ELEMENT BUDGETS IN A FORESTED WATERSHED IN SOUTHERN CHINA: ESTIMATION OF A PROTON BUDGET

摘要

We evaluated the element budgets in a forested watershed in Jiulianshan, southern China. The element input in bulk precipitation was characterized by high depositions of H~+, NH_4~+, Ca~(2+), and SO_4~(2-), i.e., 400, 351,299, and 876 eq/ha/yr, respectively. The outputs of H~+, NH_4~+, and SO_4~(2-) from the watershed were very low, while those of Ca~(2+) and Mg~(2+) were high, 712 and 960 eq/ha/yr, respectively. The element budgets suggested that i) the net retentions of H~+, NH_4~+, and SO_4~(2-) in this watershed were high, and ii) the net release of Mg~(2+) from this watershed was high mainly due to weathering. The net release of Ca~(2+) was not so high because of the high atmospheric deposition, while atmospheric deposition of Mg~(2+) was not so high (130 eq/ha/yr). Decrease of acid neutralizing capacity in the soil, i.e., net soil acidification, was caused mainly by the net release of Mg~(2+). Moreover, the net retention of SO_4~(2-) also contributed to soil acidification.