Quantity and quality of nom in 5 acid sites in mid- and southern China

Preliminary studies on dissolved organic matter (DOM) in subtropical acid soils are conducted using data from a monitoring project (IMPACTS; www.impacts.net.cn) studying the effect of acid rain on Chinese forested catchments. The Sino-Norwegian multidisciplinary IMPACTS project monitors the water quality as the water passes through the watershed at five sites, covering a large span in acid rain loading. DOC concentrations up to 10 mg C L-1 are commonly found in these watersheds. Natural organic anions play a significant role in the charge balance in sites with low atmospheric sulfur (S) and nitrogen (N) loading. As commonly seen, a good correlation between UV absorbency and DOC concentrations is found in the water samples from these Chinese sites. The specific absorption ratio (SAR) varies considerably as the water passes through the catchments as well as between different sites. Organic charge density, as inferred by means of the Oliver model, is strongly influenced by sample pH. This dependence along with other factors leads to a strong link between the importance of the organic charge and the acid rain loading.