Research Century Scale Ecological Evolution And The Relationship Between Human Activity Mortar Lake Area

The study of global changes has focused on the reconstruction of paleovegetation and paleoclimate by n-alkanes and δ13C. However, such studies must be based on precise chronology of the sediments. Lake sediments, in which has large amount of information storage, high time resolution records and wide geographical coverage, becoming one of an important carrier in the study of global climate and environment change gradually.210Pb contents were measured for dating. The combination use of deposition rate and a variety of environmental proxies revealed the evolution of eco-environment around the lake during the past150years. TOC, TN and TP contents were measured for analysis the nutrients pollution. Single factor index method was used to assess the risk of TN and TP. The distribution characteristics of n-alkanes and δ13C were used to indicate the source of organic matter in the sediments of Shijiu Lake. The relationship between eco-environmental evolution and human activities was discussed in this paper. It can provide scientific basises for preventing Lake Eutrophication and improving eco-environment effectively. The main results were showed in following:(1) The depth of210Pb dating was from0cm to26.5cm and the average deposition rate was0.18cm/a. Affected by human activities, the trend of deposition rate was increased graduatlly. Combined with specific environmental events to determine its age span was from1862to2010.(2) The combination characteristics of n-alkanes showed a significant odd-even predominance in high-carbon number and main peak at C29, suggesting that the organic matter in the sediments were mainly derived from macrophytes and terrestrial higher plants. The δ13C contents of C27, C29and C31n-alkanes were analyzed; the relative contribution of C4and C3plants was estimated by using a binary mixing model and the results indicated that C3plants are the dominant species.(3) A variety of environmental proxies in different periods revealed the impact of human activities on Shijiu Lake. From1862to1970, the low relative contents of TOC, TN, TP, C17-C25and the light δ13C25-31values showed that less human activities effects on Shijiu Lake were detected and the eco-environment around the lake was stable. From1970to1983, the relative contents of TOC, TN and C17-C25increased significantly,δ13C25-31values became weight. In this period, large areas of Shijiu Lake turned into farmland; fertilizers and pesticides pollution were serious; much of industrial and domestic wastewater were discharged into the lake. All these human activities resulted in the degradation of terrestrial higher plants around the lake. Meanwhile the eutrophication levels were increased significantly. From1983to2010, the relative contents of TOC、TN and C17-C25were still in high-value ranges, TP contents increased significantly. The risk assessment of TN and TP showed that the risk of eutrophication was strengthened. All these indicated that the problem of eutrophication was not effectively controlled and the eco-environment of Shijiu Lake was relatively degradated.