Studies On The Plant Community Functions In Lakeside Of Typical Plateau Wetland Nature Reserve In Northwest Yunnan

As an abbreviation of aquatic-terrestrial ecotone, lakeside zone has important ecological, social and economic values. It is a very important ecotone between aquatic ecosystem and terrestrial ecosystem to maintaining biodiversity and ecological balance. Lakeside is the natural defense of lake and an important component of the lake ecosystem and evaluation criteria. However, by now, the systemic and quantitative study on lakeside functions of plateau wetland are lack in China. To determine the status of the lakeside in plateau wetland, this study quantitative researched the functions of plateau wetland from water quality, bed mud, aquatic vegetation and mountain catchment area. It has an important role and practical significance for biodiversity protection of plateau wetlands, function zoning of natural reserve, legislation on conservation of wetlands, stability of ecological environment and sustainable development of social economy.Research site were Jianhu Lake and Napahai Lake, which are the representative plateau in the northwest of Yunnan.According to the representative and typical principles, this study used the combined research methods of field position sampling and laboratory analysis. The sampling points were symmetrical set in upstream face and downstream face of well-grown plants on Jianhu lakeside. Aquatic vegetations of Napahai were investigated. Meanwhile, the study compared the runoff and sediment yields which can affect the function of Lakeside among 4 different land types in collection area: the sloping farmland, wild grassland, artificial young woodland and natural secondary woodland. The results showed:1) Wetland lakeside played an important role in water quality purification and absorption, among which the average evisceration rate of NH4-N and TP were 61.97% and 47.73% respectively. Water quality changed from Class V toⅣ, which showed that the adsorption and purification functions of lakeside were effective. At the same sampling point of upstream and downstream face, the average contents of NH4-N, TN, TP and TMn in April were higher than that in August. The removal rate of NH4-N and TN in April were higher than that in August, while TP and TMn were opposite. These results showed that the nutrient material concentration of the lakeside water changed with season, but this law was not suitable for the removal rate of different nutrients.2) The soil nutrient analysis in lakeside showed that: Average content of available K was 0.19 mg·g-1, of available P was 0.68mg·kg-1 and of hydrolysable N was 0.31 mg·g-1 in upstream face of lakeside, and was respectively 0.21 mg·g-1, 0.24%, 0.54mg·g-1 in downstream face. The contents of available K, available P and hydrolysable N were decline in upstream face. Organic matter and TN of full dose had greater difference between downstream and upstream face. Gating through lakeside, accumulation of organic matter under anoxic conditions was the main part. Accumulation of organic matter was as much as 5.04~ 8.80% and TN was as high as 7.92%. A large number of sedimentary organic matters depress the decomposition and release of nutrients, which alleviates the lake eutrophication and played a carbon"sink"function. It could be concluded that the lakeside had adsorption and purification functions.3) It was notable results that the lakeside intercepts sediment entrained by surface silt and other pollutants. The average turbidity was 18.32 NTU in upstream face of lakeside, and was 1.42 NTU in downstream; the descending rate was 92.25% in downstream. The average thicknesses of mud in upstream and downstream face were 42.8㎝ and 28.3㎝respectively, that was 1.5 times in upstream face than in downstream face. The alteration of the turbidity and thickness of mud directly showed that the lakeside had filtering and subsiding functions,"the promoting siltation effects"reducd the lake deposition, and maintained the balance of wetland ecosystem.4) The composition, distribution and change trend of aquatic vegetation directly reflected the evolutionary direction of wetland ecosystem, decided the function of lakeside. According to the measurement, the emerging plant averagely removed 30% of TN and 57% of TP, for the submerged plant, they were 86% and 93.14%. This indirectly reflected the relationship between the composition of aquatic vegetation and the functions in lakeside.5) Base on the analysis of the characteristics of runoff and sediment yields in the natural secondary woodland, artificial young woodland, wild grassland and sloping farmland, the natural secondary forest could protect the soil from erosion very well, because of complexion of the community structure and well-preserved vegetation. The surface runoff content of natural secondary woodland and artificial young woodland were less than that of sloping farmland by 46.4% and 32.6%,and less than the wild grassland by 54.7% and 43.0%, which showed that the sloping farmland was the worst ecological function at soil conservation, it easily causes the soil and water loss.Therefore, by quantitative research on the water quality, bed mud and aquatic vegetation to mountain catchment's areas, the results indicated that the functions of lakeside were not fungible in the filtration, purification and the absorption of other nutrients. It was directly related to the succession progress of lake and wetland ecological system and its survival. Wetlands in the lakeside zone were very important, so it should be protected first.