How Much Acidification Has Occurred in Adirondack Region Lakes (New York, USA) since Preindustrial Times?

Abstract

Preindustrial and present-day lake water pH, acid neutralizing capacity (ANC), total monomeric aluminum (Al m ), and dissolved organic carbon (DOC) were inferred from the species composition of diatom and chrysophyte microfossils in the tops (present-day inferences) and bottoms (pre-1850 inferences) of sediment cores collected from a statistically selected set of Adirondack lakes. Results from the study lakes were extrapolated to a predefined target population of 675 low-alkalinity Adirondack region lakes. Estimates of preindustrial to present-day changes in lake water chemistry show that approximately 25–35% of the target population has acidified. The magnitude of acidification was greatest in the low-alkalinity lakes of the southwestern Adirondacks, an area with little geological ability to neutralize acidic deposition and receives the highest annual average rainfall in the region. We estimate that ~80% of the target population lakes with present-day measured pH [Formula: see text] and 30–45% of lakes with pH between 5.2 and 6.0 have undergone large declines in pH and ANC, and concomitant increases in [Al m ]. Estimated changes in [DOC] were small and show no consistent pattern in the acidified lakes. This study provides the first statistically based regional evaluation of the extent of lake acidification in the Adirondacks.