Methods of liming to accelerate the reversal of acidic deposition effects in calcium-depleted Adirondack watersheds

Acidic deposition levels in the Adirondack region of New York State at the close of 2020 declined to values estimated for the early 20th century before the emergence of large-scale industrialization. However, chemical recovery of surface waters has lagged as a result of soil calcium (Ca) depletion, and long-term monitoring has not provided a clear indication that soil Ca availability has begun to increase. Recent computer modeling of Adirondack streams suggests that recovery goals may not be met in Ca-depleted watersheds for decades even with aggressive reductions in acidic deposition. The delayed response of soils and surface waters to reduced deposition has prompted consideration of adding Ca in the form of lime to increase the rate at which the effects of acidic deposition are being reversed through decreased pollutant emissions alone. In this regard, an experiment was conducted from 2013–2019 to evaluate the utility of liming to accelerate recovery in Adirondack stream watersheds that drain directly into Honnedaga Lake, near Forestport, NY. Results of this research were combined with relevant research results from prior liming studies to develop a methodology for the use of liming to accelerate reversal of acidic deposition effects tailored for the Adirondack region of New York State. This document presents (1) a rationale for liming in the context of the current acidic deposition regime, (2) an assessment of benefits and risks to be considered with various application methods, (3) a suggested method for selecting watersheds where liming would be most beneficial, and (4) an explanation of the primary factors that need to be addressed to successfully implement watershed liming.