RAINFALL, STEMFLOW, AND THROUGHFALL CHEMISTRY AT URBAN- AND MOUNTAIN-FACING SITES AT MT. GOKURAKUJI, HIROSHIMA, WESTERN JAPAN

摘要

Rainfall, stemflow, and throughfall were collected from 1996 to 1999 at two types of forest sites: (1) forests near the traffic roads and urban areas and (2) forests away from the urban areas at Mt. Gokurakuji, Hiroshima, western Japan in order to estimate the effects of anthropogenic activities on atmospheric deposition. Rainfall deposition for major ions showed small differences between the sites. The NO_3~- and SO_4~(2-) concentrations in stemflow were higher at the urban-facing slope than at the mountain-facing slope. Throughfall deposition of NO_3~- and SO_4~(2-) was also higher at urban-facing slopes. Net throughfall (NTF) deposition (throughfall minus rainfall) of NO_3~- and SO_4~(2-) accounted for 77 and 50% of the total throughfall deposition on urban-facing slopes, respectively, while it accounted for 44 and 23% on the mountain-facing slopes, respectively. These results indicated a higher contribution from dry deposition on urban-facing slopes compared to mountain-facing slopes. Atmospheric N (NO_3~- + NH_4~+) deposition from throughfall was estimated to be around 17-26 kg N ha~(-1) yr~(-1) on urban-facing slopes, which was greater than the threshold of N deposition that could cause nitrogen leaching in Europe and the United States. The high load of atmospheric N deposition may be one of the factors bringing about the decline of pine forests on urban-facing slopes of Mt. Gokurakuji.