Distribution And Settlement Characteristics Of Suspended Particulate Matter In The Backwater Area Of Peng River, Three Gorges Reservoir

As an occurrence form and important carrier of pollution and nutritional elements, suspended particulate matter is a significant composition of water environment. After the completion of the Three Gorges Reservoir, periodic dispatching operation force on the hydrologic situation has changed dramatically which has changed the water ecology and environment ulteriorly.The concentration, composition, migration and sedimentation of suspended particulate matter in water also assume the different characteristics from natural rivers and lakes. This research takes Peng River, a typical tributaries of middle reservoir, as an research area where sampling and Settlement in situ experiment study was carried out on suspended particulate matter at the backwater area of Peng River(Gaoyang, Shuangjiang)respectively in May 2014(algal bloom period), August 2014(low water period) and November 2014(high water period). After size grading by membrane separation methods, gradation composition, distribution and sedimentation characteristics of C, N and P was analyzed. Meanwhile, morphological characteristics of suspended particulate matter were identified by scanning electron microscopy(SEM) simultaneously. Research acquires the following main results:1) Total amount characterstic of suspended particulate matter in the backwater area of Peng RiverThe mean particle size of suspended particulate matter was maximal during the period of algal bloom, which was 62.19μm.The mean concentration of suspended particulate matter was 20.7mg/L. The concentration of suspended particulate matter in the surface and bottom layer was higher than that in middle layer. The organic matter ratio of suspended particulate matter was from 16 percent to 17 percent at Gaoyang and 78 percent to 86 percent at Shuangjiang.The mean particle size of suspended particulate matter was minimal during the period of low water, which was 21.32μm. Affected by the flood, the mean concentration of suspended particulate matter increased to 61.5 mg/L. The inorganic matter ratio of suspended particulate matter turns to 82-98 percent.The mean particle size of suspended particulate matter was 32.36μm during the period of high water. Dilution and current slowed down when water level rose, which provided a superior conditions for settlement. The mean concentration of suspended particulate matter decreased to 6.77 mg/L and the water column distribution assumed obviously gradient difference. The organic matter ratio of suspended particulate matter rose from 82 to 98 percent.2) Constitution characteristics of suspended particulate matter in the backwater area of Peng RiverDuring the period of algal bloom, Mineral particles and biological particles were the main compositions of suspended particulate matter. Algal bloom broght about the maximizing of photosynthetic pigments. The mean particle size of phytoplankton was between 1.3μm and 11.2μm and microphytoplankton became the major contributor for total chlorophyll-a. The abundance of heterotrophic bacteria was 54.5×106cells/l at Shuangjiang and 117.1×106cells/l at Gaoyang. The ratio of flocculating constituent in bottom layer was higher than that in surface layer, which was between 25 percent and 65 percent; the ratio in Gaoyang was higher than that in Shuangjiang.The mineral particle was the main composition of suspended particulate matter during the period of low water. Phytoplankton reduced a lot compared with the period of algal bloom. The mean particle size of phytoplankton was between 1.3μm and 11.2μm, The picophytoplankton became the major contributor for total chlorophyll-a. The abundance of heterotrophic bacteria was from 37.6×107 to 159.3×107cells/l at Gaoyang and from 30×107 to 56×107cell/l at Shuangjiang. The ratio of flocculating constituent was between 25 percent and 65 percent, the ratio in Gaoyang was higher than that in Shuangjiang and the ratio in bottom layer was higher that surface layer.Mineral particles was the main composition of suspended particulate matter during the period of high water. The abundance of phytoplankton and heterotrophic bacteria reduced further. The mean particle size of phytoplankton was between 6μm and 9μm and the microphytoplankton was the major contributor for total chlorophyll-a. The abundance of heterotrophic bacteria was from 43.9×107 to 57.1×107 cell/l at Gaoyang and from 26×107 to 42.1×107 cell/l at Shuangjiang. The flocculating constituent took a substantial proportion in suspended particulate matter. The ratio in Gaoyang was higher than that in Shuangjiang.3) Component resolving of suspended particulate matter in the backwater area of Peng RiverDissolved C,N,P were the major forms existed in backwater area of Peng River. The PC accounts for about 2 percent to 33 percent of TC.The PN accounts for about 2 percent to 52 percent of TN. The PP accounts for about 22 percent to 62 percent of TP. The concentration of C,N,P in suspended particulate matter were comparatively highest during the period of algal bloom and the middle during low water period, the lowest during high water period. The suspended particulate matter was major in endogenous source during the algal bloom period. The suspended particulate matter was exogenous source during the period of low water. Exogenous source was significantly reduced during the period of high water and obvious gradient distribution expressed in the water volume.4)The influence of suspended particulate matter and sedimentation characteristics by reservoir operation in backwater area of Peng RiverC,N,P sedimentation flux were highest during the period of algal bloom in the backwater area of Peng River and the middle during low water period, the lowest during high water period. C,N,P sedimentation flux were gradient distribution with the increase of depth. C,N mainly precipitated with large particles and P mainly precipitated with large particles at surface layer, whereas precipitated with small particles both in middle and bottom layer during the period of algal bloom. C,N,P mainly precipitated with large particles during both low and high water period. C,N,P sedimentation flux were more uniform in size distribution during the high water period.Sedimentation particles showed the strong exogenous source during the period of algal bloom. Exogenous source was showed intensively in sedimentation particles during the period of low wate. Sedimentation particles showed exogenous source during the high water period.