Effects of acid-base chemistry on biology of streams in the Great Smoky Mountains National Park

Science Center Objects

Background Watersheds of the Great Smoky Mountains National Park (GRSM) receive high levels of acid deposition resulting from atmospheric emissions of nitrogen and sulfur oxides. Acidic deposition has been shown to reduce acid neutralizing capacity (ANC) and calcium concentrations and increase acidity and aluminum concentrations in soils and surface waters and affect forest health as well as...

 

Background

Watersheds of the Great Smoky Mountains National Park (GRSM) receive high levels of acid deposition resulting from atmospheric emissions of nitrogen and sulfur oxides. Acidic deposition has been shown to reduce acid neutralizing capacity (ANC) and calcium concentrations and increase acidity and aluminum concentrations in soils and surface waters and affect forest health as well as fish and macroinvertebrate assemblages across the GRSM. In fact, 12 streams on the Tennessee-side of the GRSM National Park are listed on the Clean Water Act’s 303d list of impaired surface waters for failing the pH standard (<6.0) as a result of atmospheric deposition of air pollutants (mainly nitrogen and sulfur). In the GRSM, water chemistry has been monitored routinely at 43-357 stream sites since 1993; fish assemblages have been quantified at nearly 300 stream sites from 1990-2014, and macroinvertebrate communities have been assessed from at least 118 stream sites from 1990-2014.

The U.S. Environmental Protection Agency (EPA) is currently developing secondary standards for nitrogen and sulfur emissions that will indirectly protect terrestrial and aquatic species and their communities from further adverse impacts and optimistically promote recovery of acidified ecosystems to an un-impaired or, at least, some acceptable condition/level. These standards will rely heavily on critical loads research which estimates threshold or target deposition loads of nitrogen and sulfur to watersheds, below which significant harmful effects on sensitive elements of terrestrial and (or) aquatic ecosystems should not occur. A number of acid-base chemistry parameters such as pH, acid neutralizing capacity (ANC), and inorganic Al (Ali) have relatively steady effect thresholds for selected aquatic and terrestrial species, which when exceeded, can impair their health, cause mortality, reduce population density, shift species distributions, and decrease overall community diversity.

The relations among (a) nitrogen and sulfur emission (and deposition) levels, (b) acid-base chemistry, and (c) terrestrial and aquatic species, and (d) species assemblages (population and/or community metrics) are complicated, regionally variable, and difficult to characterize. A better understanding of the relations between acid-base chemistry and various biological responses, however, are needed to formulate critical target loads for nitrogen and sulfur deposition that will protect natural ecosystems scales. Acid-base chemistry and biological data from long-term monitoring programs in the GRSM could help define or refine an assortment of biological-response models that are needed to evaluate, postulate, and/or verify critical (target) nitrogen and sulfur deposition loads that are protective of local and regional stream ecosystems.

Objectives

The primary objective of this study is to increase our understanding of the relations between acid-base chemistry and the condition of fish and macroinvertebrate assemblages in streams of the GRSM. Specific goals of this effort will be to: (1) develop empirical relationships between chemical indicators of acidification stress (e.g., pH, ANC, total Al, Ali, Base Cation Surplus, Ca, and others) and key fish and macroinvertebrate community metrics (e.g., species absence/presence, abundance, richness, and diversity), (2) examine these relations for prominent biological-effect thresholds, and (3) identify the range of responses that key biological characters exhibit in streams of the GRSM that are affected by acidification (see example algorithm in Figure 3, below) or which are expected to recover from decreased acidification. These algorithms will be used to illustrate how acidification has currently impacted biota of GRSM streams as well as to predict the timing of additional changes (based upon future acid deposition scenarios) and forecast how changes in stream chemistry (resulting from various target loads at different time steps) should support recovery of biological communities in GRSM streams. These field-based models or algorithms may also help inform the USEPA’s Integrated Plan for Review of the Secondary National Ambient Air Quality Standards (NAAQS) for the Effects of Sulfur Oxides (SOx) and Nitrogen Oxides (NOx) on Ecosystems.

Approach

Staff from the National Park Service (NPS) will compile five corresponding datasets: (1) macroinvertebrate-sample site, date,  and community metrics; (2) macroinvertebrate-sample site, date, and species relative-abundance data; (3) fish-sample site, date, and community metrics; (4) fish-sample site, date, and species abundance data; and (5) chemistry data that correspond to each fishery or macroinvertebrate sample collection date, and forward them to the U.S. Geological Survey (USGS) on or before October 1, 2015.

Staff from the USGS will: (1) assess the relations between relevant acid-base chemistry variables (e.g., pH, ANC, Ca, BCS, sulfate, nitrate, total Al, inorganic Al, and others) and (i) the abundance of selected fish species (e.g., Figure 1), (ii) macroinvertebrate community metrics, and (iii) fish community metrics (e.g., Figure 2); (2) define the distribution of fish (e.g., Figure 3) and macroinvertebrate characters across a maximum of three acid-base chemistry parameters, and (3) forward these algorithms to NPS personal to generate relevant stream-chemistry and biology forecasts. The empirical relationships will be developed using all available chemistry and biology datasets (data from all 303d streams will be included if appropriate) and used to project conditions within these streams and others in the same region with comparable chemistry, hydrology, and biology conditions.

There will be countless possible output scenarios from Charles Driscoll’s analysis (i.e., various time steps, reductions, chemical thresholds, etc.) which may be used to spatially or temporally predict/project/map existing biological conditions or responses to potential changes in acid-base chemistry.  Any effort to summarize all possible predictions is not practical.  Therefore, staff from the USGS and NPS will produce 5 to 6 example predictions of possible recovery or loss (data/figures/maps outputs) by combining the PnET-BGC outputs (from Driscoll’s Phase 2 - if results are available) and the empirical relationships (chemistry-biology response models) developed by the USGS

During this process, the relations between key acid-base chemistry and macroinvertebrate-community metrics and/or species relative-abundance data and relations between key acid-base chemistry and fish-community metrics and/or species relative-abundance data will be examined to evaluate and confirm chemistry thresholds for biological indicators (e.g., Figure 4, Table 1). Staff from the USGS will assemble a NPS report or a peer-reviewed journal publication that summarizes important findings with contributions (input and review) by the NPS.