|Alternative Title||Sourcing sediment deposited by tracers in the Changshou reservoir|
|Place of Conferral||北京|
|Keyword||137cs 210pbex 颗粒组成 养分 重金属 泥沙来源 长寿湖水库|
The study area of Changshou reservoir in the Longxi catchment is located in the Three Gorges Area of the Upper Yangzte River. The study area is an important component of the Three Gorges Area to protect the health of the ecological environment and the water quality. Using multiple tracer technologies to predicate the sediment source of the Changshou reservoir, it is helpful to set up scientific and reasonable control strategies of the Changshou reservoir and soil and water conservation measures in the Longxi catchment. Therefore, the present study has field investigation and experimental analysis, to reveal the characteristic of the sediment including nutrients and heavy metals, to determine the date of the sediment profiles and analysis the sediment deposited dynamic process, and to research the sediment source by using tracer technologies. The main results and conclusions in this dissertation are as follows: (1) Dating the sediment profiles and analysising sediment deposited dynamicSome sediment cores were retrieved from the Changshou reservoir in 2014, using a gravity corer equipped with an acrylic tube with an inner diameter of 6 cm. The extracted cores were sectioned at 2 cm intervals. All sediment core samples were dried, sieved (<2 mm) and weighed. Based on bulk density and particle size, human activites and nutrients, 137Cs and 210Pbex technologies, and particle size and rainfall erosivity, the present paper dated sediment profiles chronosequence, that were 1956, 1963, 1982, 1989, 1998 and 2005. Based on the significant difference between bulk density and particle size in the sediment before and after the construction of the Changshou reservoir which was constructed in 1956 with significant difference between the original river bed or soil and sediment, it determined the starting time of sediment deposited in 1956. Using the 1963 peak of 137Cs in a sediment profile, it was a reliable date marks in 1963. According to the relationship of the peak rainfall and rainfall erosivity corresponding to coarse particle size, it could find the time of 1982, 1989 and 1982 in sediment profiles. By human activities of fish farming policy, the peaks of TOC and TN content in sediment profiles was the time in 2005 due to the ban of fish culture in cage with fowl manure and chemical fertilizer. From Changhou reservoir built in 1956, the annual average sedimentation rates were 1.586 cm/a, 1.138 cm/a and 0.655 cm/a in cores A, B and C, respectively. The maximum values of annual average sedimentation rates were 2.286 cm/a and 2.000 cm/a in cores A and B, respectively. The implement of the household contract responsibility in the period, farmers strongly worked on the land, at the same time, the rainfall was heavily. The combination made strongly soil erosion in the Longxi catchment and sedimentation rate in the Changshou reservoir. The higher values of annual average sedimentation rates were 1.778 cm/a, 1.778 cm/a and 1.111 cm/a in cores A, B and C, respectively in 1989-1997. The probable reason was that human disturbance of soil surface in the early period of the implementation of returning farmland to forest and grassland, building terraces and so on made unstable soil surface to cause soil erosion easily. The lower values of annual average sedimentation rates were 1.556 cm/a, 0.444 cm/a and 0.667 cm/a in cores A, B and C, respectively in 2005-2013 due to the increase of vegetation coverage to improve environment and weaken soil erosion.Sediment below a depth of 92 cm, 66 cm and 38 cm in cores A, B and C, respectively was coarse, and this reflected the original base of the reservoir while the Changshou dam was completed. The bank erosion inputs occurred possibly as a result of soil collapse in the submerged portions and this material was delivered directly into the reservoir and deposited. Since the depths of 40 cm, 24 cm and 14 cm in cores A, B and C, respectively, that is about mid-and late-1980s, the sediment particle was coarse due to the comprehensive influence of strongly disturbance on the land by the household contract responsibility and heavily rainfall erosity by heavily rainfall. At the initial phase of the implementation of returning farmland to forest and grassland soil surface was unstable and surface soil was susceptible eroded to make coarse particle size. Since 2005, sediment particle size was fining due to vegetation coverage increased and soil erosion decreased in the Longxi catchment. (2) The vertical variation and cause analysis of nutrients and heavy metals in the reservoir sediment profilesTOC, TN and TP changed from large to small at the beginning of construction. It was found that surface sediment and soil with rich CNP eroded and ran into the reservoir when the water level was high. With surface bank or/and soil erosion with rich CNP was eroded, the content CNP of the sediment in the reservoir decreased. Since the depth of 40 cm, 24 cm and 14 cm in cores A, B and C, respectively, that was the mid- and late-1980s, TOC, TN and TP increased and showed peaks at the depth of 12-14 cm, 4-6 cm and 6-8 cm. Cage farming had been applied in the reservoir since 1980s, which made waste to accumulate in the reservoir. The local government legislated to forbid fertilizer farming fish and banned it completely in 2005. It showed that the trend in TOC, TN and TP gradually decreased because they released into the water and reduced CNP content in the sediment since 2005. Heavy metal in the sediment from big to small was Zn > Cr > Ni > Pb > Cu > Co > Cd. At the beginning of the Changshou dam was completed in 1956, heavy metals in the sediment had the trend from high values to low under the influence of sediment deposition. Heavy metals in the sediment has a increase tendency in 1989-1998 with gradually increasing of urban sewage and factory waste water in the Longxi catchment. Except Cd, heavy metals increased significantly in 2005-2013. Pearson correlation analysis showed that Cd, Co, Cr, Cu and Ni, and has significant or extremely significant correlation. Principal component analysis found that Cd, Co, Cr, Cu and Ni could explain more than 55% and natural source are the principal influence factor. Zn and Pb had weak correlation and different sources. Zn and Pb were largely driven by urban sewage and factory waste water. Cd was affected by natural and human activities.(3) Sediment source analysisUsing sediment source tracer technology to research the sediment source of the reservoir, sampling method for typical small forest and farm catchment instead of traditional method to increase the representative of soil erosion source. Based on the spatial location of Longxi catchment, the catchment was divided into upstream, midstream and downstream, and based on land use types, the sample types were forest land and farmland. Combination the vertical variation and causes of nutrients and heavy metals, sediment source tracer technologies identify sediment source. The steps, firstly was the optimum recognition statistical filtering factor, secondly combined with the multivariate linear mixed model, finally realized the quantitative portion of sediment on the various sources. Based on the land use types, forest catchment and farm catchment were about 31% and 69%, respectively, and the sediment yield per unit area was 1.43 times in farm catchment than forest catchment and farmland was the mainly sediment source with strongly worked on the farm land. Based on the upstream, midstream and downstream yield, sediment source were 13%, 71% and 16%, respectively. It showed that midstream (Dianjiang) was seriously soil erosion and the governance should take measures to prevent soil erosion and water loss.
|高进长. 长寿湖水库沉积泥沙来源的多种示踪研究[D]. 北京. 中国科学院大学,2016.|
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