| In eutrophic water, the phosphorus is generally considered as the limiting factor for phytoplankton seasonal growth which caused algal bloom. Relative to the spatial distribution characteristics of phosphorus, the vegetation will appear corresponding distribution. In phosphorus enriched area, phosphorus loss during the rainy season will pose a serious threat to the surrounding water environment. However, the research on the distribution characteristics of phosphorus and its loss in rainy season, the vegetation distribution and effective phosphorus controlling by vegetation restoration are still absent. Thus the technology of restoring the vegetation for soil erosion and phosphorus loss control is urgently needed to resolve.Therefore, we choose the Southeast of the Chaihe River watershed in Shangsuan town as the phosphorus enriched area for our research. The spatial distribution characteristics of phosphorus and other nutrient elements in soil, and the corresponding vegetation distribution characteristics are analyzed. At the same time,3runoff catchment sections were set in the study area to monitor runoff and pollutants output. We also set up9runoff plots of typically vegetation, such as Coriaria sinica community, Arundinella hirta community, Erianthus rufipilus community, Pinus yunnanensis community, Pinus armandi community, Alnus nepalensis community, pinus yunnanensis-Alnus nepalensis community, Eucalyptus globulus community and Acacia mearnsii community. The coverage of vegetation, species diversity, soil fertility, litter layer coverage, and tiller number per unit area of herbaceous plants on runoff plots had been investigated. By integrated researches, to find the effective method of vegetation restoration for phosphorus loss control. Through the investigation, the results and conclusions had been drawed as follows:(1)Soil fertility in phosphorus enrich area changes greatly, and the distribution of vegetation is limited by soil fertility In phosphorus enrich areas of Dianchi lake watershed, soil phosphorus concentration decreased from phosphate mining area to the surrounding. In the study area, soil total phosphorus concentration ranged from1.15to80.2g/kg, varied greatly. The Soil N:P ratio ranged from0.006to0.98, less than the ratio of non phosphorus enriched areas. By the soil fertility investigation of each type of vegetation distribution in the area, we found that the soil pH value, soil organic matter, total nitrogen, total phosphorus, available nitrogen and available phosphorus, have strong changes in spatial distribution. And the fertility of the soil structure is different from that of the ocean and forest. The ratio of soil N:P ratio less than1. Especially, near the phosphorus mining and bare areas, the soil N:P ratio even lower than0.006. That is to say, the concentration of soil P is the highest, about166times more than soil N content. The soil C:N:P ratio in phosphorus rich area varied drastic different. Soil fertility characteristics may affect the distribution of vegetation in soil phosphorus rich areas.(2) In the area with high soil phosphorus concentration, plants have high carbon sequestration ability with low nitrogen demandIn phosphorus ore mining and waste phosphorus mining areas, the components of dominant plants had been determined, the ratio of C:N:P had also been analyzed. By the element ratio analysis, ratio of Rumex hastatus C:N:P was104:4.7:1, Erianthus was132:4.3:1, Eupatorium was106:6:1, Arundinella hirta was189:6.4:1, Coriaria sinica was118:6.2:1. Compared with the Redfield ratio coefficient, these plants reflect the characteristics of low nitrogen content. It was indicating that these plants need only a small amount of N supply with high fixation capacity of C. Thus is also the important adaptive characteristics of the pioneer plants.(3)The correlation analysis showed that the soil total nitrogen concentration is a limiting factor for both of species richness index and vegetation coverage.We found that there are significant negative correlation-ship between plant community structure characteristics and soil total phosphorus, soil the highest phosphorus concentration,soil pH value. The vegetation coverage correlate coefficient with these3index were-0.793,-0.786and-0.714. There is a significant positive correlation between vegetation coverage and soil total nitrogen, the correlation coefficient was0.786. The study found that the plant community species richness index and soil total nitrogen showed a significant positive correlation, the correlation coefficient was0.904. Plant community species richness is limited to the total soil nitrogen, and showed a significant negative correlation with soil pH value.Although the related analysis showing related factors linked and correlation coefficient, it can not determine which is the biggest impact factor. Therefore, we adopt the principal component analysis. The first principal component contribution rate is70.7%, mainly includes the soil available nitrogen, soil total nitrogen, soil organic matter, soil total phosphorus and soil pH value information, load them with respectively value of0.925,0.894,0.859,-0.870and-0.840. In the first principal component of the load, the maximum is the soil available nitrogen, followed by soil total nitrogen. Thus, it may be speculated that in the phosphorus rich region, the limiting factor of vegetation distribution is soil nitrogen concentration.(4) Phosphate mining and bare area is the key area of phosphorus loss among phosphorus enrich areasIn Rumex hastatus community, soil erosion intensity was the highest with330t/ha2.a.The soil erosion intensity in phosphate mining area was149t/ha2.a. In farmland area, soil erosion is maximum, the amount of soil loss is988t/a, and in the bare area, the amount of soil loss is957t/a. According to estimates of total phosphorus in surface soil, the highest region of soil total phosphorus loss is the bare land area in the mining area with amounted of57.8t, the total phosphorus loss accounted for88.5%of65.3t in whole research area.The phosphate mining and bare area is only5%of the study area, but the potential phosphorus loss accounted for the study area loss of88.5%. Therefore, phosphate mining and bare area is the key area of phosphorus loss.(5)In the rainy season, runoff output is closely related to plant community coverage and litter coverageThere is negative correlation between community runoff coefficient and vegetation coverage, the correlation coefficient is-0.837with significant degree of p<0.005. In addition, there is also a significant negative correlation between the litter coverage of community and runoff coefficient, the correlation coefficient is-0.810with a significant degree of p<0.008.There is no significant correlation between runoff coefficient and other community parameters such as the tree layer coverage, the coverage of shrub layer, herb layer coverage, species richness index, the tiller number per unit area and litter quantity. The regression equation between runoff coefficient (y) and the vegetation coverage (x%) is y=4.29×10-7x3-0.011x+0.810. The regression equation between runoff coefficient (y) and the litter coverage (x%) is y=e(b0+bl)/x=e11.342/x.(6) Plant community restoration strategies for phosphorus loss controlIn the key areas of phosphorus enriched areas (phosphate mining and bare area), the vegetation coverage was closely correlated to the soil nitrogen, there was an extremely significant positive correlation-ship between them, the correlation coefficient was0.990.Secondly, the soil concentration of organic matter has extremely significant positive correlation-ship with the vegetation coverage, the correlation coefficient was0.959. In the course of time (x), the regression equation of the vegetation coverage (y%) is y=-0.2304x2+9.3781x-7.5858, R2=0.9586.In the phosphate mining and bare area, when vegetation coverage ignored as0, the runoff coefficient is0.810. And when the vegetation coverage is up to75%, the runoff coefficient is0.166. If the vegetation courage improves from0to75%in the area, the runoff was reduced at least about80%.When vegetation coverage is up to75%, total soil nitrogen content at least up for0.890g/kg. Based on the process of soil development in phosphate mining and bare area, when the total soil nitrogen increased from0.361g/kg to0.871g/kg, it needs about15.5years.Rapid restoration of vegetation coverage is the most effective way to reduce soil erosion in short period. In the phosphorus rich area, the main limiting factor for vegetation restoration is the soil nitrogen. In addition, soil mechanical composition, pH value, organic matter content and so on also have an important effect on vegetation restoration. Therefore, in the mining area, the surface soil must be properly preserved, and gradually use it to restore vegetation. Secondly, in the area of vegetation degraded seriously, the problem of low nitrogen should be solved. And Rumex hastatus, Erianthus, Arundinella hirta can be selected as the pioneer plants. These plants have the ability of efficient assimilation of carbon with low nitrogen demand. Therefore, the vegetation coverage can be improved in short term, and the soil fertility will also be improved gradually. |
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