Dennis ( 1995) lists 26 species of fish found in Shenandoah National Park ( based on the park's Fishery Management Plan). Ranges of critical pH for nine of these species were reported by Baker and Christensen ( 1991), who estimated average pH thresholds for a variety of negative effects observed in several studies for each species. Paine Run, which hosts three fish species, has been studied intensively since 1992 as part of the park's Fish in Sensitive Habitats ( FISH) Project ( Bulger et al., 1995). Episodic pH values within the critical range of all nine species have been recorded in this stream, and Paine Run's baseflow pH ( 5.7B6.0) is within the critical pH range for two of the nine species whose critical pH range is reported by Baker and Christensen ( 1991). One of these two species, blacknose dace ( critical pH range: 5.6B6.2), occurs in Paine Run, but individuals from that stream are significantly smaller than blacknose dace from higher ANC streams ( Dennis and Bulger, 1995). Indeed, pH as low as 4.11 has been recorded for a small tributary of Paine Run ( Dennis, 1995). It seems clear that elements of the fish community of Shenandoah Park are vulnerable to habitat loss resulting from future decreases in stream pH.

The NAPAP SOS/ T report used two approaches to assess acidification effects in the Mid Appalachian region: ( 1) ASI values calculated from pH, calcium, and inorganic monomeric aluminum using NSS index chemistry ( see Section 5.3.3) and ( 2) a brook trout presence/ absence model based on streams in western Maryland ( Morgan et al., 1990) and southeastern Pennsylvania ( Sharpe et al., 1987).

There are about 63,000 km of total stream length in the NSS I target population in the Mid Appalachian region. About 24% ( 15,000 km) of the NSS I target population stream length exhibits sensitive fish ASI values > 10, indicating chemistry conditions unsuitable for acid sensitive fish species. The highest ASI values occur in the western part of the region.

Potential brook trout habitat in the region was defined by the following criteria: elevation > 400 m, stream gradient 0.4B17%, and Strahler stream order ( 1: 24,000 scale map) < 4. The entire mid Appalachian region is within the zoogeographic range of brook trout, so all streams meeting the criteria were assumed to be potential brook trout habitat. About 37% ( 23,000 km) of the NSS I target population can be considered potential brook trout habitat. Of these, 18% ( 4,100 km) have ASI sensitive values > 30, indicating conditions unsuitable for brook trout.

<IP_ADDRESS> Interior Southeast Streams. In Great Smoky Mountains National Park, fish surveys conducted periodically since the 1930s indicate a steady decline in brook trout range; similar declines in brook trout range have occurred elsewhere in the SAMI region. The reasons include habitat loss through logging, overfishing, and competition from introduced brown and rainbow trouts. Acidification is not considered a major factor yet, though brook trout do not occur in streams whose pH values approach 5.0. The only documented fish kills in the area associated with stream acidity have occurred at fish rearing facilities; these incidents involved introduced rainbow and brown trout, which are more acid sensitive than brook trout.

No adverse effects of acidic deposition on biota have been demonstrated conclusively so 43 far in the southern Blue Ridge province ( SBRP), except in fish hatcheries supplied by Raven Fork ( North Carolina). Several fish kills of brown trout and rainbow trout in holding tanks supplied with water from Raven Fork have occurred during storms ( Jones et al., 1983). Stream acidification was implicated as the cause of the fish kills based on observed streamwater pH/ aluminum levels and the lack of trout mortality in limed streamwater. Elsewhere in the region, the relationship established elsewhere between low pH and species diversity indicates that any decreases in streamwater pH may produce decreases in species richness. As in the mountains of Virginia, fish assemblages in the low order, high elevation streams at risk are dominated by trout species, especially brook trout and rainbow trout, joined ( moving downstream) by mottled sculpin and blacknose dace, creek chub and longnose dace, then assemblages of introduced salmonids, minnows, suckers, and darters. Aquatic invertebrate species richness and pH are positively correlated in this province, suggesting that declines in pH would result in declines in benthic macroinvertebrate diversity ( Baker and Christensen, 1991).

Rosemond et al. ( 1992) report strong relationships between measures of benthic invertebrate community status and water chemistry in Great Smoky Mountains National Park. Baseflow pH values were 4.5B6.8, and inorganic monomeric aluminum was 3B197

g/ L. Total invertebrate density ( excluding the acid tolerant chironomids) and species richness were higher in the high pH streams; these effects were attributed to direct effects on invertebrate survival rather than on food availability.

Assessment of biological effects is limited to ASI toxicity models ( see Section 5.3.3) because no region wide surveys of chemistry and fish status are available. The highest acidic stress levels occur in the high elevation areas of the southern Blue Ridge. Extreme acidic stress levels ( ASI sensitive values > 50) occur much less frequently than in other regions. About 24% ( 63,000 km) of the NSS I target population stream length has ASI sensitive values over 10, indicating conditions unsuitable for acid sensitive species. Much of the acid related stress in this region results from the very low calcium levels which are typical of regional geology classes.

Potential brook trout habitat in the region was defined by the following criteria: elevation > 1000 m, stream gradient 0.4B17%, and Strahler stream order ( 1: 24,000 scale map) < 4. These criteria include only streams within the Southern Blue Ridge subregion, but all are within the zoogeographic range of brook trout. About 46% ( 24,000 km) of the NSS I target population can be considered brook trout habitat; of this percentage, 11.5% ( 1,400 km) has ASI sensitive values > 30. Perhaps 10% of streams otherwise suitable for brook trout are unavailable because of acidification this estimate, however, contains much uncertainty. We do not have sufficient information to construct probability of presence models. 44 4. RECENT TRENDS IN ACIDIFICATION IN THE SOUTHERN APPALACHIANS 4.1 Trends in Surface Water Chemistry Within the SAMI Class I areas, temporal trend information is available only for streams in Shenandoah National Park. In the late 1980s, White Oak Run and Deep Run both showed significant increases in SO 4 2

and decreases in pH ( Ryan et al., 1989). At Coweeta, in the North Carolina Blue Ridge, there were no significant trends in acidity but there was a significant increase in SO 4 2

concentration ( average of 0.7

eq/ L/ yr) in all control watersheds between 1974 and 1982 ( Swank and Waide, 1988). The SO 4 2

increases at these sites are consistent with a gradual saturation of soils in the region with SO 4 2

from deposition, and have been predicted by acidification models ( Church et al., 1992). More recently, the SO 4 2

trends in Shenandoah National Park have been greatly altered as a result of forest defoliation by gypsy moth larvae ( Webb et al., 1995). Defoliation has resulted in large increases in streamwater NO 3

( up to 60

eq/ L), decreases in SO 4 2

, and little change in ANC or pH at baseflow. During storms, however, the increased leaching of NO 3

in these watersheds has led to an increase in episodic acidification, with ANC decreases during episodes nearly twice the magnitude previously observed ( Eshleman et al., 1995). We do not currently know how the streams will respond as the forests recover from defoliation.

It is likely that many parts of the SAMI region have undergone increases in NO 3

over the past several decades. There are few data to verify this pattern, but it is supported by the few time series data that do exist, and by the current patterns of streamwater NO 3

distribution in the region. At Fernow Experimental Forest in West Virginia, NO 3

concentrations have increased from near zero to 50B60

eq/ L at baseflow from 1970 to the present ( Stoddard, 1994). In the Great Smoky Mountains National Park, NO 3

shows strong correlations with elevation and forest age ( Cook et al., 1994; Flum and Nodvin, 1995), with the highest concentrations ( up to 100

eq/ L) occurring at high elevations ( where deposition is highest; Shubzda et al., 1995) and in areas of old growth forest where biological demand for nitrogen is lowest ( Stoddard, 1994; Nodvin et al., 1995). It is very likely that a combination of high rates of N deposition, coupled with forest maturation in the park, have led to accelerated rates of N loss in the Smokies, and that this trend will continue as maturation of the forests at lower elevation progresses.

We do not know what effect the presumed increase in streamwater NO 3

has had in the Smokies, but it is likely to have led to substantial cation depletion and ultimately to soil acidification in the region ( Johnson and Lindberg, 1992). Many of the same streams that now show elevated NO 3

concentrations are either chronically or episodically acidic ( Flum and Nodvin, 1995; Nodvin et al., 1995).

4.2 Trends in Episodic Effects It has been proposed that episodic changes in surface water pH during stormflow conditions may represent an " early warning" of sustained, chronic acidification impacts associated with regional scale acidic deposition. However, only a few experimental or modeling studies of long term changes in episodic conditions have been conducted, due to a general lack of data with which to statistically evaluate trends or to parameterize an appropriate predictive acidification model ( Neal et al., 1992; Hooper and Christophersen, 1992; Eshleman et al., 1995). One of these studies 45 ( Eshleman et al., 1995) was conducted within the SAMI region in Shenandoah National Park.

Two modeling studies have been conducted using the predictive acidification model, MAGIC ( see section <IP_ADDRESS>). The study by Neal et al. ( 1992) used MAGIC in two component mode ( i. e., MAGIC was calibrated for two distinct soil horizons and the resulting solutions were mixed according to known proportions based on chemical hydrograph separations). The technique was applied to the Afon Gwy catchment in mid Wales, with results demonstrated in the forms of ( 1) 3 month sequences of hydrogen ion and inorganic aluminum concentrations and ( 2) chemical duration curves for hydrogen ion and aluminum. The most important finding in the study was that aluminum concentrations in the stream did not recover as rapidly as had previously been thought, in response to reductions in sulfur deposition. The second modeling study, by Hooper and Christophersen ( 1992), of long term episodic changes in stream chemistry at Panola Mountain ( Georgia) largely supported the hypothesis that stormflow conditions provide an " early warning"; while baseflow chemistry gradually became acidic over a 50 year modeling period, acidification of two upper soil layers occurred more rapidly, causing acidic conditions during stormflow periods. Although this work was located geographically outside the SAMI region, the results of Hooper and Christophersen ( 1992) appear to provide a reasonable hypothesis for long term changes in episodic conditions in other southern Appalachian mountain waters.

The analytical study of Eshleman et al. ( 1995) involved the use of a hydrological separation program and long term daily flow and weekly chemical data from White Oak Run, Virginia. A statistical analysis of 13 years of daily discharge data and weekly streamwater composition data for White Oak Run in Shenandoah National Park was performed in order to quantify episodic changes in composition and to identify long term trends in episodic acidification attributable to both natural and anthropogenic processes. An objective hydrological separation technique was used to identify more than 100 " stormflow baseflow pairs" in the database, from which episodic chemical changes could be quantified. Univariate statistical analysis suggested that mean episodic depressions of ANC in White Oak Run have increased by about a factor of 2 since the first outbreak of forest defoliation by the gypsy moth caterpillar during the summer of 1990; in addition, the mean episodic change in NO 3

concentration has increased by about 12

eq/ L, while the mean episodic dilution of C B has decreased from  8.5

eq/ L to  1.7

eq/ L during the same period. Episodic changes in SO 4 2

have remained the same, however. The results indicate that natural processes such as insect defoliations can contribute to episodic acidification through mobilization of NO 3

. Results from the study did not demonstrate any longterm changes in episodic conditions associated with atmospheric deposition, presumably due to the larger, overwhelming influence of the gypsy moth defoliations. Other experimental and modeling studies of long term trends in episodic conditions are needed for the SAMI region.

4.3 Trends in Biological Effects It is difficult to quantify trends in biological condition because few datasets have good biological data over time. It is also difficult to differentiate the effects of acidic deposition from other anthropogenic effects. Thus, it is not possible to make a definitive statement about trends in biological effects related to acidic deposition in the SAMI region. There is at least one stream in the area, however, in which fish declines are probably the result of acidification: the St. Mary's River in George 46 Washington National Forest in the Virginia Blue Ridge. Surveys in 1988, compared to those in the 1930s, showed declines in acid sensitive fish and invertebrates, coincident with lower pH values ( Webb et al, 1989a, b). 47 5. METHODOLOGIES FOR PREDICTING FUTURE EFFECTS OF ACIDIC DEPOSITION 5.1 Surface Water Chemical Models A large number of models have been developed over the years to predict and/ or explain surface water chemical response to acidic deposition. These models fall into two general categories: steady state, and dynamic. Most of these models were comprehensively reviewed and cited in the NAPAP SOS/ T Report # 14 ( Thornton et al., 1990) and the next two subsections briefly summarize those findings. Most of the NAPAP modeling effort focused on sulfur chemistry. It has become more apparent over the last 5 years, however, that NO 3

is increasing in some areas and needs to be treated more explicitly. Thus, a number of modeling efforts have recently been developed to incorporate N dynamics in future projections of surface water acid base chemistry.

5.1.1 Steady state Models Steady state refers to the condition in which outputs equal inputs. In other words, after a perturbation such as acidic deposition, lake or stream chemistry ( output) will eventually reach an equilibrium with the new chemical input levels. In general, steady state models use current water chemistry to estimate steady state conditions for both preindustrial conditions and the eventual future condition for a given level of acidic deposition. Steadystate models have no explicit time component; the lake or stream is assumed to be in equilibrium with atmospherically deposited SO 4 2

in both the past and future scenarios. Future changes in ANC are then usually estimated from the change in SO 4 2

either empirically or by using a charge balance approach that calculates ANC decline as some fraction of the change in SO 4 2

. This fraction has been named the Henriksen F factor ( after its inventor) and relates the proportion of added SO 4 2

that is balanced by increased base cation concentration. Thus, an F= 1 means that all the additional SO 4 2

is balanced with additional base cations ( no ANC or pH decline). An F= 0 indicates that no base cations are released and that all the added SO 4 2

is balanced against a decline in ANC ( additional H+ or Aln+). As one would expect, steady state models using the F factor approach are very sensitive to the value of F used in the model, and various approaches have been used to estimate F. Thornton et al. ( 1990) concluded that most steady state models were not appropriate for use in the NAPAP assessment because they had: ( 1) unrealistic assumptions concerning the level of watershed neutralization ( F factor), ( 2) a lack of biological relevance ( no aluminum predictions), and ( 3) problems in applying the models outside the regions for which they were first developed.

5.1.2 Dynamic Models Whereas steady state models have no explicit time component, dynamic models project water chemistry for specific days, months, or years. Dynamic models integrate our current understanding about the hydrological and biogeochemical processes that occur as acidic deposition falls on watersheds and is transported into lakes and streams. The modeled mechanisms include hydrologic flow routing, soil water interactions ( including soilwater contact time), anion retention, base cation exchange, mineral weathering, and other watershed processes ( e. g., vegetative uptake and organic interactions). The mechanisms are modeled with varying degrees of complexity among the different dynamic models but they are all are much more complex and time consuming and they have larger data input requirements than steady state 48 models. The two dynamic watershed models of most use to an assessment of the aquatic effects of acidic deposition in the SAMI region are the ILWAS ( Integrated Lake Watershed Acidification Study) and MAGIC ( Model of Acidification of Groundwater in Catchments) models.

<IP_ADDRESS> ILWAS. The ILWAS model ( Chen et al., 1983; Gherini et al., 1985) was developed as a research tool to further understanding about the processes affecting acidbase chemistry in Adirondack lakes. It is a process oriented model that uses both equilibrium and rate limited expressions to describe the mass balances for acid base chemistry. ILWAS has three modules: canopy, hydrologic/ soil, and within lake. ILWAS is quite complex; it models more processes with more compartments ( e. g., soil layers) than the other dynamic models. Thus it has greater input data requirements and is more time consuming to run and calibrate. ILWAS requires daily meteorological data, weekly or monthly deposition chemistry, watershed vegetation types and coverage, watershed attributes, physical/ chemical soil data, lake/ stream hydrological data, and initial water chemistry. All in all, it requires specification of more than 200 parameters, coefficients and initial conditions for model calibration Model results can be output over a range of time steps from daily to annual.

<IP_ADDRESS> MAGIC. MAGIC ( Cosby et al., 1985a, b; 1986a, b) is a lumped parameter model of intermediate complexity developed to project the long term effects ( decades to centuries) of acidic deposition on responses in average annual stream or lake chemistry. It was originally developed for streams in Shenandoah National Park. MAGIC was formulated to be parsimonious in selecting processes for inclusion in the model. It assumes that only a few key processes influence the long term response of watersheds to acidic deposition. MAGIC has a separate hydrologic flow routing component that runs on a daily time step. Hydrologic data are averaged and the rest of the MAGIC model has a monthly or annual time step. MAGIC has two soil layers and a lake/ stream component, and both equilibrium and rate limited expressions are used to describe the mass balances for acid base chemistry. MAGIC requires annual meteorological/ deposition data, watershed attributes, physical/ chemical soil data, lake/ stream hydrological data, and initial water chemistry. Model results can be output seasonally or annually. It does not simulate episodic responses.

A regional MAGIC model has been developed to project the acid base status of regional stream/ lake populations rather than individual sites ( Hornberger et al., 1986, 1987). Regional MAGIC is structurally and functionally similar to MAGIC for individual sites. It has the same data input requirements. The major difference is that in Regional MAGIC, inputs and outputs are in the form of regional distributions, not individual values. Regional MAGIC is also calibrated differently; a set of simulated watersheds is generated by random sampling from the input distribution data and then calibrated to fit an observed distribution of water chemistry from a regional survey. It is important to note that the output projects how a regional distribution will change over time and reflects simulated watersheds. It cannot be used to project conditions for any specific watershed or geographic location within the region.

5.1.3 Nitrogen Models Three models of nitrogen dynamics are being used currently, or are being developed, to assess the acid base status of surface waters. One of the models ( MAGIC WAND) is incorporated directly into the MAGIC model. The others provide input that can be used to set up the MAGIC model to run with 49 the influences of N deposition included. Each model is described briefly here.

<IP_ADDRESS> Model of Acidification of Groundwater in Catchments B With Aggregated Nitrogen Dynamics ( MAGIC WAND). MAGIC WAND is a direct modification of the MAGIC model that includes some simple representations of the N cycle ( Cosby, pers. comm.). Nitrogen is assumed to be present only in solution in soil water. Nitrogen inputs to the system are in the form of inorganic N added to the soil solution, and are represented as atmospheric deposition and mineralization. The rates for these inputs must be entered a priori. Nitrogen losses from the system are represented as hydrologic runoff and denitrification Transformations included in the model are nitrification and uptake. The primary limitation of MAGIC WAND is that it includes no internal feedbacks ( e. g., mineralization rates must be entered a priori, and do not depend on changes in other processes or on N pools). Its major strength is that it is directly incorporated into MAGIC, so that direct outputs of the variables of interest ( e. g., time series of ANC) can be made.

<IP_ADDRESS> Model of Ecosystem Retention and Loss of Inorganic Nitrogen ( MERLIN). MERLIN is a stand alone nitrogen cycling model, adapted from the Generalized Ecosystem Model ( GEM; Rastetter et al., 1991). It is probably the most realistic of the three models available, and therefore also requires the most detailed inputs ( Cosby, pers. comm.). The processes in MAGIC WAND are included in MERLIN, not as driving variables, but calculated from internal state variables. The carbon and N pools of the terrestrial compartments ( photosynthetic biomass, wood, litter, labile organic matter, refractory organic matter, etc.) are modeled explicitly and the carbon: nitrogen ratios in these pools feed back and affect the N transformation processes. Data on the carbon and N pool sizes in each compartment, plus all the fluxes between compartments, are needed for calibration. The realistic nature of this model ( particularly the division of soil organic matter into labile and refractory pools) is clearly advantageous. Its major drawback is the detailed input data required to run the model; many of the transformation rates ( e. g., into and out of the soil organic matter pools) are not known for many sites. This is still a rapidly developing model, and the results of its application to any existing sites are not yet available.

<IP_ADDRESS> Net Photosynthesis and Evapo Transpiration ( PnET) B Carbon and Nitrogen ( CN) Model. PnET CN ( Aber and Federer, 1992) has evolved from a relatively simple model of gross and net photosynthesis to one that now includes cycles of water, carbon, and nitrogen in a monthly time step ( Aber et al., in press). Because it evolved from a " treegrowing model," it focuses on the effects of forest development, and the terrestrial processes that accompany it, on N dynamics. The latest version of the model includes litter decomposition and turnover, as well as transfers between terrestrial compartments ( roots, foliage, wood, and soil), and incorporates site history ( land use disturbance) into the transformation rates between compartments. The model has been applied to a large number of sites with remarkable success, especially considering that it is not truly " calibrated" ( e. g., the model parameters are not tuned so that they reproduce current conditions before the model is run to predict future conditions) to each site. For example, it accurately reproduces the record of NO 3

outputs from the Hubbard Brook control watershed for the last three decades ( Aber et al., in press). Although the model requires a large number of parameters to run, it has been very successfully applied using literature values for different forest types ( e. g., hardwoods vs. conifers). The key site specific variables needed to run the model successfully are climatic variables 50 ( temperature and precipitation), foliar N content, and land use history.

5.2 Episodic Chemical Models The 1990 NAPAP assessment of current and future acidification impacts of acidic deposition recognized that assessments based solely on chemical conditions during " index periods" ( i. e., periods that approximate average annual or seasonal conditions) did not account for the " worst case" chemical conditions that usually occur during extreme hydrological events. However, because of the rather large uncertainties associated with incorporating episodic acidification into the regional assessment framework, model based projections of watershed responses to emissions reduction scenarios were not formulated to account for changes in episodic acidification over long time periods.

Since completion of the 1990 NAPAP assessment, several modeling approaches have been utilized to predict future episodic chemical responses to a variety of emissions/ deposition reduction scenarios ( Neal et al., 1992; Hooper and Christophersen, 1992; Eshleman et al., 1995), although none has yet been applied to a watershed in the SAMI region. Two of the published studies were conducted on individual watersheds and utilized the MAGIC model, while one of the studies was conducted at the regional scale and utilized a regional modeling approach. Depending upon the nature of the integrated assessment desired by SAMI ( local scale or regional scale), any one of these three approaches could be employed to address the issue of episodic changes in surface water acid base status resulting from changes in deposition loadings. Two key issues that will need to be addressed before conducting such an assessment are: ( 1) the assumptions inherent in each of the modeling approaches and ( 2) the availability of watershed and surface water data for model calibration and testing.

5.3 Modeling the Effects of Acidic Deposition on Fish Communities The primary goal of the mathematical/ statistical models that evaluate the effects of acidic deposition on fish communities is to predict future effects on biological resources based on projected changes in water chemistry Few models for regional assessment of acidification have been developed, and most deal only with fish responses; most of these deal with fish species presence or absence, but more sophisticated response variables are increasingly being modeled. This report considers three kinds of models: field based empirical models, toxicity models, and models that combine toxicity ( laboratory) data with field observations.

5.3.1 Empirical Models Empirical or field based models are based on associations between fish status and water chemistry as they exist in nature, and are typically constructed from survey data. The future values of variables that turn out to be most strongly correlated with fish status are estimated with the model, and fish status is predicted from its association with those variables. These models make two assumptions ( 1) the systems surveyed are in steady state, and ( 2) the observed associations between fish status and water chemistry accurately reflect what would occur over time.

These empirical models do not assume that the variables most strongly associated with fish status ( or with greatest predictive capacity) in a given data set directly control fish status in a mechanistic way, although the mechanistic linkages are often easy to imagine. For example, ANC often shows a strong relationship to fish status, but it is clear that fish do not respond directly to ANC; however, ANC controls pH, which controls aluminum, 51 which is toxic. Likewise, variables that have well understood mechanistic effects on fish do not always show strong empirical relationships with fish status in survey data. An example is calcium, which ameliorates acid stress; it is not always a good predictor of fish status, because healthy populations exist at high as well as low calcium concentrations, in the absence of acid stress; in the presence of acid stress, most of the benefits of elevated calcium are achieved at 150

g/ L, and further increases produce smaller improvements. Fish presence or absence, measures of fish population status, or the number of fish species ( richness) in a body of water or region have been estimated with empirical models. Multiple regression analysis is usually the statistical tool used in empirical models, with either a two state response variable, such as presence or absence, using logistic regression, or a multiple state or continuous response variable, using standard regression.

In all cases, the data set must be purged of bodies of water which have known explanations for fish loss other than acidification, if the remaining differences among lakes or streams are to be attributed to acidification effects on fish. In this connection, two other physical attributes of bodies of water must be taken into account in modeling efforts: size and elevation. For example, larger lakes and lakes at lower elevation tend to support more species of fish, all else being equal. For the SAMI region, focusing on mountain streams, size and elevation are probably correlated to some extent, so smaller streams and streams at higher elevation are expected to host fewer species. 5.3.2 Toxicity Models Toxicity models are covered in some detail in this synopsis because they provide the opportunity for near term assessments of acidification effects on fish populations in the SAMI region. J. Baker et al. ( 1990) define toxicity models in the context of acidification as mathematical functions fitted to fish responses in laboratory studies with constant levels of pH, inorganic monomeric aluminum, and calcium. Regression models are then used to estimate the acidification effects on fish associated with aluminum, pH, and calcium levels measured in the field. Because they are based on variables with known toxic ( aluminum and pH) or mitigating ( calcium) effects, the mechanistic linkages between fish response and acid base chemistry are established at the outset. This is an advantage, but two important disadvantages to toxicity models remain: ( 1) the field survey data used as input frequently do not capture the extreme events to which sensitive life stages of fish may be exposed in nature and ( 2) the model output is best at estimating percent mortality in laboratory studies and cannot easily be interpreted directly as a population level response. The primary advantage of toxicity models is that they can deal with the joint effects of pH, aluminum, and calcium.

5.3.3 Combined Toxicity Field Models C the Acid Stress Index The approach used to model the effects of acidity on fish in the 1990 NAPAP assessment converted the joint effects of pH, inorganic monomeric aluminum, and calcium into a single, biological response variable, called the acid stress index ( ASI). Three criteria were used for the data sets used to create the ASI toxicity models. The first was that aluminum, calcium, and pH were measured as part of the experimental design. Secondly, the data sets were based on observations of fish mortality as opposed to sublethal stresses; the reasons 52 being that mortality is most often used as an observational endpoint, and, while sublethal stresses are important, they are difficult to interpret as population level effects. Lastly, the data sets were based on observations of early life stages; the reasons being that there are large number of such studies, early stages are usually the most sensitive stage, and early life stage mortality has a clear effect on population recruitment.

Toxicological experimental elements of the Lake Acidification and Fisheries ( LAF) framework ( Mount et al., 1988a, b) were specifically designed to produce results that could be incorporated into regression models; thus the LAF data are an important resource for the ASI models. The four freshwater species used in the LAF framework were brook and rainbow trouts, smallmouth bass, and white sucker. Four levels of fish sensitivity to acidity were modeled: tolerant, intermediate, sensitive, and anadromous. Since not all fish species potentially affected by acidification can be practically modeled, three species from the LAF data were used in toxicity models as reasonable representations of the range of responses possible in fish communities.

1. Tolerant Toxicity model: 21 day survival of brook trout fry.

2. Intermediate Toxicity model: 8 day survival of smallmouth bass alevins.

3. Sensitive Toxicity model: 21 day survival of rainbow trout fry.

It became necessary to incorporate an even more sensitive life form after it was discovered that anadromous species ( those that are spawned in freshwater, spend various amounts of time there, then migrate to seawater, attain sexual maturity, then return to freshwater to spawn) are among the most acid sensitive fish in their freshwater phase, even more sensitive than rainbow trout. Example of such species include Atlantic salmon, striped bass, and blueback herring; all show acid induced stress at pH levels of 6.0B6.5. Thus a fourth toxicity model was developed specifically for use in the Mid Atlantic Coastal Plain, using 4 day survival of blueback herring alevins as the basis for the anadromous model. This fourth model would be relevant only in estimating effects of acidification outside the SAMI region.

<IP_ADDRESS> Acid Stress Index Model Structure. The proportion of fish surviving a toxic exposure was regressed as a function of the values of pH, Al, and Ca, using maximum likelihood regression; considerable literature exists to support this choice of model; the predicted variable was converted to percent mortality ( 0B100%), and adjusted for " background" ( not due to acid stress) mortality. The mortality percentage due to acid stress is referred to as " conditional mortality rate" and called the acid stress index ( ASI). Thus higher values of ASI indicate greater stress caused specifically by acidification. It is a characteristic of the water whose chemistry is modeled.

For each toxicity data set, alternative models structures were evaluated using various combinations of pH, inorganic Al, and Ca, plus squared and interactive terms. The final coefficients included for each of the four models were based on three criteria.

1. Visual ( graphical) examination of the model fit to the data set and realism of the model output outside the range of chemistry variables tested.

2. Statistical significance of model parameters ( only variables significant at p < 0.05 were included).

3. Model r2, calculated by the goodness of fit chi square for the intercept only model ( X) to the goodness of fit chi square for the full model ( Y). 53 The variables used in the toxicity models are pH in standard units, Al in

g/ L, and Ca in

eq/ L. The model r2 values were 0.70, 0.80, 0.79, and 0.78 for tolerant, intermediate, sensitive and anadromous models, respectively. The intercept and coefficients for each of the four models may be found in Table 13 42 of SOS/ T 13 ( J. Baker et al., 1990). The generalized model structure is:

ASI (% mortality) = 100/[ 1 + exp( a + b i x i)]

where x i are values of the three chemical variables and b i are their coefficients. Some restrictions were placed on model output. The ASI was assumed to be zero at pH > 8.0, and at Ca concentrations > 2000

eq/ L; inorganic Al concentrations were assumed to be zero at pH > 6.5.

<IP_ADDRESS> Acid Stress Index Model Evaluation In regional applications of the toxicity models, outputs are intended to represent index responses of tolerant, intermediate, and sensitive fish species, rather than just the species for which the models were developed. Index or baseflow levels of pH, Al, and Ca were used to calculate ASI values for individual water bodies. To determine the suitability of this approach, two types of evaluations were executed: interspecies comparisons and comparison to field population responses. For interspecies comparisons, the focus was on the applicability of the sensitive model to estimates of effects on other sensitive species. Agreement between the experimental mortalities of common shiner and blacknose dace, typical of a group of sensitive cyprinid fish, and the output of the sensitive model predictions of mortality was considered adequate.

ASI values were also compared to field observations of fish population responses. Predictions ( ASI values) derived from lab studies do not include natural variation in chemistry or other variables which affect survival in nature. Nor do these predictions consider biological compensation ( positive effects on the survivors due to reduced density resulting from deaths of some of the population Nevertheless, it is clear that the ASI has value as an index, based on comparisons with three data sets from ( 1) Adirondack lakes, ( 2) Ontario lakes, and ( 3) western Maryland streams. For lakes, the likelihood of presence of brown bullhead was about 50% when the ASI tolerant values were about 30; thus, waters with an ASI value > 30 would appear, on average, to have acid base chemistry unsuitable for the survival of brown bullheads Brook trout were lost from waters ( likelihood of occurrence = 50%) at ASItolerant values above 10. The likelihood of occurrence was 50% when ASI intermediate values were near 80 for lake trout and ASI sensitive values were near 80B90 for common shiner.

The relationship between ASI and fish presence/ absence clearly differs between streams and lakes. Stream fish populations appear to be affected at much lower values of ASI. Since ASI values are calculated from the index ( baseflow) chemistry values, this difference in response probably reflects the more significant role of episodic acidification in streams versus lakes. As a result, both brook trout and blacknose dace presence/ absence appeared to be best represented by the sensitive model in streams, with reference ASI values of > 30 and > 10 for brook trout and blacknose dace, respectively.

Although there is not a one to one relationship between ASI and population level effects, the NAPAP study concluded that toxicity based model outputs can be useful as an index of probable acidification stress at the population level. As a result, reference levels of ASI were associated with the following fish responses for streams ( Table 13 43 in SOS/ T 13, J. Baker et al., 1990): 54 $ ASI intermediate values > 30: Loss of all species $ ASI sensitive values > 30: Loss of brook trout $ ASI sensitive values > 10: Loss of acidsensitive species, e. g. minnows It is very important to note that ASI models constructed from lab experiments taken by themselves appear to underestimate the acidification stress experienced by populations in nature. For example, streams that have lost brook trout populations have index values of pH, Al, and Ca that would result in as little as 30% mortality of the more sensitive rainbow trout fry in lab bioassays ( see above, ASIsensitive > 30, associated with loss of rainbow trout populations). This is no doubt caused in part by temporal and spatial variation in chemistry, e. g., episodes of poor water quality which occur during sensitive life stages of fish. It would be preferable to include episodes into predictions of fish status, but regional scale data sets are lacking, and exposures during episodes are themselves difficult to characterize. Thus, given the uncertainties and limitations regarding chemical variation in nature, the NAPAP Assessment used ASI values based on index chemistry, but interpreted them in light of reference ASI values based on field observations as indices of probable population effects. 55 6. PREDICTIVE STUDIES OF ACIDIC DEPOSITION EFFECTS IN THE SOUTHERN APPALACHIANS 6.1 NAPAP Modeling Efforts The NAPAP efforts to model future changes consisted of the Direct/ Delayed Response Project ( DDRP) and the 1990 Integrated Assessment ( IA). In the SAMI region, both efforts focused on the potential effects of acidic deposition on surface water ANC during the spring baseflow index period defined and sampled by the NSS. The time horizon for these analyses was 50 years, starting in 1985. The primary processes modeled were ( 1) the retention of deposited sulfur within watersheds and ( 2) the supply of base cations from watersheds to surface waters. These two processes had been identified by a National Academy of Sciences panel as the most important watershed processes affecting or mediating long term surface water acidification ( NAS, 1984).

The DDRP ( Church et al., 1989, 1992) and IA ( NAPAP, 1991) modeled streamwater chemistry responses to various deposition scenarios in two regions of the eastern United States: the Mid Appalachians ( MIDAPP) and the Southern Blue Ridge Province ( SBRP). The SBRP modeling region is entirely within the SAMI region, but it does not include parts of the Blue Ridge located in Virginia and northern North Carolina. The MIDAPP modeling region contains all the acid sensitive SAMI study region in Virginia and West Virginia, plus large parts of Pennsylvania and the Catskill region of New York.

Three watershed models were applied to streams in the SBRP:

1. The Model of Acidification of Groundwater in Catchments, MAGIC ( Cosby et al., 1985a, b; 1986a, b). 2. The Enhanced Trickle Down ( EDT) model ( Lee, 1987; Nikolaidis et al., 1988; Schnoor et al., 1986).

3. The Integrated Lake Watershed Acidification Study ( ILWAS) model ( Chen et al., 1983; Gherini et al., 1985).

These models integrated the current understanding of how various watershed processes interact and respond to acidic deposition. The three models used common datasets for forcing functions ( e. g., rainfall, runoff, atmospheric deposition) and used data aggregated from the DDRP soils database for state variables such as soil physical and chemical characteristics ( Church et al., 1992).

Although absolute values of modeled concentrations of constituents varied in comparisons for individual watersheds, Church et al. ( 1989) reported that projections of changes in ANC among the models were remarkably consistent on a regional basis. Rather than repeating costly and time consuming duplicative modeling analyses, Church et al. ( 1992) used only the MAGIC model for projections in the MIDAPP. They reported that MAGIC was by far the easiest, quickest, and least expensive to apply. For the same reasons, NAPAP ( 1991) used MAGIC as the primary method for projecting and comparing the chemical responses of SBRP and MIDAPP streams to various deposition scenarios in the 1990 Integrated Assessment Report.

The DDRP and IA modeling efforts were intended to estimate the general direction and the relative magnitude of possible future changes in surface water acid base chemistry under alternative scenarios of atmospheric sulfur deposition ( Church et al., 1992). The projections of these models were not intended to be forecasts of future conditions, but tools 56 to evaluate the relative effectiveness of alternative emission controls. The modeled stream population for all three assessments is the downstream ends of NSS stream segments with drainage areas < 30 km2. In addition, only streams with ANC < 200

eq/ L and no substantial watershed sources of sulfate or chloride were included in the MIDAPP population. These criteria eliminated about 30% of the NSS target population in the SBRP and 42% in the MIDAPP, and restricted the model inferences to the subset of streams likely to respond to acidic deposition inputs over the next several decades. However, the projections were calibrated on the downstream ends of the NSS stream reaches and estimate the chemistry for these ends. ANC at the lower ends of these streams was generally higher than at the upstream ends ( Table 1), so these projections overestimate ANC and underestimate changes in ANC for the upper ends. For these reasons, the model baseline conditions will not agree with the NSS current status estimates that include streams over a broader size and disturbance spectrum.

6.1.1 Model Results The basic results and conclusions of the IA agree with the DDRP results of Church et al. ( 1989, 1992), and primarily the IA results appear in the following outline of future modeling projections. Furthermore, we have borrowed freely from Church et al. ( 1989, 1992) and NAPAP ( 1991) in the wording of most of these conclusions. Both the DDRP and the IA modeled a projection of current deposition and defined it as the 1985 level. All deposition scenarios extend to 50 years beyond 1985. The basic results and conclusions of the future modeling efforts are as follows.

<IP_ADDRESS> Sensitivity to Acidification. Three percent of the modeled MIDAPP stream population currently is acidic and 15% has ANC  50

eq/ L. The streams in the MIDAPP highlands with lowest ANC are generally restricted to small, forested watersheds at relatively high elevations (> 300 m). These streams are expected to be the most sensitive to acidic deposition. None of the streams sampled by the NSWS in the SBRP was chronically acidic, but 12% of the modeled subpopulation had ANC  50

eq/ L. Streams in the SBRP may be responsive to changes in acidic deposition, but the response is delayed more than that of MIDAPP streams because watershed soils are retaining more sulfate from acidic deposition. Church et al. ( 1989) estimated that their watersheds are currently retaining three quarters of the atmospherically deposited sulfur on the average, but projected that their soils will become more saturated with sulfur over time. As a result, they project that watershed sulfur retention will decline, increasing sulfate concentrations in the surface waters of this region. The response is projected to be marked over the next 50 years at either current or increased levels of sulfur deposition, as are decreases in streamwater ANC. Superimposed upon this effect is a relatively minor acidification effect of base cation depletion ( Church et al., 1989).

<IP_ADDRESS> Projections for Current and Increased Deposition. Streams in the MIDAPP and SBRP are projected to acidify ( decrease in ANC over time) under current levels of deposition ( Figure 12). Streamwater concentrations of sulfate are projected to increase substantially over the next 50 years, accelerating both cation leaching from soils and the projected acidification of surface waters. Median ANC of streams in the MIDAPP and SBRP would decrease about 20

eq/ L over 50 years at current levels of atmospheric sulfur deposition, because less sulfate is being retained by soils over time. ANC would change by about 3 to 4

eq/ L in addition to the 20

eq/ L decrease for each 57 Figure 12. Future projections of stream ANC and pH after 50 years for 6 sulfate deposition scenarios for ( a) Mid Atlantic Highlands ( includes Pennsylvania, Maryland, and New York) and ( b) Southern Blue Ridge. Taken from Figures 4.4 7 and 4.4 9 in 1990 NAPAP Integrated Assessment. CSC are the current ( 1985) simulated conditions at year 0. The six future deposition scenarios are:

 50%: Current levels for 5 years, ramp down 50% over 10 years, then constant.

30%: Current levels for 5 years, ramp down 30% over 10 years, then constant.

20%: Current levels for 5 years, ramp down 20% over 10 years, then constant. 0: Current deposition level for 50 years. + 20%: Ramp up 20% above current levels over 25 years, then constant. 58 + 30%: Ramp up 30% above current levels over 25 years, then constant. 59 kg/ ha/ yr change from current sulfur deposition over 50 years. Under current levels of deposition over 50 years, 46% of streams would experience ANC declines of

10  eq/ L; 15% of streams would experience pH declines of

0.3 units.

In the MIDAPP, a decline in the regional median ANC of about 25  eq/ L is projected over 50 years. After 50 years at current levels of deposition, 10% of MIDAPP streams are projected to be acidic and 24% would have ANC  50  eq/ L ( Figure 12). At sulfur deposition 20% and 30% greater than current levels, the number of acidic MIDAPP streams is projected to increase by factors of 5.4 and 6.2, respectively, over the next 50 years. In the SBRP, projections suggest that after 50 years at current levels of deposition, about 10% of the streams will be acidic and 15% will have ANC  50  eq/ L ( Figure 12). A 20% increase in deposition would result in an increase to 10 B 12% acidic streams and 23 B 26% with ANC  50  eq/ L.

<IP_ADDRESS> Reduced Deposition Scenarios. With reduced deposition, projected changes in streamwater sulfate will ultimately respond to the level of deposition. Model projections suggest that a 20 B 30% reduction in sulfur deposition would be necessary to prevent further acidification in MIDAPP streams over the next 50 years; reductions of 30 B 50% would be required in the SBRP. Because of the substantial amount of sulfate adsorption in SBRP soils, a delay in the reduction of sulfur deposition would be expected to result in acidification greater than that which would occur with no delay. These effects would occur beyond the 50 year time frame modeled.

<IP_ADDRESS> Chemical Conditions for Fish. The projected acidic stress indices for sensitive fish species suggest that biological conditions in low ANC MIDAPP streams will deteriorate under current deposition levels. The simulated current percentage of MIDAPP stream segments with downstream end water chemistry unsuitable for sensitive fish species ( e. g., rainbow trout, blacknose dace) is 21%. With a 30% increase in sulfur deposition, this percentage is projected to increase to 34%. With a 50% decrease in sulfur deposition, it would remain at 21%. A 25 year delay in the reduction of sulfur deposition is projected to increase the number of MIDAPP streams unsuitable for sensitive fish species by 6% during the 50 year modeling period. If unsuitable chemical conditions eliminate reproducing populations of fish and other aquatic biota from some streams, they will have to recolonize these streams from other locations and may not return until well after chemical conditions permit. Estimates of fish response were not made for streams in the SBRP because the IA researchers did not find field information relating fish status to stream acidbase chemistry and felt that the uncertainties of extrapolating models developed elsewhere were too great ( NAPAP, 1991).

<IP_ADDRESS> Uncertainties in Model Projections Uncertainties in the projections for timing of aquatic effects are high because of uncertainties in sulfate adsorption desorption dynamics and in the relative importance of weathering versus cation exchange processes ( NAPAP 1991). Additional uncertainty results from the fact that acidification from nitrogen deposition was not considered in the modeling. However, limited field observations of ANC trends in MIDAPP streams are in the low end of the predicted range of modeled ANC changes. Conclusions regarding future effects from acidic deposition are considerably more uncertain in the SBRP than in the MIDAPP, primarily because of the difficulty of predicting future changes in sulfur retention by soils. Effects are likely to occur beyond the 50 year time frame used in the modeling. 60 6.2 Nitrogen Bounding Study Most of the efforts at dynamic modeling of watershed acidification that were carried out as part of NAPAP ( see section 6.1) did not consider the potential influence of changes in watershed nitrogen retention on model forecasts The Nitrogen Bounding Study ( NBS; Van Sickle and Church, 1995), whose results were also reported as part of the Acid Deposition Standard Feasibility Study ( U. S. Environmental Protection Agency, 1995) was an attempt to bracket the potential effects that nitrogen saturation might have on future acidification. The NBS used the modeling techniques of the DDRP, several different scenarios for future nitrogen and sulfur deposition and hypothetical time sequences for nitrogen saturation to predict the percentages of streams that would be either chronically acidic ( ANC < 0) or susceptible to episodic acidification ( ANC < 50  eq/ L) in the future.

In the case of the Mid Appalachian region, the study predicted that 8% of streams would become acidic at current rates of nitrogen deposition and forecasted rates of sulfur deposition ( roughly half of 1985 rates), if nitrogen saturation occurs in 50 years. Approximately 40% of streams would be episodically acidic under the same scenario. If the time to nitrogen saturation is expanded to 250 years, current rates of N deposition would lead to chronic acidification in 4% of streams and episodic acidification in 28% of streams.

The NBS predicted much lower rates of acidification in the southern Blue Ridge, where 4% ( chronic) and 16% ( episodic) of streams would be acidified with a time to saturation of 50 years. With a 250 year time to saturation, the models predicted no streams would be chronically acidic, and 14% would be susceptible to episodic acidification. These modeling results are somewhat at odds with information about the current status of streams in the SBRP. Some streams in Great Smoky Mountains National Park are acidic and have high nitrate concentrations. These streams tend to occur at high elevations, whereas the DDRP sampling design was based on the lower elevation downstream segment end population. Thus, the NBS results based on the DDRP are biased toward lower elevation streams ( Cook et al., 1994), leading to more conservative forecasts for future acidity. 61 7. RECOMMENDATIONS FOR SAMI ASSESSMENT 7.1 Model Recommendations We recommend that the SAMI assessment use the MAGIC model for any quantitative future projections of surface water acid base status. The steady state models are not appropriate for the Southern Appalachians. In addition to the arguments against steady state models listed in section 5.1.1, streams in the SAMI region are not at steady state. The time required to reach steady state is one of the major unknowns that needs to be modeled in the SAMI assessment. Of the two dynamic watershed models ( ILWAS and MAGIC) suitable for SAMI, MAGIC is by far the easiest, quickest, and least expensive to apply. The two models do have some real differences in terms of some projections ( especially among alternate deposition scenarios in the southern Blue Ridge). Both models were extensively tested during the NAPAP assessment and there was no evidence that either model was more accurate than the other. Although ILWAS is more complex and models more processes and compartments, complexity does not necessarily make the model results more accurate. Therefore, it seems more cost effective to select the more economical MAGIC model.

We recommend the use of the PnET CN model as the nitrogen model for use in further assessments, because of its track record of applicability to a variety of sites with relatively little site specific information. It would require some regional compilation of climate data and land use histories, as well as the collection of foliar nutrient samples from all sites of interest ( a fairly straightforward task). One of the primary outputs of PnET CN is the time to nitrogen saturation. This information could easily be incorporated into runs of the MAGIC model, to produce desired forecasts of acid base status, given various scenarios of sulfur and nitrogen deposition ( as well as climate change, if desired).

To make projections about the effects of episodic acidification on streams in the SAMI region, we recommend linking the regression model approach of Eshleman ( 1988) to MAGIC model projections. This step would provide a first approximation of the likely magnitude of episodic impacts. The regression model is fairly robust, can be applied on a regional basis, and has already been shown to be linkable to MAGIC. The regression equations, however, should be recalibrated using new data from studies in the Shenandoah and Great Smoky Mountains National Parks.

For doing future projections of the effects of acidic deposition on fish, we recommend using the acid stress index ( ASI) approach used in the NAPAP assessment. Calcium, pH, and aluminum values can be obtained from MAGIC output to calculate ASIs under alternate deposition scenarios. Critical ASI values can then be obtained by comparing current fish distributions to current ASI levels.

7.2 Levels of Assessment For SAMI, we've devised four levels of effort for doing an aquatic effects assessment. Each additional level will require more resources but will give a more complete assessment. The final choice of an assessment approach will require decisions about the nature and objective of the assessment. For example, will the assessment focus on streams in the entire SAMI region, the acid sensitive part of the region, or just the Class I areas? Should the assessment just look at sulfur deposition or sulfur and nitrogen? How quantitative does the answer need to be? How different are the various emission management options or deposition scenarios? As the SAMI assessment is still in its formative stages, our recommended levels span a wide range of 62 options. The final decision will depend heavily on the final choice of the SAMI assessment objective.

7.2.1 Level 1 A very simple qualitative assessment could be made by examining the existing results of the DDRP and NAPAP Integrated Assessment. For example, Figure 12 in this report gives a reasonably good idea of the relative effects of various sulfur deposition scenarios on the regional population of streams in the mid Appalachians and southern Blue Ridge. This analysis focuses on the region as a whole, not the Class I areas. As the Class I areas comprise some of the most sensitive systems in the SAMI region, inferences to them could be made by examining what happens to the most sensitive streams in the regional distribution.

7.2.2 Level 2 An analysis that would require no new collection of data would involve redoing the DDRP/ NAPAP Assessment at the existing DDRP sites using new deposition scenarios provided by SAMI. The data currently exist to run MAGIC at all these sites and to calculate fish ASI values using MAGIC output. This activity would provide a quantitative regional estimate of stream acid base status for each of the SAMI deposition scenarios. This level has two major shortcomings. One drawback is that it really does not handle changes in nitrogen deposition/ dynamics; the assessment would remain driven by sulfur deposition. Secondly, as in level 1, level 2 focuses on the region as a whole, not the Class I areas that may be of primary interest to SAMI. As in level 1, some inference to the Class I areas could be made by examining what happens to the most sensitive streams in the region, but it would not be very quantitative or applicable to any specific Class I area.

7.2.3 Level 3 Level 3 efforts would be geared toward using the most current methodologies for making the projections of the aquatic effects of acidic deposition. The analysis should be done by Class I wilderness area groups ( e. g., West Virginia Plateau, southern Blue Ridge). It could be done for just one group or as many of the groups as resources allow. We would, however, make the Sipsey wilderness area group a low priority and focus efforts in the other three areas. We would recommend field efforts to collect new data on soils, watershed attributes, and hydrology for three low ANC watersheds ( along the available ANC gradient) in each group. Where water chemistry information is sparse or lacking ( see 7.4), a probability sample of 30 B 50 streams in the wilderness area group should be conducted to aid in regionalizing to the entire area group. This task would be relatively simple in the smaller areas but might require some extra effort in the GSMNP. Data necessary to run the PnET CN nitrogen model and episodic acidification model ( foliar chemistry, land use, and hydrologic information) should be collected at the same time. MAGIC and PnET CN models would be used to make future projections about average annual streamwater chemistry. The episodic model would be linked to the MAGIC output to predict episodic acidity. ASI values could then be calculated for both episodic and chronic conditions to estimate the effects on fish. All the models would need to be calibrated and run under the SAMI deposition scenarios. This approach would allow for the best available projections for the modeled Class I wilderness area groups. 63 7.2.4 Level 4 A level 4 analysis would consist of conducting the level 3 analysis for each of the DDRP stream sites ( level 2) to allow regional projections that take both nitrogen and sulfur dynamics into account. This work would involve collecting additional information at these sites to run PnET CN.

7.2.5 Fish Assessment A fish assessment could be added to Level 2, 3, or 4 quite easily using the ASI approach. However, field information on the relationship between fish distributions and ASI values needs to be collected and evaluated in order to set critical ASI levels for sensitive, intermediate and tolerant fish species.

7.3 Limitations and Relationship to a SAMI Integrated Assessment One of the conclusions of the NAPAP assessment was that " Uncertainties in the absolute magnitudes and timing of aquatic effects projections are high, but we have confidence in the projected direction of change and in the relative amounts of change." We believe that this conclusion has two important implications for the SAMI assessment:

1. Emission management options or deposition scenarios that result in very small changes in sulfur and nitrogen deposition will not cause distinguishable differences in aquatic effects. The resolution of the models is not that high.

2. Transferring absolute aquatic model projections ( e. g., miles of acidic streams) into a broader integrated effects model has a large potential for significant errors. The models are reasonably good for evaluating the relative differences of different deposition scenarios. Thus, we are fairly comfortable with running the models and making conclusions about the relative differences in aquatic effects among various deposition scenarios. However, we are uncomfortable with using the absolute results ( e. g., length of acidic streams) of these models. We are very uncomfortable with taking these absolute results, linking them together with absolute results from other effects models ( e. g., visibility, ozone), running them all through a socioeconomic valuation model, and using some kind of overall " cost" estimate as the decision making tool for evaluating different emissions scenarios. From the aquatic perspective, future projections about miles of acidic streams or miles of streams that will have impaired or absent fish populations have very large uncertainties due to model structure, sensitivity, calibration, and definition of the target population.

7.4 Data Availability The surface water chemistry and watershed data required to run the MAGIC model exist at 35 streams in the southern Blue Ridge and 36 streams in the mid Appalachians that were sampled in the NSS and DDRP. Note that only 17 of the 36 streams in the mid Appalachians were in the SAMI states of West Virginia or Virginia. Data also exist to run the MAGIC model in the streams of Shenandoah National Park where the MAGIC model was developed. We are not aware of any other locations in the SAMI region where sufficient watershed, soils, water chemistry, and hydrologic data are available or are in a form ready to run MAGIC.

Available water chemistry data sets exist in many of the Class I areas in varying degrees of resolution. The magnitude of the " No Data" column in Table 5 relates the degree of completeness. High resolution data sets exist for Otter Creek, Dolly Sods, and the Shenandoah National Park. Data sets with good resolution exist for James River Face and Cohutta. More complete data need to be collected in Sipsey, Slickrock, and Shining 64 Rock wilderness areas. Data exist for 359 stream sites in the Great Smoky Mountains National Park. These sites, however, repre sent only about one third of the stream length in the park. A population level assessment is likely to require a probability survey of the park's 2,035 km of streams ( Table 3). 65 8. LITERATURE CITED Aber, J. D., K. J. Nadelhoffer, P. Steudler, and J. M. Melillo. 1989. Nitrogen saturation in northern forest ecosystems. BioScience 39: 378 386.

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Baker, J. P., J. Van Sickle, C. J. Gagen, D. R. DeWalle, W. E. Sharpe, R. F. Carline, B. P. Baldigo, P. S. Murdoch, D. W. Bath, W. A. Kretser, H. A. Simonin, and P. J. Wigington, Jr. 1996. Episodic acidification of small streams in the northeast United States: Effects on fish populations. Ecol. Appl. 6: 422 437.

This paper largely summarizes the results from the experimental field studies of fish populations in the 13 ERP streams first reported on by Wigington et al. ( 1993).

Baker, L. A., A. T. Herlihy, P. R. Kaufmann, and J. M. Eilers. 1991. Acidic lakes and streams in the United States: The role of acidic deposition. Science 252: 1151 1154.

A short article taken from the NAPAP SOS/ T report 9 examining the likely causes of acidity in lakes and streams. It also summarizes the number and proportions of lakes and streams in the U. S. likely to be acidic as a result of acidic deposition.

Bazemore, D. E., K. N. Eshleman, and K. J. Hollenbeck. 1994. The role of soil water in stormflow generation determined from natural tracer and hydrometric techniques. J. Hydrol. 162: 47 75.

A field study that combined natural tracer methods and hydrometric observations was conducted to estimate the contributions of pre event soil water to stormflow in a small forested catchment in Shenandoah National Park, Virginia. A three component model using two naturally occurring tracers ( oxygen 18 and chloride) was used to show that pre event soil water dominated total storm runoff and peak runoff during two major rainfall events. The authors also illustrated that quantitative error analyses are advisable in chemical and isotopic hydrograph separation studies. Field observations suggested that the pre event water response could be attributed to a threshold type expansion of hillslope source areas. Results of the study are significant for understanding episodic acidification, because the chemical composition of the three end members ( soil water, groundwater, and throughfall) may vary dramatically in small headwater systems.

Bishop, K. H. 1991. Episodic Increases in Stream Acidity, Catchment Flow Pathways and Hydrograph Separation. PhD dissertation. Department of Geography, University of Cambridge, U. K.

Detailed field investigations ( including hydroisotopic separations using oxygen 18) were conducted at Loch Fleet ( Scotland) and Svartberget ( Sweden) to test the hypothesis that acid episodes are due primarily to the rapid displacement of pre event water from the catchment during stormflow events. This hypothesis was confirmed by the field investigation, although the study was unable to identify the specific mechanisms of runoff generation ( e. g., saturation overland flow, subsurface stormflow) in the two watersheds. The author also concluded that non Darcian flow ( i. e., macropore flow) could explain the field observations of rapid displacement of pre event water and increases in stream acidity during storm events.

Bradford, D., C. Swanson, and M. Gordon. 1992. Effects of low pH and aluminum on two declining species of amphibians in the Sierra Nevada, California. Jour. of Herpetology 26: 369 377.

Bradford, D. F., and M. S. Gordon. 1992. Aquatic amphibians in the Sierra Nevada: Current status and potential effects of acidic deposition on populations Final report, Contract No. A932 139, California Air Resources Board, Sacramento, CA.

Bradford, D. F., C. Swanson, and M. Gordon. 1994. Effects of low pH and aluminum on amphibians at high elevation in the Sierra Nevada, California. Can. J. Zool. 72: 1272 1279.

Bradford, D. F., M. Gordon, D. Johnson, R. Andrews, and W. B. Jennings. 1994. Acidic deposition as an unlikely cause of amphibian population declines in the Sierra Nevada, California. Biological Conservation 69: 155 161.

Toxicity testing indicated that amphibians are at little risk from low pH in water acidified to a pH level of 5.0, with Al concentrations of 39 B 80  g/ L. However, the authors observed sublethal effects ( reduced growth rate and earlier hatching) for pH as high as 5.25 at the Al concentrations tested. Field survey findings implied that acidic deposition is unlikely to have been a cause of 72 recent amphibian population declines in the Sierra Nevada.

Bulger, A. J., L. Lien, J. Cosby, and A. Henriksen. 1993. Brown trout ( Salmo trutta) status and chemistry from the Norwegian Thousand Lake Survey: Statistical Analysis. Can. J. Fish. Aquat. Sci. 50: 575 585.

The relationship between atmospheric sulfate and terrestrial calcium is the main control of acidification processes, but neither one is a good predictor of fish response; this paper provides a useful explanation of this as a general phenomenon, not limited to Norway. It also provides an explanation linking toxic mechanisms and empirical responses of fish populations in nature.

Bulger, A. J., C. A. Dolloff, B. J. Cosby, K. N. Eshleman, J. R. Webb, and J. N. Galloway. 1995. The " Shenandoah National Park: Fish in Sensitive Habitats ( SNP: FISH)" Project: An integrated assessment of fish community responses to stream acidification. Water Air Soil Pollut. 85: 309 314 This paper presents a summary to date of the overall findings of a three year project on fish community effects and acid base chemistry in mountains streams in Virginia. Both chronic and episodic acidification are occurring in these streams. Biological differences in low ANC versus high ANC streams include fish species richness, population density, condition factor, age, size, and bioassay survival. Predictive models relating fish status to future water chemistry will be produced by this project.

Carline, R. F., D. R. Dewalle, W. E. Sharpe, B. A. Dempsey, C. J Gagen, and B. Swistock. 1992. Water chemistry and fish community responses to episodic stream acidification in Pennsylvania, USA. Environ. Pollut. 78: 45 48.

Five undisturbed, wooded streams were studied on the Northern Appalachian Plateau of Pennsylvania for 9 months to determine chemical changes and fish responses that occur during episodic storm runoff. Wild brook trout were found in all streams, although only a remnant population existed in the most acidic stream. Sculpins ( Cottus bairdi or C. cognatus) were collected only in the two streams with the least severe episodes. Mortality of brook trout and sculpins in in situ bioassays ranged from 0 to about 80% among streams during acidic episodes and was positively related to concentrations of total dissolved Al. Some displaced trout were found near groundwater seeps, where pH was higher and dissolved Al lower than in the main channel.

Church, M. R., and J. Van Sickle. 1995. Potential Relative Effects of Nitrogen and Sulfur Deposition on Regional Scale Acidification of Surface Waters in the Eastern United States. U. S. Environmental Protection Agency, Washington, DC.

The Nitrogen Bounding Study used the MAGIC model to predict the future acid base status of regional populations of surface water sites under several different scenarios for future nitrogen and sulfur deposition, and several different time series for nitrogen saturation.

Church, M. R., P. W. Shaffer, K. N. Eshleman, and B. P. Rochelle. 1990. Potential future effects of current levels of sulfur deposition on stream chemistry in the Southern Blue Ridge Mountains, United States. Water Air Soil Pollut. 1990: 39 48.

This article concludes that, although little change in surface water chemistry is likely to have occurred due to acidic deposition in the region to date, soils are currently retaining a majority of atmospherically deposited S, and it is likely that marked increases in surface water SO4 2

will occur. Such increases could be accompanied by significant surface water acidification ( loss of ANC).

Church, M. R., P. W. Shaffer, K. W. Thornton, D. L. Cassell, C. I. Liff, M. G. Johnson, D. A. Lammers, J. J. Lee, G. R. Holdren, J. S. Kern, L. H. Liegel, S. M. Pierson, D. L. Stevens, B. P. Rochelle, and R. S. Turner. 1992. Direct/ Delayed Response Project: Future Effects of Long Term Sulfur Deposition on Stream Chemistry in the Mid Atlantic Region of the Eastern United States. EPA/ 600/ R 92/ 186. U. S. Environmental Protection Agency, Washington, D. C.

This is the last in the series of DDRP reports detailing the results of empirical and dynamic modeling of acidification of the regional population of surface waters in several regions. For this report, the results of the Appalachian Plateau, Valley and Ridge, and Piedmont provinces are presented together.

Cook, R. B., J. W. Elwood, R. R. Turner, M. A. Bogle, P. J. Mulholland, and A. V. Palumbo. 1994. Acidbase chemistry of high elevation streams in the Great Smoky Mountains. Water Air Soil Pollut. 72: 331 356. 73 Cook et al. report on seasonal data from eight streams in Great Smoky Mountains National Park on differing types of bedrock. They point out both the effects of the Anakeesta formation on stream chemistry ( high SO4 2

and acidic waters) and the effects of high elevation, old growth forests on NO3

concentrations.

Davies, T. D., P. J. Wigington, Jr., M. Tranter, and K. N. Eshleman. 1992. ` Acidic episodes' in surface waters in Europe. J. Hydrol. 132: 25 69.

This paper largely presents a summary of Section 3.2 of Wigington et al. ( 1990), NAPAP SOS/ T Report 12.

Dennis, T. E., and A. J. Bulger. 1995. Condition factor and whole body sodium concentration in a freshwater fish: evidence of acidification stress and possible ionoregulatory over compensation. Water Air Soil Pollut. 85: 377 382.

Acidification negatively affects ion regulation in fish. This paper shows that fish in a low ANC stream appear to be able to ion regulate adequately at current acid base conditions, but it also suggests that the added metabolic cost of ion regulation in low ANC streams versus high ANC streams my be responsible for slower growth and smaller sized individuals in the low ANC stream.

Dennis, T. E. , S. E. MacAvoy, M. B. Steg and A. J. Bulger. 1995. The association of water chemistry variables and fish condition in streams of Shenandoah National Park ( USA). Water Air Soil Pollut. 85: 365 370.

This paper demonstrates a strong relationship between water chemistry and fish condition factor, across nine montane streams in Virginia. The variables most strongly related to fish condition were those associated with ANC and SO4 2

, with condition factor poorest in low ANC streams.

DiStefano, R. J., R. J. Neves, L. A. Helfrich, and M. C. Lewis. 1991. Response of the crayfish Cambarus bartonii bartonii to acid exposure in southern Appalachian streams. Can. J. Zool. 69( 6): 1585 1591.

Tolerance of crayfish to acidity was rather high ( 96 hr LC50, range 2.43 B 2.85 for early juveniles to adults). Lowering the water temperature increased acid tolerance. Nevertheless, the authors state that gradually increasing acidity and loss of watershed buffering capacity could produce sublethal effects, such as altered reproductive activity or changes in early life history stages and more sensitive molt cycle stages, that could damage crayfish populations.

Dow, C. L., D. R. DeWalle, J. A. Lynch, and W. E. Sharpe. 1994. Blizzard's effects on Appalachian stream chemistry assessed. EOS Trans. Amer. Geophys. Union 75: 389 390.

This short paper provides a description of the hydrochemical changes observed in three small streams in Pennsylvania during an extreme rainon snow event that followed the " blizzard of 1993." This storm deposited approximately 90 cm of snow on the study catchments and was followed by about 7 cm of rainfall, which caused the highest sustained ( monthly) discharge in the Susquehanna River basin. ANC and pH depressions ( and elevated Al concentrations) during the event were quite large, although their absolute magnitude was not found to vary significantly from previously monitored conditions of lesser ( hydrological) magnitude. Nitrate and organic anion concentrations were significantly higher than those recorded previously, however, which supported the explanation that flows were attributable to movement of water through shallow soil horizons.

Downey, D. M., C. R. French, and M. Odom. 1994. Low cost limestone treatment of acid sensitive trout streams in the Appalachian Mountains of Virginia. Water Air Soil Pollut. 77: 49 77.

Based on their results in three streams, the authors suggest that approximately 88% of native trout streams in Virginia, which average 29  eq/ L ANC reduction from acid deposition, could be temporarily restored using single application liming.

Driscoll, C. T., and R. Van Dreason. 1993. Seasonal and long term temporal patterns in the chemistry of Adirondack lakes. Water Air Soil Pollut. 67: 319 344.

A long term ( 1982 present) monitoring program of 17 Adirondack lakes was conducted to examine temporal patterns in acid base chemistry. The monitoring results indicated relatively uniform SO4 2

concentrations among the lakes, while ANC variations were largely determined by differences in base cations. Lakes in the southern and western Adirondacks showed the highest levels of NO3

, during both peak and baseflow conditions. From an episodic acidification perspective, this paper is significant since it concluded that Adirondack lakes with ANC values < 100  eq/ L 74 during baseflow conditions may experience decreases in ANC to values near or below 0.

Eckhardt, B. W. and T. R. Moore. 1990. Controls on dissolved organic carbon concentrations in streams, southern Quebec. Can. J. Fish. Aquat. Sci. 47( 8): 1537 1544.

DOC concentrations in 42 streams draining small catchments in the Appalachian Uplands and St. Lawrence Lowlands were consistently related to the percentage of wetland in the catchment. The results indicate that stream DOC concentrations may be predicted from easily obtained catchment variables, such as percent wetland.

Englin, J. E., T. A. Cameron, R. E. Mendelsohn, G. A. Parsons, and S. A. Shankle. 1991. Valuation of damages to recreational trout fishing in the upper Northeast due to acidic deposition. Technical Report. NTIS Order No. DE91012029/ GAR. Battelle Pacific Northwest Laboratories.

This report documents methods used by NAPAP to model the economic value of changes in recreational fishing due to acidic deposition.

Eshleman, K. N. 1992. Comment on " The episodic acidification of Adirondack lakes during snowmelt by Douglas A. Schaefer et al. Water Resour. Res. 28: 2869 2873.

This paper is a technical comment on an earlier paper published in Water Resources Research that dealt with the significance of the linear relationship observed by Eshleman ( 1988) between ANCindex and ANCminimum for a group of lakes in the Adirondacks of New York. The author argued that the observed linear relationship is statistically and physically significant and can be applied to an entire population of lakes in the Adirondacks.

Eshleman, K. N. 1995. Predicting Regional Episodic Acidification of Streams in Western Maryland. Report CBRM AD 95 7. Maryland Department of Natural Resources, Annapolis.

This report used the empirical linear regression model first proposed by Eshleman ( 1988) and data from two studies of episodic acidification in the Appalachian Plateau to provide an estimate of the number and length of streams in western Maryland that are episodically acidic ( ANC < 0) during stormflow periods. The report concluded that about 50% more streams ( 11% of the population) are acidic during episodes than are acidic during spring baseflow conditions ( 7% of the population) in the region; the population used corresponds to those streams sampled during the Maryland Synoptic Stream Chemistry Survey ( MSSCS) in 1987. An important uncertainty is whether the linear regression model can be applied across all bedrock types found in western Maryland.

Eshleman, K. N., P. J. Wigington, Jr., M. Tranter, and T. D. Davies. 1992. Modelling episodic acidification of surface waters: The state of the science. Environ. Pollut. 77: 287 295.

This paper largely summarizes Chapter 5 of Wigington et al. ( 1990), NAPAP SOS/ T Report 12.

Eshleman, K. N., P. J. Wigington, Jr., T. D. Davies, and M. Tranter. 1995. A two component mixing model for predicting regional episodic acidification of surface waters during spring snowmelt. Water Resour. Res. 31: 1011 1021.

A two component mixing model of ANC was used to explain two observed features related to the episodic acidification of Adirondack and Catskill mountain surface waters during spring snowmelt: ( 1) maximum episodic declines in ANC are largest in high ANC systems and increase linearly with antecedent ANC and ( 2) relative depressions in ANC attributable to dilution of base cations are larger in high ANC systems. The model was calibrated using snowmelt data for 10 Adirondack lakes and was then applied to the regional population of lakes described by the National Lake Survey. The model was also linked to an empirical acidification model for predicting the future extent of episodically acidic ( ANC < 0) lakes in the Adirondacks, given various emissions control strategies. Model predictions indicated that 40% reductions in sulfuric acid concentrations will not restore to positive values the ANC of all lakes that are currently acidic during spring snowmelt.

Eshleman, K. N., L. M. Miller Marshall, and J. R. Webb. 1995. Long term changes in episodic acidification of streams in Shenandoah National Park, Virginia ( U. S. A.). Water Air Soil Pollut. 85: 517 522.

A statistical analysis of 13 years of daily discharge data and weekly streamwater composition data for White Oak Run ( WOR) in Shenandoah National Park was performed in order to quantify episodic changes in composition and to identify long term trends in episodic acidification attributable to both natural and anthropogenic processes. An objective hydrological separation technique was 75 used to ident i fy mor e than 100 " stormflow/ baseflow pairs" in the database, from which episodic chemical changes could be quantified. Univariate statistical analysis suggested that mean episodic depressions of ANC in WOR have increased by about a factor of 2 since the first outbreak of forest defoliation by the gypsy moth caterpillar during the summer of 1990; in addition, the mean episodic change in nitrate concentration has increased by about 12  eq/ L, while the mean episodic dilution of CB has decreased from

8.5  eq/ L to

1.7  eq/ L during the same period. Episodic changes in SO4 2

have remained the same, however. The results indicate that natural processes such as insect defoliations can contribute to episodic acidification through mobilization of NO3

.

Flum, T., and S. C. Nodvin. 1995. Factors affecting streamwater chemistry in the Great Smoky Mountains, USA. Water Air Soil Pollut. 85: 1707 1712.

Flum et al. summarize the results of synoptic stream chemistry surveys carried out in Great Smoky Mountains National Park during the 1990s. They focus on differences among different types of bedrock and former land use types ( e. g., old growth vs. second growth forests) and across elevations. ANC is lowest and NO3

is highest in the least disturbed ( i. e., old growth) and highest elevation watersheds.

Gagen, C. J., W. E. Sharpe, and R. F. Carline. 1994. Downstream movement and mortality of brook trout ( Salvelinus fontinalis) exposed to acidic episodes in streams. Can. J. Fish. Aquat. Sci. 51( 7): 1620 1628.

This article describes a study of two streams with severe acidic episodes and two with less severe acidic episodes. Episodes of low pH and high Al concentration were associated with net downstream movement and increased mortality of radio tagged brook trout. Study populations moved downstream hundreds of meters in the streams with more severe acidic episodes ( pH < 5.0 and Al > 200  g/ L. Median downstream movement in spring was 250 and 900 m after 20 days for fish in the more acidic streams; one third of the fish were found dead during this time. They found no net movement and no dead fish in the reference streams. Lower stream discharge in fall studies was associated with less severe acidic episodes, less net movement, and no mortality. Water samples collected at individual fish locations indicated that few fish avoided adverse effects of acidic episodes by remaining in microhabitats with higher H and lower Al concentration.

Griffith, M. B., and S. A. Perry. 1993. Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH. Freshwat. Biol. 30( 1): 93 103.

This article describes a leaf pack study of four central Appalachian streams. Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream. Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies. The differences in processing rates between the more alkaline stream and the neutral streams appeared to be related to taxonomic differences in the shredder assemblages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.

Heath, R. H., J. S. Kahl, S. A. Norton, and I. J. Fernandez. 1992. Episodic acidification caused by the seasalt effect in coastal Maine streams, USA. Water Resour. Res. 28: 1081 1088.

This field study examined the causes and characteristics of episodic acidification of low order streams in Acadia National Park ( Maine), based on samples collected during stormflow conditions using automated water samplers and analyzed for ANC, pH, DOC, Si, and major ions. The primary conclusion of the study was that the sea salt effect is the dominant cause of episodic acidification of streams in coastal Maine, owing to a depression in the Na: Cl ratio in surface waters by precipitation. No other contributors to episodic acidification ( SO4 2

, NO3

, organic acids) were able to explain the magnitude of ANC changes observed.

Herlihy, A. T., P. R. Kaufmann, and M. E. Mitch. 1991. Chemical characteristics of streams in the Eastern United States: II. Sources of acidity in acidic and low ANC streams. Water Resour. Res. 27: 629 642.

This is part 2 of a two part paper that summarizes the results of EPA's National Stream Survey, a probability survey of stream chemistry in the mid Atlantic and southeastern United States. This part of the paper describes the chemical classification scheme used to attribute sources of acidity to organics, mining, and deposition. It then uses the 76 probability design of the Survey to make population estimates of stream numbers in the different acid source classes.

Herlihy, A. T., P. R. Kaufmann, M. R. Church, P. J. Wigington, Jr., J. R. Webb, and M. J. Sale. 1993. The effects of acidic deposition on streams in the Appalachian Mountain and Piedmont region of the mid Atlantic United States. Water Resour. Res. 29: 2687 2703.

This article is an assessment of the effects of acidic deposition on streams of the mid Appalachian and Piedmont region of the U. S. It summarizes all available survey information on the effects of acidic deposition on chronic and episodic stream chemistry, and includes biological effects.

Hooper, R. P., and N. Christophersen. 1992. Predicting episodic stream acidification in the southeastern United States: Combining a longterm acidification model and the end member mixing concept. Water Resour. Res. 28: 1983 1990.

This paper addresses the problem of predicting episodic stream acidification through the use of a long term acidification model ( MAGIC) linked to a end member mixing model. The results of the modeling effort C applied to the Panola Mountain Research Watershed ( Georgia) C predicted that the two upper soil levels will dramatically acidify within the next 50 years, causing the streamwater to become unsuitable for sensitive aquatic biota for much of the year.

Hyer, K. E., J. R. Webb, and K. N. Eshleman. 1995. Episodic acidification of three streams in Shenandoah National Park, Virginia ( U. S. A.). Water Air Soil Pollut. 85: 523 528.

The short term acidification of three streams in Shenandoah National Park was studied to quantify the magnitude of chemical changes accompanying stormflow conditions and to evaluate the contributions of individual ions to changes in streamwater ANC. An important element of the study was the unique bedrock geology of each of the catchments. Data from 25 storm events were analyzed using the method of Molot et al. ( 1989). Depressions in pH and ANC were observed in all three streams, although ANC only became negative in the most acid sensitive stream, Paine Run, which drains a catchment underlain by silici clastic bedrock. Similar to other studies, SO4 2

and NO3

concentrations usually increased during storm events in all streams, although base cation concentrations typically increased. Minimum values of ANC during storm events were best predicted by a linear model using antecedent baseflow ANC as the independent variable.

Johnson, D. W., and S. E. Lindberg, eds. 1992. Atmospheric Deposition and Forest Nutrient Cycling. Ecological Studies. Springer Verlag, New York.

This book summarizes the results of the Integrated Forest Study ( IFS), and includes detailed information on the IFS sites in Great Smoky Mountains National Park ( 3 sites) and at Coweeta. The focus was on detailed measurements of deposition ( wet, dry, and cloud), soil solution chemistry, and other aspects of nutrient cycles in forests. This work clearly identifies the high elevation parts of Great Smoky Mountains National Park as the highest deposition areas in the United States.

Johnson, D. W., W. T. Swank, and J. M Vose. 1993. Simulated effects of atmospheric deposition on nutrient cycling in a mixed deciduous forest. Biogeochem. 23: 169 196.

Using the NuCM ( Nutrient Cycling Model) model, the authors investigated the effects of three S deposition scenarios on biogeochemical cycling of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina. Ecosystem S and SO4 2

leaching were almost entirely controlled by SO4 2

adsorption via the nature of the Langmuir adsorption isotherm used in NuCM. Both the simulations and field data show that the ecosystem is becoming more S saturated. Varying S deposition had very little effect upon simulated vegetation growth, nutrient uptake, or N cycling but had a strong effect on base cation and P leaching. S deposition effects on soil exchangeable pools of these elements, however, were minimal due to the size of these pools relative to the fluxes.

Kahl, J. S., S. A. Norton, T. A. Haines, E. A. Rochette, R. H. Heath, and S. C. Nodvin. 1992. Mechanisms of episodic acidification of low order streams in Maine, U. S. A. Environ. Pollut. 78: 37 44.

Observed chemical changes during hydrological events in low order streams in Maine were examined in order to understand the mechanisms of episodic acidification in this region. It was generally observed that five processes contribute to episodic depressions in pH and ANC: ( 1) increases in nitric acid concentrations, ( 2) increases in 77 organic acidity, ( 3) increases in the anion fraction of SO4 2

, ( 4) increases in acidity due to the salt effect in soils, and ( 5) hydrological dilution of ANC by increased stream discharge. The chemical composition of individual precipitation events was found to be irrelevant in the generation of acidic episodes, with the exception of those primarily attributable to high loadings of neutral salts within the coastal region of Maine.

Kaufmann, P. R., A. T. Herlihy, M. E. Mitch, and W. S. Overton. 1991. Chemical characteristics of streams in the Eastern United States: I. Synoptic survey design, acid base status and regional chemical patterns. Water Resour. Res. 27: 611 627.

This is part 1 of a two part paper that summarizes the results of EPA's National Stream Survey, a probability survey of stream chemistry in the mid Atlantic and southeastern United States. This part of the paper describes the probability design of the Survey and discusses the regional findings in terms of population estimates of condition.

Kaufmann, P. R., A. T. Herlihy, and L. A. Baker. 1992. Sources of acidity in lakes and streams of the United States. Environ. Pollut. 77: 115 122.

This paper presents and defends a classification scheme designed to attribute sources of acidity to the lakes and streams of EPA's National Surface Water Survey.

Kobuszewski, D. M., and S. A. Perry. 1993. Aquatic insect community structure in an acidic and a circumneutral stream in the Appalachian Mountains of West Virginia. J. Freshwat. Ecol. 8( 1): 37 45.

The authors report, in comparing benthic macroinvertebrates in two West Virginia streams, that density did not differ between the acidic and circumneutral stream, but species richness and evenness were higher in the neutral stream. Plecoptera and shredders dominated the acidic stream.

Kobuszewski, D. M., and S. A. Perry. 1994. Secondary production of Rhyacophila minora, Ameletus sp., and Isonychia bicolor from streams of low and circumneutral pH in the Appalachian Mountains of West Virginia. Hydrobiologia 273( 3): 163 169.

This article describes a study of three acidic streams and one circumneutral stream in Randolph County, West Virginia. Differences in secondary production of these species were associated with differences in macroinvertebrate community structure.

Kutka, F. J. 1994. Low pH effects on swimming activity of Ambystoma salamander larvae. Environ. Toxicol. Chem. 13( 11): 1821 1824.

Results suggest that salamander embryos and larvae may suffer from pH levels below 5.0, even though these levels are not directly lethal. Because of their sensitivity, the authors recommend activity tests with amphibian larvae for use in risk assessments.

Larsen, G. L., S. E. Moore, and B. Carter. 1995. Ebb and flow of encroachment by nonnative rainbow trout in a small stream in the Southern Appalachian Mountains. Trans. Am. Fish. Soc. 124: 613 622.

The results of this study suggest that encroachment by rainbow trout ( nonnative) can exhibit considerable ebb and flow in steep gradient streams of the Great Smoky Mountains National Park. Results also suggest substantial evolutionary adaptation by brook trout to the hydrological conditions in these small streams. We found this paper to be interesting, because similar resistance to rainbow trout invasion in headwater streams has been attributed to the greater tolerance of brook trout to the typically more acidic conditions in steep headwaters.

Lawrence, G. B., M. B. David, and W. C. Shortle. 1995. A new mechanism for calcium loss in forest floor soils. Nature 378: 162 164.

Concentrations of root available calcium have declined in the northeastern United States over the last 60 years. Based on data collected in red spruce forests, the authors propose a mechanism where aluminum ( mobilized in the mineral soil by acid deposition) is transported into the forest floor in a reactive form that reduces storage of calcium and thus its availability for root uptake. This would result in potential stress to trees, increased forest demand for calcium, and decreased calcium runoff to surface waters ( decreasing surface water ANC).

Loer, S. C., and J. L. West. 1992. Microhabitat selection by brook and rainbow trout in a southern Appalachian stream. Trans. Am. Fish. Soc. 121( 6): 729 736.

We were interested in this paper because it deals with the decreased range of native brook trout in the Great Smoky Mountains National Park, which 78 has been attributed to competition with introduced rainbow trout C a fish not as tolerant of acidity as brook trout. This study reports that young of theyear and to some extent age 1, brook trout shifted to habitat positions farther from overhead cover when rainbow trout numbers were reduced.

MacAvoy, S. E. and A. J. Bulger. 1995. Survival of brook trout ( Salvelinus fontinalis) embryos and fry in streams of different acid sensitivity in Shenandoah National Park, USA. Water Air Soil Pollut. 85: 439 444.

This paper demonstrates significantly higher mortality of hatchery stock brook trout embryos and fry in field bioassays in low ANC streams compared to high ANC streams in Virginia, both chronically and during acidic episodes.

McQuattie, C. J., S. L. Stephenson, and P. J. Edwards. 1993. Effect of stream acidity on decomposition of sugar maple ( Acer saccharum) and red oak ( Quercus rubra) leaves. Ohio J. Sci. 93( 2): 48.

Leaf decomposition of both species was more rapid in a pH 5.6 stream than in a pH 3.2 stream. Authors state that differences were probably due to increased numbers or types of aquatic microorganisms found in the pH 5.6 stream. Acidity level appeared to have a direct effect on cuticular wax structure of the leaves.

Miller Marshall, L. M. 1993. Mechanisms Controlling Variation in Stream Chemical Composition During Hydrologic Episodes in the Shenandoah National Park, Virginia. MS thesis. Department of Environmental Sciences, University of Virginia, Charlottesville. 165 pp.

This thesis describes both a field investigation of episodic acidification at two sites in Shenandoah National Park and a statistical analysis of longterm weekly stream chemical composition data for four sites in the Park. A major result of the study was that sulfuric acid increases and base cation dilution are the primary mechanisms contributing to the losses of ANC in streams in the Park during hydrological events, although there is evidence that nitric acid has recently become a more important contributor to ANC losses in these streams. These conclusions were based on application of an approach to partitioning ANC losses developed by Molot et al. ( 1989) and on a newer approach known as the Response Sector Model ( RSM).

Morgan, R. P., II, C. K. Murray, and K. N. Eshleman. 1994. Episodic water chemistry changes in a western Maryland watershed. Report CBRM AD 94 8. Maryland Department of Natural Resources, Annapolis. 125 pp.

This report describes a study of episodic acidification at six sites in the Big Run watershed in western Maryland. A total of 23 hydrological events ( including storm fronts, thunderstorms, and snowmelts) were sampled over a 3 year period ( 1989 92). Antecedent ANC was found to be an excellent predictor ( r2 = 0.91) of ANCminimum at the six sites and ANC depressions were largely attributable to increases in sulfuric acid concentrations and dilution of base cations. Nitric and organic acids were secondary contributors to the loss of ANC.

Murdoch, P. S., and J. L. Stoddard. 1992. The role of nitrate in the acidification of streams in the Catskill Mountains of New York. Water Resour. Res. 28: 2707 2720.

The authors of this paper presented a statistical analysis of long term ( 23 B 70 year records) chemical data from 19 streams and rivers in the Catskill mountains of New York revealing that SO4 2

concentrations are generally declining, while NO3

concentrations are increasing. The NO3

trend appears to be attributable largely to higher concentrations of NO3

during peak flow conditions ( particularly spring snowmelt). The magnitude of episodic nitrate increases has increased since about 1970.

Neal, C., A. Robson, B. Reynolds, and A. Jenkins. 1992. Prediction of future short term stream chemistry C a modeling approach. J. Hydrol. 130: 87 103.

This paper addresses the problem of predicting future short term stream chemistry in acidic and acid sensitive streams under various deposition scenarios. The approach used a hydrograph separation based on ANC, coupled to the twocomponent version of MAGIC and ALCHEMI. The technique was applied to the Afon Gwyn catchment in mid Wales, with results demonstrated in the forms of ( 1) 3 month sequences of hydrogen ion and inorganic aluminum concentrations and ( 2) chemical duration curves for hydrogen ion and aluminum.

Newman, K., and A. Dolloff. 1995. Responses of blacknose dace ( Rhinichthys atratulus) and brook char ( Salvelinus fontinalis) to acidified water in a laboratory stream. Water Air Soil Pollut. 85: 371 376. 79 This study was based on Shenandoah National Park fish. Both species actively avoided an acid pulse ( ambient pH 7.1 shifted to 5.1) by moving to a pH neutral refuge, demonstrating at least the potential of two regionally important species to recognize waters with either lethal or sublethal acid base chemistry and seek better water quality.

Nikolaidis, N. P., P. K. Muller, J. L. Schnoor, and H. L. Hu. 1991. Modeling the hydrogeochemical response of a stream to acid deposition using the enhanced trickle down model. Res. J. WPCF. 63( 3): 220 227.

The enhanced trickle down model was applied to White Oak Run, a second order stream in Shenandoah National Park in Virginia. Model results demonstrated the " delayed response" of this system, projecting that SO4 desorbed from the soils after 40 B 50 years, assuming no reductions in the current deposition. This finding has significant policy implications, because reduction in deposition levels will not result in a quick recovery of this system.

Nodvin, S. C., H. Van Miegroet, S. E. Lindberg, N. S. Nicholas, and D. W. Johnson. 1995. Acidic deposition ecosystem processes, and N saturation in a high elevation southern Appalachian watershed. Water Air Soil Pollut. 85: 1647 1652.

This paper describes a field study of biogeochemical processes in the Noland Divide watershed in the Great Smoky Mountains National Park ( GSMNP). The watershed is dominated by a high elevation spruce fir forest that receives the highest loadings of atmospheric S deposition in North America. Watershed NO3

export was extremely high, exacerbating the loss of base cations from the system. Stream ANC was extremely low (

10 B 20  eq/ L) and depressions in pH of a full unit for as long as several weeks were associated with stormflow conditions. Nitrate concentrations actually exceeded SO4 2

concentrations during episodes, which was attributed to substantial SO4 2