Ecological Risk Assessment Of Zuojiang River Basin Base On GIS And RS

Ecological risk assessment is one of the focuses of eco-environmental problemsresearch, because of the karst landform have a wide range development in watershed,affected by both of natural and artificial factors, as a result, the ecological problems isincreasingly outstanding, evaluation the ecological risk is in favor of risk management,watershed comprehensive treatment, sub-watershed management.Taken soil erosion and landscape pattern into consideration, the soil erosionsensitivity index and landscape interference index were constructed. Took this twoindexes as risk source of ecological risk, evaluated the ecological risk in study area baseon GIS and RS technology. Extracted watershed by simulation hydrologicalcharacteristics with DEM, and then combine with the national boundaries, finallyconfirmed the study area. Reference the USLE and nature environment characters,establish the index system of soil erosion assessment, the grades of soil erosion weredivided according to certain standard, and then the soil erosion modulus wasreclassified and assigned, at last obtained the soil erosion sensitivity index. Land useand land cover information was interpreted accoding to the interpretation symbol withTM Image which band combination is4（R）3（G）2（B）. Extracted the landscape patternindex from the land use and land cover information, construction landscape interferenceindex which measured different landscape suffering disturbance degree. Be acquaintedwith hydrological characteristics, land use, soil erosion intensity, landscape paten, etc,evaluation the ecological risk in Zuojiang river basin.The main research conclusions as below:（1） Base on the method of drainagedensity, determined the catchment area is18km²and the drainage density is0.196km·km^-2extracted the natural river network, confirmed the water outlet,covered thewatershed, which total area is33427.70km², quantitative analyzed river bifurcation ratio,river length ratio, fractal dimension., and then take the national boundaries in1:250,000databases as separation line, extracted the domestic area is22009.59km², Vietnam areais11418.11km².In order to convenient for ecological risk assessment, ultimately dividedthe domestic part into106sub catchments. （2） The soil erosion modulus of Zuojiang river basin was between from0to9086t/（km²Â·a）,base on USLE, slightly soil erosion and light soil erosion play a dominant role,accounts for93.3%of the total area, moderate and above soil erosion take the6.7%.The area where the erosion intensity is lower mainly distribute in the river valley, gentleslope hills, low mountain and mesa in the central and south of the basin,the highererosion intensity is comparatively dispersion, which mainly influenced by soil propertyand topographic relief, which mainly distributed in purple soil and significant reliefdisplacements.（3） Used the soil erosion sensitivity index and landscape interference index toestablish ecological risk index, and then to calculate the ecological risk of sample plots,with which conducted geostatistics interpolation, revealed the spatial differentialfeatures and spatial distribution pattern of ecological risk: There was great differene inecological risk spatial pattern of Zuojiang river basin, as a result of soil properties,geologic lithology, topography and geomorphology, rainfall and human activity. Theecological risk level of peak-cluster was higher than tsuchiyama hills area, the zuojiangvalley plains was the lowest. The semivariogram analysis showed that the regionalecological vulnerability had a medium intensity spatial correlation in the study area, theratio of Nugget and Partial Still is53.66%, which was controlled by natural factors andrandom factors.At4km range of resample distance, there are some small scale randomfactors affected the ecological risk such as human activities, but the structuralfactors（soil properties, lithology, geological structure） are the dominate factors whichinfluence the spatial differentiation of ecological risk. The average level of ecologicalrisk in Zuojing river basin is0.509, the fluctuation range ecological risk of sub-basinrage from0.429to0.5848,60of106sub catchments’ ecological risk higher thanaverage level, ecological risk of the general level was on the high side.