Trends in the output of first-order basins at Turkey Lakes Watershed, 1982-96

In 1981, we began to monitor the stream flow and chemistry of 13 first-orde r basins at the Turkey Lakes Watershed, with the objective of measuring the response of an undisturbed forested ecosystem to acid deposition. There wa s no trend in total annual precipitation received by the watershed, but the average annual water yield (percentage of annual precipitation) declined o ver the observation period. The proportion of runoff occurring in different seasons also changed, decreasing in the winter and increasing in the sprin g. in most streams the concentration of SO42- has decreased coincident with the decline in precipitation inputs. Recovery of the basins from acid depo sition (as evidenced by increased pH, increased alkalinity, and decreasing base cation fluxes) has not been uniform. Basins that do not show signs of recovery are characterized by deeper flowpaths and greater potential neutra lizing capacity, which minimizes the impacts of acid deposition. Basins tha t are dominated by shallow flowpaths and lower levels of potential neutrali zing capacity are showing some signs of recovery, but their recovery is not complete and it is possible that cation depletion may prevent or retard it .