Re-examination of the role of landscape change in the acidification of lakes in the Adirondack Mountains, New York

The impacts of atmospheric deposition of sulfur and nitrogen on aquatic ecosystems have been well recognized. However, the interactions between acidic deposition and concurrent changes in landscape cover have received relatively little attention. A review of recent literature suggests that changes in landscape, or land use, and hydrology can influence the delivery of sulfur, nitrogen and base cations to drainage waters and consequently modify acid-base chemistry and catchment responses to acidic deposition. Research has focussed heavily on the importance of acidic deposition as an agent of surface water acidification, with less emphasis on other important acidifying or alkalizing processes associated with deforestation, forest regrowth and other agents of catchment disturbance. This omission can have important effects on model estimates of future acidification or recovery of surface waters in response to various atmospheric deposition scenarios. A case study was conducted, using available paleolimnological data, for the Adirondack Mountain region of New York, USA, the most intensively studied region in the world regarding the aquatic effects of acidic deposition. The onset of acidification for most paleolimnological study lakes in the Adirondacks corresponded temporally with both the onset or increase in acidic deposition and also the occurrence of major landscape disturbances associated with logging and windthrow. Although such landscape changes are unlikely on their own to cause lakes to become acidic, model scenarios have suggested that they can cause decreases in the base saturation of soils, thereby predisposing sensitive watersheds to subsequent acidification from acidic deposition. Failure to include landscape processes in modeling efforts may cause biased forecasts, with the extent of the bias depending on the nature and magnitude of landscape changes that were not taken into account.