Shenandoah NO--Impacts of Acid Deposition

Technical Report NPS/NER/NRTR—2006/066

Bernard J. Cosby, James R. Webb, James N. Galloway
and Frank A. Deviney

Department of Environmental Sciences
University of Virginia
Clark Hall
P.O. Box 400123
Charlottesville, VA 22904-4123

November 2006

U.S. Department of the Interior
National Park Service
Northeast Region
Philadelphia, Pennsylvania
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Executive Summary

The goal of the Acid Impacts Project has been to develop an assessment of the extent of possible adverse effects of acidic deposition on resources in Shenandoah National Park (SHEN). The assessment approach utilized maps of the park highlighting areas of concern with respect to adverse effects on aquatic and terrestrial systems. The maps were constructed to display past, present, and future areas of concern in response to changing levels of acidic deposition.

Four categories of concern were adopted for soil and surface water conditions in SHEN: 1) Low Concern; 2) Moderate Concern; 3) Elevated Concern; and 4) Acute Concern. While the same category names were used for maps of adverse effects on both surface water and soils, the biological effects for each category are specific to either aquatic or terrestrial ecosystems.

Concern for Adverse Effects of Acid Deposition on Aquatic Ecosystems in Shenandoah National Park

The categories of concern for surface water conditions are based on stream water Acid Neutralizing Capacity (ANC) and include a number of observed effects for a number of aquatic organisms in SHEN.

Low Concern. (Average ANC greater than 100 ueq/L). Reproducing brook trout populations expected where habitat is suitable. Fish species richness probably unaffected. Diversity and/or evenness of aquatic macroinvertebrate communities unaffected. Number of families
and/or number of individuals of aquatic insects unaffected.

Moderate Concern. (Average ANC in the range 50–100 ueq/L). Reproducing brook trout populations expected where habitat is suitable. Fish species richness much reduced. Diversity and/or evenness of aquatic macroinvertebrate communities begin to decline. Number of families and/or number of individuals of aquatic insects begin to decline.

Elevated Concern. (Average ANC in the range 0–50 ueq/L). Brook trout populations sensitive and variable, lethal and sub-lethal effects possible. Fish species richness much reduced. Diversity and/or evenness of macroinvertebrate communities decline markedly. Number of families of aquatic insects declines markedly. Number of individuals in most aquatic insect families declines markedly. Number of individuals of acidophilic aquatic insect families increases sharply.

Acute Concern. (Average ANC less than 0 ueq/L). Lethal effects on brook trout populations probable. Complete extirpation of fish populations expected (species richness equal zero). Extremely low diversity and/or evenness of aquatic macroinvertebrates communities. Extremely reduced number of families of aquatic insects. Extremely reduced numbers of individuals of most aquatic insect families. Large numbers of individuals of acidophilic aquatic insect families.

Concern for Adverse Effects of Acid Deposition on Terrestrial Ecosystems in Shenandoah National Park

The categories of concern for soils are somewhat problematic in that direct observations of adverse effects of acidification are lacking in SHEN for terrestrial organisms. Nonetheless, there exist strong correlations between soil base saturation (BS) and measures of base cation availability for both forests and streams in SHEN. Because the relationships for effects of soil acidification are weaker than for surface waters, the expected effects for each category are less specific than for surface waters, but nonetheless represent best current knowledge.

Low Concern. (Average soil BS greater than 20%). No effects. Base cation availability for forests and surface waters not affected.

Moderate Concern. (Average soil BS in the range 10–20%). Moderate effects probable. Base cation availability for forests reduced and forest growth probably slowed. Base cation availability for surface waters reduced and moderate effects on aquatic biota expected (lowered stream water ANC).

Elevated Concern. (Average soil BS in the range 5–10%). Moderate effects certain and severe effects probable. Base cation availability for forests greatly reduced with resultant risk of mortality from various stresses (particularly if the base saturation was previously above 10% during the life of the tree). Base cation availability for surface waters greatly reduced producing sharp declines in stream water ANC (particularly during storm events) and resultant moderate to severe effects on stream water biota.

Acute Concern. (Average soil BS less than 5%). Severe effects certain. High risk of forest mortality from various stresses including direct acidification effects on roots and seedlings. Surface water ANC’s are likely to be in the range of severe biological effects (certainly episodically and perhaps chronically).

Conclusions

Although baseline, pre-industrial resource conditions are not well known in Shenandoah National Park, the analysis here suggests that ranges of both soil and stream conditions that would occur in SHEN in the absence of acid deposition impacts would not include any areas of “acute concern” or “elevated concern”. However, the historical mapping exercise also suggests that large areas of SHEN, especially in the southern district, may have always been of “moderate concern” reflecting the inherent sensitivity of the siliciclastic bedrock that dominates the southern district.

Simulation and mapping of watershed responses to historical changes in acidic deposition (from pre-industrial to current) suggest that large areas of SHEN have suffered deterioration of both soil and stream conditions. The changes in soil condition have been relatively modest up to the present time, with small areas in the southern district of SHEN moving from “moderate concern” (the historical baseline) to “elevated concern” as a result of leaching of base cations from the soils in these areas. Deterioration in stream conditions has been more severe than for soil conditions, with large areas in the southern district and some smaller areas in the central and northern districts moving from “moderate concern” to “elevated concern”. Neither soil nor stream conditions have shown any improvement from 1980 to the present in response to the decline in acidic deposition over the last 25 years.

Simulation and mapping of watershed responses to predicted future changes in acidic deposition (from current through several decades into the future) relied upon a comparative approach. Several scenarios of possible future acid deposition were developed for this report following U.S. Environmental Protection Agency (EPA) methods for preparation of emissions inventory inputs into air quality modeling for policy analysis and rule making purposes. These alternate scenarios were based on existing emission control regulations and several proposed alternatives.

With respect to future soil conditions, the assessment suggests that the responses of soil conditions to changes in acid deposition are relatively slow. In the short term (by year 2020), neither improvement nor further deterioration is likely to be observed in soil condition regardless of the future deposition scenario considered. However, by the year 2100 it becomes clear that constant deposition at 1990 levels would produce worsening soil conditions in SHEN with the development of areas of “acute concern” in the southern district. Perhaps more importantly, while the two scenarios of reduced future deposition did not produce worsening soil conditions, neither did they indicate any improvement in soil condition even in the long term. It is possible that emission control activities (and therefore emissions reductions) currently being considered in the policy arena would all be insufficient to reverse the soil acidification that has occurred in SHEN and start soil conditions on a path to recovery to pre-industrial conditions.

With respect to future stream conditions, the assessment suggests that the responses of stream conditions are relatively more rapid than those of soils. In the short term (by year 2020), while constant deposition at 1990 levels would likely produce further deterioration in stream condition, the two scenarios of future deposition reductions do nothing to reverse the deterioration of stream condition that has occurred in SHEN. In the long term (by year 2100), the effects of the two deposition reduction scenarios begin to diverge. The moderate deposition reduction scenario still produces no improvement in stream conditions relative to current conditions. The largest deposition reduction scenario, by contrast, produces modest improvements in stream conditions by 2100. It is important to note, however, that even the relatively large deposition reductions of this scenario do not result in a return of stream conditions in SHEN to the pre-industrial state. It is unlikely that the pre-industrial state for streams in SHEN can be reached until deposition reductions sufficient to stop the soil acidification (discussed above) in SHEN are achieved.

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