THE COMPARISON OF PHOSPHORUS AND NITROGEN POLLUTION STATUS OF THE XIANGXI BAY BEFORE AND AFTER THE IMPOUNDMENT OF THE THREE GORGES RESERVOIR

As the first tributary of Changjiang River nearby ThreeGorge reservoir, the water quality of Xiangxi River could directlyinfluence the water quality of the Three Gorges reservoir, thus the research of phosphorus of Xiangxi River could provide usefulinformation for preventive measures.Water and sediments samples along theXiangxi River were collected before and after the impoundmentof the Three Gorges Reservoir at 1996-1997 and 2004, respectively.Total phosphorus and nitrogen of water samples, as well as species of phosphorus of sediment samples were determined to reveal the pollution status of the River.The resultsindicated the concentrations of total phosphorus was lower than 0.05mg/L for the upper reaches and 0.22-0.34mg/L for thelower reaches before the impoundment of the Three Gorges Reservoir, which was mainly influenced by the discharge of industrywastewater as well as domestic sewage.However, the concentrations of nitrogen mainly depended on agricultural pollution andshow little difference along the river, which was among 0.7-1.1mg/L.After the impoundment of the Three Gorges Reservoir,the concentrations of phosphorus and nitrogen increased obviously except for phosphorus of the backwater area, which was causedby the deposit process of the particle phosphorus.Even though, as the ratios of nitrogen to phosphorus were general greater than10 in the backwater area as well as the slower water flow, the possibility of algae bloom eruption increased.Also, compared withsome other rivers in China, the phosphorus pollution of the sediment of the Xiangxi River was serious.The concentration of totalphosphorus in the sediments is as high as 1221mg/kg, with the inorganic phosphorus as the main portion.In addition, with theaverage concentration of 609.4mg/kg, the calcium bound phosphorus is the main form among different inorganic phosphorusforms, compared with labile phosphorus and iron/aluminium bound phosphorus.This research suggested that the adverse impactcaused by the Three Gorges Reservoir emerged and necessary measure is urged to prevent the eutrophication.