-------
I
tOr
0.5
0.0
-0.5
•10
-ts
-2.0
-2.5
SBRP Stream Reaches
Model « MAGIC
Deposition «= Constant
Year = 50
6.0 6.5 7.0 7.5 8.0
Simulation Year 0 pH
SBRP Stream Reaches
Model = MAGIC
Deposition ~ Ramp 20% Increase
Year = 50
10
0.5
0.0
. -0.5
3 -tO
-1.5
-2.0
-2.5
6.0 6JS 7.0 7.5 8.0
Simulation Year 0 pH
CL
to
0.5
0.0
-0.5
-ts
-2.0
-2.5
Deposition = Constant
Year - 100
"6.0 6.5 7.0 7^ 8J3
Simulation Year 0 pH
Deposition •= Ramp 20% Increase
Year - 100
10
0.5
0.0
-1.5
-2.0
9JS 70) 7.5 8.0
Simulation Year 0 pH
o.
<
to
0.5
0.0
-0.5
-10
-ts
-2.0
-2.5
Deposition •-- Constant
Year - 200
6.0 8.5 7.0 7.S 8J3
Simulation Year 0 pH
Deposition = Ramp 20% Increase
Year - 200
3
to
0.5
0.0
-0.5
-10
-ts
-2.0
8.0 «£ 7.0 7.5 8.0
Simulation Year 0 pH
Figure 10-99. Comparison of the change in pH after 200 years as a function of the initial calibrated
pH for MAGIC on SBRP streams, Priority Classes A - E.
789
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10.12 DISCUSSION
10.12.1 Future Projections of Changes in Acid-Base Surface Water Chemistry
The Level 111 Analyses used typical year deposition scenarios to examine the potential effects of
alternative deposition levels on future changes in surface water chemistry. The typical year, as discussed
in Section 5.6, represents the average meteorology for a 30-year period of record and the average
deposition for a 3- to 7-year period of record adjusted for the average meteorological year. Deposition
was then estimated for each of the watersheds considered in the Level III Analyses. The typical year
scenario enabled each modelling group to use the same input and provided a common basis for
comparing changes in surface water chemistry as functions of comparable deposition among all the
models. The intent was not to forecast future meteorological or deposition conditions, but rather to have
a common basis for comparison among model results. Comparable watershed morphometry, physical
and chemical soils data, and surface water chemistry data also were provided to each of the modelling
groups, enabling them to assess and contrast the different model formulations and projections. These
models integrate much of our knowledge on how watershed processes control surface water acidification,
and comparing the output from these models, in part, provides a test of how well we understand these
processes. There are different hypotheses on how these processes operate and different philosophies on
how to integrate this information in the models (Eary et al., I989; Jenne et a!., 1989). These results are
not intended, and should not be interpreted, as forecasts of conditions that might be expected over the
next 50 to 200 years.
10.12.2 Rate of Future Change
The Panel on Processes of Lake Acidification raised questions on the extent of surface water
acidification, the processes that control changes in surface water chemistry (including surface water
acidification and chemical improvement), and the rate at which these processes occur. The extent of
acidic and low ANC surface waters in the United States was addressed through the NSWS. The
processes that control changes in surface water chemistry were discussed in Section 3 and summarized
in Galloway et al. (1983a), Church and Turner (1986), Reuss and Johnson (1986), and Martin (1986).
The DDRP was initiated because scientists did not concur on how watershed processes control the
rate and magnitude of surface water acidification and how to project such changes in surface water
chemistry. A primary area of disagreement among scientists on the Panel was whether future ANC
decreases would be gradual over a period of centuries or perceptible over years to decades, i.e., they
disagreed about the rate at which acidification might occur. The rates at which changes in sulfate
adsorption and base cation supply and surface water acidification and chemical improvement might occur
in northeastern lakes and SBRP streams are discussed below.
10.12.2.1 Northeast
Changes that might occur in the NE over the next 100 years (summarized in Figure 10-92) are
consistent with various conceptual models of surface water acidification (Galloway et al., 1983a; NAS,
1984; Church and Turner, 1986; Cosby et al., 1985a,b,c; Reuss and Johnson, 1986).
790
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Sulfate deposition in the NE has declined since the 1970s concurrent with declining sulfur emissions
in the NE (OTA, 1984; Kulp, 1987). The decline in sulfate concentrations at the start of the projections
for the NE under current deposition (Figure 10-92) reflects this deposition decrease as the watersheds
approach a sulfate steady-state concentration that is lower than it was in the 1970s. The relatively
constant ANC concentrations under current deposition for the first 20 years of the projection occurred
primarily because the decline in sulfate concentrations of about 8 /jeq L"1 was compensated by a decline
of about 8 /zeq L" in calcium plus magnesium concentrations. Sulfate concentrations asymptotically
approached steady state after 20 years, changing by about 2 to 3 peq L'1 over the next 80 years. A
continual depletion of about 8 //eq L"1 in base cation concentrations (calcium plus magnesium) was
projected during this 80-year period as sulfate approached steady state, however, which resulted in the
continual decline in ANC of about 4 /*eq L"1 over this same 80-year period. These results are consistent
with observations made in Plastic Lake, Ontario, Canada where ANC concentrations continued to
decrease following a reduction in sulfate deposition even though sulfate concentrations remained relatively
constant in the lake (Dillon et al., 1987). The ANC decrease in Plastic Lake was attributed to depletion
of the available pool of base cations in the watershed (Dillon et al., 1987), although no soil measurements
were made. A depletion of the pool of available soil base cations was projected for the northeastern
watersheds using both ILWAS and MAGIC and resulted in similar ANC decreases in the northeastern
lakes.
All three models projected that northeastern watersheds might be at or near sulfate steady state
within 50 years assuming either current or decreased deposition. All three models projected decreased
ANC concentrations over 50 years and that additional lakes might become acidic, because of the slow
but continual decrease in base cation and ANC concentrations. The lakes currently not acidic that might
become acidic over the next 50 to 100 years represented about 3 percent of the 3227 lakes in the MAGIC
target population. When compared with the ELS-I target population of 7157 (many of which have ANC
concentrations exceeding 400 peq L'1), this additional percentage of acidic lakes represents less than
1 percent of the population. The ELS-I target population, however, included only lakes larger than 4 ha.
Ongoing analyses of small lakes indicates that the ratio of smaller acidic lakes (< 4 ha) to acidic lakes
larger than 4 ha is about 2:1 (Sullivan et al., submitted). Considering these small lakes might increase the
projected percentage of acidic lakes over the next 50 years to 2 percent. The models, however, support
the hypothesis that future ANC decreases in the NE will be gradual over a period of decades to centuries
rather than years to decades.
Following the 30 percent decrease in sulfate deposition beginning in year 10, there was a rapid
increase in projected ANC over the next 40 years (Figure 10-92). This 11 fj.eq L"1 increase in ANC
occurred because the concurrent projected decrease in median sulfate concentrations of about 22 /*eq
L" occurred with a projected decrease in median base cation concentrations (calcium plus magnesium)
of about 11 jueq L"1. This rapid increase in ANC probably occurred because the watersheds were initially
near sulfate steady state. A rapid increase in ANC might not be expected if the systems are not at or
near sulfate steady state (Cosby et al., 1985a,b,c). All three models projected this rapid increase in ANC
following the 30 percent decrease in sulfate deposition. Even though the watersheds were nearly at
sulfate steady state within 50 years under decreased deposition, there was a continued decrease in base
cations projected from year 50 to year 100, which resulted in a small but continued decrease in ANC
concentrations.
791
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Although there was no apparent relationship between the rates of change in ANC and sulfate and
the initial ELS-I ANC concentration, the projected rate of change under current deposition in the NE was
small. If the majority of the watersheds are near sulfate steady state, then most of these systems might
be expected to respond relatively quickly to changes in sulfate concentration regardless of the initial ANC.
Projections for all three models indicated that as many as 125 currently acidic lakes might
chemically improve (increase in ANC) in 50 years assuming a 30 percent deposition decrease. This
estimate represents about 77 percent of the estimated 162 currently acidic DDRP target population lakes,
but only about 4 percent of the 3277 lakes in the MAGIC target population. The number of lakes
estimated to chemically improve was moderated by the continued decrease in ANC from year 50 to year
100: after year 100, the estimated number had decreased to 113 (70 percent).
Differences among model projections were more apparent for Priority Class A and B lakes for three
reasons. First, the sample size for this priority class is small and are available for comparison. Second,
this priority class includes low ANC systems, which have the greatest variability in terms both of ANC
measurements (Linthurst et al., 1986a) and model calibration. The ILWAS and MAGIC models are
calibrated on base cations and acid anions and ANC is a computed, not a calibrated value (i.e., ANC =
sum base cations - sum acid anions). ELS-I field measurements for many lakes indicate cation or anion
deficits that reflect the accepted sampling and measurement error in the analysis. The models, however,
require charge balance so the calculated ANC concentrations following calibration might not equal the
measured ANC in the lake or stream. This difference between calibrated and measured ANC values for
the models was generally greatest at the low ANC concentrations where the relative measurement errors
also are greater. The differences between models, however, are well within the uncertainty bounds about
the projections. Third, MAGIC performs hindcasts as part of its calibration/projection exercise and, thus,
simulates the declining sulfur deposition levels over the past 10 years. These declining sulfur deposition
levels continue to exhibit a cumulative effect over the first 10-20 years of the projections. ILWAS and ETD
assume historically deposition values are the same as current deposition values and calibrate to them,
which also contributes to the differences among models.
The change in pH projected using MAGIC might be underestimated because the initial or calibrated
ANC concentrations at year 0 were greater than the ELS-I ANC concentrations. Because of the pH - ANC
relationship, the unit change in pH for each unit change in ANC decreases as the ANC increases (i.e.,
at higher ANC concentrations, pH changes are less). To assess this possible underestimate in pH
change, the change in ANC projected using MAGIC was added to the ELS-I ANC, and a derived pH was
estimated using the pH - ANC relationship incorporated in MAGIC (Figure 10-100). The change in the
derived pH is similar to that in the modelled pH for current deposition, although the maximum change
is greater. Under decreased deposition, the estimated change in pH is greater with the derived rather
than modelled pH values, but only for a few lakes (Figure 10-100). Because the changes in ANC are
both small and not influenced by the initial ANC, the change in pH does not appear to be greatly
underestimated.
10.12.2.2. Southern Blue Ridge Province
Projected changes in surface water chemistry that might occur in the SBRP were shown in Figure
10-98. ILWAS and MAGIC projected similar changes in ANC, calcium plus magnesium, and sulfate over
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CO
2.0
1.6
0.8
0.4
o
in o.o
-0.4
-0.8
NE Lakes
Model = MAGIC
Deposition = Constant
o Model pH
A Derived pH
A A A
1 - 1 - 1 - 1
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
Simulation Year 0 pH
NE Lakes
Model = MAGIC
Deposition = Ramp 30% Decrease
2.0 r
1.6
0.8
o
10 o.o
-0.4
-0.8
o Model pH
A Derived pH
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
Simulation Year 0 pH
Figure 10-100. Comparison of projected MAGIC change in pH versus derived pH after 50 years
for NE lakes.
793
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the 50-year period. MAGIC projections for the SBRP, however, suggest that substantial changes also
occur between 50 and 200 years. This discussion, therefore, focuses on the MAGIC projections.
For the first 50 years, both models projected a decrease in ANC and an increase in base cation
and sulfate concentrations for both deposition scenarios. The decrease in ANC concentrations over the
first 20 years was slight, but a relatively constant linear decrease in ANC after 20 years was projected.
Under current deposition, sulfate concentrations increased linearly for the first 50 years from about 37 to
75 /teq L" while base cations increased from about 110 to 123 jueq L"1 by year 30. Increased sulfate
concentrations were compensated by increased base cation transport from the watershed and relatively
little change in ANC for the first 20 to 30 years. However, when base cations began to decrease, ANC
concentrations also decreased from about 122 to 100 peq L"1 from year 20 to year 100, respectively.
Over the interval from year 30 to year 100, sulfate concentrations increased by about 35 neq L"1, base
cations declined by about 15 /zeq L'1, and ANC decreased by about 20 /*eq L'1, projections which are
consistent with charge. balance requirements and current understanding of soil processes (Reuss and
Johnson, 1986; see Sections 3 and 9). Although the rates of sulfate increase and base cation decrease
changed from year 100 to year 200 compared with year 50 to year 100, the ratio or relationship between
increased sulfate concentrations and decreased base cations remained relatively constant because the
rate of change in ANC concentrations was relatively linear from year 30 to year 200. The SBRP
watersheds were asymptotically approaching sulfate steady state by year 200, and median watershed
sulfur retention had declined to about 5 percent.
The two models differed in the projected number of streams that might become acidic within 50
years under current deposition. The ILWAS model projected no acidic streams while MAGIC projected
130 streams that might become acidic in 50 years assuming current deposition. The estimate of 130
acidic stream reaches, however, is derived from differences in the projections for one SBRP stream with
a relatively large weight. This stream's ANC decreased from an initial concentration of about 20
" "
to 3 /zeq L"1 within 50 years. Given the uncertainty in the projections, 130 is probably the maximum
estimated number of streams that might become acidic within 50 years. MAGIC projections also indicated
additional streams might become acidic over the next 200 years in the SBRP, with between 12 and 15
percent of the systems potentially becoming acidic by 100 years and 200 years, respectively, under
current deposition.
Changes in surface water chemistry projected for the SBRP under increased deposition showed
similar patterns to those projected under current deposition (Figure 10-98). The rate at which sulfate
asymptotically approached the steady-state concentrations with increased deposition was greater than
that under current deposition because of the change in sulfate loading during the first 100 years. The
rate of increase in stream sulfate concentrations during the initial phase of approaching steady state is
nearly linear and becomes asymptotic as the soil solution sulfate concentration approaches the steady-
state sulfate concentration. Higher loadings with the 20 percent increased sulfur deposition scenario
resulted in the SBRP soils approaching the new sulfate steady state more quickly on the linear portion
of the curve. The rate of change in sulfate from year 100 to year 200 under increased deposition was
less than under current deposition because the increased loading over the first 100 years resulted in the
watersheds being nearer to sulfate steady state. This increased sulfate loading also resulted in greater
base cation depletion rates over the first 100 years. The rate of change in base cations from year 100
to year 200 under increased deposition was slightly greater than under current deposition. Because the
794
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rate of change in sulfate under increased deposition was less and the rate of change in base cations was
greater than under current deposition, there was a slight decrease in the rate of change in ANC
concentrations from year 100 to year 200.
The increased deposition and more rapid increase toward sulfate steady state resulted in a larger
number of streams that might become acidic by year 200. The estimated numbers of streams that might
become acidic by year 100 and year 200 were 159 (11 percent) and 337 (24 percent) streams.
The models also support the hypothesis that future ANC decreases in the SBRP will be gradual
over the period of decades to centuries rather than occur over years to decades. Streams in the SBRP
might experience a slow but steady decline in ANC over the next 200 years assuming constant or
increased deposition. The stream population in the SBRP typically had higher initial ANC concentration
than streams in other geographic regions of the Southeast. Thirty percent of the DDRP SBRP stream
population had ANC concentrations between 25 and 100 /*eq L"1, and 70 percent of the stream reaches
had ANC > 100 /*eq L'1 . Extrapolating results from the SBRP to the population of other streams in the
Southeast, therefore, might not be appropriate because the proportion of streams with lower initial ANC
concentrations in other southeastern regions is greater than in the SBRP (Kaufmann et al., 1988). In
addition, the projected changes in pH in the SBRP stream accompanying these changes in ANC might
range from -0.5 to -1.0 over 50 years and up to -2.0 pH unit changes over 200 years. Other southeastern
streams with lower current ANC might exhibit even greater pH changes within 50 years than projected
for SBRP streams.
10.12.3 Uncertainties and Implications for Future Changes in Surface Water Acid-Base Chemistry
Uncertainty is defined as intrinsic variability plus error. Intrinsic variability represents the natural
variability or noise in the systems that cannot be reduced. The components of error include
measurement error, sampling error, model structural error, prediction error, and population estimation error
(Beck, 1987). The uncertainty analyses conducted for the Level III models quantitatively estimated many
of these error components (although the total error was not partitioned into its respective components)
and incorporated this error in the confidence bounds around the model projections. Unknown or poorly
understood processes, however, are more difficult to estimate quantitatively but can be qualitatively
discussed. The implications of these processes on estimates of future change in ANC and pH are listed
in Table 10-20.
10.12.3.1 Deposition Inputs
Analyses were performed to determine the effect of deposition input uncertainty on the model
projections (Section 10.10.2). These uncertainty estimates were used to establish confidence intervals
about the model projections in Appendix C. Analyses indicated the input uncertainty contributed about
half of the total uncertainty in the projections with the other half arising from parameter uncertainty.
Uncertainty in dry deposition, particularly of base cations, is certainly a major contributor to deposition
input uncertainty. The approaches used to estimate the deposition inputs, however, were reasonable,
based on input from the deposition modellers, conversations with technical experts on dry and wet
deposition, analyses of existing data, and conventional theory. In part, underestimates or overestimates
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Table 10-20. Effects of Critical Assumptions on Projected Rates of Change
Assumptions Resulting in Under-
Estimates of ANC and pH Changes
1. Mineral weathering overestimated
2. Nitrate assimilation overestimated
3. Total sulfur deposition underestimated
4. Calibrated ANC greater than observed
5. Watershed land use changed
6. Episodic acidification of surface waters
7. Biotic uptake/assimilation reducing
available base cation pool
8. Effects at distribution extremes over-
smoothed through aggregation
Assumptions Resulting in Over-
Estimates of ANC and pH Change
1. Mineral weathering underestimated
2. Organic acids buffer surface water chemistry
3. Total sulfur deposition overestimated
4. Calibrated ANC less than observed
5. Watershed land use changes
6. Desorption is not the reverse of adsorption-
hysteresis-related delays in change
7. Weathering and sulfate adsorption increased by
decreased soil pH
796
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in anion or cation deposition inputs are compensated by increasing or decreasing mineral weathering
rates, respectively, of the anion or cation species to match observed surface water chemistry Watershed
exchange pools are tightly coupled with deposition inputs.
This tight coupling of declining base cation concentrations to declining surface water sulfate
concentrations was recently reported for Hubbard Brook (Driscoll et al., 1989b). Two mechanisms were
md.cated that can contribute to this coupling: (1) atmospheric deposition of base cations and (2) release
of base cations from mineral weathering or watershed pools of exchangeable base cations (Driscoll et
3l., 1989D).
For the Level III projections the typical year deposition/precipitation scenario was repeated each
year for 50 years, so annual atmospheric deposition was constant for the 50-year period (with daily
meteorological variations). For the 30 percent deposition decrease, only sulfate concentrations were
reduced in deposition with charge balance maintained by adjusting hydrogen ion concentration Base
cation concentrations were not decreased in either deposition scenario. For these projections, surface
water base cation concentrations were tightly coupled with sulfate concentrations through the depletion
of soil exchangeable base cations. Depletion of soil exchangeable base cations occurred because sulfate
moved through the watersheds as a mobile anion. Under decreased deposition, the reduction in sulfate
concentration was compensated by soil base cations and a subsequent increase in ANC. These patterns
were consistent with those observed at Hubbard Brook.
While the projected changes in surface water sulfate concentrations are consistent with the
depletion of watershed pools of base cations, these processes cannot be decoupled from atmospheric
processes in natural watersheds. Atmospheric deposition of base cations clearly is an important process
that must be investigated in assessing the effects of sulfate deposition on surface water chemistry The
calibrated models used in the Level 111 Analyses represent an excellent opportunity for evaluating different
hypotheses related to atmospheric deposition and watershed processes. Simulation experimentation on
different hypotheses represents one of the most important uses of watershed models.
The deposition inputs, indeed, might be highly inaccurate. The intent, however, was not to forecast
but rather to project the effects of alternative sulfur deposition scenarios on future changes in surface
water acid-base chemistry. Additional analyses are being proposed as part of the 1990 NAPAP Integrated
Assessment but it is likely that this issue will remain beyond 1990.
10.12.3.2 Watershed Processes
Each of the three models has different formulations and different data requirements. If the three
models provide similar projections for similar reasons, however, greater confidence can be placed in the
conclusions. Questions remain, however, as to whether the models incorporate the key watershed
processes affecting surface water acidification and how important the model formulations, operational
assumptions, and parameter selection are on the long-term projections.
The key watershed processes incorporated in each model were listed in Table 10-1 and are
discussed in detail in Eary et al. (1989) and Jenne et al. (1989). All three models focus on the effects
of sulfur deposition on surface water acidification. Each model considers total deposition acidity,
797
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including nitrate, but the nitrogen dynamic formulations included in each model, including ILWAS, are
rudimentary. Because most of eastern forested watersheds are nitrogen-limited (Likens et al., 1977;
Swank and Crossley, 1988), nitrogen inputs are effectively removed from the soil complex. Deposition
inputs of nitrate are about twice the ammonium inputs for the eastern United States (Kulp, 1987).
Although nitrification has an acidifying effect (Lee and Schnoor, 1988), nitrate assimilation has an alkalizing
effect (Lee and Schnoor, 1988). Nitrate concentrations are low in receiving lakes and streams, indicating
nitrate is not moving as a mobile anion. Median nitrate concentrations measured during the ELS-I for
northeastern lakes were less than 1 ^eq L'1. Median nitrate concentrations for SBRP streams were about
10 peq L" . This does not preclude soil acidification, however, because biotic processes might influence
surface water chemistry. The assumption that nitrogen is not a primary contributor to chronic surface
water acidification and, therefore, that nitrogen dynamics do not have to be explicitly modelled represents
a limitation of the models, rather than a short-coming in the DDRP design. Nitrate also might be an
important component of episodic acidification. The DDRP, however, is not addressing episodic
acidification.
Changes in soil pH might influence mineral weathering rates and sulfate adsorption capacities. Plot
experiments have indicated these processes can be affected by decreased soil solution pH. Although
these effects might occur, median soil solution pH were projected to change less than 0.1 units in the
NE and less than 0.2 units in the SBRP.
One of the operational assumptions of the Level III Analyses was that the relationship of organic
acids to other chemical species would remain constant. Krug and Frink (1983) hypothesized that
reversing surface water acidification by strong mineral acids could result in increased dissociation of
humic acids and mobility of organic acids and, therefore, return naturally acidic lakes to their original
state. The historical acidic status of the currently acidic lakes is unknown, so the estimated chemical
improvement of the 125 currently acidic lakes might be liberal. Historical reconstruction of water
chemistry for Adirondack Lakes should be available in the fall of 1989 and might be compared with the
DDRP projections of chemical improvement for the same lakes.
Mineral weathering is critical for all long-term projections, but is the process about which little
information can be obtained. The mineral weathering parameters are calibration parameters but are not
completely unconstrained. The range over which these parameters can vary while maintaining reasonable
ranges for other, better characterized parameters (e.g., selectivity coefficients) and still match observed
surface water chemistry constituent concentrations (e.g., silica, calcium, sodium, and other base cation
concentrations) is bounded. All three models yield similar long-term projections, even though ETD and
ILWAS use a fractional order weathering formulation based on hydrogen ion and MAGIC uses a zero
order weathering formulation. Long-term projections, however, are sensitive to the mineral weathering
parameters in all three models. The sensitivity of the MAGIC and ETD models to changes in the mineral
weathering parameters was identified in Table 10-10. Although mineral weathering rates cannot be
unequivocally estimated, the model formulations and mass balance approaches used in the models might
be analogous to the mass balance approaches used to estimate weathering in watershed studies (Velbel
1986b; Paces 1973).
Data aggregation might result in underestimates of change in the tails or extremes of the
distributions. Soil horizon physical and chemical attributes are averaged (weighted) to Master horizons,
798
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Master horizons aggregated to sampling classes, and sampling class attributes aggregated to the
watershed values, which are used for model calibration. This averaging or aggregation process will
preserve the central tendency in watershed attribute, and subsequent projected effects, but will reduce
the variability or extremes in the distribution of soil horizons through watershed attributes While these
extremes represent a small proportion of the target population, the changes in these watersheds might
be underestimated so the changes in ANC or pH might be greater than projected.
Although data are not available for model confirmations of long-term projections short-term
calibration and confirmation studies on Woods Lake, Panther Lake, and Clear Pond indicate the RMSEs
among the models and the observed standard errors of the data were similar. Identical data were
provided to each of the modelling groups in performing the projections; a consistent, methodological
approach was used for the sensitivity analyses and the long-term projections; and uncertainty analyses
were performed for all three models. The rates of change for different constituents were comparable
among models and the processes controlling changes in surface water chemistry under different
deposition scenarios and among regions were similar among and between models. Even through there
are differences in model structure, process formulations, and temporal and spatial scales the model
projections were remarkably similar. Regardless, long-term projections can be confirmed only with long-
term periods of record (Simons and Lam, 1980), which do not exist. Moreover, this study does not
establish the adequacy of the formulations representing important watershed processes, the procedures
for spatial aggregation of data, or the calibration approaches for long-term acidification projections.
10.13 CONCLUSIONS FROM LEVEL III ANALYSES
Conclusions from the Level III Analyses follow:
All three models produced comparable results for the northeastern watersheds. ILWAS and
MAGIC produced comparable but more variable results for the SBRP.
All three models projected minimal changes in ANC and sulfate concentrations and pH for
lakes in the NE over the next 50 years at current deposition rates. The median changes
in ANC, sulfate, and pH over the next 50 years were -1 to -5^eq L'1, <0.1 PH units, -0.1
to -5 /*eq L-1, respectively, each of which is within the projection error of the respective
analyses.
ETD and MAGIC projected about 3 percent and 5 percent, respectively, of the lakes in
Priority Classes A - E that are currently not acidic might become acidic within 50 years at
current deposition and 2 and 3 percent, respectively, at decreased deposition. ETD estimated
about 22 and 46 percent of the currently acidic lakes in Priority Classes A - E might
chemically improve (i.e., increase in ANC) in 50 years for current and decreased deposition
respectively. MAGIC estimated about 39 percent and 77 percent, respectively, of the currently
acidic lakes might improve in 50 years for the entire target population.
All three models projected reduced lake sulfate and increased ANC concentrations and pH
with a 30 percent reduction in deposition. The median changes in sulfate, ANC, and pH,
799
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respectively, were -23 to -28 /zeq L"1, +6 to +10 peq L'1, and 0 to +0.5 pH units over 50
years.
MAGIC and ILWAS projections of changes in ANC, sulfate concentrations, and pH for SBRP
streams over 50 years were similar but there was considerable scatter in the comparisons
because of the small sample size.
For current deposition, MAGIC projections in the SBRP indicated the change in median sulfate
after 50, 100, and 200 years was 38, 60, and 74 /^eq L"1, respectively. The changes in
median ANC after 50, 100, and 200 years were -11, -23, and -46 peq L"1, respectively. The
median percent sulfur retention at 0 years and after 50, 100, and 200 years was 65 percent
and 27 percent, 15 percent, and 6 percent, respectively. The changes in median pH after
50, 100, and 200 years were -0.04, -0.09 and -0.20, respectively.
The percentage of SBRP stream reaches that might become acidic after 50, 100, and 200
years was < 9, 11, and 14 percent, respectively, for current deposition and 11, 11, and 24
percent for increased deposition.
With a 20 percent increase in deposition, MAGIC projections for the SBRP indicated the
changes in median sulfate concentrations after 50, 100, and 200 years, respectively, were 55,
87, and 96 /*eq L"1. The changes in median ANC after 50, 100, and 200 years, respectively,
were -19, -41, and -64 /teq L"1. The changes in median pH after 50, 100, and 200 years,
respectively, were -0.07, -0.12, and -0.32.
Based on the Level III projections, lakes in the NE might not change significantly over the
next 50 years with current deposition.
Acidic lakes in the NE might improve chemically with a 30 percent reduction in deposition
assuming organic acid relationships with other chemical constituents remain constant,
although some lakes might continue to acidify.
Streams in the SBRP might experience a slow but steady decline in ANC and a linear
increase in sulfate concentration over the next 50 years assuming current or increased
deposition. About 10 percent of the SBRP streams might become acidic within 50 years.
The stream population in the SBRP typically had higher initial ANCs than streams in other
geographic regions of the Southeast. Thirty percent of the population had ANC
concentrations between 25 and 100 /*eq L"1, and 70 percent of the stream reaches had ANC
> 100 peq L"1. Care should be taken in extrapolating results from the SBRP to the
population of other streams in the Southeast.
800
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SECTION 11
SUMMARY OF RESULTS
11.1 RETENTION OF ATMOSPHERICALLY DEPOSITED SULFUR
11.1.1 Current Retention
On average, watersheds in the Northeast have sulfur budgets near steady state, with negligible net
retention of atmospherically deposited sulfur (Section 7). A small proportion of northeastern watersheds
have significant net retention, which appears to be controlled by reduction in wetlands or within lakes. In
contrast, net retention in stream systems of the Southern Blue Ridge Province is high, averaging about 75
percent. These observations are qualitatively consistent with theory (Galloway et al., 1983a; NAS, 1984) and
with site-specific budgets summarized by Rochelle et al. (1987).
The Mid-Appalachian Region is a zone of transition between the NE and SBRP in terms of observed
current sulfur retention. Because of the similarities between soils in this region and the SBRP, it is likely that
this region at one time retained as much of the elevated sulfur deposition as is now evident in the SBRP (i.e.,
70 - 80 percent). It is also likely that continued high sulfur deposition is bringing soils near steady state,
leading to reduced sulfur retention, perhaps very dramatically in the westernmost area (Subregion 2Cn of
the National Stream Survey, which now has median percent sulfur retention of only 3 percent) (Plate 11-1),
and has led to the low ANC and acidic stream reaches (excluding stream reaches affected by acid mine
drainage) identified there by the National Stream Survey (Kaufmann et al., 1988). The Mid-Appalachian
Region is the subject of additional in-depth soil sampling and analyses now underway within the DDRP.
Results of the sulfur input-output analyses are consistent with results of Level I regression analyses
summarized in Section 8. Regression analyses indicate that in the NE, sulfate concentrations are more
highly correlated with sulfur deposition than with any watershed characteristic, as would be expected for
systems at or near steady state (i.e., systems where sulfur input equals output). Additionally in the NE,
percent watershed sulfur retention is correlated with the extent of wetlands and wet soils on watersheds
(Section 8.5). This provides empirical support for the hypothesis that, to the limited extent sulfur retention
is observed in NE watersheds, reduction in wetlands is the principal retention mechanism.
In the SBRP, sulfate concentrations are correlated principally with edaphic factors. Sulfate
concentrations are relatively high in watersheds with high proportions of shallow soils and in catchments
having soils with low adsorption capacity. Similarly, percent sulfur retention increases with soil depth and
with sulfate adsorption capacity of soils. In both the NE and SBRP, watershed disturbance (e.g., mining
activity) is associated with elevated surface water sulfate concentrations.
11.1.2 Projected Retention
Using deposition scenarios described in Section 5.6, projections were made of future sulfur retention
in the NE and SBRP using both a single factor (Level II) adsorption model (Section 9.2) and the three
integrated models discussed in Section 10. For the sake of consistency, projections presented graphically
801
-------
Plate 11-1. Sulfur retention and wet sulfate deposition for National Surface Water Survey subregions
in the eastern United States.
802
-------
NSWS SUBREGIONS
MEDIAN % SULFUR RETENTION
AND WET SULFATE DEPOSITION
a.as
MEDIAN PERCENT
SULFUR RETENTION
H 20 - 40
40 - 60
60 - 80
80 - 100
2-50
2.25-.
2.00''
Average Annual
Wet Sulfaie
Deposition (g nfa yr~')
Eastern Lake Survey
2.25
Median
Subregion X Retention
1A
IB
1C
ID
IE
-H
8
-9
-12
X2.00
Notional Stream Survey
Subregion % Retention
2Cn
2Bn
3B
n
2As
3A
3
40
34
50
75
Deposition for 1980 - 1984
(A- Olsenr Personal Communication)
-------
in this section are from the Level ill MAGIC model. Because different target populations were modelled by
the four models (i.e., Level II and three Level III models) and because the projected results vary somewhat
among those populations, comparisons will be discussed qualitatively.
In the NE, median lake sulfate concentrations are already very close to steady state. For the scenario
of constant deposition, all of the models thus projected only small changes in median sulfate concentration,
and projected those changes t© occur relatively rapidly (10-20 year lags). Among the Level fll models,
MAGIC and ETD project small decreases in median sulfate concentration during the next 20 to 50 years,
whereas ILWAS projects very small increases. Slight (3 - 5 percent) positive sulfur retention is projected by
all three models by year 50, with in-lake reduction as the principal retention mechanism. The differences
in the direction of changes for sulfate concentration result from differences in target lake populations, in
process representation by the models, and in calibration procedures; absolute differences among projections
are minor and are relatively unimportant. For the scenario of decreased sulfur deposition, the models
consistently project substantial decreases in median lake sulfate concentration by year 50. MAGIC and ETD
project decreases in median sulfate of about 40 /*eq L1 in 50 years; ILWAS projects a somewhat slower
decrease and a smaller, but still significant decrease of 21 Ateq L1 in median lake sulfate.
Changes projected by the Level II sulfate model are very similar to those projected by MAGIC and
ETD. The Level II model projects only a small median decrease (7 peq L1 ) in sulfate concentration by year
20 for the constant deposition scenario, and a decrease in median sulfate of 40 ^eq L1 by year 50 for the
decreased sulfur deposition scenario. The principal difference in projections between the Level II and III
models is that the Level II model projects all watersheds to eventually reach exactly steady state, rather than
the small positive sulfur retention projected by Level 111 models. This results from differences in the
processes considered by the models; the Level II model considers only sulfate sorption by soils, whereas
the Level III models include in-lake reduction, which accounts for the slightly positive retention at long time
intervals.
Projected changes in sulfate concentrations for SBRP surface waters occur much more slowly than
in the NE, and are much larger in magnitude. Median sulfate retention in SBRP watersheds is currently about
75 percent, but retention is projected to decrease sharply over the next several decades (Plate 11-2).
Results were available for the Level II model (Section 9) and two of the Level III models (MAGIC and ILWAS)
(Section 10); all three models projected generally similar changes for sulfate in the SBRP. For the constant
deposition scenario, the two integrated models project increases in median stream sulfate of roughly 15 Meq
L1 in the next 20 years and about 40 neq L1 in 50 years; median percent retention is projected to decrease
by about 40 percent over the 50-year period. For the increased deposition scenario, slightly larger increases
in median sulfate concentration, of slightly over 50 peq L'1, are projected by year 50. The Level II model
projects somewhat faster increases for sulfate, with increases of 31 and 56 ^eq L1 in median sulfate
concentration at 20 and 50 years, respectively. The Level II model and MAGIC both project that rates of
increase in sulfate concentration will decrease by year 100 as SBRP watersheds approach steady state
(ILWAS projections were not made beyond 50 years) (Section 10). The cumulative increases projected for
median sulfate at 100 and 200 years are 60 and 74 /*eq L1 for MAGIC and 66 and 81 peq L1 for Level II.
The differences among the models at 20 and 50 years are attributable to differences in hydrologic routing
in the models and to assumptions about the chemistry of deep subsoils. The 20- and 50-year projections
803
-------
Plate 11-2. Changes in sulfur retention in the Southern Blue Ridge Province as projected by MAGIC
for constant sulfur deposition.
804
-------
I SULFUR RETENTION
Model = MAGIC
Deposition = Constant
'YEAR 0 = NSS Sample
3rd Quariile +
(1.5 x Interquartile Range)
3rd Quoftile
Uean
tsl Ouarliie
I 1st Quortile -
(1.5 x Interquartile Range)'
' Not to exceed extreme value.
-------
occur during the period when the models project the most rapid changes in suifate concentration, and can
be regarded as a measure of uncertainty in the projections. In terms of the most important aspects of sulfur
dynamics, the three models are consistent. All project that under the deposition scenarios simulated, the
delayed response phase of SBRP watersheds would end for suifate, and that there would be substantial
increases in suifate concentration in the next 20 to 50 years. Such changes would be accompanied by
decreases in surface water ANC to a degree dependent upon the relative leaching of acids and base cations
from watershed soils.
The results of the various suifate analyses are all internally consistent. Level II projections of base year
suifate in watersheds of the NE and SBRP are consistent with, and provide a mechanistic explanation for,
analyses by Rochelle and Church (1987), summarized in Section 7.3, showing watersheds in the
northeastern United States to be at or near steady state for sulfur and watersheds in the SBRP to have high
net sulfur retention. The very short suifate response times projected for the NE are also consistent with
results of regression analyses in Sections 7 and 8, which indicate that deposition is the principal control on
surface water suifate in the NE, and that significant sulfur retention (where observed), is probably attributable
to suifate reduction in lakes and/or wetlands rather than to sorption. Similarly, the long response times
predicted by dynamic models for the SBRP are consistent with results of the Level I regression analyses,
which found suifate concentration and percent sulfur retention to be correlated with soil variables directly
affecting adsorption capacity of soils (i.e., soil thickness and isotherm parameters).
11.2 BASE CATION SUPPLY
11.2.1 Current Control
Base cations are supplied from watersheds to surface waters by two processes acting in concert. The
initial source is mineral weathering, which is a slow process that supplies base cations to the soil exchange
complex. Equilibrium between the exchange complex and soil water (and thus waters delivered to lakes
and streams) is reached quickly. It is generally accepted that weathering rates are likely to change
negligibly or increase only slightly due to the effects of acidic deposition since only slight decreases in soil
pH are likely. If weathering supplies base cations to surface waters at rates equal to or greater than rates
of acid anion deposition, then systems would be relatively "protected". If weathering rates are low and
cation exchange dominates base cation supply rates, then the rate of depletion of base cations from the
exchange complex becomes an important determinant of rates of surface water acidification. Our analyses
indicate that surface water ANCs > 100 jueq L1 cannot be explained by the cation exchange model of Reuss
and Johnson (1986); thus, ANC generation appears to be dominated by weathering in these systems and
they, presumably, are relatively protected against loss of ANC (Section 9). Surface waters with ANCs < 100
neq L1 are likely controlled by a mix of weathering and cation exchange. The exact proportion of the mix
is difficult to determine.
11.2.2 Future Effects
Single factor base cation analyses, using the models of Reuss and Johnson (1986) and of Bloom and
Grigal (1985), were developed as a "worst-case" analysis by (1) considering only processes occurring in the
top 1.5-2 meters of the regolith and (2) setting mineral weathering rates to zero (i.e., assuming that the
805
-------
supply of base cations was totally controlled by cation exchange). This analysis indicated that depletion
of base cations from the exchange complex would occur under the sulfur deposition scenarios simulated.
The effect on surface water ANCs was initially slight but was not negligible. The magnitude of soil base
cation depletion was projected to accelerate in the future. At current levels of deposition, about 15 percent
of the lakes in the ELS target population are potentially susceptible to significant depletion of exchangeable
cations and, thus, depletion of associated surface water ANCs. The greatest portion of such changes is
projected to occur on a time scale of about 50 years. In the SBRP, a greater percentage of systems are
projected to be susceptible to adverse effects, but at longer time scales (i.e., about 100 years) than
northeastern systems.
Any effects of base cation depletion would be superimposed upon effects resulting from changes in
sulfate mobility in soils. The combined effects were simulated using the Level III watershed models and are
summarized in the next section.
11.3 INTEGRATED EFFECTS ON SURFACE WATER ANC
The three Level III watershed models (Section 1.3.4) were used to project the integrated watershed
and surface water responses to the sulfur deposition scenarios. Results among the models were remarkably
comparable. For example, within modelling Priority Classes A and B in the NE (Section 10) and for the
decreased sulfur deposition scenario, the MAGIC, ETD, and ILWAS models project changes (at 50 years)
in the median target population ANC for ANC groups <0 and 0 - 25 peq L1 within 2 /zeq L1 (5 - 7 peq L"1)
and 3 peq L'1 (10 -13 ^eq L"1), respectively. For the ANC group 25 - 100 ^eq L"1 the ILWAS and MAGIC
models project increases in median ANC within 1 /*eq L'1 (5.4 - 6.3 /*eq L'1). Increases in the median ANC
of this group (25 -100 ^eq L"1) under these conditions projected by the ETD model are quite a bit greater
(i.e., ~14^eq L"1 vs. ~6 ^eq L"1).
The greatest disagreement among the model projections (at 50 years) is for the increased sulfur
deposition scenario in the SBRP. For modelling Priority Classes A and B and ANC group 100 - 400 /*eq L1,
the ILWAS model projects a decrease in median ANC of 7 peq L'\ whereas the MAGIC model projects a
decrease of 24 jueq L1. Otherwise, comparative results among the models are remarkably uniform,
especially among the lower ANC groups of systems that are of the greatest concern.
Results from MAGIC are presented here because this model was successfully calibrated to the largest
number of watershed systems in the two regions (i.e., 123 of the 145 DDRP sample watersheds, representing
a target population of 3,227 systems in the NE; and 30 of the 35 DDRP sample watersheds, representing
a target population of 1,323 stream reaches in the SBRP).
As discussed in Section 10, the watershed modelling analyses make use of watershed soil
representations as aggregated from the DDRP Soil Survey. Because of the focus of the DDRP on regional
characteristics and responses, soils data were gathered and aggregated so as to capture the most important
central tendencies of the study systems. As a result, extremes of individual watershed responses probably
are not fully captured in the analyses presented here (see discussion in Sections 8 and 10). Those systems
that are projected to respond to the greatest extent or most quickly to current or altered levels of sulfur
deposition might, in fact, be expected to respond even more extensively or more quickly than indicated here.
This should be kept in mind when reviewing the simulation results presented in this Section.
806
-------
11.3.1 Northeast Lakes
Results of the projections for both deposition scenarios are presented in a couple of ways. Plate 11 -3
and Table 11-1 illustrate the projected change in the median ANC at 50 years for lakes classified into four
ANC groups (i.e., <0 peq L'1, 0 - 25 /*eq L1, 25 -100 /*eq L'1, and 100 - 400 /teq L1). These projections
indicate a general, very slight decline in ANC over the 50-year period under the current deposition scenario
and an increase of roughly 5 - 15 ^eq L'1 in ANC for all groups under the decreased sulfur deposition
scenario. Plates 11-4 and 11-5 illustrate the overall projected ANCs for the target population at 20, 50 and
100 years for the constant and decreased deposition scenarios, respectively.
Table 11-2 presents the population estimates (with 95 percent confidence intervals) of northeastern
lakes having values of ANC <0 ^eq L1 and <50 /zeq L1 at 20 and 50 years as projected by the MAGIC
model for the two deposition scenarios. The ANC = 0 /*eq L1 value is used to define acidic systems, and
the ANC value of 50 /zeq L1 (for index values as sampled in the NSWS, see Section 5.3) has recently been
suggested as useful in approximating the level at or below which systems are susceptible to severe episodic
acidification (i.e., brief periods of ANC depression to very low or negative values) (Eshleman, 1988) with
consequent adverse effects on biota. It is extremely important to keep in mind that these values only serve
as indices in an otherwise smooth continuum of surface water chemistry conditions and responses to acidic
deposition. It is also important to remember that adverse biological effects occur at higher ANCs (i.e.,
greater than 50 ^eq L1) in systems that previously (i.e., prior to the advent of acidic deposition) were
adapted to more circumneutral conditions (Schindler, 1988).
As indicated in Table 11 -2, under the constant deposition scenario, the number of lakes with ANC <0
»eq L1 increases at 50 years whereas the number of lakes with ANC <50 peq L'1 remains essentially
constant. For the scenario of decreased sulfur deposition, a marked decrease is projected in the number
of systems with ANC <0 and ANC <50 ^eq L1. Plate 11-6 shows the changes in pH for northeastern lakes
at 50 years as projected by MAGIC. MAGIC projects the greatest change for the lowest ANC group. For
this group the change projected by ILWAS is virtually identical to that projected by MAGIC. Projections by
ILWAS and ETD for the higher ANC groups are somewhat greater than projections by MAGIC (see Section
10).
Model projections indicate a mixed response of northeastern lake systems at current levels of sulfur
deposition. Slight decreases in median ANCs are projected for all ANC groups, along with a slight increase
in the number of systems with ANC < 0 ^eq L1. The number of systems having ANC < 50 /*eq L'1 (and
thus potentially susceptible to episodic acidification), however, is not projected to change appreciably.
Projected responses to decreased sulfur deposition show a clearer pattern; MAGIC projects surface water
ANCs to increase and the number of lakes with ANC <0 /jeq L1 and ANC <50 peq L1 to decrease. Such
a response would be consistent qualitatively with reported changes in the chemistry of lakes near Sudbury,
Ontario, following reductions of sulfur dioxide emissions from the Sudbury smelter (Dillon et al., 1986;
Hutchinson and Havas, 1986; Keller and Pitbaido, 1986).
807
-------
Plate 11-3. Change in median ANC of northeastern lakes at 50 years as projected by MAGIC (see
Section 1.3.4 for definition of the deposition scenarios used).
808
-------
CHANGE IN MEDIAN ANC
Year 10 to Year 50
Model = MAGIC
-------
Table 11-1. Weighted Median Projected Change in ANC at 50 Years for
Northeastern DDRP Lakes
<0
ANC Group (neq L1)
0-25 25-100 100-400
Target
Population
162
Change in Median faeq L"1) -2
(deposition = constant)3
Change in Median (/j.eq L'1) 5
(deposition = decreased)
398
-2
10
1054
-1
10
1612
15
See Section 1.3.4 for definition of the deposition scenarios used.
809
-------
Plate 11-4. ANCs of northeastern lakes versus time, as projected by MAGIC for constant sulfur
deposition.
810
-------
ANC vs. TIME
Mode I - MAGI C; Depos i t i on
ANC Group(s) = A
= Constant
Maximum
3rd Quartile i
(1.5 x Interquartile Range)"
3rd Quartile
Mean
Median
1st Quortile
1st Quartile -
(1.5 x Interquartile Range)"
Minimum
Not to exceed extreme value.
'YEAR 0 = Phast I NSWS Sample
-------
Plate 11-5. ANCs of northeastern lakes versus time, as projected by MAGIC for decreased sulfur
deposition.
811
-------
ANC vs, TIME
Mode I = MAG 1C; Deposition
ANC Group(s) = Al
= Decreased
Maximum
3rd Quartile -f
(1.5 x Interquartile Range)"
3rd Quortile
Mean
Median
1st Quartile
1st Quartile -
(1.5 x Interquartile Range)"
Minimum
Not to exceed extreme value.
NSWS Sample
-------
Table 11-2. Lakes in the NE Projected to Have ANC Values <0 and <50 ueq L'1
for Constant and Decreased Sulfur Deposition8-1*
Time from
Present (yr)
°NSWS *
°calibrated *
20 #
50 #
Constant
ANC <0
162d
5
161e
5
161 (245)
5(8)
186 (251)
6(8)
Deposition
ANC <50
880d
27
648e
20
648 (319)
20 (10)
648 (329)
20 (10)
Decreased
ANC <0
162d
5
161e
5
136 (230)
4(7)
87 (237)
3(7)
Deposition
ANC <50
880d
27
648e
20
621 (313)
19 (10)
586 (331)
18 (10)
Projections are based on 123 lake/watersheds successfully calibrated by MAGIC. Projections at 20
and 50 years are based on the MAGIC calibrated values at year 0. The calibrated values at year 0
can vary from the values observed by the NSWS (see footnote "e" this table and also Rgure 10-42).
If modelled changes in ANC are combined with observed NSWS ANC values at year 0 (rather than
with model-calibrated ANC at year 0), resulting projections of ANC in years 20 and 50 are obtained
that sometimes differ from the values given here (for example, 248 lakes [rather than 186] would be
projected to be acidic at year 50 under current levels of deposition). Projections presented in
this table, therefore, are best used to indicate the direction and relative magnitude of potential
b changes rather than absolute numbers of systems with ANC values less than 0 or 50 ^eq L"1.
See Section 1.3.4 for definition of the deposition scenarios used.
# is the number of lakes; % is percent of the target population of 3,227 lakes; () indicate 95
percent confidence estimates relative to NSWS estimates at year 0.
Indicates estimate from NSWS Phase I sample for the same 123 lakes; target population = 3 227
lakes.
# is the number of lakes and % is the percent of target population of 3,227 lakes as estimated
from the MAGIC calibration to the NSWS Phase I sample.
812
-------
Plate 11-6. Changes in median pH of northeastern lakes at 50 years as projected by MAGIC (see
Section 1.3.4 for definition of the deposition scenarios used).
813
-------
CHANGE IN MEDIAN pH
Year 10 to Year 50
Model = MAGIC
-------
Because of the highly organic nature of some soils in the NE, the exact nature of chemical "recovery1
of northeastern lakes is uncertain. To our knowledge, there are no field studies in that region that carefully
document such a situation over a sufficient time period to cast much light upon this subject. As discussed
in Section 1, it has been hypothesized that leaching of organic acids could be controlled by changes in soil
water pH (e.g., as caused by acidic deposition) and that this, in turn, could have important effects on surface
water pH values (Krug and Frink, 1983; Krug, 1989). In this hypothesis, a decrease in precipitation acidity
would result in an increase in leaching of organic acids to surface waters, partially offsetting (i.e., toward
lower pH) pH increases associated with the "improved" chemical quality of the atmospheric deposition.
Recently, Wright et al. (1988) noted such an effect in a stream catchment in Norway where acidic deposition
was excluded and reconstituted, more circumneutral waters were substituted as "rain". The catchment
studied by Wright et al. (1988) has extremely thin, organic soils and, thus, is a site almost ideally suited to
the observation of such an effect. Wright et al. (1988) noted that in other areas of Norway having soils of
a more mineral nature (and probably much more similar to soils of the type found on DDRP northeastern
study sites) the potential for enhanced mobilization of organic anions would likely be much suppressed and
minor relative to the effects of decreasing sulfur deposition.
Even if there was an appreciable increase in organic acid leaching as a response to reduced
deposition acidity, the net effect would be beneficial to aquatic biota inasmuch as it would most likely be
accompanied by reductions in surface water concentrations of inorganic monomeric aluminum, which is
highly toxic to fish (Baker and Schofield, 1982).
Thus, although the exact chemical response of the northeastern DDRP systems is unknown,
projections indicate an improvement in surface water quality as a consequence of reduced sulfur deposition
in the region.
11-3.2 Southern Blue Ridoe Province
Plate 11-7 and Table 11-3 illustrate the projected changes (MAGIC model) in median ANC at 50 years
for stream reaches in the SBRP. The MAGIC model used in this analysis was successfully calibrated to 32
of the 35 DDRP SBRP stream reach watersheds. Two stream reaches had ANC > 1000 neq L"1 and were
dropped from this presentation. The remaining 30 stream reaches had ANC > 25 /zeq L"1 and < 400 fieq
L1 and represent a target population of 1,323 stream reaches in the SBRP. The projected changes in median
ANCs have been computed for the same ANC groups (25 -100 /jeq L1 and 100 - 400 //eq L1) as for the
NE (Plate 11-3). Plates 11-8 and 11-9 illustrate the overall projected ANCs for the target population at 20,
50, 100, and 200 years for the current and increased deposition scenarios, respectively.
Table 11-4 presents the population estimates (with 95 percent confidence intervals) of SBRP stream
reaches having ANC <0 Meq L"1 and <50 peq L"1 at 20 and 50 years as projected by the MAGIC model for
the two deposition scenarios. The 95 percent confidence intervals about these projections are broad but
understandable, given the low number of systems available for simulation (30) and the inherent uncertainties
involved in such a complex simulation of environmental response.
814
-------
Plate 11-7. Change in median ANC of Southern Blue Ridge Province stream reaches at 50 years as
projected by MAGIC (see Section 1.3.4 for definition of the deposition used).
815
-------
CHANGE IN MEDIAN ANC
Year 10 to Year 50
Model = MAGIC
ncreased
5 Deposition
-------
Table 11-3. Weighted Median Projected Change in ANC
at 50 Years for DDRP SBRP Stream Reaches
ANC Group Cueq L'1)
(deposition = constant)
25-100
100-400
Target
Population
Median Change (p
eq L1)
. .\ 9
407
-14
916
-24
Median Change (/jeq L1)
(deposition = increased)
-20
-34
aSee Section 1.3.4 for definition of the deposition scenarios used.
816
-------
Plate 11-8. ANCs of Southern Blue Ridge Province stream reaches versus time, as projected by
MAGIC for constant sulfur deposition (see Section 1.3.4 for definition of the deposition scenarios
used).
817
-------
ANC vs, TIME
Model = MAGIC; Deposition = Constant
ANC Group(s) = <400 ueq I/1
3rd Quariile +
(1.5 x Interquartile Range) '
3rd Ouorlile
Uean
Median
Is! Quortile
1st Quortile -
(1.5 x Interquartile Ronge) '
'YEAR 0 = NSS SdmpU
' Not to exceed extreme value.
-------
Plate 11-9. ANCs of Southern Blue Ridge Province stream reaches versus time, as projected by
MAGIC for increased sulfur deposition (see Section 1.3.4 for definition of the deposition scenarios
used).
818
-------
r
ANC vs, TIME
Model = MAGIC; Deposition = Increased
ANC Group(s) = <400 ueq L'
-i
3rd Quarlile
(1.5 x Interquartile Range
1st Quortile
1st Quortile - .
(1.5 x Interquartile Range) *"
'YEAR 0 = NSS Sample
1 Not to exceed extreme value.
-------
Table 11-4. SBRP Stream Reaches Projected to Have ANC Values <0 and
<50 //eq L'1 for Constant and Increased Sulfur Deposition8^
Time from
Present (yr)
°NSWS f
0 *e
calibrated £"
20 #
50 #
Constant
ANC <0
Od
0
oe
0
0
0
129 (295)
10 (22)
Deposition
ANC <50
58d
4
187e
14
187 (310)
14 (23)
203 (333)
15 (25)
Increased
ANC <0
Od
0
Oe
0
0
0
159 (291)
12(22)
Deposition
ANC <50
58d
4
187e
14
187 (314)
14 (24)
340 (359)
26 (27)
Projections are based on 30 stream/watersheds successfully calibrated by MAGIC. Projections at 20
and 50 years are based on the MAGIC calibrated values at year 0. The calibrated values at year 0
can vary from the values observed by the NSWS (see footnote "e" this table and also Figure 10-70).
If modelled changes in ANC are combined with observed NSWS values at year 0 (rather than with
model-calibrated ANC at year 0), resulting projections of ANC in years 20 and 50 are obtained that
sometimes differ from the values given here (for example, zero stream reaches [rather than 129]
would be projected to become acidic by year 50 under current levels of deposition; also, although
projections from the ILWAS model for median regional decreases in ANC over 50 years are comparable
to those projected by MAGIC for the same watersheds [see Table 10-15], ILWAS does not project any
SBRP watersheds to become acidic by year 50). Projections presented in this table, therefore, are
best used to indicate the direction and relative magnitude of potential changes rather than absolute
numbers of systems with ANC values less than 0 or 50 peq L"1.
See Section 1.3.4 for definition of the deposition scenarios used.
# is the number of stream reaches; % is percent of the target population of 1,323 stream
d reaches; () indicate 95 percent confidence estimates relative to NSWS estimates at year 0.
Indicates estimate from NSWS Pilot Stream Survey sample for the same 30 stream reaches;
target population = 1,323 stream reaches.
# is the number of stream reaches and % is the percent of the target population of 1,323 stream
reaches as estimated from the MAGIC calibrations to the NSWS Pilot Stream Survey sample.
819
-------
Plates 1 1 -1 0 and 1 1 -1 1 show decreases in pH of SBRP stream reaches as projected by MAGiC and
ILWAS, respectively, for the increased sulfur deposition scenario. Changes projected by the two models
are highly comparable.
Model projections for the SBRP stream reaches indicate decreased surface water quality under
scenarios of either current or increasing sulfur deposition. As noted in Sections 9 and 10, responses to
changes ,n sulfur deposition levels in the SBRP are projected to be slower than those in the NE- i e
there is a considerable lag in the response of the systems due to the storage of sulfur in the soils ' The
result is that there is a delay not only in the acidification of surface waters in the region, but also in any
potential recovery if sulfur deposition were to be decreased. Due to the fact that soils in this region are
much less organic in nature than those in the NE (e.g., wetlands in the SBRP are virtually non-existent-
mean stream DOC at lower nodes was <1 mg L~\ these model projections are uncomplicated by
potential effects of organic acid leaching.
Projections of stream water quality response for the DDRP SBRP target population clearly indicate
future adverse effects of sulfur deposition at increased or current levels.
11.4 SUMMARY DISCUSSION
The NE is currently at sulfur steady state and sulfate concentrations in surface waters would
respond relatively rapidly to decreases in sulfur deposition. Associated with these changes would be
increases in surface water ANC. Continued sulfur deposition at current levels is gradually depleting the
cat,on exchange pool in northeastern soils with consequent decreases in surface water ANC Such
changes are relatively slow and minor, however, relative to direct effects of increased anion mobility in
watersheds on surface water chemistry.
H *" ^ CUITently retai"nin9 "^ ^ee^^^ of the atmospherically
the average but soils are projected as becoming more saturated with regard to sulfur
?, nr? TT Ttl0nS ^ Pr°JeCted t0 bS inCreaSI'ng iP the SUrfaCe Waters of the re9jon- ™« response
•s projected to be marked over the next 50 years at either current or increased levels of sulfur deposition
as are decreases in stream water ANC. Superimposed upon this effect is a relatively minor acidification
effect of base cation depletion.
fGaHow o °\DDRP ana'yses are
-------
Plate 11-10. Changes in pH of SBRP stream reaches as projected by MAGIC (see Section 1.3.4 for
definition of the deposition scenarios used).
821
-------
pH vs, TIME
Model = MAGIC; Deposition = Increased
ANC Group(s) = <400 ueq I/1
3rd Quorlile +
(1.5 x Interquartile Range)'
3rd Ouartile
Uedion
1st Quortile
1st Quortile -
(1.5 x Interquartile Ronge)"
'YEAR 0 = Uodel Year 0
1 Not to exceed extreme voltie.
-------
Plate 11-11. Changes in pH of SBRP stream reaches as projected by ILWAS (see Section 1.3.4 for
definition of the deposition scenarios used).
822
-------
pH vs, TIME
Model = ILWAS; Deposition = Increased
ANC Group(s) = <400 ueq I/1
'YEAR 0 = yodel Year 0
3rd Quartile
1.5 x Interquartile Range}'
1st Quartile
1s,i Quartile -
1.5 x Interquartile Range)'
1 Not to exceed extreme value.
-------
SECTION 12
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855
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SECTION 13
GLOSSARY
13.1 ABBREVIATIONS AND SYMBOLS
13.1.1 Abbreviations
ADS
AERP
ANC
AREAL-RTP
CDF
Cl
CIR
Acid Deposition System
Aquatic Effects Research Program
Acid neutralizing capacity
USEPA Atmospheric Research and Exposure Assessment Laboratory - Research
Triangle Park
Cumulative distribution function
Confidence interval
Color infrared photography
DDRP
DEM
DOC
DQO
ELS-I
EMSL-LV
EPA
EPRI
ERL-C
ERP
ETD
GIS
IBM PC
ILWAS
IQR
LAI
LTA
Direct/Delayed Response Project
Digital elevation models
Dissolved organic carbon
Data quality objective
Eastern Lake Survey-Phase I
USEPA Environmental Monitoring and Systems Laboratory - Las Vegas
U.S. Environmental Protection Agency
Electric Power Research Institute
USEPA Environmental Research Laboratory - Corvallis
Episodic Response Project
Enhanced Trickle Down Model
Geographic Information System
International Business Machines Corporation - personal computer
Integrated Lake/Watershed Acidification Study
Interquartile range
Leaf area index
Long-term annual average deposition
856
-------
MAGIC
MLRA
NAS
NADP/NTN
NAPAP
NCDC
NE
NHAP
NOAA
NRC
NSS-I
NSWS
ORNL
OTA
PCA
PNL
QA
QC
RADM
RELMAP
RCC
RILWAS
RMSE
RSD
SAB
SAS
SBR
SBRP
SCS
SE
SOBC
SOEBC
SUNY-P
TMY
Model for Acidification of Groundwater in Catchments
Major land resource areas
National Academy of Sciences
National Acid Deposition Program/National Trends Network
National Acid Precipitation Assessment Program
National Climatic Data Center
Northeast Region
National High Altitude Photography
National Oceanographic and Atmospheric Administration
National Research Council
National Stream Survey-Phase I
National Surface Water Survey
Oak Ridge National Laboratory, Tennessee
Office of Technology Assessment
Principal component analysis
Battelle-Pacific Northwest Laboratories
Quality assurance
Quality control
Regional Acid Deposition Model
Regional Lagrangian Model of Air Pollution
Regional Coordinator/Correlator
Regional Integrated Lake/Watershed Acidification Study
Root mean square error
Relative standard deviation
Science Advisory Board
Statistical Analysis System
Southern Blue Ridge
Southern Blue Ridge Province
Soil Conservation Service
Standard error
Sum of base cations
Sum of exchangeable base cations
State University of New York, Pittsburgh
Typical meteorological year
857
-------
UMW
UDDC
USDA
USDOI
USFS
USGS
UTM
WA
WBA
Upper Midwest
Unified Deposition Database Committee
U.S. Department of Agriculture
U.S. Department of Interior
U.S. Forest Service
U.S. Geological Survey
Universal Transverse Mercator
Watershed area
Watershed Based Aggregation
13.1.2 Symbols
2As
2Bn
2Cn
2X
3A
3B
A
AC_BaCI
AH
AL
AI_AO
AI_CD
AI_PYP
AI3+
ALPOT
ANN_AVG
AVG_EL
AW
B_CENT
B_LEN
B_PERIM
B SHAPE
Southern Blue Ridge subregion (NSS Pilot Survey)
Valley and Ridge subregion (NSS Pilot Survey)
Northern Appalachians subregion (NSS Pilot Survey)
Southern Appalachians subregion (NSS Pilot Survey)
Piedmont subregion (NSS Pilot Survey)
Mid-Atlantic Plain subregion (NSS Pilot Survey)
acid that is leached out of the soil
barium chloride triethanolamine exchangeable acidity
area of all open water bodies in drainage basin, in kilometers squared
area of primary lake, in kilometers squared
aluminum, acid oxalate extractable
aluminum, citrate dithionite extractable
aluminum, pyrophosphate extractable
aluminum ion
aluminum potential (pH - 1/spAI)
flow-weighted annual average sulfate concentration
average elevation; (MAX_ELEV + MIN_ELEV)/2, in meters
total watershed area, in kilometers squared
drainage basin centroid expressed as an X,Y coordinate
length of drainage basin: air-line distance from basin outlet to farthest upper point
basin, in kilometers
the length of the line which defines the surface divide of the drainage basin, in
kilometers
basin shape ratio; B_LEN2/WS_AREA
858
-------
B_WIDTH
BS Cl
C
C_TOT
Ca + Mg-DRY
Ca+Mg-WET
Ca_CI
Ca2+
CaCI2
CEC_CI
cr
C02
COMPACT
DDENSITY
ELONG
FRAG
LJ +
total
H20_WS
H2O
H2S04
H5up
ha
HC03-
H-DRY
H-WET
I
IND_AVG
INT
K
average basin width; WS_AREA/B_LEN, in kilometers
base saturation calculated from unbuffered 1N ammonium chloride CELod
exchangeable bases
correction factor for the decrease in acidity due to the protonation of bicarbonate
carbon total
the annual loading of Ca plus Mg in dry deposition
the annual loading of Ca plus Mg in wet deposition
exchangeable calcium in unbuffered 1N ammonium chloride
calcium ion
calcium chloride
unbuffered 1N ammonium chloride cation exchange capacity
chloride ion
carbon dioxide
compactness ratio; ratio of perimeter of basin to the perimeter of a circle with equal
area; (PERIM)/(2 * (* AJ5)
drainage density; TOTSTRM/WS_AREA
elongation ratio; (4 * WS_AREA)/L_BEN
fragments > 2 mm diameter
hydrogen ion
total effective acidity (H+ + NH4+ - NO3")
ratio of open water bodies area to total watershed area; H20_AREA/ws_area
water
sulfuric acid
the percent of a watershed covered by bedrock with sensitivity codes of 5 and 6
hectare (2.47 acres or ten thousand square meters)
bicarbonate ion
annual hydrogen ion loading in dry deposition
annual hydrogen ion loading in wet deposition
amount of effective acidity in deposition
flow-weighted average sulfate concentration for the index sample time frame (spring
or fall)
total length of intermittent streams as defined from USGS topographic maps of
aerial photos, in kilometers
hydraulic conductivity.
859
-------
K+
K_CI
Keq ha"1
kg
km
kso4
L_CENT
L_PERIM
LIMEPOT
ln(a/TanB)
ln(a/KbTanB)
LTA-rbc
LTA-zbc
M_PATH
M04
MAX_EL
MAX_REL
"1
mg
Mg_CI
Mg2+
MINEL
Na+
Na_CI
NECMPON
NECMPOS
NEIDLGD
NH/
potassium ion
exchangeable potassium in unbuffered 1N ammonium chloride
Kiloequivalent per hectare
kilogram
kilometer
sulfate mass transfer coefficient (m yr"1)
primary lake centroid expressed as X,Y coordinates
perimeter of primary basin lake, in kilometers
lime potential (pH - i/apCa)
an index of flowpath partitioning used in the TOPMODEL hydrologic model
an index of flowpath partitioning used in the TOPMODEL hydrologic model
long-term annual average, reduced dry base cation
long-term annual average, zero dry base cation
estimate of mean flowpath, in meters
miscellaneous land area mapped as quarry pits
elevation at approximately highest point, in meters
maximum relief; MAX_ELEV - MIN_ELEV, in meters
microequivalents per liter, unit of concentration
milligram
exchangeable magnesium in unbuffered 1N ammonium chloride
magnesium ion
elevation of primary lake, in meters
sodium ion
exchangeable sodium in unbuffered 1N ammonium chloride
data file with soil and miscellaneous area components of map units for the DDRP
Northeast region
map unit composition data file for the DDRP Northeast region
identification legend data file for the DDRP Northeast region
ammonium ion
nitrate ion
hydroxide ion
860
-------
PC02
PER_DD
PERIMRAT
PERIN
PH_01M
PH H2O
REL_RAT
ROTUND
RTR
S
SBC_CI
Sd ~
SE_MP_CM
SE_MP_UN
SECMPNT
SEDBMNT
Si02
SO4_B2
SO4_EMX
SO4_H2O
SO4_PO4
SO4_SLP
SO4_XIN
S042'
SO4-DRY
SO4-WET
[S042-]ss
SOILDEN
partial pressure of carbon dioxide
drainage density calculated from perennial streams only; PERIN/WS_AREA
ratio of the lake perimeter to the watershed perimeter; Lake Perimeters/B_PERIM
total perennial stream length as defined from USGS topographic maps and aerial
photos, in kilometers
pH (0.01 M CaCI2)
pH (deionized water)
runoff estimate (length time"1)
Average annual runoff; interpolated to each site from Krug et al. (in press) runoff
map, in centimeters
correlation coefficient
coefficient of determination, the proportion of variability explained by a regression
model
relief ratio; (MAX_ELEV-MIN_ELEV)/B_LEN
rotundity ratio; (B_LEN)2/(4 * WS_AREA)
lake retention time, in years
sum of base cations
sum of base cations as measured in unbuffered 1N ammonium chloride
dry sulfur deposition (mass length'2 time-1)
map unit composition data file for the DDRP Southern Blue Ridge region
map unit identification legend data file for the DDRP Southern Blue Ridge region
data file with soil and miscellaneous area components of map units for the DDRP
Southern Blue Ridge region
Southern Blue Ridge Mapping Database Management System
silicon dioxide
half saturation constant
adsorption asymptote
sulfate, water extractable
sulfate, phosphate extractable
slope of sulfate adsorption isotherm at zero net adsorption
zero net adsorption concentration for sulfate, determined from adsorption isotherms
sulfate
annual loading of sulfate in dry deposition
annual loading of sulfate in wet deposition
steady state sulfate concentration
soil bulk density
861
-------
STRMORDER
SUB_BAS(n)
THKA
TOT_DD
TOTSTRM
V6
WA:LA
WM_PATH
WS_AREA
WS LA
surface water sulfur (mass length"3)
maximum stream order (Horton) of streams in the watershed
area of each subcatchment in the drainage basin, in kilometers squared
wet sulfur deposition (mass length'2 time'1)
soil thickness, adjusted for FRAG
estimated drainage density based on crenulations
identified on topographic map
total stream length; combination of perennial and intermittent, in kilometers
hydraulic residence time, in years
hydrologic retention time, in years
volume of primary lake, 106m3
watershed area to lake area ratio
estimate of weighted mean flowpath, in meters
total watershed area, in kilometers squared
ratio of the total watershed area to the area of the primary lake
13.2 DEFINITIONS
texa soiutiono ** appr°ximate solution obtai^ using a numerical mode, and
the exact so ution of the govern.ng equations (or a known standard concentration), divided by the exact
solution (or known standard concentration). Y
ACID ANION - negatively charged ion that combines with hydrogen ion to form an acid.
"**" '
produce
ions-
Sx.DA?ION fnE " Tff WJth hjgh C0ncentration of meta|s. sulfate, and acidity resulting from the
OXIDATION of sulf.de mmerals that have been exposed to air and water (usually from mining activities).
862
-------
an
to
° <
" B"
W'" a" AC'D NSJTRAUZIN8 CAPACITY less than or
ACID
crY. h exp9rienced any temporary or permanent •»•
CAPACITY or a so.l that has experienced a reduction In BASE SATURATION.
USed to transfom <=oncen,ra«on data to sal,
anaiysis' modffied
AFFORESTATION - the natural process through which non-forested lands become forested
AGGRADING FORESTS - forests in which there Is a net annual accumulation of biomass.
a set of data to a sinaie °aicuiated °
SO"S W*h an
35 percent
The
may
a spunous periodic solution or mask a real periodic phenomenon.
863
-------
^^^
^^^
"
*"»— •*"* commonly .hough, ,o be a pre.
in
ALUMINUM BUFFER RANGE - pH 4.2 - 2.8
either an acid °r
ANAEROBIC - without free oxygen (e.g., hypolimnetic lake waters, sediments, or poorly drained soils).
ANALYTE - a chemical species that is measured in a water soil, or tissue sample.
• physicai and chemicai ™s °- — «*
ANALYTICAL DUPLICATE - a QUALITY CONTROL sample made by splitting a sample.
ANION - a negatively charged ion.
ANION CATION BALANCE - a method of assessing whether all CATIONS and ANIONS have been
^
^ *• - in whlc, ANIONS are
ANTHROPOGENIC - of, relating to, derived from, or caused by human activities
-imate form °f a
or actions.
AQUEOUS SPECIES - any dissolved ionic or nonionic chemical entity.
864
-------
AQUIC - a moisture regime of soils in which a water table and reducing conditions occur near the
SUfTaCG.
AQUIFERS - below-ground stratum capable of producing water as from wells or springs.
AQUO LIGAND - a water molecule held to Fe or Al in a clay edge or hydrous oxide by ligand exchange.
ARC -represents line features and borders of area features. One line feature may be made up of many
arcs. The arc is the line between two nodes.
ARC/INFO - a commercial geographic information system (GIS) software used to automate, manipulate
analyze, and display geographic data in digital form.
' CharaCteriStiCS °r Other Pr°Perties associated with a specific feature, area on a
AVAILABLE TRANSECT - a transect identified to represent a map unit and listed for random selection.
BASE CATION - a nonprotolytic CATION that does not affect ACID NEUTRALIZING CAPACITY- consists
principally of calcium, magnesium, sodium, and potassium.
BASE CATION EXCHANGE - the process by which BASE CATIONS (Ca2+ Mg2+ Na+ K+) are
adsorbed or released from negatively charged sites on soil particles from or to, respectively, soil solutions
buch exchange processes are instrumental in determining pH of soil solutions.
h* CAT'°NhS"PPLY - 0).«he POO. of BASE CAT.ONS (Ca2+, Mg2+, Na+, K+) in a soil availab.e for
exchange with hydrogen ,ons (H+). The base cation pool is determined by the CATION EXCHANGE
CAPACITY of the soil and the percentage of exchange sites occupied by BASE CATIONS.
BASE SATURATION - the percentage of total soil CATION EXCHANGE CAPACITY that is occupied by
exchangeable cations other than hydrogen and aluminum, i.e., the base cations Ca2+, Mo2-, Na+, and
BEDROCK - solid rock exposed at the surface of the earth or overlain by unconsolidated material.
BEDROCK GEOLOGY - the physical and chemical nature and composition of solid rock at or near the
earth s surface.
BEDROCK LITHOLOGY - see LITHOLOGY.
BEDROCK SENSITIVITY SCORES - a six point sca.e, developed for DDRP, designed to distinguish the
relative reactivities of different lithologies.
BEDROCK UNITS - the smallest homogenous entity depicted on a bedrock map.
865
-------
B.AS - a systematic error in a method caused by artifacts or idiosyncracy of the measurement system.
B10MASS - the quantity of paniculate organic matter in units of weight or mass.
e°n
func,,ons
from
""
samp,e with
°' a U°'Ume °' «* ""**• "« "-». «• solutions, vote,
CALCITE - a mineral with the formula CaCO3. A carbonate mineral
^^
C°NTBOL
contains on,y the
°f 3 SyStem defined as a function °f the quantity or size of
ag" SU'fate ads°rption or cation e-hange) for which
866
-------
CARBON-BONDED SULFUR - a reduced form of organic sulfur, charactered by C-S bonds.
reactions gene n
CATCHMENT - see WATERSHED.
CATION - a positively charged ion.
"' ra*°"+"°** '" — '• Association
°' " * ^"^ "
' in which ACIDI° OATIONS
CATiON EXCHANGE CAPACITY - the sum total of exchangeable cations tna, a soil can absorb.
- •* '
CHRONIC ACIDIFICATION - see LONG-TERM ACIDIFICATION.
C.RCUMNEUTRAL - close to neutrality with respect to PH (pH = 7); in natural waters, pH 6 - 8.
^
"
*" *- "*
'" • - °' temperature
CLOSED LAKES - a lake with a surface water inlet but
no surface water outlet.
COLLINEAR - see MULTICOLLINEARITY.
867
-------
°r more dissimiiar
COMPONENTS - see MAJOR COMPONENTS, MINOR COMPONENTS, and MAP UN.T COMPOS.TION.
CONSOCIATION - a map unit dominated by a singie soil taxon (or miscellaneous area) and similar soils.
CONTOUR LINE - a line connecting the points on the land surface that have the same elevation
COOK'S D - a regression statistic designed to indicate LEVERAGE POINTS.
COVERAGE - a digital analog of a single map sheet; forms the basic unit of data storage in ARC/INFO
=-
DATABASE FILE - a collection of records that share the same format.
t0 the 6arth>S Surface * -y of a number of chemical
DEPTH TO BEDROCK - depth to solid, fixed, unweathered rock underlying soils.
LAYER - depth to a layer in soils or
!.g., bedrock, dense till or fragipan).
SAMPLE - a QUALITY CONTROL sample that contains the ANALYTE
:he contract required detection limit.
DIAZO - a photocopy whose production involves the use of a coating of a diazo compound.
DIGITIZATION - the process of entering lines or points into a GEOGRAPHIC INFORMATION SYSTEM.
868
-------
COORDINATES - lines or points that have been entered into a GEOGRAPHIC INFORMATION
REDUCTION - a
'" «*"* ^ oxidized chemical species (e.g., SO, - S) i
in the absence <* free
is
DISSOCIATION - separation of an acid into free H* and the conjugate base of that acid (e.g.. H,CO -
NH4OH -> rS/ " OrT"0" * ' **** "° " "" ^'^ "" *"' ^'"^^ ^ °' the ""«
-------
iakes sampied
by
" '" S°"
°RDER °' mi"6ra' S°"S Wlth "° <* ™y P°°"/ developed genetic
CAPAC.TV dunng s,orm ,,cws
" "
" S°" °r9anl°
characterized by 0-0-SO3 or N-
CATI°NS '" **
EXTENSIVE PAPAMETERS - variables that depend on the size (extent) of the
that
in exchange
system.
FELDSPARS - a group of tectosilicate minerais that are the most abundant group in the earth's crust
of boundaries, and map detail in relation to survey objectives. Placement
870
-------
°< tores< ta" "—i on present occupancy of an
ers;
roughly 3.5. p = 1'0) fractlon of an alkali-soluble soil extract; pK
GAINES THOMAS FORMULATION - a formu.ation used to describe exchange processes.
GAPON - a formulation used to describe exchange processes.
GENERIC BEDROCK TYPE - see GENERIC ROCK TYPE.
GENERIC ROCK TYPE - a general classification of different BEDROCK i INIITQ int
the primary LITHOLOGY. BCUHUOK UNITS into groups according to
GEOGRAPHIC INFORMATION
-------
GREAT GROUP - in Soil Taxonomy, the level of classification just below SUBORDER, e.g., Haplorthods.
GROUNDWATER - water in the part of the ground that is completely saturated.
HETEROSCEDASTIC - referring to a statistical situation in which variances are not all equal
condition as
HISTIC SOILS - organic-rich soils.
HISTOSOLS - in Soil Taxonomy, the ORDER of soils formed from organic PARENT MATERIAL
HOMOSCEDASTIC - referring to a statistical situation in which the variances may all be considered
physioai and/or
HYDROLOGIC RETENTION TIME - see HYDRAULIC RESIDENCE TIME.
csr r,
872
-------
o™* '™
<* a"
(-Pec,a»y S or N) to
nstructlon - a dam: ais°
INCLUSIONS - see MINOR COMPONENTS.
average annual runofl.
poten"ai °f °°ntact
"*"* "°W rate
-------
shorthand ,o desc^lZn "" ° C°mP°UndS °" S* b"-1" th<* «"«• *
KAOLINITE - a two-layer day mineral with the chemical formula ALSLO (OH)
2 2 5* '4"
KRIGING - a technique for spatial interpolation.
LABEL - represents point features or is used to assign identification numbers to POLYGONS.
°f ^' — s, and dams as
LAND COVER - see FOREST COVER TYPE.
LAND USE - the dominant use of an area of land (e.g., crop land).
'" °' «" to' -*™ « * -** related ,o Escape
pTcesles™
LANGMUIR ISOTHERM - hyperbolic adsorption isotherm (used in this proiec, for sulfate) o, the form
LARGE-SCALE MAPS - 1:24,000, 1:25,000, or 1:62,500 sca,e U.S. Geological Survey topographica, map,
LEACHING - the transport of a solute from the soil in the soil solution.
LEVERAGE POINT - a data point that strongly influences the parameter estimates in a regression
LIMESTONE - a rock type consisting primarily of CALCITE.
LINEAR BUFFER - land area within a set distance of a lake or stream.
874
-------
rock or
BEDROCK
• *""
USUa"y
etc., ,ha, compose ,he bu,k of ,he
landform "»' is *•'—• ^ tocalfced landscape
LOWER NODE - the downstream NODE of a STREAM REACH.
area characterized by
°r miSCe"aneOUS
are identified in the name of a
MALLOWS' CP - a criterion for selecting one of a sequence of regression models.
MAP COMPILATION - the process of checking and measuring soil map unit data.
MAPP.NG PROTOCOLS - instructions that guide the fie,d mapping and provide for quaiity control.
MAP SYMBOL - a symbol used on a map to identify map units.
MAPPING TASK LEADER - the person responsible for field mapping activities.
MAP UNIT - see SOIL MAP UNIT.
P~
of a,, sol, components and
a DATABASE FILE that contains a" components and
(c°mp0nents are identified by an assigned code, i.e.,
MAP UNIT CORRELATION - see SOIL CORRELATION.
875
-------
™nh °" 3 maP Unique'y identified with a sVmbo1- A delineation of a soil
map has the same major components as identified and named in the map unit.
as
th
C°EfT'CIEIIT8 '
^ t
—ation-of-mass
r "*' COnStant USed in models of "^ alkalinity
rem°Val rate of a reactant from «lullon. Specific
andiffusion S6diment by a" pr°CeSSeS' includi"9 sedimentation
for sSracrossr" T H-' 6 ^ tranSfer C°effiCient f°r SU'fUr iS eSSentia"y a diffusion ~
for sulfate across the water-sed.ment interface; for nitrate a biological uptake/sedimentation rate.
MASTER HORIZONS - the most coarsely based delineations within a pedon. Usually A/E horizons
"' B horbons ar
i"9 known
, ^ ANAL/TE to a
3iiquot.
MAX - the maximum sensitivity code observed on a WATERSHED.
MEAN - the weighted average of sensitivity codes for a WATERSHED.
MEDIAN (M) - the value of x such that the cumulative distribution function F(x) = 0.5; the 50th percentile.
METASEDIMENTARY - rocks or bedrock formed from metamorphosis of sedimentary rocks.
MICAS - a group of primary phylosilicate minerals, frequently including biotite and muscovite.
REG'°N " ^ °f *" *"* ^oac "*** considered by the DDRP, consisting
MINERAL WEATHERING - dissolution of rocks and minerals by erosive forces.
876
-------
™puvs, mlSC*'ne°us — «« « « ktaflM in ,he name of
map unit. Many areas of these components are too small to be delineated separately.
MISCELLANEOUS LAND AREAS - see MISCELLANEOUS AREA
STOCHAST'C
or selection of random numbers to
MOTTLING - spots or blotches of different color in a soil, including gray to black blotches in ooorlv
drarned soils due to presence of reduced iron and other metals. P V
srs^r1*11 processes throu9h wwch **" •*— '- »
NODE - the points identifying either an upstream or downstream end of a REACH.
dO88 nOt make the dassical Distributional
NON-SILICATE IRON AND ALUMINUM - soil iron and/or aluminum occurring in the soil as an
amorphous or a (hydrous) oxide phase rather than as an ion incorporated within a sHicate minS lattice
DESCR1PTION ' a record <* ^ Definitions of a soil series and other relevant
in to h eneS' TheSe definiti°nS are the framework within whi^ ™* of the detailed
inftxmabon about so.ls of the United States is identified with soils at specific places These demons
also provide the principal medium through which detaHed information about the soi and te ^hlvoTa
one place is projected to similar soils at other places. oenavior at
ORDER - in Soil Taxonomy, the highest level of classification, e.g., SPODOSOLS.
ORGANIC ACID - organic compound possessing an acidic functional group; includes fulvic and humic
877
-------
ORGANIC ANION - an organic molecule with a negative net ionic charge.
r^^
'dentfflable M» h°ri2°" »«** '" —- - ^0 percent organic matter
OUTLIER - observation not typical of the population from which the sample is drawn.
lns ' from a lower to a hisher
PARENT MATERIAL - the material from which soils were formed.
S°"
POLYGON - represents area features.
8ample that fe
""e particular
«• Mu-y about , ^ a
whioh 9ases' "quids' or plant roots penetrate
to provwe reproducibie
with
878
-------
e^na newMcoordENtTS " T^T *"" C°mbinations " the «Wha. data, which geometrically
represent a new coordinate system with axes in the directions of maximum variability.
PROBABILITY SAMPLE - a sample in which each unit has a known probability of being selected.
QC CHECK SAMPLE - a QUALITY CONTROL sample that contains the ANALYTE of interest at a
concentration in the mid-calibration range.
StUdy iS adequate'y planned and implemented to
to ensure that data quaiity meets the
°3) that divide a population into four equal classes- each
QUARTZ - a crystalline form of silicon dioxide (SiO2).
QUARTZITES - a metamorphic rock-type composed of primarily QUARTZ.
crernHn ***** ^ ' °2 ' °3 ' ^ ^ dMde 3 P°pulation into five e^' classes,
each representing 20 percent of the population; used to provide additional values to compare
characteristics among populations of lakes and streams. compare
nnt.K '" Weatherin9) for wh^h the long-term ability to supply
ion products (e.g., base cations) is constrained by reaction or transport kinetics.
RCC TRANSECTS - transects conducted by the Regional Coordinator/Correlator (RCC).
Sum rePresented as blue lines on 1 :250,000-scale U.S. Geological
Survey maps. Each reach (segment) is defined as the length of stream between two blue line
confluences. In the NSS-I, stream reaches were the sampling unit.
SIht H^ rf"°"Ship between the rate of « <*emical reaction and the concentration of
substrate, defined by the value of the exponent of, that substrate.
REACTIVITY SCALE - any of a number of relative scales designed to categorize the qeneral
"weatherability" of different LITHOLOGIES. eyunze ine general
REACTIVITY SCORE - see REACTIVITY SCALE.
, that C°ntains a" the rea9ents used ^d in the same
used in preparing a soil sample for analysis.
879
-------
REDUCTION/OXIDATION - chemical reaction in which substances gain or lose electrons.
.S^ri^ the ?Tt6rminOUS United States where a substantial number of streams with
less than 400 /zeq L can be found.
" PhySI'°graphiC 3reaS that reflect a maJ°r 'and-shaping process over a long
" a correlated and controlled legend for an entire region (see SOIL
S°UrCe-reCept0r model desi9ned to estim*e dry deposition of sulfur; not used directly in
elative to GIS activities> a format designed by the user for printing out information containin9
RESERVOIR - a body of water collected and stored for future use in a natural or artificial lake.
Variable a"d *• value
REUSS MODEL - a numerical model used to describe exchange processes in a soil environment.
RIPARIAN - a zone bounding and directly influenced by SURFACE WATERS.
ROBUST - a statistical procedure that is insensitive to the effect of OUTLIERS.
ROUTINE TRANSECTS - transects conducted by field soil scientists responsible for the mapping.
™« displaced for the soil exchanae complex by
BASE CATIONS (from neutral salts). The result is a short-term increase in the acidity of associated water
SAMPLING CLASS - see SOIL SAMPLING CLASS.
SAMPLING CLASS CODE - a three-character code assigned to each SOIL SAMPLING CLASS.
SAMPLING CLASS COMPOSITION - the relative proportion of sampling classes in a map unit.
nnt 7T T^" ^ "* ^ mm '" diameter; also a soil texture class Gaining at least
percent sand, and whose percentage of silt, plus 1.5 times the percent clay, does not exceed 15.
880
-------
-
(S°
Pr0dUCt (°f diSSOlved ions> to the s°^ility Product
dS 1'°' the SO'Uti0n iS s"P^aturated with respect to
eandu81'0" S6qUenCe f0"OWing imPlementation of a controi or mitigation
strategy and the subsequent effects associated with this deposition sequence.
minerai phase formed
SEEPAGE LAKE - a lake with no permanent SURFACE WATER inlets
or outlets.
*«*•
spec.es ,„ an
SENSITIVITY CODES - see BEDROCK SENSITIVITY SCORES.
SILICA - the dissolved form of silicon dioxide (SiO2).
SILT - a soil separate consisting of particles between 0.05 and 0.002 mm in equivalent diameter- also a
so,l texture class containing at least 80 percent silt and < 12 percent clay.
SILVICULTURAL PRACTICES - forest management practices to increase wood yields- thinning prunina
fertilization, spraying with herbicides/insecticides, and irrigating. 9>
SIMULATION - replication of the prototype using a model.
SKELETAL SOILS - soils with at least 35 percent rock fragments in the control section.
SLOPE PHASE - the slope gradient of a soil map unit or taxonomic unit expressed in percent.
c^vex, plane?
""*"*
°f the landscaPe ^ concave-
SLOPE SHAPE DOWN - shape of the land surface at right angles to the contours of the landscape.
SMALL-SCALE MAP - 1 :250,000-scale U.S. Geological Survey map.
881
-------
SMECTITES - a family of three-layer day minerals.
'hat Sen/es as a natural ""*"" *»• «*>
,o°h?sys,emR'NG
' *"
fr°m
" S°" "
'"
«««on o, acids
' 3"
°' 3 S°" ^ »«* » 'hs Absence o, exchange
ln soil Taxonomy in w*h ciasses
SOIL
SOIL LEGEND - see SOIL IDENTIFICATION LEGEND.
mLirousaLc8--!*^0!^?,^^.^ "amed * te™ - •* ~ components or
is uniquely identified c
states-
SOIL SOLUTIONS - those aqueous solutions in contact with soils.
°f
882
-------
SOIL TAXONOMIC UNIT - a kind of soil described in terms of ranges in soil properties of the
polypedons referenced by the taxonomic unit in the survey area.
SOIL TEXTURE - the relative proportion by weight, of the several soil particle size classes finer than 2
mm in equivalent diameter (e.g., sandy loam).
SOIL TEXTURE MODIFIER - suitable adjectives added to soil texture classes when rock fragments
exceed about 15 percent by volume, for example, gravelly loam. The terms "very" and "extremely" are
used when rock fragments exceed about 35 and 60 percent by volume, respectively.
SOIL TRANSECT - a distance on the surface of the earth represented by a line on a map. Transects
can be straight, dogleg, or zigzag.
SOLID PHASE EXCHANGERS - those components of soils, primarily organic matter, clay minerals and
mineral oxides, that serve as the sites for exchange reactions.
SOLUM - soil layers that are affected by soil formation.
SPECIATION MODEL - a numerical model used to describe the distribution of aqueous species among
various possible complexes and ion pairs; usually for the purpose of estimating single ion activities.
SPECIFIC ADSORPTION - adsorption of sulfate by ligand exchange, often involving exchange of two
ligands and formation of a bridged (M-O-SO2-O-M) structure.
SPODIC HORIZONS - a soil horizon in which iron oxides, aluminum oxides, and organic matter have
accumulated from higher horizons.
SPODOSOLS - in Soil Taxonomy, the ORDER of mineral soils with well-developed SPODIC HORIZONS.
SPRING BASEFLOW INDEX PERIOD - a period of the year when streams are expected to exhibit
chemical characteristics most closely linked to ACIDIC DEPOSITION. The time period between snowmelt
and leafout (March 15 to May 15 in the NSS-I) when NSS-I stream reaches were visited coinciding with
expected periods of highest geochemical and assessment interest (i.e., low seasonal pH and
sensitive life stages of biota).
STABILITY (NUMERICAL OR COMPUTATIONAL) - ability of a scheme to control the propagation or
growth of small perturbations introduced in the calculations. A scheme is unstable if it allows the growth
of error so that it eventually obliterates the solution.
STANDARD DEVIATION - the square root of the variance of a given statistic.
STEADY-STATE - the condition that occurs when a property (e.g., mass, volume, concentration) of a
system does not change with time. This condition requires that sources and sinks of the property are in
balance (e.g., inputs equal outputs; production equals consumption).
883
-------
, processss b
, or prevented from reaching receiving SURFACE WATERS
or a compound containing
losss eiectrons
SULFITIC - containing sulfide minerals, usually pyrite.
SURFACE WATER - streams and lakes.
SURFACE WATER RUNOFF - preclpfction ,ha, flows
overiand ,o reach SURFACE WATERS.
SYNOPTPC - re.a,ing ,o or displaying oondMons as they ex,s, a, a poin, in ,ime over a broad area.
commoniy
by
TICS - registration or geographic control points for a COVERAGE.
TILL - unstratified material deposited by glaciers.
TOPMODEL - topographically based, variable
source area hydrologic model.
885
-------
TOPOGRAPHIC MAP - a map showing contours of surface elevation.
TRANSECT - see SOIL TRANSECT.
TRANS^C ™
°f
a'°ng
line (see
TRANSECT POINTS - locations along a TRANSECT where data are collected.
TRANSECT SEGMENT UNION - all transect stops in the same map unit on a WATERSHED.
TRANSECT STOPS - see TRANSECT POINTS.
TRANSFORMATION ERROR - ca.culates the residual mean square error of the digitized TIC locations
ana the existing TICs.
" *
^ *** i
°bservation at unc°ntrolled representative locations in the
TYPICAL YEAR (TY) DEPOSITION DATA - a dataset of atmospheric deposition developed within the
UURP for specific use with the integrated watershed models.
UNCERTAINTY ANALYSIS - the process of partitioning modelling error or uncertainty to four sources-
intrinsic natural variability, prior assumptions/knowledge, model identification, and prediction error.
UNIVERSAL TRANSVERSE MERCATOR (UTM) PROJECTION - a standard map projection used by the
U.S. Geological Survey.
UPPER NODE - the upstream NODE of a STREAM REACH.
UPSTREAM REACH NODE - see UPPER NODE.
°r P°intS 3S rePresented in a UNIVERSAL TRANSVERSE MERCATOR
VALIDATION - comparison of model results with a set of prototype data not used for verification
Comparison includes the following: (1) using a dataset very similar to the verification data to determine
he vahdity of the model under conditions for which it was designed; (2) using a dataset quite different
from the verification data to determine the validity of the model under conditions for which it was not
designed but could possibly be used; and (3) using post-construction prototype data to determine the
validity of the predictions based on model results.
VANSELOW EXCHANGE FORMULATION - a formulation used to describe soil exchange reactions.
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VARIABLE - a quantity that may assume any one of a set of values during the analysis.
VARIABLE SOURCE AREA - A topographically convergent, low transmissivity area within a watershed
that tends to produce saturation excess overland flow during storm runoff periods.
VEGETATION - see FOREST COVER TYPE.
VERIFICATION - check of the behavior of an adjusted model against a set of prototype conditions.
WATERSHED - the geographic area from which SURFACE WATER drains into a particular lake or point
along a stream.
WATERSHED STEADY STATE - a condition in which inputs of a constituent to a WATERSHED equal
outputs.
WATERSHED SULFUR RETENTION - retention of sulfur by any of a number of mechanisms within a
WATERSHED.
WEATHERED BEDROCK - soft or partly consolidated BEDROCK that can be dug with a spade.
WEATHERING - physical and chemical changes produced in rocks at or near the earth's surface by
atmospheric agents with essentially no transport of the altered materials.
WEIGHT - the inverse of a sample's inclusion probability; each sample site represents this number of sites
in the TARGET POPULATION.
WET DEPOSITION - for the purposes of the DDRP, atmospheric deposition of materials via rain or snow.
WETLAND - an area, generally with hydric soils, that is saturated, flooded, or ponded long enough during
the growing season to develop anaerobic conditions in the upper soil horizons and that is capable of
supporting the growth of hydrophitic vegetation.
ZERO-ORDER REACTION - a chemical reaction, the rate of which is independent of reactant
concentration.
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