Tracking response and recovery of surface water chemistry to changes in acid deposition in the northeastern U.S.
Kahl, Steve*,1, Haeuber, Rick2, Stoddard, John3, 1 Plymouth State University, Plymouth, NH, USA2 US EPA, Washington, DC, USA3 US EPA, Corvallis, OR, USA
ABSTRACT- The Clean Air Act Amendments (CAAA) of 1990 resulted in substantial reductions in the atmospheric deposition of acidifying substances. Because the response in surface waters is a result of interactions at the ecosystem-scale, neither deposition data or lake chemistry data alone are sufficient to address the science and policy questions. The EPA surface water research programs LTM (Long-Term Monitoring) and TIME (Temporally Integrated Monitoring of Ecosystems) were designed to quantify the changes in surface water chemistry in the northern and eastern US since 1991 and 1982, respectively. LTM is a group of sites selected for pre-existing data and specific chemical characteristics, notably low ANC (Acid Neutralizing Capacity). TIME is a statistical sub-population of lakes from EPA EMAP (Environmental Monitoring and Assessment Program. These aquatic systems were used to quantify the watershed response and assess recovery in biologically relevant aquatic chemistry. Data from NADP (National Atmospheric Deposition Program) indicate that atmospheric deposition has changed in positive ways as intended by the CAAA. The decrease in sulfate concentrations in surface waters is a direct result of the decrease in atmospheric deposition. Other changes in surface water chemistry have not followed directly from changes in deposition, especially for nitrate (little change) and base cations (decreases). Recovery in surface water chemistry will not necessarily be a linear nor rapid process because of the complexities of whole-ecosystem response that are influenced by a variety of confounding factors such as changes in climate, forest condition, and organic acidity.
Key words: acid rain, Clean Air Act, acidic deposition
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