bogs in North America
through funding provided ny the National Science Foundation. Sites of
study are restricted to ombrotrophic bogs which receive all of their
hydrologic and nutrient inputs from the atmosphere. Therefore, these
systems are ideal for studying certain aspects of atmospheric
processes. Bogs are characterized by low pH and basic cation
concentrations, and high organic carbon and color. In attempting to
determine the ages associtaed with various peat horizons, we
discovered that many elements or species which normally behave
conservatively in the profile did not. Examples are the radionuclides
Cs-137 and Pb-210. Dated profiles are needed to establish mass and
chemical accumulation rates, which presumably represent historical
atmospheric deposition. It occurred to us that hydrophobic organics
such as DDT and PCBs might bind strongly to peat organic matter and
behave conservatively in the core. Also, peat profiles should provide
horizons indicating the onset of DDT use in the environment, its peak
use in the early 1960's, and the falloff following the 1972 ban.
Realistically, the 1960 peak might be the only feature that could be
applied to the dating problem.
To this end, peat cores were collected from Minnesota to Maine,
and north to Nova Scotia for study of biogeochemical processes, and
-four were were analyzed for t-DDT. Figure S shows a comparison of the
DDT use and production curves to DDT accumulation rates. The depth of
each core was 50 to 60 cm, and the core was segmented into 2.5 or 5.0
-------
U. S. PRODUCTION AND USE Of OPT
Unit - K>*g
29 90 79
no
t-DDT ACCOM, (/ig/nAyr)
0 5
10
I-DOT ACCUM. (jig/m'.yr)
0 I 2
1971-'
1964
1944
Year
1924
I9O4
16*4
. i i i
\2== ^
" S^"*' "^ :£•
¥ ..f*-^
"s^ — *rc^
, ^» . ^-=* ^» PRODUCTION
^^
art-'
1964.
1944.
Year
1924.
1904.
1864.
3^
' '
Marcill. MN
(NO
/9ft—
1964.
1944.
Y«or
1924 j
1904.
iBBa
T
\
i
Diamond , ON
I-OOT ACCUM. l/ig/m'.yr) 1- DOT ACCUM. (/tg/m'.yr) 1- DOT ACCUM. (/ig/m'.yr)
0 3 10 o 9 10 0 10 21
!97t-~
1964
1944.
Y*ar
1924.
1904.
1864.
r
_________ 1 — -
1
Fourchu. NS
i •
i»rt— •
1964
1944.
Y«ar
1924.
1904.
1884. I
=>,
• Alfred. ON
!9Te—
1944.
Y»or
1924.
1904.
1884.
• " : 'f "••"• '7 •' •-•: • |
. :, i
1
Big H«olh. ME
Figure 8. t-DDT in Peat Cores from Eastern North America.
Comparison to DDT Use and Production Curves.
O
cn
-------
406
cm sections. The ages of the depth increments are derived from a
novel ash dating technique and Pb-210. These pro-files show a peak
accumulation at about 20 years ago, and a dramatic decrease in the
early 1970's. In some cores, t-DDT increases at the surface and in
others, remains at higher than expected levels. Closer analysis o-f
the cores shows that >757. o-f the t-DDT in the sur-face peat is
untrans-formed p,p'-DDT. Remembering that little parent DDT ought to
be present at the sur-face -from historical use patterns, then we can
only conclude that recently-deposited species must, o-f necessity, be
derived from new source(s). This conclusion is supported by finding
largely parent DDT species in snow and rain in northern Minnesota.
Figure 9 shows that present day fluxes of t-DDT, which is mostly
fresh DDT, are about 10 to 207. of the peak accumulations in 1960.
Since the ecological consequences of historical DDT use are well
documented, the increase of DDT inputs via atmospheric deposition to
North America is cause of some concern. We hypothesise that the
likely source of new DDT is material emitted into the atmosphere in
Mexico and Central America, and delivered to eastern North America by
long range traport. The meteorological pattern shown in Figure S
makes transport of fresh DDT to North America as a gas or aerosol a
likely possibility. It should be noted also that t-DDT profiles in
peat cores has evolved into a rather useful technique for dating peat
cores.
-------
407
NORTH AMERICA
PACIFIC OCEAN
1
ATLANTIC
OCEAN
TOTAL
DDT
SURFACE
CPEAK DDT
T ACCUMULATION
i
f°,p' +
\p,p'DDT
I i
yr
Figure 9. Recent and Historical DDT Fluxes to Areas in
Eastern North America. Source of New and
Continued Input is Likely Mexico and Central
America.
-------
408
References
1. Eisenreich, S.J., Capel, P.O., Robbins, J.A., Bourbanm'ere, R., Accumula-
tion and diagenesis of chlorinated hydrocarbons In lake sediments. 1984,
in preparation.
2. Eisenreich, S.J.,unpublished data.
3. Eisenreich, S.J., Johnson, T.C., Hollod, G.J., Geochronology of PCB and
DDT inputs to Lake Superior. 1984, in preparation.
4. Petersen, J.C., Freeman, D.H. 1982. Phthalate ester concentration varia-
tions in dated sediment cores from the Chesapeake Bay. Environ. Sci.
Tech., J6, 464-469.
5. Oliver, B.G., Nicol, K.D. 1982. Chlorobenzenes in sediments, water and
selected fish from Lakes Superior, Huron, Erie and Ontario. Environ.
Sci. Tech., 16, 532-536.
Acknowledgments
This research is based on part on funding from the U.S. EPA, NSF and NOAA.
-------
409
MAGNETIC MEASUREMENTS OF ATMOSPHERIC PARTICULATES AND OMBROTROPHIC
PEAT; A REVIEW
*
F. Oldfield, J. Bloemendal , L. Barker, A. Hunt, J.M. Jones, M.D.H Jones,
R. Maxted, N. Richardson, J. Sahota, Dept. of Geography, University of
Liverpool, U.K. and K. Tolonen, Dept. of Botany, University of Helsinki,
Finland.
* Present address - Graduate School of Oceanography, University of Rhode
Island, U.S.A.
This contribution reviews research efforts designed firstly, to use
magnetic measurements to characterise and differentiate sources of
urban-industrially derived atmospheric particulate material; and
secondly, to use magnetic measurements to study the history and spatial
variation of urban-industrial pollution as preserved in recent
ombrotrophic peat deposits and lake sediments. In doing so, it attempts
to define the future role of magnetic measurements in acid rain and trace
metal deposition studies. Part of the rationale for the emphasis on the
use of ombrotrophic peat in the work reported here is that depositional
environments in which geochemical inputs are exclusively atmospheric are
clearly advantageous.
The presentation is divided into four sections: The first reviews
the production of magnetic particulates by fossil fuel combustion and
illustrates the use of magnetic measurements in characterising urban
aerosols; the second reviews the stratigraphic and spatial record of
magnetic deposition as recorded in ombrotrophic peat; the third shows
that in certain situations lake sediments can record the deposition
-------
410
history of industrially-derived magnetic material; and the fourth
outlines some future research priorities. Definitions of the magnetic
parameters referenced are given in Table 1.
SECTION ONE
Figure 1 illustrates the process of fly ash formation in a
coal-fired power station. Raw coal is pulverised, producing particles of
~ 10-100 microns diameter. Further mechanical breakup yields particles of
~ 0.1-50 microns diameter (accounting for 99% of the final product).
Vapourisation, nucleation and condensation produce particles of ~ 0.1
micron diameter (accounting for only 1% of the final product). Sulfur
compounds, magnetic iron oxides and trace metals all become enriched
during this process and trace metals are further enriched in the magnetic
fraction.
Figure 2 illustrates the production of ferrimagnetic material during
fly-ash formation. There are two main pathways: Firstly, with a short
combustion period and/or low temperatures, magnetite is produced from
pyrite framboids with little dimensional change or melting. Secondly,
with higher temperatures and/or a longer combustion period, pyrite is
oxidized eventually producing hematite, which dissolves in a Mg-rich
silicate melt, eventually yielding ferrous silicate and a Mg-rich
magnetite; then depending on the rate of cooling either stoichiometric
magnetite or eqimolar mixtures of magnetite and maghemite are produced.
The ferrimagnetic grains are spherical in shape. Regarding their size,
production models and indicate that magnetic spherules generated by all
of the relevant industrial processes will be ~ 2 microns diameter or
greater. This is consistent both with their reported sizes and with their
magnetic properties. Spherule size is important, since magnetic
properties are highly dependent upon grain size. Their size is such that
-------
411
they can be magnetically distinguished from generally much finer-grained
magnetic material of crustal/pedogenic origin.
The relationship between magnetic oxides and heavy metals in fly
ash, industrial particulates and vehicle emissions is poorly understood.
Two schemes have been suggested (Figure 3): Firstly, ferrospheres in the
form of an Al-substituted ferrite accept transition metal ions by
isomorphic substitution. Secondly, condensation of volatilised trace
species occurs on particulate surfaces in cooler parts of the system.
Where a single emission source is dominant, magnetic mineral
concentrations in samples taken using air samplers are often roughly
proportional to trace metal concentrations. Table 2 shows magnetic:metal
ratios of samples from the two Mersey tunnels in Liverpool, England. The
sampler used was an Andersson 2000 four stage cascade impactor mounted on
a high volume air sampler (20 CFM). The magnetic:metal ratios for the two
tunnels are quite similar. However, particle-size dependence of
magnetic:metal ratios may complicate this picture. Table 3 shows the data
from Table 2 broken down according to particle size. The 50% effective
cutoff diameters for impactor stages 1-4 are 7.0, 3.3, 2.0 and 1.1
microns. There is a tendency for higher magnetic:metal ratios to occur in
the coarser particle size ranges.
Magnetic:metal ratios may vary considerably with particulate source.
Table 4 compares magnetic:metal ratios for the two tunnel sites with
those for particle-sized resuspended fly ash. The ratios for the fly ash
are several orders of magnitude higher.
Different combustion processes give rise to particulate emissions
with distinctive magnetic characteristics as well as diferent
magnetic:metal ratios. Magnetic measurements alone or in combination with
measurements of metal concentrations can aid the identification of
-------
412
aerosol sources in areas of mixed emission. This is illustrated in Figure
4 which compares the 'S' ratios of fly ashes from Hams Hall power station
in the West Midlands, England, with those of leaf samples from urban and
rural areas in Yorkshire, England, and the Mersey tunnel samples
referenced earlier. The tunnel samples, dominated by vehicle exhaust
emissions, are dominated by magnetite, while the fly ashes and leaf
samples have a significantly greater hematite component. This
relationship is independent of particle size.
On a larger geographical scale, magnetic measurements can
differentiate dusts of urban-industrial origin from those resulting from
deflation processes. Figure 5 plots the susceptibility:Al ratio versus
atmospheric Al concentration for a suite of samples obtained from the
Mediterranean atmosphere by R/V Shackleton. Samples with the highest
susceptibility:A1 ratios are associated with the lowest atmospheric Al
concentrations. This relationship is interpreted as resulting from
varying degrees of dilution of a relatively highly magnetic
urban-industrially derived aerosol from the European mainland by crustal
material with relatively low concentrations of magnetic material, derived
from sources such as the North African arid zone.
Figure 6 gives another example of the use of magnetic measurements
for aerosol source differentiation. The samples shown are fly ashes,
North Atlantic dusts and two sets of dusts from Barbados, a red-brown
coloured summer set, derived from the North African arid zone, and a grey
winter set derived from a more local source, in South America. The
gradient from high to low SIRM:ARM ratios reflects a declining proportion
of relatively coarse grained magnetic material of urban-industrial
origin, while the gradient from low to high values of frequency-dependent.
susceptibility reflects an increasing proportion of very fine-grained
-------
413
magnetic material of inferred crustal origin. The diagram clearly
differentiates the fly ashes, dominated by relatively coarse magnetic
material, and the North Atlantic and Barbados dusts with a progressively
increasing proportion of very fine soil-derived magnetic grains.
The main conclusion from this section is that irrespective of the
feasibility of directly estimating heavy metal concentrations from
magnetic parameters, the use of magnetic measurements to separate
particulate sources appears viable, Also, although no direct
sulfur-magnetic particulate link may exist the ability of magnetic
measurements to differentiate aerosol sources is clearly of considerable
value in the context of acid rain studies.
SECTION TWO
Figure 7 shows plots of volume, specific and cumulative SIRM for a
series of short ombrotrophic peat profiles from Cumbria, England. At all
of these sites, and at many others studied subsequently, peaks in
magnetic concentration occur near the present day surface. At all of the
Cumbrian sites it is known from pollen-analytical evidence that the depth
of peat accumulated since 1800 AD seldom exceeds 20 cm. Likely sources of
magnetic input to these sites include local sources such as
Barrow-in-Furness and a steelplant at Millom, as well as extra-regional
sources such as the heavily industrialised areas of South Lancashire.
Spatial variations in the concentration of magnetic material reflect
distance from industrial sources: this is the case for either peak
concentrations or cumulative deposition above the point of initial
magnetic increase. This is shown in Figure 8 which maps specific SIRM for
surface peat samples from the northeastern U.S. and eastern Canada. The
sites with highest values are located close to major sources of
industrial pollution. They are as follows: sites 2 and 3, Toivola Bog and
-------
414
Ely Lake Bog, northern Minnesota, near the Mesabi Iron Range; and site 4,
Guilletville Bog, Sudbury, Ontario, located 12 km northeast of the
Sudbury nickel smelter and lying in the prevailing wind direction. Figure
9 maps the SIRM:ARM ratios of the same sites shown in Figure 8. The
pattern of variation of this parameter, with the highest values
associated with the most contaminated sites, is consistent with the
expected size range of industrially generated magnetic spherules.
The effect of microtopography on magnetic mineral accumulation
within peat bogs is reflected in higher magnetic accumulation rates in
hummock sites than in pool sites; the differences are especially
pronounced at British sites. This may result from the prefential
deposition of magnetic material on hummocks, but may also reflect the
dissolution of magnetic material in pools. Where pollen analysis has been
used as an independent test of the synchroneity of magnetic changes
between pool and hummock cores from the same bog site, initial magnetic
increases and subsequent changes in both concentration parameters and
normalised interparametric ratios are clearly synchronous. Examples are
given in Figures 10-12, which show SIRM profiles together with the
variation of selected pollen taxa from cores from Heathwaite Moss,
Cumbria, England, Axe Edge Moor, Derbyshire, England, and Ely Lake Bog,
Minnesota. At each site, comparison of the pollen curves between hummock
and pool sites indicates a high degree of synchroneity of the SIRM
stratigraphy.
At several British sites there is a strong positive correlation
between magnetic mineral concentrations and those of Cu, Pb and Zn. Fe,
Mn, Cd and Ni correlate less consistently. Figures 13-14 show the results
of magnetic measurements and heavy metal analyses from two sites, Whixall
Moss, Shropshire, England, and Loch of Lowes, an ombrotrophic peat site
-------
415
in Perthshire, Scotland. In each diagram the base of the most pronounced
increase in magnetic concentration is marked with a dashed line. At both
sites, the large increases in the concentration of Pb, Cu and Zn occur at
the same depth as the increase in magnetic mineral concentration. At Loch
of Lowes, the magnetic mineral-heavy metal relation is equally clear in
both pool and hummock cores.
Where accurate dating is available, variations in the magnetic
stratigraphy of ombrotrophic peats correlate with the history of regional
industrialization. Figure 15 shows four superimposed magnetic profiles,
together with the mean (solid line), from Karpansuo Bog, situated in a
remote part of central Finland. An absolute chronology has been
established by the annual moss increment counting. The S1RM values have
been used to estimate magnetite accumulation rates. Accumulation rates
begin to increase above background levels from around 1860, and by 1900
the mean annual accumulation rates are 2 to 5 times the pre-1860 level.
However, the sharpest increase occurs just prior to 1950, and in all
profiles the maxima occur during the last 30 years. This mirrors the
relatively late spread of heavy industry to eastern Finland during the
post-war period. Work in progress on the moss increment dating of
magnetic profiles from hummocks in ombrotrophic peat sites in Maine and
New Brunswick indicate a trend of declining magnetic accumulation rates
for the last 30 years, possibly reflecting the greater use of oil
relative to solid fuel in the U.S. over the last few decades.
'S' ratios reveal distinct temporal differences in magnetic
grainsize and/or mineralogy within ombrotrophic peat sites. At several
sites, the earlier industrial phases appear to be characterised by the
production of magnetic material with a higher hematitermagnetite ratio
than modern phases. Figures 16-17 show examples from Ringinglow Bog, near
-------
416
Sheffield, England, and Heathwaite Moss, Cumbria, England. At Ely Lake
Bog, Minnesota (Figure 18) a similar magnetically 'hard' component is
associated with the earlier stages of iron-ore mining the Mesabi Range.
The main conclusions from this section are that although we cannot
demonstrate that the mineral magnetic record in peat is unaffected by
post-depositional solution, diagenesis or downwash, the evidence favours
the view that the magnetic record is sufficiently well preserved to
provide a basis for correlation and relative chronolgy. Its relation to
trace metal deposition suggests it may aid reconstruction of emission
histories, by reflecting variations in magnetic flux density and
mineralogy in response changing technology and energy base. Direct
comparison between records magnetic deposition and vegetation change at
degraded sites may permit evaluation of the causes of such degradation.
SECTION THREE
In lake watersheds where the flux of terrestrially-derived magnetic
minerals is low, atmospheric deposition can affect the magnetic
mineralogy of the recent lake sediments. The most favourable sites are
likely to be those located close to major industrial sources, with
watershed lithologies with low concentrations of ferrimagnetic minerals,
and with low rates of .allochthonous sedimentation. Newton Mere, Cheshire,
England, meets some of these criteria. Newton Mere (Figure 19) is a
closed glacial kettle lake situated between the industrialized zones of
South Lancashire, Deeside and the West Midlands. The recent sediments are
highly organic muds. Figure 19 shows the lake basin and watershed
together with the results of magnetic measurements and heavy metal
analyses for four cores. The curve of frequency-dependent susceptibility
is shown for core J, and lead-210 ages are shown for core G. In all
cores, magnetic mineral concentration increases in the top 18-30 cm,
-------
417
coresponding to the last 70 years on the basis of the lead-210
chronology, the timespan over which the main increase in magnetic
material flux to peat surfaces in Northern Europe occurs. The curves for
Cu closely parallel the increase in magnetic mineral concentration,
although this is less clear in the case of Zn, Pb and Ni. Significantly,
the zone of increased magnetic mineral concentration is also
characterised by a reduction in frequency-dependent susceptibility,
consistent with the presence of a relatively coarse-grained
industrially-derived magnetic component.
Therefore, under favourable circumstances magnetic measurements of
recent lake sediments can provide a record of the history of trace metal
deposition. The advantages of the technique lies in its speed and
non-destructiveness. Also, magnetic measurements may be of indirect value
to lake sediment-based studies of acid rain and trace metal deposition
histories by providing a basis for inter-core correlation and by
identifying shifts in allochthonous particulate input. In addition to
mineral magnetic appliactions, studies of recent paleomagnetic secular
variation in lake sediments can provide rough timescales of sediment
accumulation for the last 100-10,000 years and may be used to extend
timescales based on lead-210.
SECTION FOUR
Amongst future research priorities we would consider the following
to be the most important:
1) The exploration of extreme situations in terms of Eh, pH and sulfur
concentrations to test magnetic mineral persistence and the relative
importance of diagenesis.
2) Further characterization of magnetic extracts using optical, XRD, SEM,
-------
418
Mossbauer and related techniques.
3) Direct comparisons of the peat and lake sediment records of
atmospheric deposition and ecosystem modification over the last 200-300
years.
4) Use of trees established on ombrotrophic peat and the record in the
peat beneath and beyond them to establish the relative importance of
filtering to all aspects of emission-associated deposition.
5) Further evaluation of mineral magnetic parameters in characterizing
and establishing the source of dusts and aerosols on spatial scales
relevant to acid rain and trace metal deposition studies.
6) Detailed case studies of degraded peat systems linking technological
history to ecological change through the mineral magnetic record of
anthropogenic deposition.
-------
00
c
rt
h4-
8
Raw
Coal
Pulverised
Coal
H- a
FLY ASH FORMATION
Fly
Ash
ro
o
-------
421
FEED COAL
PYRITE
I
as
Frarnboids
Combustion Period Short
and/or
Combustion Temperatures Low
Little Dimensional Change
Little or No Melting
MAGNETITE
oxidation
Haematite
dissolution in an Mg
rich silicate melt
Ferrous
Silicate
I
fusion and ablation
V
Mg RICH MAGNETITE
\
Slow Cool
Rapid Cool
few large
particles
many small
particles
STOCHIOMETRIC
MAGNETITE
EQUIMOLAR
MIXTURES
of
MAGNETITE
and
MAGHEMITE
PULVERISED
FUEL
ASH
Figure 2. Production of ferrimagnetic material during fly ash formation.
-------
422
TRACE ELEMENT CONTENT
OF
FERROSPHERES
Substitution
Ferrospheres in the form of an
Aluminium substituted Ferrite
Fe2-3 AI0-7%
or as an
Mg Rich Magnetite
accept
V,Cr.Mn.Co.Ni.Cu.Zn Transition Metal Ions
by fSOMORPHIC SUBSTITUTION
Volatilisation/Condensation
Condensation of
Volatilised Trace Species on Particulate
Surfaces
in cooler parts of the system
Figure 3., Trace element content of ferrospheres.
-------
423
Sample SIRM against Metal Concentration (nricrograms) for Sunned Stages
Summed
Stages
SIRHx
x-fe
SIIVU SIWV
x'ur x^Mn
SIWJ^
x-Ni
1 to 4 0.4050
1 to 5
0.8942 1.0940 6.638 46.62 88.33 11.86 218.6
TABLE 17
qUEENSWAY TUNNEL
Sample SIRM against Metal Concentration (m-icrograms) for Summed Stages
Summed
Stages
1 to 2
1 to 3
1 to 4
1 to 5
SIRM, SIRM, SIRMx
^xre x^Al x'Pb
0.4441 1.555 3.8832
SIRMx SIRJJ^
^^^7p j^^CU
13.611 51.97
SIRMx- SIRMx Sim^
15^-9
17.97
TABLE 17
KINGSWAY TUNNEL
Table 2. Magnetic:metal ratios for air samples from the Mersey
tunnels, Liverpool, England.
-------
424
Sample SIRM against Metal Concentration (micrograms)
Impactor
Stage
1 1
i 2
J
5
Sample SIRM
Summed
Stages
1 to 4
1 to 5
SIRM,
0.4421
0.4217
0.2746
0.3890
against
SIRJJ,
XTe
0.4050
SIRM,
XAI
0.8289
0.8401
1.1125
1.323
SIRMx
/Pb
2.3451
1.2605
0.3583
0.5824
!xfc
9.021
8.240
4.631
2.950
TABLE 16
SIRM,
/Cu
80.41
38.68
23.37
29.19
Metal Concentration (micrograms) for
SIRMx
/A1
0.8942
SIRM,
XPb
1 .0940
SIRM,
/£n
6.638
SIRM,
XCu
46.62
SIRMx
X^1"
112.99
120.99
40.60
58.24
Summed
SIRMx
XCr
88.33
SIRM,
/*n
10.358
15.122
12.179
14.563
Stages
SIRfJx
x^Mn
11.86
SIRMx
xfo
248.61
302.43
243.78
97.06 !
i
SIWJ, 1
x-Ui j
218.6 j
i
TABLE 17
9UEENSWAY TUNNEL
Sample SIRM against Metal Concentration (micrograms)
Impactor
Stage
1
2
3
4
5
SIRMx
x'Fe
0.4876
0.4240
0.3437
0.4368
SIRM,
/Al
1 .2744
2.0086
1 .5836
3.599
SIRMx
x""Pb
9.9009
6.4720
14.2566
0.646
SIRMx
/Zn
16.323
14.821
9.536
8.571
SIRM,
x^Cu
85.88
56.03
24.411
26.454
SIW,
x^Cr
183.90
116.51
-
-
SIRK,
X^Mn
16.09
19.41
28.50
-
SIRM,
/Ni
.
_
.
-
TABLE 16
Sample SIRM against Metal Concentration (micrograms) for Summed Stages
Summed
Stages
1 to 2
\ to 3
1 to 4
1 to 5
SIRMx SIRM, SIRMx
0.4441 1.555 3.8832
SIRM, SIRMx SIRMx SIRMx SIRMx
17-07
13.611 51.97
TABLE 17
KINGSVAY TUNNEL
Table 3. Particle size variations for magneticrmetal ratios for
air samples from the Mersey tunnels, Liverpool, England^
-------
425
Sample SIRM against Metal Concentration fmic'agrams)
Imoactor SIRMx
Stage x^e
2
3
4
0.4217
0.2746
0.2890
SIRMx
0.3401
1.1125
1.222
1
0
0
x^b
.2605
.2583
.5824
/£
8.240
4.631
2.950
SIRMx
x'fu
38.68
23.37
29.19
SIRMx
120
40
58
.99
.60
.24
SIRMx
15.122
12.179
14.563
SIRMx
302
243
97
.43
.78
.06
qUEENSVAY TUNNEL
Sample SIRM against Netal Concentration (•icrograms)
Impactor
Stage
2
3
4
SIRMx
x're
0.4240
0.3437
0.4368
SIRM,
2.0086
t .5836
3.599
Sx%
6.4720
14.2566
0.646
SIR*,
x'fn
14.821
9.536
8.571
xfc
56.03
24.411
26.454
SIRM,
XCr
116.51
.
SI*x-
/&n
19.41
28.50
SIM"
_
KINGSVAT TUNNEL
Sample SIRM against MetaJ Concentration (ppn)
Impactor
Stage
2
3
SIRM
SI
5230 817
4871 661
3748 470
62O51 14O80 452O
68431 15127 3992
53363 11244 3265
SIRM,
19789
2O529
17152
RESCSPENDED WLVERISEO FUEL ASH
Irapactor
Sta
-------
426
-05-
-0-6-
-07-
-200mT
SIRM
-0-8-
-09-
-1 O-1
SIRM
0-3 0-4 0-5
_J \ L-
^T Haroa Hall
if Kingaway
if Quaanaway
X Laaf samplaa
/() o«
• /
I /
1
x\
0-6
'
07
1
E.C.D.
O 7-0 pm
A 3-3 |im
O 2-0 |im
0 1-1 n"»
if Backup filtar
Figure 4. Plot of -20mT/SIRM versus -200mT/SIRM for leaf samples
and particle sized Hams Hall fly ash and Mersey tunnel
dusts.
Source: Hunt, A., Jones, J.and Oldfield, F.
The Science of the Total Environment. 33. 129-139. (1984),
-------
IO
10 -
in
O
X
,o
10'
IO1
10
Mediterranean « 0
North Atlantic x
o
*o •
AI ng m3
SUSCEPTIBILITY and ALUMINIUM Concentration
427
10
Figure 5. Susceptibility/Al ratios for soil-sized particuiates and
atmospheric Al loadings.
Source: Chester, R., Oldfield, F., Sharpies, J., Sanders,G
and Saydam, A.C. Water. Air and Soil Pollution, in press.
-------
428
500-
J1
I V)
IJ
1
r
4004>-
II _J
1
II u.
300-
SIRM
ARM
200-
-
100-
•
^.
o A Resuspended and particle sized
<
/
flyash
North sea and North
Atlantic
5 • dusts (SIRM SOxlO'3)
•
^
1
V :
\ •
o
irt
uidjb
w
_>
•§ a
o c
" 0
>>M |
Jo '3 <•>
•o c o
C OlrS
S *
<> ^
>
Q-i
0
More secon
: ie. most 'polluted
: OT North Atlantic dusts
2S (SIRM 16-21 xlO"3)
• (V
u 01 North Atlantic dusts
\ ® (SJRM 5-IOxlO'3)
• ie. least 'polluted'
Barbados dust set
A (Red /brown 'Saharan
dusts) (SIRM 4-8x
Barbados dust set
\
^ A (Grey'winter' dusts)
(SIRM 4-8 xlO'3)
c
g
S~^/£>
^k A — — *
90 J ^~~
— I r 1 —<— — >
S 10 15 20 25
XqV.
dary soil derived ferrimagnets~0 03»i
summer
HT3)
30
diameter
Figure 6. Plot of frequency-dependent susceptibility versus SIRM/ARM
ratio for resuspended fly ash and North Atlantic and Barbados
dusts.
-------
429
00:0
no
HEATHWAITE MOSS HI
Pool
WHITE MOSS Wl
BANK END MOSS 81
RUSLANO MOSS R2
RUSLANO MOSS RS
OMO pool
•ialuirt SIRM
Tptat cumulative
Ftc. J Sacuruion ruMtemul reauneM maimeiizxiiufl i SIR Ml values in recent pent ai Henn«aiic
iruj Rutuml MtMMi. r>ic finiotnm t^ut cnante^ m content ration »nh Occ'i. ifw mini line OKJU the
^umuiaii*e SIRM at » magnetic motncm >n M.\ m- tn«m me f*c«mnmt u( mi.rci\cd Cuncemraitoni up
ine inr r»rv
MOSS Ml
10 recem cvats at Bana
4» lor f:i^iiv 5.
i r -~ „ _ «- ...
Flgure 7- short
Source: Oldfield, F., Brown, A. and Thompson, R.
Quaternary Research, 1£, 326-332 (1979).
-------
430
MAGNETIC DEPOSITION ONTO OMBROTROPHIC
PEAT—SJRM IIO-WK,INorth East USA—E. Canada
Figure 8. Specific SIRM values of surface samples from ombrotrophic peat sites
in the northeastern U.S., and eastern Canada.
-------
431
RATIO; MAGNETIC DEPOSITION ONTO
OMBROTROPHIC PEAT—North East USA-
E Canada
Figure 9. SIRM/ARM ratios of surface samples from ombrotrophic peat sites in the
northeastern U.S. and eastern Canada.
-------
10
Of---
100
1000
10000
10
15
20
25
E
o
a
4)
0 0 1
10
15
HEATHWAITE MOSS : HUMMOCK
HOLLOW
I'HIUS Ulmus Ainu:.
0 20 0 10 0 20 40 0 6
V
% A.P.
r
Figure 10. SIRM profile and selected pollen curves for a core from Heathwaite Moss, Cumbria,
England.
CO
r\>
-------
0
2
4
£ 12
o
tfl
20
in
3
C
£
1
I
1
0
5
i
i
i
i
J
i
AInus
1
«
i
i
i
i,
i
1
i
5
I
f
1
!
o
3
1
1
ll
1
1
1
1
§
1
1
Q
04
2
t
6
-•
10
Spacific SIRM HO-6 Gg''cm3 I
4000 8000 12000 16000
•— 1
| '
I
J Hummock
AXE EDGE HUMMOCK
100 10 0 10 20 0 100 10 20 30 40 0
Ptrctnloges of Tola) Polltn Counttd
I
20
60
60
L
Spacific SIRM 110*0 g ' cm' I
.0 UX> 800 1200
2
4
6
-a
10
12
Pool
AXE EDGE -POOL
0501001020050100 20
fin
Figure 11. SIRM profile and selected pollen curves for a core from Axe Edge Moor, Derbyshire
England.
CO
OO
-------
SIRM
Pinus
Ambrosia
10
10
15
20
100
1000
10000
E
u
0
Q
01
o
10
15
20
ELY LAKE BOO : HUMMOCK
HOLLOW
0 40 80 0 40
% Upland Pollen
Figure 12. SIRM profile and selected pollen curves for a core from Ely Lake Bog, Minnesota.
CO
-------
435
~6
SIRM (10~ Am* kg"
0 2000 WOO
104
01
^
o
20-H
WM 2 Depression
ug g~ ary weignt
20 30 Cu
200 3GC ?b
— Pb
— Cu
20-"
WM 2 Depression
100
200 Zr,
0 2000
WM 3 Hummock
WM 3 Hummcck
Figure 13. Results of magnetic measurements and heavy metal analyses of
cores from Whixall Moss, Shropshire, England.
Source: Jones, J.M. Journal of Applied Ecology, in press.
-------
436
SIRM (10~5 Am2 kg1
2000
a.
-------
437
1975-
1950-
1925-
in
i_
03
CD
1900-
1875-
Magnetic deposition kg(x10 m y1)
0
1
10
1 1
20
— i 1
30
40
50
r-J ' {
H
HE
ET
IX
Mean values
KARPANSUO BOG
MAGNETIC DEPOSITION RATES
1840 -1975 A.D
• —I
I
1850-
Figure 15. Magnetic accumulation rate curves for cores from Karpansuo Bog,
central Finland.
-------
RINGINGLOW BOG
438
£20-
Q.
OJ
•o
30-
40J
SIRM (10~6Am2kg~1)
2000 4000
6000 8000
RB 1
Pool
0-6
0-4
0-2
0-2
0-4
0-6
0-8
1-0
IRM
-20mT
IRM
UOmT
IRM
-100rrf
IRM
IRM
300mT
IRM
300mT
IRM
300mT
IRM
300mT
Figure 16. SIRM and 'S1 value profiles from a core from Ringinglow Bog,
Sheffield, England.
-------
-IRMX/IRM300°
439
0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0
0 ' '
a.
a»
a
10
15-
20-
25-
-200
Hummock
-1000
S
a.
01
10H
Pool
-200
-1000
HEATHWAITE MOSS - Backfield ratios
Figure 17. 'Sf value profiles from cores from Heathwaite Moss, Cumbria,
England.
-------
10
10
15
20
25
~B
Z 0
5-
10
15
20
100
i iw ~u uiry 'I
1000 10000
-IKM/SIKM
100000 06 0.4 0.2 0 -0.2 -0.4 -0.6 -0.6 -1.0
_i i i 1 1 1 1 • 1 •
ELY LAKt BOG-d)Hummock
ELY LAKE BOG-(2) Hummock
-200
-I I L.
4 ^
-1000 -9000
Figure 18. SIRM and 'S1 value profiles from a core from Ely Lake Bog, Minnesota.
O
-------
441
BUL« u*GNE' C MEASUREMENTS BULK CMCuiC*!. MOSURCMCN1S .mq g
SIBM "C';«-«-«3 '•> SlBw/x. '•!« S M*»ff0t»> Ptt —•— Zn —
X lO"--^:"' — '0-«m Cu —— Ni
,0 D6 ' 0 ' 2 3 -06 -l 0 1035
NEWTON MERE
fi'y. <. Newton Mere. Cheshire. U.K. showing bathymetry.
catchment limns and coring locations.
CORE J
NEWTON MERE
Magnetic measurements and heavy metals
Fig. !. Magnetic measurements and heavy metal analyses for Mackereth mimcores from Newton Mere.
Figure 19. Magnetic and heavy metal profiles from cores from Newton Mere, Cheshire,
England.
Source: Oldfield, F., Barnosky, C., Leopold, E.F. and Smith, J.P.
Hydrobioloeia. 103. 37-44 (1983).
-------
442
VARIABILITY AND ERRORS IN PALEOLIMNOLOGY
David Parkhurst - Ind. Univ.
In paleolimnology, as in all science, we would like to be
correct. Failing that, we would like to have some idea how far from
correct we are. In general, we are interested both in our degree of
accuracy and in our degree of precision.
These ideas can be put together by reference to Figure 1, which
uses the example of dates corresponding to various depths in a core, as
210
reconstructed from Pb dating. In that figure, the solid line
represents the true, but unknown, relationship of date to depth; the
bold aashed line represents our best estimate of that relationship; and
the light dashed lines represent an estimate of the imprecision of our
estimate (for example, 95% confidence limits). At any given depth the
closeness of the bold dashed line to the solid line represents our
accuracy, or oeing right on average, or a lack of bias. The width of
the lignter dashed lines represents the variability of our estimate, or
the uegree of imprecision in that estimate.
Accuracy
I would like to emphasize that I believe our most important job as
paleolimnologists is to try to be accurate. That is, we need to get
our science right, so that our best estimates are correct on average
for whatever it is we are trying to estimate. At the same time, we
can't ignore the fact that even if we are correct on average, there
will still be statistical variation around our averages. So, we ought
-------
443
to attempt to put some sort of error bars on every estimate we make.
In what follows, I would like first to give some examples of how good
science can lead to better accuracy, and then to discuss the question
of variability estimates. The examples are:
1. Steve Norton has suggested that we should work with absolute
concentrations of chemicals rather than with the relative proportions
of each. If we fail to do this, and one component of the mixture
changes, we may conclude that all the other components have changed as
well because their proportions will change. This is clearly an
inaccurate conclusion that can be avoided by clear thinking and good
science.
2. Peter Campbell tells us that for certain measurements we need to
freeze our samples and to keep oxygen away from them, in order to
measure what was really there in the original sediments. If we fail to
do these things, the composition of the sediment will change before we
measure it -- tnen we can never get an accurate measurement of what had
oeen there. In such a case, knowing the precision or even the accuracy
with wnicti we have measured the changed composition is not of very much
interest, particularly if that imprecision is small relative to the
size of tne cnange that has occurred.
210
j. Mike Binford and others have talked about Pb dating. There it
is clear that we must use a correct model. If we assume a constant
210
initial concentration of Pb when that assumption is untrue, then
our dates assigned to various depths in the core cannot be accurate,
particularly in the deeper sediments. Also, we may need to correct for
biological mixing; if we do not, our dates may again be wrong on
-------
444
average. If they are very wrong, the precision of the CIC estimate is
hardly of any interest.
4. Ron Davis spoke about pH reconstruction. To paraphrase him in
mathematical terms, we might use a model which stated:
log a = a*pH + b*alkalinity + c*S04 + d*f(fish).
Here we often regress log a on present day pH; then we turn the
relationship around at various depths in the core to estimate pH from
log ex. As Davis pointed out, all the variables on the right hand side
of tnis equation tend to co-vary. That is, they are not independent.
Given that, it is okay to back-calculate pH from a if all the covarying
relationsnips between the variables remain the same. If the
relationships among them change, however, it may be quite incorrect to
do this type of back calculation. (For further comments about this
problem see an informative paper called "Use and abuse of regression"
by Box, 1966.)
If the covariance structure of the "independent" variables changes
with depth in the core, then we introduce a potential inaccuracy in our
dates but have no way to estimate that inaccuracy. If this actually
happens, then the precision estimates which are readily available from
regression analysis may be misleading.
5. As a final simple example, Rick Battarbee pointed out the
importance of identifying each diatom taxon correctly when we use
diatoms to reconstruct pH.
-------
445
To summarize so far, let me reemphasize the importance of being
accurate. To be accurate we have to get the basic science right.
Generally, and this is a real problem, we can't know how accurate we
are on average. The best we can do is try to get many independent
lines of evidence for any given phenomenon, or try to measure each
variaole in several different ways and then look for agreement.
Precision
As stated above, we often will not know how accurate our estimates
of a given quantity are. Even so, for almost any quantity we measure
or derive, statistical techniques are available to estimate the lack of
precision in that quantity. We should be using these more often than
we do in paleolimnology, I believe. Let me give two examples:
1. The Electric Power Research Institute is currently sponsoring a
large project, Paleolimnological Investigations of Recent Lake
Acidification (PIRLA). As part of that work, Russell Kreis is
coordinating a variability study to help estimate precision.
In this, a few of the many lakes in the overall project have been
selected for special attention. Each of these lakes will be cored
three times. (Most of the lakes will be cored just once.) Then each
core will be suosampled in numerous ways. As an illustrative example,
consider estimating pH values using the regression method of Charles
(1985). A variability study for this reconstructed pH from a given
time interval in a given lake might take the form shown in Fig. 2.
-------
446
In this example, three cores are taken from the lake. Each
sediment interval is cut into two halves; those are weighed and
digested, and a microscope slide is made from each. The diatoms are
identified and counted by five different diatomists, each making
duplicate counts of each slide. The data from these 60 counts could
then be plugged into the pH reconstruction equation to yield 60
estimates of pH (for a given time interval). These estimates can then
be analyzed by nested analysis of variance (Sokal and Rohlf, 1981,
Chapter 10).
This information can be used in two ways. First, it will identify
which step in the pH-reconstruction process introduces the greatest
variability. One can relate the variability in each step with the
human effort involved in that step to make future studies more
efficient. Second, variances derived in this way can be used as
variance estimates for all lakes in the PIRLA study. These can be
combined with other variance estimates (such as those related to using
a regression equation to derive pH values from diatom counts) to put
error bars on pH estimates. Similar procedures could be used, of
course, for aluminum concentrations, pollen counts, or any other
variable.
The example given would be tremendously time-consuming to carry
out, and indeed the PIRLA variability study will not follow that exact
procedure. It is infeasible to replicate every measurement to such a
degree. Nevertheless the variance estimates obtained will be
exceedingly valuable, and similar procedures are to be recommended for
at least a subset of any large study.
-------
447
2. One crucial component of paleolimnological reconstruction is the
date estimates assigned to various depths in the core. The most
generally applicable methods for dating sediments appear to be those
210
making use of Pb. However, to date we know of no published
methods for putting confidence limits (or other forms of error bars) on
derived dates. J. Robbins (pers. comm. 1984) has developed an error
210
propagation method which makes use of estimated errors in Pb and
?i n
uPo counts, in the mass of the Po spike used in the Pb
count, and in other variables (e.g., estimated sedimentation rate) to
put error bars on dates. Battarbee, Digerfeldt, Appleby, and Oldfield
(1980) indicated error bars for estimated dates, but did not describe
the methods used to obtain them. Mike Binford has begun to estimate
uncertainties in dates from the CRC model using Monte Carlo
simulation. In my opinion, the Monte Carlo method has greatest promise
for estimating 95% confidence limits on dates, because it is very
general ana flexible.
In any case, developing methods to estimate uncertainties in
estimated dates should have high priority, because of the central
importance of the dates to any interpretation of a core. There remains
210
the problem of uncertainty in the accuracy of the Pb dates,
resulting from the difficulty of choosing a correct model for any given
core. For some cores (and particularly for older sediments), this
uncertainty may exceed that associated with the fit of the data to the
chosen model. Even so, we should estimate the latter uncertainty if
only because it provides a minimum estimate of the total uncertainty.
-------
448
Conclusion
In any field of science, including our own, both accuracy and
precision are important. Generally speaking, statistical methods are
available to estimate the uncertainty associated with lack of precision
in our measurements or in quantities derived from them. Just as
generally, inaccuracy usually arises from unknown sources of bias;
because they are unknown, these uncertainties are difficult or
impossible to estimate.
For these reasons, we should as far as feasible do three things.
First, we should use replicates and statistical methods to estimate
imprecision uncertainty -- this at least produces a lower bound on our
total uncertainty. Second, we can try to measure each important
quantity by several independent methods, hoping that these methods do
not share the same biases. If they all tell us the same story, we
certainly have greater faith in our accuracy. Finally, we must
continue to develop and refine the basic scientific understanding of
the phenomena we are studying; this is the most direct and fundamental
way to reduce inaccuracies.
-------
449
ACKNOWLEDGMENT
I thank Donald Charles for comments on the manuscript.
REFERENCES
Battarbee, R.W., Digerfeldt, G., Appleby, P.G., and Oldfield, F.
1980. Paleoecological studies of the recent development of Lake
Vaxjosjon, III. Reassessment of recent chronology on the basis of
modified 210Pb dates. Arch. Hydrolbiol. 89:440-446.
Box, G.E.P. 1966. Use and abuse of regression. Technometrics
8:625-629.
Charles, D.F. 1985. Relationship between surface sediment diatom
assemblages and lake water characteristics in Adirondack lakes.
Ecology 66, in press.
Sokal, R.R. and F.J. Rohlf. 1981. Biometry (2nd edn.) W. H.
Freeman, San Francisco.
David F. Parkhurst
School of Public and Environmental Affairs
Indiana University
dloomington, Indiana 47405
July 1984
-------
450
Figure 1. A hypothetical data-depth curve derived from
measurements at one-centimeter intervals in a core. The true
relationship, an estimate of that relationship, and 95% confidence
limits for the estimate are diagrammed.
-------
451
DATE
o
o
00
o
U">
00
o
o
CD
o
in
o
O
O
CO
0
Tfi
J True date
I Estimated date for I-cm interval
I I 95% Confidence limits of estimate
10.—
20 —
DEPTH
(CM)
30-
40"
-------
— CORES
__SUBSAMPLES
_ DIATOHISTS
_ COUNTS
PH2141
Figure 2. Example of a nested experimental design, generally similar to those in the PIRLA variability
study. The diagram represents data for a single time interval from one lake. The pH value shown is
that estimated from diatom data, obtained in the first count by the fourth diatomist, of the slide
prepared from the first subsample (of the time interval under analysis) from the second core. The
scheme shown would yield 3-2-5-2=60 such pH estimates, which would then be available for analysis of
variance.
en
(V)
-------