| The Three Gorges reservoir area is located in the hilly area of the western Hubei mountainous area and in the eastern part of the Sichuan Basin.The agricultural population is intensive and the agricultural reclamation intensity is high.At the same time,the soil loss is serious,the planting method is rough and the utilization rate of fertilizer is low.Midsummer period,heavy rains often occur,leading to serious pollution of agricultural phosphorus,and become to the main source of pollution for the reservoir.Therefore,it is of great theoretical and practical significance to study the characteristics of phosphorus pollution in the reservoir area because of the special geographical and climatic conditions and human activities in the reservoir area.In this paper,the temporal and spatial distribution of adsorbed phosphorus load in the Three Gorges Reservoir area was simulated by constructing a spatiotemporal distribution model of adsorbed phosphorus load,and the critical source areas of adsorbed phosphorus load were identified and the effects of different conservation measures were predicted.The main research results are:?Proposed the spatial distribution of hillslope sediment delivery ratioThe simulation of sediment load is the basis of simulation of adsorbed phosphorus load.In the calculation formula of sediment delivery,the hillslope sediment delivery ratio reflects the sediment transport capacity,which is related to topography,vegetation cover and watershed size.This study analyzes the existing calculate method of sediment,and based on the previous researches,we considered from the two aspects of “downslope” and “upslope” sediment transport to calculate the hillslope sediment delivery ratio,then we proposed the runoff connectivity index based on hydrology.And the spatial distribution of the hillslope sediment transport ratio is formed according to the runoff connectivity index.?Constructed the spatial distribution model of adsorbed phosphorus loadBased on the Revised Universal Soil Loss Equation,combining with the proposed hillslope sediment transport ratio and the enrichment of phosphorus in the soil,the spatial distribution model of adsorbed phosphorus load was constructed.Take the Three Gorges Reservoir Area as a example,the spatial distribution of adsorbed phosphorus load during 2005~2014 was simulated and validated by the measured value of Xiaojiang watershed and Daninghe watershed.Good agreement between the measured values and the simulation shows that the proposed model and calculation method of hillslope sediment delivery ratio are feasible.?Identified the critical source areas of adsorbed phosphorus load in the Three Gorges reservoir areaBased on the spatial mapping technology of GIS,the critical source areas were identified,and the adsorption of phosphorus load in the reservoir area was analyzed.The areas of large load intensity were concentrated in the Three Gorges reservoir area southwest,that is,Fuling,Fengdu and other regions,as well as central Yunyang,Wanzhou,Kaixian and other places.The load is 27.89% of the total reservoir area,where the load intensity is 0.62 ~ 0.92 kg/hm2.It is worth mentioning that the area is only 1.04%,where the load intensity is 1.37 ~ 3.09 kg/hm2,the load accounted for 6.59% of the total load,these are the critical source areas of governance.?Predicted adsorbed phosphorus load reduction under different measuresAccording to the model,the adsorbed phosphorus load reduction effect under different measures was forecasted.The measures were as follows:(1)changing land use(transfer cultivated land with load intensity greater than 1.37 kg / hm2 to the forest land);(2)taking conservation tillage measures(using cross slope and contour farming and planting hedgerows);(3)reducing the amount of 30% fertilizer.The forecast results show that the pollution reduction rates are 17.26%,21% and 13.75% respectively under the three measures. |
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