SEASONAL CHANGES OF DISSOLVED AND PARTICULATE ORGANIC CARBON IN DONGHU LAKE, CHINA

Concentrations of dissolved and particulate organic carbon (DOC and POC) were documented in 1996-1997 at 4 different trophic state stations in Donghu Lake, a typical shallow eutrophic lake along the Changjiang River's middle reaches. The mean concentrations of DOC were 15.11±3.26, 15.19±4.24, 14.27±3.43, and 13.31±3.30 mg/L in Station I, II, III, and IV, respectively. The DOC concentrations of the studied area were very similar to that in other lakes along the Changjiang River's middle reaches. The POC mean of the whole lake was 5.01 mg/L due to the large amount of organic detritus of both allochthonous and autochthonous origin. Significant linear relationship was found between POC and chlorophyll a at all 4 stations, which presumably reflect that phytoplankton, its exudates and its metabolic products were the main contributors to the POC pool in the water column. The slope of such linear relationship at Station IV was significantly steeper than that at Station I, II and III. In addition, the DOC/POC ratios (mean value: 4.40) indicated that the organic detritus was the most important component of the particulate organic matter; in other words, next to organic detritus, phytoplankton dominated the particulate organic matter in Donghu Lake.