Nitrogen and phosphorus loadings in branch backwater reaches and the reverse effects in the main stream in Three Gorges Reservoir

Through analyzing the source, amount and time-space character of NP in the backwater reach of Daning river in Three Gorges Reservoir (TGR) area, the reverse effect of main stream on secondary branch backwater reach at the incipient and stable running periods of TGR formation was studied. At the incipitant period, the NP distribute character of branch backwater reach expressed initially the main stream reverse effect with respectively 19.05%, 28.93% of TN and TP from main stream reverse input. Due to the main stream top support action, N, P expressed possessing space distribution character of peak value. At the stable running period, the N, P source and amount of branch backwater reach should have obvious main stream reverse effect, in which adoptable to algae growth period. The TN, TP of Daning River backwater reach main stream reverse input were almost 3, 10 times higher than the upstream runoff input, higher obviously than incipient period of the reservoir formation. When the water level of TGR rose from 145m to 175m, the TN, TP from main stream reverse input could reach respectively 15484.99t, 1185.75t. The main stream reverse effect could aggravate the eutrophication of TGR water.