Lake Sediments Record And The Catchment Environmental Changes In The Upper Reaches Of The Hangbu River Over The Past 50 Years

Catchment environmental changes, as one of the major and disputive subject internationally, is tackled in the paper, focusing on the estern part of China and the lower reaches of Yangtse River,a region characterized for the monson climate and the intensity of human activities. This paper selects Longhekou reservoir of Hangbu River catchment in Chaohu as study area. Samples, including surface soil and ALE core, were collected to obtain information about past environmental evolutions by means of environmental magnetism, grain size, X-ray and geochemical lements. By the help of water datum and comparing the information from the sediments with historical data, the influences of human activities in the past 50 years on the lake sediment are revealed. Through these analyzing and researching some conclusions were reached and acquired.(1)Through analyzing about grain size and SCP, combining Anhui fire power generation and runoff datum,it set up high-resolution age sequence in the past 50 years.(2) Sediment can record the evolvement of lake environment, Considering environmental magnetism and grain size etc. Longhekou reservoir can be devided five phases in the past 50 years. The first phase (1958~1968a): The grain sizes are small and the value of xfd% is high and the C/N is low because of relatively low rainfall and the human destroying activity; The second phase (1968~1976a): mainly influenced by human activity, the soil erosion is quite grave and the ecological environment is worsen.As a result, the grain sizes are coarse and the x becomes high in evidence. The C/N is also high because more fragments of terrestrial creatures are taken into reservoir by big rainfall. The third phase(1976~1979a): The grain sizes are very small because of drought and the contents of TP, TN etc. are high due to strong vaporize. The fourthly phase (1979 - 1992a): the sediment became small and the C/N also falls because of the management of human.The fifthly phase (1992~2003a): the aggradations is still graveness because new sedimentary source.(3)The rainfall and the human activity are the major elements influencing the Hangbu River catchment deposition, and the former element is mainly water resources for the river. In the past fifty years the high flow year and the low flow year appear in turn with quite great difference in the amount of rainfall. There are also great differences in rainfall due to monsoon climate within a year with autumn receiving most of the rainfall resulting in floods. Because of the big current of runoff, the sediment grain sizes in the reservoir region are wide and the fragments of terrestrial creatures in the sediment are abundant in the high flow year. While in low flow year the grain sizes are small with little fragmental deposition of terrestrial creature.