Technical Report NPS/NER/NRTR2006/066
Bernard J. Cosby, James R.
Webb, James N. Galloway
and Frank A. Deviney
Department of Environmental
University of Virginia
P.O. Box 400123
Charlottesville, VA 22904-4123
U.S. Department of the Interior
National Park Service
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 50100 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 050 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.
Adverse Effects of Acid Deposition on Terrestrial Ecosystems in Shenandoah
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 1020%). 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
Elevated Concern. (Average soil BS in the range 510%). 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
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 ANCs
are likely to be in the range of severe biological effects (certainly
episodically and perhaps chronically).
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
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
is available to view or download in PDF file format. It has been divided
into several pdf files so that it will download quickly. Using pdf files
requires the free Adobe Acrobat Reader. If you do not already have it
installed on your computer, you may download it now. Download
a pdf file, click on this icon in the toolbar of the pdf window: .
This will allow you to save the file on your computer. If you want to
copy or print only a small part of the saved file, click on this icon
to select the desired text: .
The file for
this report is large, therefore it has been divided into five pdf files.
Click on a file to open it.
Front matter through Chapter 2
Chapters 3 and 4
Chapters 5 through References