A Study On Transportation Process And Regularity Of Soil And Water In Middle-Eastern Section Of The North Shore Of Lake Chaohu

Lake Chaohu,located in middle of Anhui Province,is one of the five big fresh water lakes in China.In 1980s the water body of the lake started to present the eutrophication condition,later the eutrophication is intensified gradually,and it has already been evolved into one of most bad lakes,which has serious influence on industry,agriculture production and on the people's living water security along lake area.Lake Chaohu is already listed as one of key lakes to control,but so far the eutrophication condition in Lake Chaohu remains severe.This phenomenon is due to no fundamental control measure to implement the endogene repair and the extraneous source prevention.Soil and water migration is the main way and the important forms to the nonpoint source pollution and it can also create the water eutrophication of Lake Chaohu through carrying large sediment,nitrogen,phosphorus and other substances into the water body.In this article water and soil transition process and rugularity in north shore of lake Chaohu are discussed.It is revealed that water and soil migration and the nutrient migration characteristic.And it is proposed the comprehensive measures to control water and soil migration in order to provide the theory basis and the actual reference for preventing and controlling the extraneous source pollution to Lake Chaohu.The study includes five parts.The first part is not only the review of research development about water and soil migration in the domestic and foreign but also the analysis of the question and the research condition about Lake Chaohu basin.The second part is involved in the field investigation and experimentation so as to study the temporal and spatial variation of soil nutrients and output characteristics of hillslope.In the third part the hillslope runoff,sediment and the nutrient transition process and the characteristic are researched by lab simulation experiment.In the fourth part it is discussed that the water and soil and nutrient migration prediction by applying water and soil transport model and nutrient transport model with experimental data.In the fifth part,according to the research foundation of the Lake Chaohu basin,the water and soil migration's prevention technological measures are proposed.The research results are as follows: (1) The investigation and experimentation carried in the field show that nitrogen and phosphorus elements in the slope soil will be decreased in the overall with time and the altitude increasing,which is due to soil and water movement and migration of nutrients.In the process of rainfall,the clay,silt and the elements of nitrogen and phosphorus in the surface soil will migrate, so that the nutrient contents of the soil will decline.The declined ratio of hydrolysable nitrogen (＞7.5%) and rapidly available phosphorus(＞8.5%) is obvious,while that of total nitrogen (＜2.17%) is low and that of total phosphorus(＜0.27%) is lowest.The declined ratio of clay and silt and the increased ratio of sand are different with different land use after a rainfall,among which the change ratio in watermelon land is large,while in rape land is the small.The experiment further confirms that in sediment the clay and nutrient enrichment will occur.In watermelon land,rape land,and fallow land,the enrichment ratio of the clay is more than 1.20, and that of total nitrogen and rapidly available phosphorus is between 1.28-1.39,while that of the total phosphorus and hydrolysable nitrogen is basically between 1.13-1.30.The enrichment ratio of nitrogen is 1.26 and phosphorus 1.15 in Ma'anshan slope.Through monitoring and predicting, the transport estimation of soil is 5 412 t/km²Â·a,nitrogen is 9.12 t/km²Â·a,and phosphorus 2.30 t/km²Â·a in Ma'anshan slope.(2) The simulation test has been carried on by using yellow brown earth,yellow cinnamon soil,fragmental soil for the first time,which are the main soil types in the middle of the north shore of Lake Chaohu.Experiments show that the process of runoff on the slope is related to rainfall intensity,slope,soil type,reliminary moisture content of soil and so on.The emerging time of runoff is remarkably negatively interrelated with the rainfall intensity,the slope,the preliminary water content of soil.Slope runoff has positive correlation to the rainfall intensity. The emerging time of the maximum runoff is negatively interrelated with the preliminary water content of soil.Different types of soil have different process of runoff because they have different texture and porosity.The emerging time of the maximum content of sediments in runoff is negatively interrelated with rainfall intensity and the slope.The sum of sediment is remarkably positively interlated with rainfall intensity,slope,and runoff sum.The slope nutrient lost is taken by runoff and sediment.Among them,nutrient transfer taken by sediment is the main form.The sum of the nutrient migration is positively interlated with the sum of runoff and sediment.The simulation test by using three types of soil(yellow brown earth,yellow cinnamon soil, fragmental soil) also shows that:The content of nutrients in sediment is generally higher than that of the original soil,in another word,sediment has the characteristics of nutrient enrichment.The enrichment rate of fragmental soil is the large,while that of yellow brown earth is the small.On the forms of nutrient,the regularity of enrichment rate is:rapidly available phosphorus＞hydrolysable nitrogen＞total nitrogen＞total phosphorus.(3) In the studied area,the estimation of runoff is 470.0mm by utilizing SCS model.(4) The estimation of soil transportation is 4 107.57 t/km²Â·a by utilizing nailing,and 3 847.6 t/km²Â·a by utilizing USLE model,which demonstrates that the forecasting results have a basic consistency between nailing and USLE model.(5) Through using nutrient transportation formula E=(Er₁ ^*S+ Er₂ ^*Q)^*C,the forecast and estimation of nutrient transportation are conducted in the studied area.The results shows that the estimation of the nitrogen transportation is 8.027 t/km²Â·a and that of phosphorus is 2.903 t/km²Â·a. Nitrogen transportation in sediments accounts for 90.92%,and phosphorus transportation in sediments accounts for 90.36%,which further confirms that sediments carrying is the main form of nutrient loss.(6) On the basis of studying on soil and water transportation and nutrient transportation,the integration measures of the local farming technology,bio-technology and engineering is proposed to prevent and control the migration of water,soil,and nutrient in neighboring shore of Lake Chaohu.In hilly areas,by biological measures of planting trees and grass,in post areas,by agroforestry production,contour farming,contour terrace and other measures,in the alluvial plain areas,by conservation tillage and construction of multi-level buffer zone,the loss of pollutants or the nutrient could be controlled,which can fundamentally control the pollutants of the extraneous source to import to Lake Chaohu,so as to achieve a radical improvement of the water quality.