Target loads of atmospheric sulfur deposition protect terrestrial resources in the Adirondack Mountains, New York against biological impacts caused by soil acidification

Abstract

The model of acidification of groundwater in catchments (MAGIC) was used to simulate a matrix of target load (TL) values for use in protection and restoration of forest resources in the Adirondack Mountains of New York against soil acidification by acidic deposition. Modeling results were extrapolated to the population of 1,320 watersheds in the Adirondack Ecoregion that contain lakes expected to be >1 ha and >1 m deep and that have acid neutralizing capacity <200 μeq/L. Results of the TL simulations were combined with regional estimates of atmospheric sulfur deposition to calculate the extent to which ambient deposition exceeds the TL needed to achieve forest ecosystem protection. Modeling results were highly uncertain for estimating the TLs to protect against changes in soil solution chemistry. Although simulation uncertainty was generally lower for TL projections calculated to protect against changes in soil percent base saturation (% BS), TL modeling results based on soil chemistry were strongly dependent on selection of an appropriate % BS threshold. In order to more effectively model critical loads and TLs to protect and restore acid-sensitive terrestrial resources using a dynamic model such as MAGIC, additional information regarding dose/response relationships is needed to determine the % BS levels at which adverse impacts to sensitive plant species occur.