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 (Alm), 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 [Alm]. 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.