Most efforts to quantify aquatic and terrestrial ecosystem damage from sulfur (S) and nitrogen (N) air pollution in the Adirondack Mountains and to examine more recent ecosystem recovery in response to emissions control have focused on lakewater chemistry. However, relatively large decreases in regional upwind S emissions and generally similar decreases in S deposition in the Adirondack Mountains over the past two to three decades have resulted in limited recovery of lakewater acid‑base chemistry. The limited nature of the observed surface water chemical recovery response to date has largely been attributed to depletion of exchangeable base cations on the soil. There is an important management need to quantify the acidic deposition levels that will be required to affect full chemical, and hopefully also biological, recovery. Calculation of the critical loads (CL) of atmospheric S and N deposition can help to fill that research need. The CL is the level of sustained atmospheric deposition of S, N, or acidity below which harmful effects to sensitive ecosystems do not occur according to current scientific understanding.
This research was undertaken in collaboration with scientists from Syracuse University, the University of Virginia, Oregon State University, and the U.S. Geological Survey to determine the CL values that will promote resource recovery in aquatic and terrestrial Adirondack ecosystems. We are focusing on the Adirondack Ecoregion, and in particular the intensively monitored watersheds, many of which are in the southwestern portion of the Adirondack Ecoregion. This research builds upon an earlier E&S research project, completed in 2006, in which the same research team modeled the acid-base response of 70 Adirondack lakes in response to historic acidic deposition and several scenarios of future emissions controls using the Model of Acidification of Groundwater in Catchments (MAGIC) and the Photosynthesis and EvapoTranspiration BioGeoChemistry (PnET-BGC) model. Study lakes included statistically selected lakes from the U.S. Environmental Protection Agency’s (EPA) Environmental Monitoring and Assessment Program (EMAP) and a group of intensively studied long-term monitoring lakes.