The Sediment Environment Of Yunnan Fuxian Lake And Its Resoponse To Human's Disturbance

This paper chooses Fuxian Lake, the deep lake of fresh water located in the tableland of Yuxi district, Yunnan, as the research object. With the tread experiment of polymetallic nodules mining system, the author particularly analyzes the chemical composition of the water body, the earth chemical of the sediments and the earth chemical interstitial water, and he also investigates the difference of fore-and-aft disturbance of the sediments caused by the tread experiment of mining system.The paper reveals the sediment environment feature around the lake and its response to human's disturbance. The result of the research indicates that there is a obvious seasonal change of the suspending granules in Fuxian Lake, and this change is controlled by the local climate. Similarly, some parameters that are correlated nearly with the biological activity in the water body, such as the nutritional salt and dissolved oxygen, has a relationship with the environment. The content of minim heavy metal, such as Cu, Ni and Cd, is relatively low in the water body. Moreover, it is affected mainly by the weathering and denudation in the drainage basin of the lake. The research of sediment earth chemical also testified that the chemical composition of the sediment is mostly correlated with the followings: the chemical condition of it, the earth chemical background in the drainage basin and the intensity of weathering and denudation. Interstitial water is the intermediary during the course of transference and transform between the sediment and superjacent water. The minim elements in the interstitial sediment water are the integral interaction of premature diagenesis andman's impact. And the depositional environment in the interstitial water affects the distribution of minim heavy metals greatly. There is a steep concentration gradient near the interface of water and sediment. The resuspending granules will affect the water body near the bottom. The sediment formed by the disturbance of treading is mainly distributed in the water area below 70 meters deep, and its diffusing area is relatively small and is controlled mainly by the water direction. Moreover, it has a distinct influence on composition of the nutritive salt, especially in the water body close to the bottom. The influence of mining experiment on the minim elements in body water will be different to the different elements. As to the elements sensitive to the environmental change (for example Mn and Pb), the influence will be rather large, and it is a positive one in Fuxian lake, that is, if the composition in the water body is increased, especially in the bottom layer, the influence will be negative to some elements( for example Zn and Ni), and the water body is reduced, while it has no obvious influence on the relative inert elements(such as Cd and Cu). As to the sediment, although the mining experiment has not changed its overall distribution of chemical composition, there is a definite change of the content of different elements. Probably this is because the mining experiment disturbs sediment in the original superficial coat, and the some of the sediments will be lose. As a result, the distribution curve of the chemical composition will move downward. The experiment has a rather large influence on the composition of interstitial water, it changes the distribution of the original interstitial water on the whole.On the basis of the research work, the influence of environment by deep-sea mining is forecasted, and the concept of friendly-to-environment deep-sea mining system is put forward in this paper. It has significance to the design and manufacture of the deep sea mining system.