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Title: Experimental Acidification Causes Soil Base-Cation Depletion at the Bear Brook Watershed in Maine
Author: Fernandez, Ivan J.; Rustad, Lindsey E.; Norton, Stephen A.; Kahl, Jeffrey S.; Cosby, Bernard J.
Source: Soil Science Society of America Journal. 67: 1909-1919.
Description: 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 (NH4)2SO4. 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 basin, 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 0 horizon compared to underlying mined soh, 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-' of exchangeable Ca and Mg, respectively, after accounting for soil mass differences between watersheds. This was comparable with tbe total cumulative excess stream Ca and Mg export in West Bear after 9 yr of treatment of 55 and 11 kg ha-', 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-', 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.
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Fernandez, Ivan J.; Rustad, Lindsey E.; Norton, Stephen A.; Kahl, Jeffrey S.; Cosby, Bernard J. 2003. Experimental Acidification Causes Soil Base-Cation Depletion at the Bear Brook Watershed in Maine. Soil Science Society of America Journal. 67: 1909-1919.
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