PB81-216822
Response•of Phytoplankton to Acidification in
Experimental Streams
Minnesota^ Univ.
Minneapolis
Prepared for
Environmental Research Lab -Duluth
Monticello, MN
Jun 81
U.S. Bsp§rtegirt of
ftstmssl Technical Information Service
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EPA 600/3-81-042
June 1981
RESPONSE OF PHYTOPLANKTON 70
ACIDIFICATION IN 'EXPERIMENTAL
STREAMS
A THESIS
SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF THE UNIVERSITY OF MINNESOTA
By
THOMAS WALTER WEBER-II
IN PARTIAL FULFILLMENT OF THE'REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE
Fall 1980
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TECHNICAL REPORT DATA '
(Please read /nttruciions on the reverse before completing)
1. REPORT NO.
EPA-600/3-81-042
2.
ORD Report
3. RECIPIENT'S ACCESSION.NO.
5.ACCESSION NO.
1 2 1682 2
4. TITLE AND SUBTITLE
Response of Phytoplankton to Acidification in
Experimental Streams
5. REPORT DATE
June 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Thomas W. Weber, II
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Minnesota
Minneapolis, Minnesota 55455
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Monticello Ecological Research Station
P.O. Box 500
Monticello, Minnesota 55362
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
In order to examine the response of stream phytoplankton communities to acldlfIcatlon, three artificial
streams along the Mississippi River were sampler) at biweekly Intervals. This study took place nt Monticello,
Minnesota, during late spring—early summer, 1979. One stream served as a control with an ambient pH of 8.1,
and two streams were maintained nt pll 6-3 and 5.3 by the addition of stilfurlc acid. The streams provided a
unique replicate system whereby physical and chemical parameters could be controlled and continually
monitored In a field situation. The phytoplankton samples were filtered onto membrane filters and the
constituent phytoplankton species were enumerated. The diversity of pltytoplanktnn was similar throughout all
three pit regimes. However, phytoplankton community similarity decreased over the course of the six week
experimental period. Blomass, measured by ^jj vivo chlorophyll fluorescence and .is the density of the algal
cells, showed a similar pattern. The pattern of algal community development differed across the pll
treatments. The phytoplankton at pll 6.3 and 8.1 attained their maximum blomass during the first month of
sampling (June). There Is a lag In the population maxima cf phytoplnnktt.n at pll 5.3, possibly due to a slower
division rate caused by a less than Ideal pH environment. Species composition was nearly Identical across the
pH range, dominated by diatoms In each stream. The most extreme pH value, pll 5.3, seemed to be a sublethal
value for the diatoms existing there.
17.
KEY WORDS AND DOCUMENT ANALYSIS
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RELEASE TO PUBLIC
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49
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22. PRICE
EPA Form 2220-1 (R»v. 4-77) PREVIOUS COITION is OBSOLETE
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Abstract
In order to examine the response of stream phytoplanfcton communi-
ties to acidification, three artificial streams along the Mississippi
River were sampled at biweekly intervals. This study took place at
Monticello, Minnesota, during late spring—early summer, 1979. One
stream served as a control with an amoient pH of 8.1, and two streams
were maintained at pH 5.3 and 5.3 by :he addition of sulfuric acid. The
strsams provided an unique replicate system whereby physical and chemical
parameters could be controlled and continually monitored in a field
situation. The phytoplankton samples were filtered onto membrane filters
and the constituent phytoplankton species were enumerated. The diversity
of phytoplankton was similar throughout all three pH regimes. However,
phytoplankton community similarity decreased over the course of the six
week experimental period. Bio'nass, measured by in vivo chlorophyll
fluorescence and as the density of the algal cells, showed a similar
pattern. The pattern of algal community development differed across the
pH treatments. The phytoplanxton at pH 6.3 and 8.1 attained their maxi-
mum biomass during the first month of sampling Mune). There is a lag
/
in the population maxima of phytoplankton at pH 5.3, possibly due to a
slower division rate caused by a less than ideal pH environment. Species
composition was nearly identical across the pH range, dominated by
diatoms in each stream. The most extreme pH value, pH 5.3, seemed to be
a sublethal value for the diatoms existing there.
iii
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Acknowledgements
I would like to extend thanks to the U. S. Environmental Protection
Agency's Monticello Environmental Research Station for their invitation
to use their facility and their assistance, especially that of Kenneth
E. F. Hckanson, in providing data crucial to the study's success. I am
grateful for financial support from the Department of Biology at the
IS
University of Minnesota, Duluth. I thank Dr. Paul Monson for his assis-
tance with the field work. I also thank Dr. John B. Carlson and
Prof. Walter Fluegel for their review of the manuscript. I am especially
indebted to Dr. Jack R. Hargis for his valuable time and advice through-
out the planning of the research, exceedingly critical revr.rf of the
manuscript, and financial support in the form of two research assistant-
ships.
iv
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TABLE OF CONTENTS
ABSTRACT 111
ACKNOWLEDGEMENTS iy
LITERATURE REVIEW .... 1
INTRODUCTION 12
MATERIALS AND METHODS 14
RESULTS 17
DISCUSSION 21
LITERATURE CITED 26
TABLES AND FIGURES 30
APPENDIX ONE 44
APPENDIX TWO 45
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Literature Review
Research concerning the effects of increasing hydrogen ion concen-
tration on freshwater organisms has become more prevalent recently.
This interest has been spurred by knowledge that fresh water in some
areas of the world is especially susceptible to inputs of acid precipi-
tation, resulting in the lowering of pH in these waters. This suscepti-
bility occurs in watersheds which have a poor ability to neutralize acid
precipitation di:e to heavily leached, non-calcareous soils derived from
hard crystalline rocks (Gorham 1976). Bodies of fresh water in such
areas have a poor buffering capacity and the incoming acids from precipi-
tation have a drastic effect on the water's pH.
On an annual basis, rain and" snow over large regions of the world
are from 5 to 30 times more acid than the lowest pH value expected (pH
5.6) for unpolluted atmospheres. The rain from individual storms can be
from several thousand to several hundred times more acid than expected
(Likens et al. 1979). Pure water in equilibrium with atmospheric CO-
would have a pH of 5.6. Added to this primary source of acidity are
strong mineral acids, predominantly sulfuric acid (H-SO^) (Gorham 1976).
The origin of H-SO, is the oxidation of sulfur in fossil fuels. Also,
natural biogenic emissions of sulfur produce acid precipitation, but
presumably these sources have been in balance with natural sources of
neutralizing bases (Gorham 1976). Oxides of nitrogen (NO and NO*) are
also important sources of acid precipitation. Hydrochloric acid (HC1) is
an important source of acidity in some areas, as well. In 1977, sulfur
and nitrogen oxides together contributed 26% (50.4 million metric tons)
to the total air pollution in the United States (Schaefer 1979).
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Another source of acid to fresh water is bituminous coal mine drain-
age. This acid is formed by the oxidation of sulfur occurring in exposed
coal or in rocks adjacent to exposed coal seams. Iron sulfides bound as
pyrites, marcasites, and sulfates (in much smaller quantities) are
exposed to the oxidizing action of the air, water, and sulfur-oxidizing
bacteria such as Thiobacillus zhicsrldar,8. The resultant sulfuric acid
and ferrous iron drastically increases the acidity of streams receiving
acid mine drainage. The annual acid discharge from bituminous coal mines
of western Pennsylvania is equivalent to one nil lion tons of sulfuric
acid. Downstream from the pollution effluent, the acid ferrous solution
is diluted and neutralized and the pH rises. Ferrous iron is slowly
oxidized to Fe which hydrolyzes to ferric hydroxide: Fe(OH).j. This
precipitate covers the stream bottoms with a yellow-brown slime inhibiting
the growth of benthic algae and creating a sterile zone in the stream
(Parsons 1957; Koryak et al. 1972).
Both planktonic algae and benthic forms are affected by the level of
acidity present in fresh water. Transparency of lakewater is enhanced by
low pH. Kwaitkowski and Roff (1976) found secchi disc readings to be
highly correlated with pH. Turbidity is reduced by less bicmass of
plankton at lower pH, and also, colloidal particles may become flocculated
which increases water clarity. Aimer et al. (1974) reported very clear
lakes resulting from decreased algae content and the precipitation of
humic substances under greatly acidic conditions.
Acidification, and consequently oligotrophication, of lakes is
accelerated by retarding the rate of nutrient supply to the primary
producers. Bacterial productivity declines with lowering of pH and an
\
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accumulation of coarse detritus in the hypolimnion covers the mineralized
sediments, preventing exchange of nutrients and other ions between sedi-
ments and the overlying water. Fungi thrive better in acid solutions than
bacteria. Fungal hyphae may produce a dense felt on lake bottoms replac-
ing the bacteria as the major decomposers. Fungal decomposition is less
efficient than bacterial decomposition resulting in slower nutrient
recycling. Sp'nagn-jr., a ,-noss found in acidic fresh water, has a strong
ion exchange capacity and binds ions from the surrounding water, with-
drawing these important nutrients from use by other organisms (Grahn
et al. 1974). In acid streams, inhibition of bacterial growth (and other
organisms' growth) destroys a stream's natural self-purification process.
Thus, allochthonous organic matter accumulates in acidic portions of
streams, and will not decompose until it reaches a neutralized reach of
the stream (Koryak et al. 1972).
Primary productivity is decreased in more acid conditions.
Kwaitkowski and Roff (1976) found production (measured in milligrams
C • meter" • hour ) was reduced in lakes below pH 5.5. However, an
increase in the depth of the euphotic zone accompanying more acidic con-
_o
ditions kept primary productivity (measured in milligrams C • meter" •
hour ) at high levels down to pH 4.4, below which it was drastically
reduced. Oxygen depletion occurred in more neutral lakes, reflecting
higher production in the euphotic zone, and thus more decomposition of
algal biomass. Johnson et al. (1970) found primary productivity per unit
volume generally greater in an unaffected lake than in acid-contaminated
lakes. Patrick et al. (1968) found that a pH of 5.2—5.4 affected diatom
productivity by slowing the division rate, resulting in lower standing
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crops. Furthermore, this effect of acid was more pronounced when water
temperature was lower.
Some authors have not found a reduction in algal biomass with
increasingly acid conditions. Accumulation of benthic algae in three
streams, similar except for pH, was compared by Leivestad et al. (1976).
Chlorophyll estimates of algal standing crop were significantly higher
at pH 4 than at pH 6 and usually higher than at the natural pH (which
ranged from 4.3 to 5.5). These results were attributed to the success of
two acid-tolerant filamentous algae at pH 4. Van et al. (1977) raised
the pH of a Canadian Shield lake experimentally from pH 5.7 to 6.7. There
was no significant change in biomass. Van (1979) found that an acidified
lake (pH 4.2) had no biomass reduction, but an atypical structure of
phytoplankton developed, compared to uncontaminated lakes. Phytoplankton'
community biomass was more highly correlated with phosphorus concentra-
tion than with H+ ion concentration. Yan and Stokes (1978) stated that
biomass should not be used as an index of acidification since it is only
a sensitive enough measurement under conditions of extreme acidification.
They suggeite
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reduction in phytoplankton diversity in La Cloche Mountain lakes contami-
nated by acid mine drainage when compared to uncontatr.inated lakes nearby.
Leivestad et al. (1976), in a study of 55 Norwegian lakes found a signifi-
cant correlation between phytoplanktnn spacies number observed versus pH.
Kwaitkowski and Roff (1976) found the Chlorophyta (green algae) diversity
to be especially low 1n lakes of low pH (4.05—5.65) compared to more
neutral lakes. In experiments with polyethylene cylinders filled with
lakewater and with pH altered experimentally, Van and Stokes (1978)
reported a reduced diversity of phytoplankton below a pH of 5.8. The
number of phytoplankton taxa was reduced by one-half in a contaminated
lake (pH 4.2) compared to unconta.-ninated conditions in a control lake
(Van 1979).
Another useful indication of acid affecting freshwater algae can be
seen in changes of species composition. Johnson et al. (1970) noted that
lakes contaminated with acid mine wastes had very simple algal composi-
tions consisting of blooms of the blue-green (Cyanophyta) alga Pleatanera
notation. Uncontaminated, but otherwise similar, lakes nearby had algal
assemblages common to lakes of the region consisting of the Chrysophyceae,
Cyanophyta, and Bacillariophyceae. In a study of 400 lakes along Sweden's
southwest coast, where an influx of acid precipitation froin western Europe
impinged, Aimer et al. (1974) were able to conclude that the species com-
position of phytoplankton in these lakes was. Indeed, related to lake pH.
Lakes of pH 4.0 were composed mainly of the Pyrrophyta (Gyrnnodiniwn spp.
and Peridinium inconspicuum) and a few Chlorophytes (Ankiatrodesmua
!• Taxonomy is after Prssaott 1964.
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cor.volut 13, Cocy3ti3 submzrina, and 0. laauxtria). At pH 5.0, lakes
commonly had a species composition of diatoms and the blue-greens
Chrooococoua and Merismopedia. When the pH was greater than 6.0, species
composition was diverse and all taxonomic groups *ere found. The
greatest change in algal composition was found between pH 5 and 6. Sedi-
ment cores of these lakes revealed that the planktonic diatoms were
replaced by other species when acidification of the lake district occurred.
Kwaitkowski and Roff (1976) studied lakes similar chemically except for
pH (ranging between 4.1 and 7.2) and found the Chlorophyta increased in
abundance and diversity with ?.n increase in pH, while the opposite was
true for the Cyanophyta. The relative dominance of the Chlorophyta
changed from 40—50% at hich pH to only 252 in lower pH lakes (below 5.65).
Conversely, the relative dominance of the Cyanophyta increased from 30%
to 60% when pH was lowered. Yan (1979) found that a Canadian Shield lake
of pH 4.k was predominated by the Pyrrophyta, but stated that the
Chrysophyceae would dominate the phytoplar.kton if the pH was less acidic.
More subtle changes have teen observed in samples of benthic algae
from streams. Benthic diatom samples *rom seven locations affected by
add precipitation in Norway were compared between 1949 and 197S. Quali-
tatively, the diatom flora was similar between the two sampling periods.
However, considerable changes had occurred in the proportion: of various
species, with an increase in the proportion of species which are acido-
philous (acid preferring) or acidobiontic (acid requiring) (Leivestad
et al. 1976). Patrick et al. (1968) found that experimentally shifting
the pH to 5.26 from more circumneutral conditions caused no significant
shifts in the kinds of species present. Diatoms accumulating on glass
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slides were the same in each stream, but the few species which became
dominant at 5.26 were not coinnon in the control condition. It was sug-
gested that the total chemical characteristics of a naturally occurring
acir! stream are very different from those of a circumneutral stream, and
changing only one parameter (pH) would not necessarily cause the develop-
ment of an acid water flora.
Oftentimes, high levels of acidity in fresh water a: a accompanied by
high concentrations of metals dissolved there. Consequently, it is
impossible to separate the effects of these metals from the acid effects.
The two together may produce some synergistic effects on algae. In
Hormidiim rivulare, a benthic green alga found in very low pH waters, zinc
and copper toxlcity has been found to become markedly greater above pH 4.0
(the optimal growth range for H. rivulcre is pH 3.5 to 4.0) {Hargreaves and
Whitton 1976b; Say and Whitton 1977). In a study with five species of
algae isolated from extremely low pH habitats, Hargreaves and Wh'tton
(1976a) found growth rates to be reduced at pH 7.0 when iron .vas present
in the growth medium. With iron absent, there was no such reduction of
growth and iron's presence at lower pH values did not cause a reduction
of growth rate. The authors suggest this may be the result of a direct
toxic effect of the metal on the algae, although indirect effects
associated with iron precipitation in the water at the higher pH may have
oeen involved.
Just which physiologic features of specific algae determine their
tolerance to acidic conditions is a rather unstudied area of phycology.
In this, studies involving organisms other than algae can provide some
clues. Mosses of the genus Sphagnum are very.common in acidic freshwater
areas. They, in fact, lower the pH of the surrounding medium by exerting
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a very high ion exchange capacity. They absorb cations, preferentially
those of the highest valence, and release hydrogen ions into the water.
This exchanging ability varies with the nature and concentration of the
cation, and with the pH of the medium. Correlation has been found between
Sphagman cation exchange ability and content of unsterified polyuronic
acids in the cell walls (Bell 1959; Clymo 1963). The expulsion of H*
ions from the cells has also been found to occur in animal cells where H
ions and ammonium (NH, } ions are secreted in exchange for sodium (Na )
uptake, as may occur in stomach lining cells that acidify the external
medium (Maetz et al. 1976). Freshwater or anadromous fishes require
active salt uptake by specialized epithelial cells, whereby H ions from
the body ara exchanged for Na ions from the water, and bicarbonate ions
are exchanged for chloride ions (Leivestad et al. 1976).
In algae, a cell boundary phenomenon may exist in low pH tolerant
species whereby cation exchange or outpumping of H ions by active trans-
port exclude H ions from the cell interior. Additional specializations
may include proteins in the cell membrane of tolerant algae that are
able to withstand denatun'zation (which could happen with acid stress)
by having very.low isoelectric points (Cassin 1974). Brock (1973)
suggested that the lower pH limits for the existence of blue-green algae
may be due to its proct».ryotic nature. He hypothesized that eucaryotic
cells are potentially more tolerant of acid environments because their
chlorophyll is "protected" within membrane-bounded organelles. Cassin
(1974) believed it unlikely that hydrogen ions entered cells found at
extremely low pH because the chlorophyll in the cells would degrade below
pH 5.0 and the cells would no longer be green. However, Lane and Burn's
(1979) determined that Chlorella pyrenoidosa, naturally occurring through
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the pH range of 3.0 to 8.0, was able to adjust the pH of the cell's interior
depending on the external pH of the medium. The measured internal fluctua-
tion in pH was not as great as the variation in external pH, though.
How algae are able to tolerate high concentrations of heavy matals
.•nay provide insight into the tolerance capabilities to hydrogen ions.
Sicko-Goad and Stoermer (1979) found that tne effects of lead and copper
on Dictcma tenue var. elcngaiMm can be negated by the ability of phosphates
in the cells to complex with metals into polyphosphorus bodies. These
stored bodies can exist as long as the storage phosphorus is not needed
for other essential activities. The toxicity of zinc is ameliorated in
Bormidiim pivulare by thepresence of phosphorus, magnesium, and calcium
in the external medium. Raising the total hardness and the alkalinity
also makes zinc strikingly less toxic (Hargreaves and Whitton 1976b; Say
et al. 1977; Say and Whitton 1977). In Stigeoolonium tar.ue, Say and
Whitton (1977) reported that lead can be inactivated by its binding onto
the cell wall. Large quantities of lead can be found there while the
alga is physiologically unaffected by this very toxic metal.
Shifts in the H ion concentration of the water also affects the
equilibrium of inorganic carbon dissolved there. Atmospheric C0~ readily
dissolves in water. A reaction of CO^ with water yields a very, dilute
solution of carbonic acid. This carbonic acid can dissociate into
2
bicarbonate (HCO-, ) and carbonate (CO^" ) forms depending on the water's
pH. In the presence of alkaline earth metals, COg becomes HCOj" and more
CO- from the atmosphere can be dissolved. As COg is removed by autotrophs
or converted to HCO ", the pH of the water rises. Diel changes in pH can
be quite dramatic due to the photosynthetic uptake of COg in fresh water
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which has a low buffering capacity (Coie 1975; Tailing 1976).
Many researchers have wondered how shifts in pH may affect the
ability of algae to take up inorganic carbon for photosynthesis.
Schindler (1971; 1972) stated that a shortage of C02 in water could
practically never occur. Even at very high concentrations of phosphorus
and nitrogen, rapid uptake of C02 in a low-buffered Canadian Shield lake
(with a consequent pH risa to 9.5) failed to cause CO- limitation. A
pronounced CO^ gradient between atmosphere and lake epilimnion kept
diffusion of C02 into the water at a rate high enough to maintain the
phytoplankton crop.
Moss (1973a) reported that many oligotrophic algal species which he
studied failed to grow above a pH of 8.6, and that eutrophic algae he
studied had their best growth rates between pH 8.4 to 9.3 or above.
Although hardness of the water was greater at the higher pH, total ionic
content was presumably an unlikely factor controlling these observations.
He suggested instead that the eutrophic species were able to utilize
bicarbonate as a carbon source for photosynthesis while oligotrophic
3p5Ciei: do not grow above pH 8.6 , since free CO- is only available at the
lower pH values. It is widely assumed that some algae possess this capa-
bility to directly take up HC03" ions while others cannot (Moss 1973a).
Scldman (1973) believed that the ability of the procaryotic algae
(Cyanophyta) to become dominant at high pH must be explained by something
other than the inorganic carbon equilibrium. He suggested that the reason
for their success may be explained by enzyme systems that function best at
higher pH or nutrients, such as phosphorus, which are more available at t!;c
higher pH.
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Many algae tolerate extremely acid conditions. Numerous flagellates
have been recorded in Sphagnum bogs, streams receiving acid mine wastes,
and other acid environments: Several species of Peridini.m, one species
of Spematozapis, Trachelorras volvocina, Suglsna mutabilis, E. vzridis,
C/vpysococcous asper, Spongemonas uvella., Cryptotnonas ovate., and several
species of Chlam/domonas. Chlamydamonas acidcphila is extremely resis-
ant to H ion stress, growing better at pH 2.0 than at pH 4.0—5.0.
Euglana mutabili.3 is very common in fresh water receiving mine wastes
and growth has been documented in water within the pH range 2.1—7.7.
Flagellates listed as indicators of high acidity in water supplies
include Chlamydomonas spp., Chromulina ovalis, Cryptomonas erosa, Euglena.
spp.., Lepoainclis ovum, and Ochromonas spp. (Lackey 1938; Von Dach 1943;
Joseph 1953; Palmer 1962; Bennett 1969; Cassin 1974; and Hargreaves and
Whitton 1976a).
Benthic filaments of green algae can be very successful in acid
environments, some times clogging streams with dense growths. Commonly
occurring types include Mougeotia sp., Eormidiwn nvulare, Stichoaoccous
bacillus, and Ulothrix zonata. Other Chlorophytes common to acid bogs,
and generally common to soft water areas, are within the family
Desmidiaceae. Among these, Desmidium sp. and Stawcastnm sp. have been
recorded in areas receiving acid mine drainage (Lackey 1938; Round 1964;
Bennett 1969; Hargreaves and Whitton 1976a; and Leivestad et al. 1976).
The Cyanophyta is generally thought to thrive in neutral to alkaline,
eutrophic fresh water (Brock 1973; Mc.s 1973a). There are, however,
exceptions. In studies of several La Cloche Mountain lakes in Ontario
(Johnson et al. 1970; Kwaitkowski and Roff 1976), lakes contaminated by
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acid input developed a blue-green flora including Plectonenz
Aphanocapsa sp., Chroococaoua dispersus, C. limneticus, and Oadllatorio.
sp. •-•-
Many diatoms have long been indicators of acid fresh water in
streams, riustedt (1939) grouped diatoms according to the hydrogen ion
concentration in which their occurrence was optimal. In extremely acid
streams receiving coal mine wastes, fleviaula viridisf numerous other
Naviculoid species, Eunotia tsnella, and Pinnularia braunii have been
found (Lackey 1938; Joseph 1953; Bennett 1969). Besch et al. (1972)
studied stream diatoms existing in a low pH environment complemented by
high levels of dissolved zinc and copper. Here the dominant species were
Eitnotia exigua, Aelw.anthis microcephala, A. rrtinutitiss'ima, Finnularia
interncpta, and Synedra ulna. Abundant diatoms of the epipelic habit in
acid waters include many species of the genera Evnot-ia and Pinr.ularia,
tfelosira distorts, Frustulia rhomboidss, and Frag-ilaria vir'escens (Round
1964). Leivestad et al. (1976) observed thriving growths of Tdbellaria
flocaulosa in a stream of pH 4.0. Patrick et al. (1968) found that the
inost common diatoms accumulating on artificial substrates at pH 5.26 were
Gcmphonema parvalum, G. commutation, Naviaula pupula, Syr.edra rumpens, and
Melosira granulata.
Introduction
Today, more than ever before, atmospheric oxidation of sulfur and
nitrogen from anthropogenic sources and their ultimate precipitation is
endangering freshwater ecosystems. In especially susceptible areas around
the world, the results of acid precipitation and acid coal mine drainage
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on freshwater acidity are well documented (Gorham 1976; Likens et al. 1979).
The rise in sulfur and nitrogen emissions to the atmosphere accompany the
rise in the burning of fossil fuels. Due to wide demand and dependence
on increasingly dwindling global oil sources, emissions of nitrogen and
sulfur oxides are expected to rise as coal usage increases.
European interest in this problem began after World War II, in the
1940s, when the chemistry of acid rainfall, and later, its effects on
freshwater life were studied. Early data from Eastern North America were
generally lacking until the 1970s (Gorham 1976). Current knowledge on the
effects of high acidity on the freshwater biota includes information on
many trophic levels of aquatic ecosystems. Entire populations of fish
hsve been eliminated from heavily acidic lakes (Beamish et al. 1975;
Leivestad et al. 1976). The structure of stream zoobenthos and lake
zooplankton is also affected. The simplification of food chains results
from elimination of non-tolerant species while a general increase in acid-
tolerant invertebrates occurs (Koryak et al. 1972; Sprules 1975b).
Algae in fresh water is a primary source of food for aquatic consumers
and also plays an important role in reoxygenation (self-purification) of
water (Bennett 1969). Changes in phytoplankton communities have
accompanied acidification in many studies. The best documented of these
changes is a reduction in community diversity which is first evident at pH
levels of 5.0—6.0 (Patrick et al. 1968; Johnson et al. 1970; Leivestad
et al. 1976; Kwaitkowski and Roff 1976; and Van and Stokes 1978). Shifts
to rather atypical species composition have occurred in phytoplankton
(Johnson et al. 1970; Aimer et al. 1974) and in benthic algae (Patrick
et al. 1968; Leivestad et al. 1976).
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Various studies have been concerned with observation of algae present
in freshwater bodie-; of many pH values (Merilainen 1967; Johnson et al.
1970; Besch et al. 1972; Aimer et al. 1974), laboratory studies of
species tolerance to acidity (Moss I973a; Cassin 1974; Hargreaves and
Whitton 1976b), and studies where pH is extremely low and an algal flora
of acid-tolerant species develops (Lackey 1938; Joseph 1953; Bennett
1969). Some investigators have experimentally changed pH to determine
its effect on freshwater algae (Patrick et al. 1968; Leivestad et al.
1976; Van et al. 1977; and Van and Stokes 1978). The present work studied
the phytoplankton in shallow pools of three artificial streams, and com-
pared phytoplankton community structure between three different pH
regimes. The system was maintained so practically all physical and
chemical parameters were similar during the deliberate addition of acid
to these streams.
Materials & Methods
This study was conducted in three outdoor channels at the U. S.
Environmental Protection Agency's Monticello Ecological Research Station
(MERS) near Monticello, Minnesota. Each stream had 30.5 meter long
alternate riffles and pools. The depth and width of the riffles were
10—20 centimeters and 2.4 meters, and of the pools 76—86 centimeters
and 3.7 meters. The pools were mud-bottomed while the riffles were con-
structed with 2—5 centimeter diameter gravel. Experimental water was
pumped in from the Mississippi River beginning in April, 1379. Discharge
in each channel was measured daily and averaged 761 liters • minute" over
the six week course of the experiment, ranging from 700—847 liters
-14-
minute" .
-------
One channel was maintained with Mississippi River water alone. It
was not dosed with acid and thus it served as a control. Here the ambient
pH averaged 8.1 and ranged from 7.8—3.6. Two other streams were dosed
with technical industrial grade sulfuric acid (see Appendix 1). The
acid was stored in a 500-gallon polyethylene tank. The bottom of the
tank was connected with CVPC plastic pipe to a variable speed pump. The
pump could meter amounts of acid at a rate between 20 and 600 ml/minute.
From the pump, the acid was conveyed to the streams with CVPC pipe. The
first riffle was deepened and functioned as a mixing compartment. One of
these streams was maintained at an average pH of 6.3 (ranging between
6.0—6.6) and the other at an average pH of 5.3 (ranging from 5.0—5.7)
(Figure 1). From this point on, the ambient and two experimental streams
are referred to as 8, 6, and 5 respectively. Riffles and pools are coded
by numbers and letters from the upstream end of each stream. All phyto-
plankton samples were collected from pools 4, 150 meters below the point
of introduction and mixing of acid into the channels.
The upstream riffles and pools of each stream were shaded by A-frame
canvas shading modules. The purpose of the shades was to inhibit macro-
phyte growth in that portion of the streams.
MERS personnel collected information concerning various physical and
chemical parameters of the streams. Both morning (5—9 a.m.) and after-
noon (3—5 p.m.) temperature readings were taken from mid-depth in pools
3 and 4. Morning and afternoon pH measurements were taken from pools 3,
and from riffles c and d. Measurements of dissolved oxygen, specific
conductance, hardness, total acidity, and alkalinity were also collected
(at mid-depth in pools 3) weekly.
*
-15-
-------
Plankton sampling occurred at two-week intervals from May 30, 1979,
to July 11, 1979. Approximately one month of. equilibration was allowed
under experimental conditions before sampling began. One-liter water
samples were taken from mid-depth from pools 4. The samples were stored
on ice in the dark during transit to the laboratory (approximately 4
hours) where analyses were conducted, in vivo chlorophyll fluorescence
(Lorenzen 1966) of 5 ml aliquots from each sample was measured using a
Turner Model III Fluorometer equipped with a primary blue filter allowing
a maximum transmittion of light at 430 nm and a secondary red filter allow-
ing a maximum transmittion at 650 nm. Dry weights and ash-free dry weights
were obtained for all samples. Two 250 ml samples from each sampled pool
were filtered through membrane filters (pore size 0.45 urn) at a filtering
pressure of one-half atmosphere. The filters were then dried at 60° C for
24 hours, allowed to cool to room temperature in a dessicator, and weighed
-4
to the nearest 10 gram. The organic matter present in the filter:, was
burned in a muffle furnace at 500° C for one hour. Following this, the
clays present in the samples were rehydrated (American Public Health
Association 1975) and the residue weighed. The major portion of each
sample was fixed with acid-Lugol's solution and permanent slides were
prepared using a method of concentrating phytoplankton on a membrane
filter. Enumeration of thr alga.3 on each filter was performed after
McNabb (1960) by counting the algae present in 30 random fields on each
filter. The taxa observed were usually determined to the specific level,
although identification problems infrequently required identification only
to genus. Identification of algae was aided by use of two taxonomic
references (Tiffany and Britton 1952; Prescott 1964).
-16-
-------
Results
Summarized data on temperature, dissolved o.\ygen, and hydrogen ion
concentration collected from May 14, 1979, to July 11, 1979, is presented
in Figure 2. Temperaturo readings displayed are the average of morning
and afternoon measurements from mid-depth in pools 3 and 4. The greatest
difference in temperature readings between the morning and afternoon of a
single day was 2.3° C. Records of temperature in the unshaded pools were
not made until late June. Even after this time, however, temperatures
never differed more than 1° C between the shaded and unshaded pools on a
given date. Mean daily temperature i."icrea?id *rom 10.4° C in mid-May to
23.5° C in mid-July.
Dissolved oxygen measurements (mg/liter) jre displayed as a function
of temperature in percent saturation. Each print represents the mean of
six readings (a morning and afternoon reading from each of the 3 streams).
Dissolved oxygen readings were obtained at mid-depth in pools 3. The
averag-j difference in dissolved oxygen readings between streams was less
than 3%. The dissolved oxygen concentration was always somewhat higher
during the afternoon. Throughout the period of sampling, the dissolved
oxygen concentrate remained between 77 and 91 percent saturation.
• • *
For each stream, the pH is shown by two lines. One line is pH as
recorded at mid-depth in pools 3 (the average between morning and
afternoon readings). The other line is the average of readings taken from
riffles 3 and 4. Generally, the pH in the riffles was slightly higher
than the readings from mid-depth in the pools. There is no clear trend
between morning and afternoon readings, although the difference was some-
times greater than 0.5 pH units. The pH in Stream 8 varied between 7.8
-17-
-------
and 8.6 with a mean recorded reading of 8.1 for the entire eight-week
period. Stream 6 had a mean recorded pH reading of 6.3, varying between
6.0 and 6.6. Stream 5 had a mean of pH 5.3, varying between.5.0 and 5.7.
Thus, three clearly defined pH regimes were present within the system
throughout the experimental period.
Weekly measurements of four other chemical parameters are presented
in Table 1. Specific conductance is similar over time and is always highest
in Stream 5 and lowest in Stream 8 due, no doubt, to the sulfuric acid ,
*
added to the experimental streams. Hardness is similar oetween the three
streams but showed an increase in all three streams between late May and
mid-July. As would be expected, the total acidity is by far the greatest
in Stream 5 and lowest in Stream 8. Accordingly, alkalinity is lowest
in Stream 5; highest in Stream 8.
Since the discharge of the streams was known, it was possible to
compute the velocity of flow in riffles and pools, and hence, a theoreti-
cal residence time for phytoplankton in the system. Hynes (1970) presents
the following equation:
0
wda
where D = discharge, V is stream velocity, w and d are the values for mean
stream width and depth, and a is the coefficient representing stream
roughness. Rather high coefficients of 4.0 for pools and 2.7 for riffles
were computed. These values took into account the dense growth of macro-
phytes present in the streams. These values were developed using infor-
mation from Chow (1959). The -esidence time of stream phytoplankton was
computed to be 6-2/3 hours 1n a pool, and for a riffle it was 1/2 hour
-18-
-------
(33 minutes). It follows then that the theoretical exposure time of
stream phytoplankton to the various pH regimes is approximately 24-1/2
hours before reaching the sampling area in pools <*.
The overall results of phytoplankton enumerations are shown in
Figure 3. It can be seen that the total phytoplankton density differs
in each stream. Each stream also differs in its pattern of phytoplankton
community development over the course of the samplirg period. The density
of phytoplankton in Streams 8 and 6 was highest during the first month of
sampling. Conversely, the phytoplankton in Stream 5 increased in density
gradually, reaching its highest value by the second month of sampling.
Phytoplankton density at the end of the sampling period (mid-July) was
low in all three streams. Figure 4 displays relative phytoplankton
»
biomass as indicated by in vivo chlorophyll fluorescence. The trend for
chlorophyll a in each stream is roughly equivalent to the trends in total
algal density. Figure 5 shows the ash-free dry weights, derived from
phytoplankton samples collected on all sampling dates.
Measurements of phytoplankton community structure were calculated
from the phytoplankton data and are presented in Table 2. Simpson's
Index of Diversity (Simpson 1949) measures the probability that two
individuals picked at random from one community will belong to different
species. Thus, a value of zero would indicate that there is only one
taxon in the community and a value of one indicates that the community is
Infinitely diverse. By this measurement, it becomes evident that all
three streams have a similar diversity over the course of the experimental
period. Morisita's Index of Community Similarity (Morisita 1959) is
derived from Simpson's index, arid measures the probability that two
-19-
-------
Individuals taken from different communities will belong to the same taxor.
In this case, a value of zero would indicate that there is no similarity
between the two communities,andavalue of one would indicate that the com-
pared communities are identical. During each sampling period, the phyto-
plankton communities of each stream are compared to each other (Table 2).
A clear trend of divergence emerges, each stream community becoming "lore
dissimilar from the others over the course of the study.
Figure 6 provides a detailed look at growth trends for eight domi-
nant algal taxa. These taxa constituted as much as 94» of the algae
present and alv/ays represented the majority of each stream's phytoplankton
community. By July 11 (at the end of the study), these eight taxa were
not nearly as important as in earlier sampling periods. They were not,
however, replaced by other species becoming dominant.
The algae of Stream 5, the most acidic stream, showed a pattern of
development markedly different fron: the patterns exhibited by Streams 6
and 8. During mid to late June, each of the eight taxa had a higher
density in Stream 5 than in the other two streams. But, over the dura-
tion of exposure to acid, the density of algae in Stream 5 declined mora
rapidly than in the other two streams.
The oveiall species composition was similar in all streams throughout
the course of the study. Cyclotella meneghiniana was the most dominant
single species; two species of Meloaira together accounted for more biomass
:lun ; meneghiniana due to the large size of chains that Melosira forms.
The other five taxa were always present in the samples. Diatoms (Bacillario-
phyceae) were overwhelmingly the dominant algal group in the Monticello
streams. Diatoms averaged 89.62 of the algae enumerated from pnytbplankton
-20-
-------
samples (with a range from 81—98%). The Chlorophyta, mainly Ulotkriz,
ScemdeamuSj, and Sp-irogyra, were also common. Very few of the 48 algal
taxa identified (Appendix 2) displayed intolerance to any of the three
pH regimes. However, Eunotia limaria was never present in the ambient
stream, while it became very common in Stream 5. Three species of ftavicula
were present in Streams 8 and 6, but they never were found in Stream 5.
Discussion
The Monticello streams provided an unique replicate system whersby
physical and chemical parameters could be controlled in a field situation.
The stream beds were uniform and the rate of flow remained constant in
all three systems. Water from the Mississippi River, nearly saturated
with dissolved oxygen was provided to all streams. The temperature in
each stream was nearly identical to the others at all times and water
!
hardnbs.- was the same. These streams were ideal habitats for the coloni-
zation of algae and macrophytes. The density of algae in the sampled
pools developed significant densities in each stream according to the
environmental conditions in that stream. Residence time for algae in
the streams was undoubtedly longer than calculated for streamwater (24
hours) since most algae probably grew within the artificial streams them-
selves, after an initial inoculation of that particular taxon to the
streams.
The addition of sulfuric acid to the experimental streams altered
the pH regimes there, making each of the three streams distinct from the
others. The acid addition raised the specific conductance and total
acidity of water in the experimental channels; bicarbonate alkalinity
-21-
-------
correspondingly declined and was especially low in Stream 5. Thus, the
regulation of most parameters and the alteration of pH provided an excel-
lent opportunity for studying the response of stream phytoplankton to the
stress of increased hydrogen ion concentration.
Colonization of the streams with different types of algae from the
Mississippi River was equally successful in each stream, as measured by
the index of diversity. Diversity of algae was quite high in each stream
throughout the course of the experimental period. Patrick et al. (1963)
in a study of stream diatoms found Vittle or no change in the diatom
diversity at pH 5.2 in one experiment. However, many authors report a
decrease in the diversity of the phytoplankton community with increasingly
acidic conditions (Johnson et al. 1970; Kwaitkowski and Roff 1976;
Leivestad et al. 1976; Van and Stokes 1976; and Van 1979). The diversity
ir. each stream of the present study was represented by a similar species
composition consisting mainly of diatoms.
Although community diversity was similar under these three pH regimes,
the similarity between communities decreased over the course of the six
week experimental period. This can be considered an effect of varying
conditions (mainly pH) between the three streams, since the other variables
changed in concert. - ..,
Biomass shov/ed similar patterns whether measured by in vivo chlorophyll
fluorescence or as the density of algal cells. The algae in Streams 6 and
8 attained their maximum biomass during the first.month of sampling.
There is a lag in the maxima of diatoms in Stream 5, in that the point of
highest algal biomass occurs during the beginning of the second month.
Patrick et al. (1968) found that attached stream diatoms at pH 5.2 had a
-22-
-------
slower division rate than those in more neutral streams. A slower divi-
sion rate due to less than an ideal pH environment may have caused the
lag in the maxima of diatoms in Stream 5. Biomass as measured by dry
weights and ash-free dry weights gave inconclusive results. Sometimes,
Spirogyra and other filamentous benthic algae were included in water
samples, and this may have contributed to the variable results.
By mid-July phytoplankton density was at its lowest in all three
streams (Figures 3 and 6). A combination of factors, such as reduced
nutrient supply or steadily ri •,ing water temperature, may have caused
the phytoplankton decline to occur. In the Monticello streams, dense
macrophyte stands (chiefly Potamogeton crispus) had accumulated in all
three streams by mid-July. This submerged vegetation led to reduced
light penetration in the streams, which could also have reduced phyto-
plankton growth.
Figure 6 shows that the most dominant algal taxa found in the
Monti cello streams occur in great abundance under each of the pH condi-
tions. Nygaard (1956) reported that Cyclotella meneghiniana. is an
alkaliphilous species, although it showed no such preference in this
study. Round (1964) found Melosira distcns to be abundant under extremely
acidic conditions, and Merilainen (1967) reported it to be acidophi'ious.
In confirmation, it should be noted that this species reached its greatest
abundance in Stream 5 in this study. Melosira. italics, (also reaching its
greatest abundance in Stream 5) is reported as alkaliphilous (Nygaard
1956; Merilainen 1967). Patrick et al. (1968) found the abundance of
Fragilaria crotonensia to be reduced at pH 5.2 (compared to more neutral
conditions). Nygaard (1956) reported it to be alkaliphilous. No such
-23-
-------
preference for alkaline conditions was indicated by this species in
Monticello streams. NitzsaHa palea, which did best in Stream 5, is
reported to be indifferent to pH (Merilainen 1967), but has been noted
under acid conditions (Round 1964; Patrick et al. 1968).
Just which physiologic features of specific algae actually determine
their tolerance to acidic conditions is a rather unstudied area of
phycology. It has been suggested that cells which are tolerant of acid
environments are able to restrict hydrogen ions from entering their cells
(Cassin 1974), while intolerant types may not have this ability. Clymo
(1963) found that the acidophilous moss Sphagnum has the ability to
release H ions into the surrounding medium and exchange these ions for
other cations that it takes up. Polyuronic acids in the cell boundary
appear to be involved in this exchange. Lane and Burris (1979) suggested
that acid-tolerant species either exclude hydrogen ions or have adapted
to low 'internal pH levels. Internal pH determined in Chlorella pyrenoidosa
showed that internal pH does indeed vary with environmental pH, although
the magnitude of variation internally is not as great as the external
fluctuation.
In the present study, it is possible that the potential stress of
the average pH 5.3 in Stream 5 is ameliorated by otherwise optimum condi-
tions for algal growth. Temperature in the streams was in the range of
optimal conditions for the growth of the taxa present there (Patrick
1969). Also, most chemical characteristics of the Monticello streams were
similar to those in circumneutral waters and not of naturally occurring
acid waters. Even without the contribution of high hydrogen ion concen-
tration in the experimental channels, the conductivity of the water was
-24-
-------
rather high. A medium water hardness of similar value existed in all
three streams, regardless of the adjusted acidity.
The mechanism of ion transfer in phytoplankton may be altered by low
pH levels and these mechanisms may be less altered when levels of salt
are at.high concentrations, as has been found with other freshwater
organisms. Tolerance of trout to low pH is increased when the concentra-
tions of salts is increased (Leivestad et al. 1976). Heavy metal tolerance
by algae can also be enhanced by the presence of other salts. Hargreaves
and Whitton (1976b) found the tolerance of Eorm'id'ium rivulare to zinc was
increased by the presence of calcium, phosphorus, or magnesium in the
growth medium. Patrick et al. (1968) stated that when otherwise circum-
neutral conditions occurred in a stream, the altering of one parameter
(pH) would not necessarily be expected to change diatom community structure
significantly. Accessory environmental factors can often act to increase
tolerance to a lethal agent (Warren 1971). In the present study, a pH of
5.3 did not alter phytoplankton community diversity or species composition
(compared to more neutral conditions). However, the pattern of community
development was markedly different between an acid stream and streams of
higher pH, suggesting that high acidity may slow the division rate of algal
cells there, decreasing productivity. Certainly pH 5.3 proved to be a
sublethal value for the diatoms present but further increases in acidity
""*•
could undoubtedly result-in more drastic changes in community structure.
The somewhat equivocal results from the various studies cited suggest
that further investigation is needed to clarify relationships between the
phytoplannton community and acidification.
-25-
-------
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Table 1. Summary of four chemical characteristics of Monticello streams
obtained from weekly samples over the course of the experiment.
Specific Conductance
Total Acidity
[wmhos • cm'1 (25°C)]
Date
May 26
June 2
June 9
June 16
June 23
June 30
July 7
July 14
8
244
281
307
258
293
268
284
291
Bicarbonate
Date
May 26
June 2
June 9
June 16
June 23
June 30
July 7
July 14
(mg CaCo-,
8
119
130
144
134
158
146
152
148
Stream
6
282
292
312
269
302
275
308
300
Alkalinity
/liter)
Stream
6
46
56
55
60
57
66
62
69
5
293
316
333
276
336
307
340
317
Date
May 26
June 2
June 9
June 16
June 23
June 30
July 7
July 14
(mg/ liter)
8
4
4
4
4
3
5
4
2
Stream
6
43
50
62
65
63
62
64
62
5
67
92
180
102
113
104
no
116
Hardness
5
10
8
10
17
6
9
7
8
Date
May 26
June 2
June 9
June 16
June 23
June 30
July 7
July 14
(mg/li
8
119
130
144
.134
158
146
152
148
ter)
Stream
6
121
132
144
134
154
150
150
152
5
121
133
144
136
154
152
150
152
-30-
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Table 2. Measurements of phytoplankton community structure in all
streams on each sampling date.
Stream
8
6
5
8
6
5
8
6
5
8
6
5
No. Taxa
Observed
25
25
21
27
29
27
27
29
28
32. .
22
26
Simpson's Index
of Diversity
May 30
0.08
0.81
0.66
June 13
0.80
0.84
0.80
June 27
0.80
0.84
0.86
July 11
0.89
0.77
0.89
Morisita's Index of
Community Similarity
- Stream
6 5
s 8 0.33 0.51
£ 6 — 0.33
to
Stream
6 5
f 8 0.21 0.24
-------
Figure 1. The three Monticello artificial streams. Arrow indicates
the direction of flow. Dark patching indicates upstream
area shaded by canvas, me - mixing compartment, 1—4 = pools
one through four, b—d - riffles two through four.
-32-
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FROM
MISSISSIPPI RIVER
-------
Figure 2. (a) Average mid-depth temperature in shaded and unshaded
pools over the course of the experiment.
*'-<•'•"*= shaded pool temperature, •• « - unshaded pool
temperature.
(b) Average percent saturation of dissolved oxygen at mid-
depth in pools ovsf the course of the experiment.
(c) Average hydrogen ion concentration for each _>tr-?am .over
the course of the experiment. — • = pH in riffles,
pH in pools, @= phytoplunkton sampling dates.
-34-
-------
22_
S 16.
oc
O
10.
90.
52
s>-
8.0.
e 7.0.
z
6.0-
5.0J
V
A
v
«r*a
I
20
MAY
I
31
10
I
20
I I
JUNE
I
30 10
JULY
'?
-
-------
Figure 3. Overall phytoplankton density in all streams on each sampling
date. «•«•=' Stream 8, ««HII= Stream 6, "•~--*= Stream 5.
-36-
-------
o
M
g 25-
<§ 15-
5
30
-------
Figure 4. In vivo Chlorophyll fluorescence of phytoplankton in all
streams on each sampling date. •"•••• = Stream 8,
i ••• » = Stream 6, •••••• = Stream 5.
-38-
-------
JULY
11
_ 3') -
-------
Figure 5. Ash-free dry weight of phytoplankton samples from all streams
on each sampling date. Each bar represents the average weight
of two duplicate samples. m*as» = Stream 8,
Stream 6, •§••§= Stream 5.
-40-
-------
404
0-i
-------
Figure 6. Density of eight major phytoplankton taxa in three distinct
pH regimes on each sampling date. 1—4 = the four sampling
dates (May 30, June 13, June 27, July 11 respectively), A =
Cyclotella ir.er.eghinianz, B = Melosira distans, C = !-!elosira
•italics., D = Astartcnella fozmosa, E = Fragi.lax*ia crotor.er.s~i3,
F = NawLcxla spp. (seven species), G = Nitzschia spp. (three
species), H = Total Chlorophyta taxa
-42-
-------
TOTAL NO. COUNTED/UTER (*105)
-------
Appendix 1
Metal Characteristics of the Sulfuric Acid
Maximum Amount
Metal Content (mg/liter)
Iron 35
Arsenic 3
Manganese 0.3
Zinc 0.4
Selinum 1.2
Copper 1
Nickel 0.3
Lead 4
Sulfur Dioxide 20
Chloride 2
Nitrate 3
Fixed Residue 75
Brand:
ASARCO H2S04, Commercial 66°
Bought From:
Thompson-Hayward Chemical Company, Minneapolis,
Minnesota.
-44-
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Appendix 2
Phytoplankton Observed in Experimental Streams
Taxa Stream
865
Chrysophyta
Asterionella formosa VC VC VC
A. gracillims. VR VR —
Cocconeis plaoentula R C VC
Cyclotella bcdanica. R R R
C. menegkinicna VC VC VC
Cymbellc. cistula R R R
C. gracilis R R R
Diatcma vulgare VC VC VC
Epithemia turgida VR — —
Eunotia lunaris VR R VC
Pragilaria capucina R R C
F. crotonensis VC VC VC
Gomphanema constriction — VR —
G. montanum — R —
G. olivaceum — — VR
Gyrosigma. acuminatum R — —
G. scaproides . VR VR VR
Melosira distans VC VC VC
M. italica VC VC VC
Meridian circulate VC R C
Navicula cryptocephala C C VR
N. cuspidata R — —
N. platystcma R — —
N. radioes VR VR —
N. tuscula C R R
N. viridula R R R
N. spp. C R C
Nitzschia linearia R R VC
H. palea R R VC
Nitzschia sigmoides VR VR VR
Rhoicosphenia curvata R R R
Stephanodiscua niagore R . R R
Synedra ulna R VC R
Tabellaria fenestrata R — . R
-45-
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Taxa Stream
365
Chlorophyta
Ankistrodesrrus sp. VR — —
Closteriwn sp. - — — VR
Mougeotia sp. C C C
Psdiaatrian angulusam — R —
?. duplex R VR R
Scenedssmus obliquus C C C
Spirogyra sp. C C C
Ulothrix zanata C VC R
Unidentified colonial flagellate — C —
Unidentified unicell. flagellate R R VR
Cyanophyta
Anabaena sp. R R R
Anacyatia morginata — — VR
Aphanizamenon sp. VR R —
Synechocystis aquatis R C C
n
1. VC = very common (found at a density over 10 cells/liter at least
once)
C = common (between 50,000—10 cells/liter at least once)
R » rare (always under 50,000 cells/liter)
VR = very rare (found only once)
-46-
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