Factors influencing critical and target loads for the acidification of lake–watersheds in the Adirondack region of New York

Qingtao Zhou,Charles T Driscoll,Afshin Pourmokhtarian,Timothy J Sullivan

doi:10.1007/s10533-015-0102-7

Qingtao Zhou, Charles T Driscoll + Show 2 more

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https://doi.org/10.1007/s10533-015-0102-7

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Abstract

Critical loads (CLs) and target loads (TLs) are tools used to guide air emissions control strategies for recovery of forest and aquatic ecosystems impacted by elevated atmospheric deposition. We use the dynamic hydrochemical model-PnET-BGC (photosynthesis evapotranspiration biogeochemical) to evaluate biophysical factors that affect CLs and TLs of acidity for the Constable Pond watershed, as an example of a chronically acidic drainage lake in the Adirondack region of New York, USA. These factors included a range of future scenarios of decreases in atmospheric nitrate, ammonium and sulfate deposition from present to 2200; historical forest harvesting; supply of naturally occurring organic acids; and variations in lake hydraulic residence time. Simulations show that decreases in sulfate deposition were more effective in increasing lake acid neutralizing capacity (ANC) than equivalent decreases in nitrate deposition, 4.6 times greater in 2040–2050 but decreasing to 2 times greater by 2200. Future lake ANC is anticipated to increase to a greater extent when the watershed experiences past forest cutting compared to a scenario without historical land disturbance. Under higher rates of watershed supply of naturally occurring dissolved organic carbon (DOC ~1000 µmol C/L), ANC is lower than under relatively low DOC supply (~100 µmol C/L) due to strongly acidic functional groups associated with dissolved organic matter. Lakes with longer hydrologic residence time exhibit less historical acidification and can achieve a greater ANC from recovery than lakes with shorter hydrologic residence times due to in-lake production of ANC. This study improves understanding of how biogeochemical processes at the landscape level can influence the rate and extent of recovery of lake–watersheds in response to decreases in atmospheric deposition.

Highlights

Over the past century, acid deposition has caused environmental impacts across North America, Europe and Asia (Driscoll et al 2010)
We evaluated the agreement between model simulations and observed water chemistry data using normalized mean error (NME) and normalized mean absolute error (NMAE) (Janssen and Heuberger 1995)
The model under-predicts the increase in measured acid neutralizing capacity (ANC) observed in recent years (Fig. 3) and does not depict the increase in dissolved organic carbon (DOC) observed in Constable Pond in response to decreases in acid deposition (Driscoll et al 2007)

Summary

Introduction

Acid deposition has caused environmental impacts across North America, Europe and Asia (Driscoll et al 2010). Concern over the effects of acid deposition has largely focused on high elevation eastern forested regions, with limited availability of base cations (Greaver et al 2012). Elevated inputs of acid deposition to acid-sensitive areas contribute to the acidification of naturally acidic (base-poor) soils through the depletion of available nutrient cations (calcium [Ca2?], magnesium [Mg2?]), the mobilization of dissolved inorganic aluminum (Ali) and the enrichment of soil nitrogen (N) resulting in changes and health impacts to forest vegetation (Driscoll et al 2001; Juice et al 2006; Thomas et al 2009). The Adirondack region of New York receives relatively high rates of atmospheric sulfur (S) and N deposition due to elevated S and NOx emissions in the eastern U.S Forest and aquatic ecosystems of the Adirondacks have been impacted by these inputs (Driscoll et al 2001). An estimated 26 % of the surveyed lakes had pH \5.0, 26 % had ANC \0 leq/L and 50 % had ANC \50 leq/L (Kretser et al 1989)

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