THE ADIRONDACK MANIPULATION AND MODELING PROJECT (AMMP) - DESIGN AND PRELIMINARY-RESULTS

The Adirondack Manipulation and Modeling Project (AMMP) was initiated in 1990 to investigate the effects of changing chemical inputs in the Adirondack Mountains of New York (USA). The four study sites are locat ed across a west to east gradient of declining atmospheric deposition, increasing acid neutralizing capacity (ANC) and decreasing NO3- conce ntration in surface waters in the Adirondacks. We hypothesize that the two sites in the western Adirondacks (Woods Lake (WL) and Pancake-Hal l Creek (PHC)) exhibit lower critical loads of N, S and H+ than the ce ntral and eastern sites (Huntington Forest (HF) and Pack Forest (PF), respectively). To test this hypothesis, chemical treatments of plots w ere initiated in 1990 including (NH4)(2)SO4 (1000 and 2000 eq ha(-1) y ear(-1)), H2SO4 (1000 eq ha(-1) year(-1)), HNO3 (1000 eq ha(-1) year(- 1)), Ca+Mg+SO42- (1000 eq ha(-1) year(-1)). Three of the sites (WL, PH C and HF) are northern hardwood ecosystems underlain by Spodosols. The PF site is a Pinus resinosa plantation on a glacial outwash plain (Ty pic Udipsamment). Ions in total deposition, throughfall and soil leach ates were monitored continuously. Changes in the solid phase chemistry of the mineral soil were assessed annually using the buried soil-bag approach. Vegetation responses to chemical treatments were analyzed by ascertaining changes in growth, composition and nutrient concentratio ns of both the overstory and understory. Elemental cycling models used in the AMMP include NuCM and VEGIE-CHESS. Preliminary results of bulk precipitation and throughfall from 1991-1992 suggest that the western sites may have greater inputs of SO42- and have lower capacity to ret ain NO3- passing through the foliage. Soil solutions (1991-1992) in re ference plots of the western sites (WL and PHC) had higher concentrati ons of NO3- in soil solution than the central and eastern Adirondack s ites (HF and PF). For all sites except PF, ammonium sulfate additions resulted in increased concentrations of SO42- and NO3- in soil solutio ns. Results of model simulations with NuCM for HF are presented which suggest that the model adequately simulated the pattern of increasing SO42- concentrations in response to (NH4)(2)SO4 treatment, but that th e increase in NO3- was underestimated.