SPATIOTEMPORAL DISTRIBUTION OF DOC AND DON IN WATER AFTER DAMMING OF THE THREE GORGES RESERVOIR

Large reservoirs always influence water environment, the change of which in turn has direct impacts on biogeochemical cycles. In this study, we measured dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the water of the Three Gorges Reservoir Region (TGRR) from February to September of 2008 at seven sites, in order to understand the spatiotemporal features of DOC and DON in this region after the dam impoundment. The concentration of DOC in water collected at all sites ranged from 0.02 to 54.48 mg.L-1 (average 3.85 mg.L-1), and for DON the range was 0.01 to 2.60 mg.L-1 (average 0.88 mg.L-1). The concentration of DOC was the highest at Sandouping, immediately before the dam, ranging from 1.65 to 54.48 mg.L-1 (average of 11.41 mg.L-1), much higher than the average value for several other reservoirs. It is probably because a large amount of organic matter from upstream erosion was accumulated at the reservoir. Through measurement of the DOC, DON and total carbon (TC) along the TGRR, we did not find vertical variation except for DON. However, we noticed a fluctuation of DOC and DON with time. Moreover, we found DOC concentration for the drawdown area was markedly lower than that of the permanently flooded sites. This was partly because the drawdown area provided a relatively long retention time for the microbial community to decompose the soluble carbon substrate. These results were consistent with our previous study reporting a high CH4 emission in the drawdown area of the TGRR.