W6 PM Environmental Changes in Response to China's Economic Expansion
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 324-326

(AAA-1117-765881) Seasonal and vertical variation of dissolved fluorescent organic matter in two Chinese lakes affected by human activities.

Wu, F.¹, Fu, P.¹, Bai, Y.¹, Wang, L.¹, Li, W.¹, Liu, C.¹, ¹ Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou, China

ABSTRACT- Fluorescence has been widely used to elucidate the origin and structure of dissolved organic matter (DOM) in the past years. In this study, seasonal and vertical variation of fluorescent DOM was investigated in two Chinese lakes: Lake Hongfeng and Lake Baihua from southwestern China, and the effect of human activities on DOC variation and water quality were discussed. Results show that there were two major distinct fluorophores in the DOM samples: two fulvic-like fluorescence (one stimulated by UV excitation: Peak A; the other by visible excitation: Peak C) and protein-like fluorescence. The fulvic-like fluorescence was existed in all samples. Protein-like fluorescence (Peak B) was observed more obviously in samples from Lake Baihua, which was affected by the farm and industrial wastes. DOC concentrations in Lake Hongfeng (ranging from 1.60 to 3.08 mg L-1) was higher in rain season (May-Sept) than that in dry season (Nov-March), indicating that terrestrially-derived DOC was a major source. However, Lake Baihua had higher DOC concentrations (ranging from 1.71 to 3.69 mg L-1) than that in Lake Hongfeng. In the downstream Lake Baihua, DOC displayed a different seasonal variability, this may be because the lake was seriously affected by the wastes. In the vertical profiles of the fluorescence and DOC concentrations in both lakes, it seems that fluorescence was a poor predictor of DOC concentration. However, a good correlation (R2 = 0.35, n = 247) was observed between fluorescence intensities and DOC concentrations in the annual DOM samples. The relative fluorescence intensity of UV/visible humic-like peaks i.e., r(A,C) had a linear relationship with pH (Lake Hongfeng: R2=0.95; Lake Baihua: R2=0.70). A good correlation between protein-like fluorescence and Chl a was found in Lake Hongfeng while no correlation was found in Lake Baihua. These observations suggest that the inputs of terrestrial DOC varied with the seasons and lakes, the waste input and human activities in the watershed were the major factors affecting the seasonal distribution of DOC. This study has significant implications for the understanding of effects of human activities on the water quality and consequent environmental effects in lakes.

Key words: dissolved organic matter, fluorescence, lake, seasonal variation