Modeling the response of forest and aquatic ecosystems of northeastern United States to changes in atmospheric deposition

In this study the integrated biogeochemical model (PnET-BGC) was applied to nearly 100 forest watersheds of the U.S. Environmental Protection Agency Direct/Delayed Response Program in the northeastern U.S. to investigate response of soil and surface waters in the northern forest region to effects of atmospheric deposition and changes in atmospheric deposition. Through application of the model, factors affecting spatial and temporal patterns in lake sulfate concentrations were investigated. The responses of soil and surface waters in the region to past changes in acidic deposition and three future emission controls were also evaluated. The structure of PnET-BGC was altered by adding multiple soil layers to better simulate seasonal patterns in surface water chemistry.; Results of the regional application of the model indicated that besides atmospheric sulfur deposition, landscape characteristics of elevation, vegetation type, wetland coverage and surficial geology also affect the retention of sulfate within watersheds, influencing spatial and temporal patterns in lake sulfate across northern forest areas of the Northeast. In response to the three future emission control scenarios, soil and surface waters in the region are expected to recover from previous chronic acidification, with the most aggressive control scenario resulting in the fastest rates of recovery. Although marked recovery is expected, biologically relevant soil and surface water chemistry at regional sites are not expected to fully recover above the threshold indicator values by 2050. As a result, recovery of forest ecosystems from elevated atmospheric acidic deposition is expected to be a slow process requiring many decades to accomplish.; The two-layer formulation of the model is able to depict changes in hydrologic flow paths among different seasons and simulate stream water as a result of the mixing of soil water from upper and lower soil layers. The two-layer model was applied to a northern forest ecosystem in New Hampshire, the Hubbard Brook Experimental Forest (HBEF), demonstrating the ability of the model to effectively simulate seasonal variations in stream chemistry. The two soil-layer model was also used to evaluate management options for mitigating the short-term acidification. The results indicated that a full year nitrogen reduction is more effective in mitigating the short-term acidification than a summer-only reduction scenario and a same equivalent reduction in sulfate deposition will better mitigate the seasonal acidification than an equivalent reduction in nitrate deposition.