Decadal Trends Reveal Recent Acceleration in the Rate of Recovery from Acidification in the Northeastern US

Previous reports suggest variable trends in recovery from acidification in northeastern U.S. surface waters in response to the Clean Air Act Amendments. Here we analyze recent trends in emissions, wet deposition, and lake chemistry using long-term data from a variety of lakes in the Adirondack Mountains and New England. Sulfate concentration in wet deposition declined by more than 40% in the 2000s and sulfate concentration in lakes declined at a greater rate from 2002 to 2010 than during the 1980s or 1990s (-3.27 mu eqL(-1)year(-1) as compared to -1.26 mu eqL(-1)year(-1)). During the 2000s, nitrate concentration in wet deposition declined by more than 50% and nitrate concentration in lakes, which had no linear trend prior to 2000, declined at a rate of -0.05 mu eqL(-1)year(-1). Base cation concentrations, which decreased during the 1990s (-1.5 mu eq L-1 year(-1)), have stabilized in New England lakes. Although total aluminum concentrations increased since 1999 (2.57 mu g L-1 year(-1)), there was a shift to nontoxic, organic aluminum. Despite this recent acceleration in recovery in multiple variables, both ANC and pH continue to have variable trends. This may be due in part to variable trajectories in the concentrations of base cations and dissolved organic carbon among our study lakes.