| Environmental evolution of Honghu Lake in past 1300 yearsForming sediments is the result of physical biological chemical interaction in lakes. Sediments record the past climate, environmental change and the influence imposed by human being in lake in truth, which include double effects of climatic change and human being's activities. We can recover past climatic change series through translating some environmental substitution proxies that implicate the information about environmental evolution. Therefore, research on these proxies is the necessary means in order to reflect past environment. This thesis depends on geochemistry and environmental magnetism to reveal environmental evolution of Honghu Lake.The author went to Honghu Lake to survey and take samples. The Core H2002-2 (presenting to past 1300 years) is 150cm long and is divided into samples of 1 cm each, 150 samples were retrieved and code them from 1 to 150 accidentally. Then analyzed samples with number from 1 to 50 and even number from 51 to 150 and got valuable datum. Meanwhile, collect environmental magnetic datum of core 92-D (taken in 1992) with length of 140cm. Take advantage of these datum and other documents of prior researchers, recover the record of the environmental evolution in past 1300 years of Honghu Lake. It has been shown that:(1) The accumulate rate is between 0.092-0.129cm/a resulting from AMS dating of sediments in Honghu Lake, and the average accumulate rate is 0.11 cm/a. 137Cs and 210Pb dating were not be employed in the ground of the reliability of data which is in accord with the results derived from Prof. Cai Shuming and J.F.BOYLE. Besides, there are many floods. Outflow and inflow bringing bed load to increase the accumulate rate so that huge difference exists among different year. So to define the range of accumulate rate is more meaningful than to measure a definite rate.(2) Geochemistry analysis indicates that value of TN, TOC and Ca are very high in 150-120cm; Value of TN and TOC have no distinct change in 120~20cm, and the variety of Ca value is mild with a higher value in 40cm. when approach to top layers, the values of TN, TOC, TP and sulfide show ascending except Ca. TP and sulfide values are stable basically without great fluctuate.(3) the curve based on statistical datum in recent years of Jianli shows that dosage of fertilizer and pesticide, total agricultural production value are ascending, through which we can deduce that the content of TN, TOC and TP in up layers has some connection with human's activities in agriculture. And output and dosage of phosphide can illustrate it.(4) the environmental magnetism measurement shows that core HD has quite high values of low frequency susceptibility (xlf) , saturation isothermal remanent magnetization (SIRM), soft isothermal remanent magnetization (SOFT) and anhysteretic remanent magnetization (xARM)- Generally, xlf = 22-130 10-5 m3kg-1, SIRM = 3~19 10-3 Am2kg-1, SOFT = 596.8-4013.4 10-6 Am2kg-1, XARM= 97.6-625.0 10-5 m3kg-1', F300mT = 82-92 %. The results suggest that the character of sediments is dominated by stable single domain and fined viscous ferromagnetic minerals. The magnetic minerals grain size increasingly reduces from the bottom to top. Moreover, magnetic character change corresponds to palaeoclimatic change. In cold and dry condition, the magnetic parameters are higher than in warm and wet. They record the course that Honghu Lake extends and shrinks along with climate; at one time reflects the human activities' impact on the lake.(5) The variation of magnetic parameters reflects the change of substantial origin and territorial environment and climate. Sediments of Honghu can precisely illustrate this c.orresponding relation. However, environmental magnetic mechanism is not alwaysin accord with the modal of climatic and environmental change so the magnetic character can't perfectly reflect outside change of lake. Due to geographical position of Jianghan Plain, some e...
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