| In recent years,the problem of water pollution in our country has become increasingly severe.The problem of eutrophication has always been the focus of the whole society.Non-point source pollution has become the main cause of water quality deterioration.The study of it is very important for the protection of basin ecosystem and the management of resources.The Taihu Basin is the representation of plain water network region,with complicated river systems,which make it difficult to study the dynamics of pollutants.At the same time,because of the convenient transportation,abundant resources and flat terrain,the plain water network area has experienced fast develop of economy and society,the level of urbanization,industrialization and agricultural modernization is relatively high.As a consequence,the problem of eutrophication in Taihu Lake has been severe since the end of the last century,especially the algae bloom in 2007 which affected the water safety of the 13 million inhabitants in the basin.Therefore,it is very urgent to study the mechanism of non-point source pollution in the plain water network.Based on surveys and monitoring of hydrological and water quality,we adopted two models?Net Anthropogenic Nitrogen Input method,Export Coefficient Model?to study the patio-temporal characteristics of nitrogen,phosphorus and COD.The results show that:?1?The water quality in the upstream of the Li River watershed is good,and the pollution in the downstream estuary is serious.The concentration of pollutants is gradually increased from upstream to downstream due to the influence of planting,breeding,life,and industry.As the driving force of pollutants migration,rainfall has a greater impact on the concentration of pollutants,making it have obvious seasonal differences.Changes in the types of land use,especially the increase in urban area,are the major factors leading to the deterioration of water quality.Living sources and livestock are the major sources of pollution in Li River basin.?2?The results of 6 years water quality monitoring showed that the water pollution of Wuxi Port is severe.The annual average value of total nitrogen is between 4.41 and 5.92 mg·L–1,and the ammonia nitrogen is between 1.09 and 1.72 mg·L–1.The total nitrogen and ammonia nitrogen concentration showed obvious seasonal changes,with high concentrations in spring and winter and low concentrations in summer and autumn.At different rainfall intensity,the response of pollutant concentration is different.Under light rain and moderate rain intensity,the nitrogen concentration was low;under medium and heavy rain intensity,the nitrogen concentration increased;under the heavy rain and heavy rain intensity,the nitrogen concentration was lower.Erosion and dilution caused by rainfall together affect the concentration of nitrogen in the water.?3?The spatial and temporal variations of nitrogen input and export in the Taihu Basin have significant differences.N inputs and exports in 1980 were 6431.97 and 3169.84 kg N km-2 yr-1,but increased to9722.42 and 4581.73 kg N km-2 yr-11 by 2010,respectively.The N inputs and exports varied considerably across the basin,reflecting land use patterns in the different counties.The N loads increased as both the population density and the urban areas increased.?4?Approximately 38%of the N inputs were exported in 2010,but only 19%were exported in 1980.The results illustrate that the balance of N cycle in the Taihu Basin has been broken by anthropogenic activities especially the urbanization and the population increase.This study demonstrates that a theoretical approach,supported by statistical data,can be used to gain insights into the sources of N in a basin.This approach therefore can be used to support decision making and to facilitate the development of measures to conserve N in the future. |
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