Study On Vegetation Pattern Changes And Its Response To Water Quality In Dan River Basin

Vegetation is the main body of terrestrial ecosystem,vegetation coverage and its spatial pattern are of great significance to prevent soil erosion and protect water resources.Aiming at the key problems of ecological construction and protection of water resources in Dan River Basin,applied theoretical knowledge of landscape ecology,soil erosion,hydrology and other disciplines,combined RS and GIS technologies,used soil/water sampling and the simulation rainfall experiment,researched vegetation pattern change and its relationship with water quality.This paper illustrated spatial-temporal distribution characteristics and change regulation of vegetation coverage and its pattern,analyzed spatial-temporal variation of land use,and identified the relationship between land use change and vegetation pattern change combination with topographic features,illustrated the spatial distribution characteristics of soil nutrients under different vegetation coverage and terrain conditions,revealed the soil nutrient transport regulation under different land use and vegetation coverage conditions,constructed the relationship between vegetation pattern and water quality parameters in different spatial scales,proposed optimization measures of vegetation pattern,provide reference for ecological security and water environment protection.The main conclusions of this paper are as follows:1)The spatial-temporal distribution characteristics and variation regulation of vegetation pattern was analyzed in Dan River Basin.The change trend of NDVI values showed an inverted"U" distribution in annual,its minimum and maximum values appeared in February?0.387?and in August?0.866?,respectively.The order of NDVI in each season was displayed as following:summer>autumn>spring>winter,and there was significant difference?P<0.05?.From 2000 to 2010,NDVI showed an increasing trend,with the range of 0.61?0.73.In spatial distribution NDVI increased gradually from valley to mountains.The Moran's I value of NDVI was 0.858,and which is the largest in northwest-southeast direction,with 0.116.The area of high-high vegetation was mainly distributed in Xinkai Mountain with north and Mang Mountain with south.However,the area of low-low vegetation was mainly distributed in the"Shangluo-Danfeng basin".The area with sustainability and severe degradation,sustainability sustainability slight improvement,sustainability slight degradation accounted for 2.70%,3.46%,42.67%and 40.54%of the total area,respectively.Additionally,the undetermined area only accounted for 8.40%of the total area.The area with vegetation temporal stability accounted for 6.73%of the total area,and the area of representative plots of vegetation temporal stability accounted for 5.15%of the total area.Furthermore,the sub-basins with strong vegetation temporal stability were located in the downstream.However,the sub-basins with weak vegetation stability is located in the upstream and mid-stream,especially,2#?3#?5#?7#?10#and 13#sub-basin.In spring,summer and autumn,the 4#sub-basin was strong for vegetation temporal stability,but the 8#sub-basin in winter.For different terrain factors,the regions of vegetation temporal stability were mainly distributed in the elevation of 800?1000m,slope of 15°?20°.2)The relationship between land use change and vegetation pattern variation was analyzed.The grassland,forestland and farmland were mainly land use types in Dan River Basin,which accounted for more than 90%of the total area.However,there were obvious differences for composition of land use type,such as the area of construction land and farmland accounted for more than 25%in 3#and 5#sub-basin,the area of forestland accounted for more than 40%in 6#,8#,11#and 13#sub-basin,the area of grassland accounted for more than 30%in each sub-basin.During the 11 years,except the area of farmland reduced by 3.729%,the rest of land use area have a slight increase.The mutual conversion of land use was mainly carried out among farmland,forestland and grassland.Moreover,the construction land had a net increase,and mainly come from the farmland.The order of NDVI values in different land use types was as followed:forestland>grassland>farmland>construction land.Compared with 2000,in 2010 the NDVI of forestland,grassland and farmland increased by 12.88%,13.10%and 13.33%,respectively,while the construction land only increased by 2.89%.Additionally,the coefficient of variation?CV?of NDVI in construction land and farmland increased,and that in forestland and grassland decreased.The relationship between land use and NDVI showed that the low NDVI was significantly correlated with the construction land,and nevertheless the middle and high NDVI were significantly correlated with farmland,grassland and forestland.The vegetation temporal stability was reduced with the increase of farmland area,while that of the forestland was opposite.From 2000 to 2010,there was decreasing trend for NDVI in farmland,and was increasing trend in forestland and grassland.When the farmland converted to grassland and forestland,grassland converted to forest land,NDVI showed an increasing trend;when the forestland converted to farmland and grassland,and grassland converted to farmland,NDVI showed a decreasing trend.The explanations degree of land use for 6 schemes of vegetation coverage degree were more than 80%,among them the fifth scheme was the best,up to 88.65%.3)The spatial distribution characteristics of soil nutrients under different vegetation and terrain conditions were analyzed,and the soil nutrient transportation under different land use and vegetation coverage conditions was revealed.The average contents of AN,NN and TN were 1.12 mg/kg,1.74mg/kg and 0.47g/kg,respectively,in the surface soil of Dan River Basin.There was a significant effect on the AN and NN?p=0.001,p=0.005?along altitude grade.The spatial distribution of soil nutrients was affected by NDVI,relative elevation,terrain humidity,surface roughness,slope and slope length factor,fluctuation degree and so on.The results showed that the spatial distribution of soil nutrient content was reduced from river valley to the mountainous area by the regression Kriging interpolation analysis.Furthermore soil nutrient content was lower under the high NDVI than that under the low NDVI.Under the condition of simulated rainfall fixed rainfall intensity,runoff,sediment yield and nutrient loss were decreased with the increase of vegetation coverage.Compared with the bare slope,in the runoff plot with 40%,60%and 90%of vegetation coverage the total amount of runoff reduced by 58.61%,88.85%and 90.20%respectively,the total amount of sediment yield reduced by 55.10%,95.25%and 98.24%,and the total amount of nutrient loss reduced by 17.45%-24.02%,41.68%-59.39%and 45.88%?66.02%.The function expressions of vegetation coverage and nutrient loss was y=ae^-bx?a,b>0?4)The relationship between vegetation pattern and water quality at different spatial scales was analyzed.The range of R² values was 0.6V?0.80 by constructing multiple linear regression model between landscape indexes of land use and water quality.However,after NDVI was introduced into the multiple linear regression model,the R² values increased by 1 times for prediction of ammonia nitrogen and total phosphorus,and increased by 20%?50%for prediction of nitrate nitrogen,total nitrogen and available phosphorus.For the sub-basin scale,water quality parameter was significant positively correlated with CONTAG and LPI,and significant negatively correlated with SHDI.LPI and LSI were positively correlated with water quality under low vegetation coverage degree,and the landscape index under high and relative high vegetation coverage degree was negatively correlated with water quality.For different buffer zones,NP,LSI,IJI and SHDI increased with the increase of buffer distance,LPI,CONTAG and AI decreased with the increase of buffer distance,and COHE remained stable.And NP,LSI,SHDI and IJI were negatively correlated with water quality,LPI,CONTAG,AI and COHE were positively correlated with water quality.Under the low vegetation coverage degree,the strongest correlation with water quality was LPI?positive correlation?and LSI?negative correlation?,and the relationship between IJI,COHE and water quality was the closest under the high vegetation coverage degree.The explanation degree of vegetation landscape indexes for water quality reached 65.80%in sub-basins scale by using redundancy analysis,in which the explanation degree of LPI,SHDI,and CONTAG for water quality was over 13%.The analysis of vegetation ecological efficiency showed that the average value of ecological efficiency was 0.989 in the 14 sub-basins.And ecological efficiency value was the highest in 6#sub-basin,and was the lowest in 14#sub-basin.For the decomposition efficiency,the technical efficiency is higher than scale efficiency.According to the input-output redundancy,the 14 sub-basins were divided into 4 categories by using the clustering analysis,including two types of vegetation optimization direction,i.e.insufficient input and excess input,and put forward the vegetation coverage and its spatial structure optimization measures according to the characteristics of each types.