The Impacts Of Different Types Of Reservoir Siltation On The Burial Fluxes Of Total Organic Carbon And Total Nitrogen

This article conducted sub-bottom profiles observation of the channel-type reservoirs?Huangbai River Cascade Reservoirs?East branch?,Yichang?and lake-type reservoir?Xin'anjiang Reservoir,Hangzhou?in May and November 2016,respectively.At the same time,sedimentary samples were collected from different parts in each reservoir and brought back to the laboratory for determination of particle size,total organic carbon?TOC?and total nitrogen?TN?,in order to investigate the impacts of dfferent types of reservoir siltation on the buried fluxes of total organic carbon and total nitrogen.We roughly divide each reservoir into three parts based on the distance from the dam in the longitudinal direction.Upstream region?UR?is the part that far away from the dam and occupies about one-third to one-fourth of the whole reservoir.Middle region?MR?is the part that in the central of each reservoir,whose length is approximately half of the whole reservoir.Lower region?LR?is the part that near the dam and occupies about one-third to one-fourth of the whole reservoir.The main results are as follows:?1?At the initial operation stage of the channel-type reservoirs,sediments mainly accumulate in the UR of the reservoir.After the completion of new reservoirs in the upstream,those sediments deposited in the UR will be gradually transported to the MR or LR under long-term hydrodynamic conditions because of the sand blocking effect of the dams.In lake-type reservoir,sediments are mainly deposited in the UR of the reservoir,forming a"tail delta"structure.Sediment composition of each reservoir is dominated by clay silt,and a small amount is silty clay.The average particle size of surface sediments generally decreases from the UR to the LR.Water content?dry weight?decreases from the surface to bottom in vertical and gradually tends to be stable after reaching a certain depth.?2?We distinguish the thickness of sediments according to the sub-bottom profiles and calculate the average siltation rate of sediments in each reservoir through gridding interpolation.In channel-type reservoir,the average siltation rate of sediments ranges from 0.54 to 1.91 cm·y^-1,which is higher than lake-type reservoir(0.39 cm·y^-1).We calculated the burial rates of TOC and TN with the determination results of sediment samples.In channel-type reservoirs,the burial rate of TOC ranges from 65.34 to 182.84g·m^-2·y^-1 and the burial rate of TN ranges from 7.61 to 23.4 g·m^-2·y^-1,which are higher than lake-type reservoir(TOC:29.4 g·m^-2·y^-1,TN:3.37 g·m^-2·y^-1).In channel-type reservoirs,the burial rates of TOC and TN in different regions are consistent with the sediment siltation rates,while the lake-type reservoir shows an opposite trend.?3?In channel-type reservoirs,the high sediment siltation rate is the main factor controlling the burial fluxes of TOC and TN.While in lake-type reservoir,whose sediment siltation rate is relatively low,organic matter degradation is a factor that affects the burial fluxes of TOC and TN.