The Evolutional Characteristics Of Water Environment And Total Amount Control Of Pollutant In Datong Lake Basin Based On GIS

The deterioration of water quality in the scale of river basin has posed a severe threat to the sustai nable development and challenged ecol ogical civilization construction in China. Datong lake basin, which is the biggest inland freshwater lake in Hunan province, is located in the city of Yiyang. In recent years, a large amount of industrial effluent, agricultural wastewater and domestic sewage has been poured into Datong lake basin, aggravating the water pollution and exacerbating the degradation of water quality in this area. Based on spatial geographic inform ation(GIS) technology, this paper analyzed t he natural environment characteristics of Datong lake basin, set up the control units which served the purpose of water quality target management, revealed the spatial and temporal distribution feature of different COD concentrations in various sections of Datong lake basin from 2007 to 2011 and identified the primary driving force of the water quality deterioration in this basin.This paper obtained the re mote sensing(RS) image information as th e data source, then get the current land us e classification information after interpretation for remote sensing image. Based on the overall consideration of the point source and non-point source pollution, this paper calculated COD polluti on load and water environment capacity of each control unit in every month of the year, established an allocation system of total po llutant load and brought forward the pollutant contr ol measures, enabling t he implementation of th e technology on water quality tar get management in all control units throughout the whole lake basin, bearing a profound and far reaching signif icance for the water qu ality improvement in Datong lake basin.The main conclusions drawn in this paper are as follows:(1)Water quality target managementThe full paper contain the idea of “gross – capacity- reduction” of contaminant gross control. Based on the principles of “ by type, by region, by grade, by term ”, the program of pollutant allocation was c onstructed combined with the f eature of natural topography characteristics and administration. Enable the implementation of the technology on water quality target management in all control units.(2)The division of the control unit of water quality management in Datong lake basinBased on the natural topography characteristics of Datong lake basin, combined with the feature of control section of monitoring of river water quality and administrative boundaries, Dat ong lake basin has been divi ded into four ba sic control units f or water qua lity target management. Guid ing by the existing local policies and regulations, we determined the water quality target of the control unit.(3) Pollution load accounting on a monthly basis in Datong lake basinBased on t he existing control units, pollution load accounting was ma de in accordance with the classification of the point source pollution(industrial pollution sources and urba n pollution s ources) and non-point source pollution(farmland runoff pollution sources, livestock breeding pollution sources and rural pollution sources). The calculation results showed t hat the total amount of COD fl owed into the rivers in Datong lake basi n was 1 4610.1t/a, in which the non-point sour ce pollution accounted for 77.6% and the point source pollution accounted for 24.80%, indicating that non-point source polluti on was the primary pollution s ource in Datong lake basin. Viewing from the perspective of the control units, it was clear to see that as much as 30.3% of the total amount of COD flowed i nto the rivers came from unit 4, c ompared with 27.0% of the total that cam e from unit 2, 23.9% of the total from unit 1 and 18.9% of the total from unit 3. Control unit 3 accounted for the highest percentage of the non-point sour ce pollution, which was as high as 95.0%, while control unit 2 acc ounted for the highest percentage of the point source pollution, which was up to 42.3%.(4)The variation characteristics of COD concentration and driving factorsDuring the period f rom 2007 to 2011, the water qualities in all control units within Datong lake basin had s hown various degrees of deterioration, among which control unit 3 had shown the relatively severest degree, with the water quality being equivalent to level Ⅳ, followed by control unit 1 a nd 2 with the same quality level. Control unit 4 was the only exception, with its C OD concentration showing relatively least change and thus indicating that there is no violation of water quality standard. Judging by the seasonal differences in the aspect of COD concentrations, it was clear that COD concentration in rainy season was higher than that in dry season in most of the water quality monitoring sections, which reflected a phenomenon that the organic matter pollution in the river was corr elated to seasonal precipitation change in this area and th at the degree which the seasonal change was impacted by precipitation was variable ac cording to dif ferent types of pollution in dif ferent control units.Combined with the data of socio-economic indicators, the partial least squares regression model was built, an d the driving f orces of the deterioration of water quality analyzed. The result showed primary driving force was different in different control units. Specifically, primary driving force in control unit 1 and unit 4 was the economic development factors, and the primary driving force in control unit 2 a nd unit 3 was the population development factors.(5)The pollution load allocation in Datong lake basinBy the aid of one-dimensional river water quality model, the water environment capacities of COD in each cont rol units on a monthl y basis were calculated in thi s paper. The results showed that the tot al water environment ca pacity of COD in Datong lake basin was 10961.02 t/a, in which unit 1 to 4 reached an amount as much as 1743.3t/a, 3917.4t/a, 1960.6t/a and 3339.7t/a respectively. By us e of t he three-layer distribution system, pollutant reduction was allocated to each pollutio n source by month. Finally, suggestions were brought for ward for poll ution control and countermeasure.