|关键词: 环境变化 人类活动 环境指标 鄱阳湖
|Distinguishing the Change of Lake Level and Human Activities during Historical Period in Poyang Lake by Environmental Proxies
Nanjing institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008
|Human activity is one of most important factors that affect the change of environmental proxies in lake sediment records during the historical period. In this paper, based on the analysis of multiple proxies (graim size, organic carbon, magnetic measurements and radiometric methods) and historical document records, the history of water-level fluctuations and the changes of human activities were reconstructed in Dachahu Lake area, the west part of Poyang Lake, the largest freshwater lake in China during the past 2 ka and probed into the linkage between human activities and environment changes. The studies show that there are striking responses in magnetic records to human activities and grain-size records to water level fluctuation documented by historical record. The following processes that the lake have undergone may reveal the corresponding changes of human activities or land use from lakeshore to hillside area in historical times. (1) Before AD 155, the environment of this area was fluvial depression or small shallow pond and sightly influenced by human activities. (2) In AD 155—480, the water level of Poyang Lake expanded southwards and the large water surface formed gradually, which provided good condition for the development of agriculture in the area and the impact of human activities was greatly enhanced. (3) After AD 480, the extension of Poyang Lake was at its climax, which forced human being withdraw from lakeshore area and turned to exploit hilly land. The alternation also caused the increase of soil erosion processes and the development of exploit delta in Poyang Lake quickly. (4) From AD 955 to 1180, there was a short dry period and water level began to descend, resulting in huge wetland formed and the increase of human activity in lakeshore area. (5) About AD 1545, the water level of Poyang Lake rised again because the outlet of the lake to the Changjiang River was obstructed gradually by he development of shoals. (6) During last 200 years, especially since the 1950s the greatest changes in evnironment proxies occurred due to the drastic increase of human activities, such as reclamation and deforestation on a large scale. The result is helpful for interpretation of the process of controlling the change of human aca-tivities in great shallow lake area.
|Key words: Environment change human activity environmental proxy Poyang Lake