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There is concern that changes in atmospheric deposition, climate, or land use have altered the biogeochemistry of forests causing soil base-cation depletion, particularly Ca. The Bear Brook Watershed in Maine (BBWM) is a paired watershed experiment with one watershed subjected to elevated N and S deposition through bimonthly additions of [(N[H.sub.4]).sub.2]S[O.sub.4]. Quantitative soil excavations in 1998 measured soil pools of exchangeable base cations 9 yr after treatments began. Stream sampling at the weirs on a weekly and event basis, and weekly precipitation sampling, were used for input-output estimates. The treated watershed had lower concentrations of exchangeable Ca and Mg in all horizons, with evidence for the greater depletion in the O horizon compared to underlying mineral soils, and in softwoods compared to hardwoods. This difference between watersheds is interpreted to be treatment-induced base-cation depletion, which was reinforced by model simulations. The difference between watersheds was 66 and 27 kg [ha.sup.-1] of exchangeable Ca and Mg, respectively, after accounting for soil mass differences between watersheds. This was comparable with the total cumulative excess stream Ca and Mg export in West Bear after 9 yr of treatment of 55 and 11 kg [ha.sup.-1] respectively. Model simulations of watershed response to treatments predicted excess soil exchangeable Ca and Mg losses in the treated watershed of 47 and 9 kg [ha.sup.-1] respectively. These results indicate that the response to a step-increase in N and S deposition during the first decade of treatments in this experimental forested watershed was to invoke cation-exchange buffering, resulting in a net decline in soil exchangeable base cations.

Nitrate loss leads to the depletion of nutrient cations in soils and may lead to the eutrophication of natural water resources especially coastal waters. An analysis of the patterns of nitrate concentration in four forested watersheds located in the Northeastern US shows synchronous patterns of nitrate concentrations of drainage waters. High nitrate concentrations resulted in high drainage water losses followed a significant decrease in nitrate levels.

The condition of terrestrial nitrogen saturation due to the excess of vegetative demand in forested ecosystems is discussed. Nitrogen deposition was experimentally increased in one of two watersheds of the Bear Brook watershed in Maine. Results indicate the possibility of inducting nitrogen saturation, soil acidification and altered nitrogen cycling in forested watersheds at lower nitrogen deposition rates.

The article discusses about amendment of some acts. In the late 1950's, reports first established that acidic lakes existed in North America and Europe. However, the effects of acidity on fish were not widely recognized until the mid-1970's. As researchers collected more data over the years, they established more robust links between atmospheric deposition and acidic surface waters (5-8). In the past 30 years, the U.S. Congress has modified the Clean Air Act (CAA) several times. In 1990, legislators passed Title IV of the CAA Amendments (CAAA), which was intended to reduce acidic deposition by regulating sulfur and nitrogen emissions, largely from coal-burning power plants. These reductions built on a 20-year trend of decreasing sulfur deposition.