Influence of land use and rainfall on the optical properties of dissolved organic matter in a key drinking water reservoir in China.

The concentration, source and composition of dissolved organic matter (DOM) in aquatic ecosystems are associated with land use and hydrological connectivity between terrestrial and aquatic systems. However, direct evidence of the effects of rainfall and land use on the variability of DOM in aquatic ecosystems is very limited. In this study, chromophoric DOM (CDOM) absorption and fluorescence spectroscopy were used to elucidate how rainfall and land use affect the variability of CDOM in the watershed of Lake Tianmu, a key drinking water reservoir in the Yangtze River Delta. The mean values of the fluorescence intensity (F) of parallel factor analysis-derived humic-like components (C1, C3, C6) and tryptophan-like components C5 were higher in the southeastern inflowing river mouths than those downstream of the lake outlet regions. The upstream tributaries were mainly dominated by humic-like materials, while the lake was mainly dominated by protein-like materials. The F values of four humic-like components and two tryptophan-like components all increased significantly as the %woodland decreased, but %anthropogenic land use (%cropland+%urban construction area) increased. The F of the humic-like components at the inflowing tributaries and the lake increased with increasing rainfall during storm events, and the value was especially pronounced at the inflowing river mouths. We concluded that land use and hydrological conditions play an important role in influencing the CDOM source and optical composition, and these findings provide insights for the understanding of aquatic ecosystem metabolism and reservoir water quality management.