Studies On The Purification Function Of Water-Soil-Plant System In Typical Plateau Wetland Lakeside, Northwestern Yunnan

Jianhu wetland was chosen as study site in this article. The Jianhu wetland is animportant wetland in northwestern Yunnan. Jianhu lake is the same as other plateau lakes,it is a freshwater lake dispersed on the Yunnan plateau isolatedly through surface faultingand downthrow. This wetland is a typical wetland with complete lakeside in Yunnan. Dueto relatively closed terrain environment, all of the water went into the Jianhu Lake throughlakeside. The lakeside is initial pollution receiving body as industrial and agriculturalproduction and life pollution into Jianhu wetland. With bearing complex and diverse waysof human activities, Jianhu wetland ecosystem continues to maintain its stability. It meanscomplete and complex lakeside of Jianhu wetland, playing an important role inmaintaining lake ecosystem balance. This article was from the changing of physical andchemical property of soil in the lakeside, and the changing of water quality through thelakeside plant communities, to understand effect of pollutant purification and sedimentretardation by the lakeside. The important function of maintaining wetland ecologicalbalance by the lakeside was revealed. It provided a theoretical basis for ecological systemrestoration in plateau wetland.Two different methods (field investigation and laboratory experiment) were used inthis study. Soil samples and water samples were collected in front and back of the lakesideseparately. For the laboratory experiment we constructed5different matrix slots by using6kinds of materials, which included red soil, cinders, ceramsite, vermiculite, flyash andgravel. The pollutant removal efficiency without plants by matrix was recorded andanalyzed. In addition, we chose four common wetland plants (Zizania caduciflora, Trapaincisa, Ceratophyllum demersum and Potamogeton pectinatus) in nature wetland inYunnan plateau to construct four different plant communities by using differentconfiguration modes. The clean-up effect of different plant communities on domesticsewage was observed and compared by laboratory experiment. The results were as follows:(1)the average silt thickness of front and back of the lakeside were139.67cm,87.33cm.The lakeside had obvious effect on stopping sediment into the lake. The lakeside hadreduced the amount of silt into the lake basin by about62%;(2)the content of hydrolysisnitrogen, total phosphorus, available phosphorus of the silt in back of the lakeside zone significantly reduced, while the content of organic matter and total nitrogen increased;(3)each water-quality index in back of Jianhu lakeside significantly reduced. It basicallyachieved GradeⅢwater in lake outlet (total nitrogen1.71mg·L-1±0.04mg·L-1,ammonium nitrogen0.22mg·L-1±0.00mg·L-1, nitrate0.004mg·L-1±0.000mg·L-1, totalphosphorus0.02mg·L-1±0.00mg·L-1, phosphate0.005mg·L-1±0.000mg·L-1, COD19.50mg·L-1±2.12mg·L-1), this showed plants in lakeside fixed carbon by photosynthesis. Theplant residues accumulated at back of the lakeside. The content of organic matter and totalnitrogen in silt increased. Greenhouse gas in the atmosphere was deposited into wetlandthrough this process. The plants in lakeside played an important role of "carbon sink".Meanwhile the nutrient which came fiom the sewage going into the lake, was absorbed andutilized by the plants in lakeside. The pollutant content in back of the lakeside reduced.This demonstrated lakeside plants had purification function. In addtion, the deposition andadsorption of organic matter and total nitrogen by the silt as well as reflected the functionof collecting carbon and nitrogen. The silt reduced pollution from organic matter and totalnitrogen into lake water. The silt played a role in water purification;(4)by using differentmatrixes slot, reduction rate of total nitrogen, total phosphorus, COD were respectively upto22.46%±0.27%,56.80%±6.21%,71.15%±1.96%. The matrixes displayed obviouslypurifying effect;(5)with different plant communities, reduction rate of total nitrogen,ammonium nitrate, total phosphorus, phosphate, COD were54.44%±0.29%,80.85%±0.31%,65.72%±0.35%,64.31%±0.56%,69.66%±4.15%. From laboratoryexperiment results, matrixes and the different plant communities had good purificationfunction could be found. This result was consistent with the field investigation andanalysis.According to the results of field investigation and laboratory experiment, thewater-soil-plant system in lakeside played an important role in purification of sewage intothe lake. It is an important ecological burrier to maintain the surface faulting anddownthrow lake wetland ecosystem.