Water Environmental Effect And Dominant Factors Of Different Plant Communities At Samachang Of Mid-vunnan,China

Recently, water pollution of plateau lakes mainly derived from the output of mountain non-point source pollution. In addition to soil source that affected the output of non-point source pollutants, rainfall was the power of output of the non-point source pollutants source; and plant community reduced the power of output of non-point source pollutants based on the rainfall redistribution. The studying for the factors that effected on output of mountain non-point source pollutant, which had very important significance for controlling mountain non-point source pollution effectively.In this study, five types of vegetations, including shrubland, pinus forest, semi-natural forest, natural secondary forest and eucalyptus plantation in Yunnan province were investigated by field investigation to reveal their community structure, ecological processes including ecodydrological responses and soil improvement was experimented. To assess the water environmental effect of different plant communities, we based on community structure, soil source, characteristics of litters and intergrated ecological processes, then analyzed main factors affecting the output of non-point source pollutants. The main conclusions could be drawn as follows:(1) The higher complexity of structure of community indicated the simpler shrub layer. From the simple shrubland to the complex natural secondary forest, the plant density, crown-diameter, plant height, DBH, species richness, crown-density and diversity index of the tree layer of the communities had a significantly increasing trend, the increasing ratio was1.97～10.80, an average of5.12times; while that of shrubs decreased, the indexes were reduced to0.09-0.67, an average of0.45.(2) In different periods and plant communities, soil source indicated different trends. The principal component analysis showed that major factors influencing the source were nitrogen and phosphorus. From the dry season (march) to the rain-dry period (november), Soil total nitrogen of five typical communities had a significantly decreasing trend, an average reduction of19.61%; while that of the available nitrogen increased(except for eucalyptus plantation), the average increase of27.89%; soil nitrogen had a trend which transformated to available nitrogen. Soil total phosphorus had an increasing trend from the dry season to the wet and dry period, the average increase of8.85%; while the soil available phosphorus had a decreasing trend, the average decrease of32.16%; however, the region was short for phosphorus, nitrogen had been the main factor of the output of non-point source pollutant. By the system perturbation analysis, the results showed:the soil source of natural secondary forest (perturbation value:0.260～0.461) was significantly higher than any other communities (perturbation value:0.552～1.408), while that of eucalyptus plantation (perturbation value:0.913) and pinus forest (perturbation value:1.408and1.397) was significantly lower than any other communities.(3) In the same rainfall conditions, the more complex plant communities were, the higher canopy interception and the canopy interception-rate were, canopy interception was in the range of3.33-17.71mm, and canopy interception-rate was in the range of13.32～51.65%. The storage of litter had increased with the plant community complexity increasing, which was in the range of1.94-17.66t/hm; in addition, the maximum water-holding capacity of litter was in the range of1.86-3.03g/g in the region. Generally, the water holding capacity of litter of natural secondary forest and pinus forest was significantly higher than that of Shrubland and eucalyptus plantation.(4) In different periods and plant communities, the output of runoff and non-point source pollutants had significant difference at Samachang. The output of the runoff and non-point source pollutants were mainly concentrated in the6-9month, accounted for more than65%of the total output, the average was about75%. The annual total output of runoff, TN, TP, COD from five plant communities respectively:16.88m3/400m2,13.98g/400m2,4.08g/400m2,2279.51g/400m2. From the shrubland to natural secondary forest, the output of runoff and non-point source pollutants substantially decreased; while that of shrubland was more on average3.88times than natural secondary forest.(5) The output of non-point source pollutants at Samachang was related to the comprehensive effects of many factors, as well as the rain was the power of output of non-point source pollutants. The output of runoff and non-point source pollutants increased with the increasing of rainfall. When the rainfall was larger than a certain figure or absorption and regulation ability of the community was completely beyond, rainfall had become the main factor that affected the output of non-point source pollutants, it was called "critical rainfall". Then the"critical rainfall" related to influence on output of runoff, TN, TP and COD were:30mm,35mm,45mm,30mm. The output of non-point source pollutants was affected by all kinds of factors liked structure of community, source intensity, litter and etc. at Samachang. We found that community structure played an important role in preventing the output of non-point source pollutants by studying, especially between the leaf area index, species richness of tree layer, tree crown, plant height of tree layer,species shannon-wiener index and the output of non-point source pollutants showed a evidently relativity.