Distribution Characteristics And Pollution Evaluation Of Pollutants In Lake Sediments Of Dongting Lake Plain

[SEM-AVS] evaluation model was used in this thesis to analyze systematically distribution characteristics of heavy metals in sediment and to evaluate the pollution of plain lakes of Dongting Lake. The study of AVS (acid volatile sulfides), SEM (Simultaneous extracted metals) and organic matter in the sediments of Dongting Lake enriched the data on pollution of heavy metals in this area, which provided relevant scientific researchers with a more comprehensive knowledge of sediment pollution around Dongting Lake and a more scientific and reasonable evaluation on the related pollution. The systematical analysis on sediments of 10 medium-small sized lakes in Dongting Lake plain filled up the blanks in this field and provided the partial support for further development and pollution treatment in this area. The main results of this thesis were given as follows:1. Pollution status of sediments in Dongting Lake(1) Applying [SEM-AVS] model to evaluate heavy metals in surface sediments of Dongting Lake showed that potential ecological risks existed in general areas of Dongting Lake, and heavy metals in the sediments might cause negative effects on aquatic organisms and human beings. For the pollution level of heavy metals, the sequence was East Dongting Lake>West Dongting Lake>South Dongting Lake. AVS contents in the surface sediments (0-5 cm) were very low. The contents gradually increased downwards, reached the maximum at the depth of 10-20 cm, and then decreased, indicating that AVS contents were controlled by the redox circumstance in sediments. SEM contents increased gradually upwards from the bottom to the surface, which showed that there was an increasing trend of heavy metal pollution year-on-year in the Dongting Lake.(2) Contents of organic matter in the sediments of Dongting Lake in wet season were higher than those in dry season, and the sequence was Middle East Dongting> South Dongting>West Dongting. The evaluation results showed that the sediments in Dongting Lake area were not polluted by organic matter.2. Pollution status of sediments in 10 medium-small sized lakes in dongting lake plain (1) Chrome contents in the surface sediments in 10 medium-small sized lakes in Dongting Lake plain were generally higher than the background values. The highest concentration was 101.2 mg/kg at Site 4 in Datong Lake. The sequence of average chrome contents in the surface sediments was Yueyangnan Lake>Datong Lake>Shanpo Lake> Dong Lake>Huanggai Lake>Anle Lake>Beimin Lake>Liuye Lake>Maoli Lake>Bajiao Lake. According to the types of lakes, the highest chrome contents were found in urban lakes, followed by fertilization lakes and artificial-natural lakes. The evaluation results using geo-accumulation model indicated that among the 10 selected lakes,10 sampling sites in 4 lakes belonged to middle pollution level,18 sampling sites in 9 lakes belonged to mild pollution level, and 1 sampling site belonged to non-pollution level.(2) Average arsenic contents in the surface sediments followed the sequence of Yueyangnan Lake>Bajiao Lake>Huanggai Lake>Anle Lake>Maoli Lake>Liuye Lake> Dong Lake>Shanpo Lake>Datong Lake>Beimin Lake. The evaluation results using geo-accumulation model indicated that among the 10 selected lakes,1 sampling sites belonged to middle pollution level,16 sampling sites in 8 lakes belonged to mild pollution level, and 12 sampling sites in 5 lakes belonged to non-pollution level. Arsenic contents in the sediments increased gradually upwards from the bottom to the surface, showing an increasing trend of arsenic pollution year-on-year in these lakes. Generally, arsenic contents in the surface sediments followed the sequence of the lakes in Li River systemNi>Pb>Cu>Zn, and the potential ecological risk due to multi factors influence was given to Datong Lake>Bajiao Lake>Liuye Lake>Huanggai Lake>Yueyang Lake>Shanpo Lake>Maoli Lake>Dong Lake>Beimin Lake>Anle Lake. Evaluation results using AVS-SEM index indicated that heavy metal contents at Sites 3 in the surface sediments in Datong Lake and Shanpo Lake reached the level that was harmful to organisms. Contents of heavy metals in column sediments increased unstably upwards from the bottom to the surface. The trend of increased heavy metal contents from-10 cm to 0 cm reflected a great impact of human beings on these lakes. (4) Contents of organic matter in the surface sediments in the 10 medium-small sized were quite low and did not cause any pollution organic matter. The average contents of organic matter were Hanggai Lake>Yueyangnan Lake>Bajiao Lake>Datong Lake>Liuye Lake> Beimin Lake>Maoli Lake>Shanpo Lake>Dong Lake>Anle Lake.