The Effects Of Landscape Pattern On Water Quality In Yihe River Basin

The basin is a geographical unit which connected to the upper,middle and lower reaches of the river with water as a link.The structure,process and function of river eco-hydrological system will be significantly influenced by the composition of landscape type and the change of its spatial pattern.Yihe River Basin situated in the center of the middle and lower reaches of the Yellow river basin,where is rich in natural resources and have high species diversity.However,the accelerated urbanization process changed the landscape pattern within the basin and significantly affects the river water quality.Based on the remote sensing image date(2017)and the Henan zhongyuan economic zone elevation model(DEM)of precision of 30 m,ENVI5.1,Arc GIS10.3 and Fragstats4.2 platform were used to obtain the 2017 landscape pattern features and landscape index date of Yihe River Basin.In this study,29 water quality monitoring points in the Yihe River Basin during the 2016-2017 year were selected,and 7 water quality indicators,including p H,EC,DO,Turbidity,COD,NH4+-N,TP,in three periods of low-flow,mean-flow and high-flow were selected to sample and monitor,through the principal component analysis(PCA),cluster analysis(CA),discriminant analysis(DA)and one-way ANOVA methods to explore the characteristics of water quality according to the time shifts and the spatial differences.Pearson’s correlation analysis,multivariate linear stepwise regression analysis and redundancy analysis were used to explore the relationship between landscape pattern and water quality in the Yihe River Basin.Finally,based on the the “source and sink” landscape theory and the landscape status around water quality monitoring points,and the response relationship between landscape pattern characteristics and water quality indicators,a proposal for landscape pattern optimization is put forward to improve the water quality and reduce the non-point source pollution.The main conclusions are as follows:(1)Forest and cultivated land are the main landscape types of the Yihe River Basin,which account for more than 84% of the total basin area.The dominance and connectivity of forest are the best,and gradually decrease from the upper reaches to the lower reaches of the river basin,while the construction land and cultivated land are opposite;the connectivity of canals is just lower than forest.The area proportion of reservoirs and ponds,grassland and unused land are relatively small,scattered distribution,their natural connectivity is poor.On the whole basin scale,the patch density(PD)and Shannon’s diversity index(SHDI)is high,landscape division index(DIVISION)and area-weighted mean fractal dimension index(FRAC_AM)showed that the landscape pattern has a tendency of fragmentation.The landscape pattern in the upper reaches of the basin are relatively intact,less disturbed by human activities,the shape of landscape patch is more complicated,the degree of fragmentation is lower,while the middle and lower reaches are the opposite.(2)The overall water quality of Yihe River Basin is good,DO and TP can basically meet the standard of class Ⅱ water of surface water environmental quality standard in GB3838-2002,COD and NH4+-N exceed the standard in some sections of the time.The principal component analysis shows that the water pollution sources in the basin are mainly organic pollution in the low-flow period,nitrogen pollution in the mean-flow period,and the high-flow period was dominated by nitrogen and organic pollution.In terms of temporal and spatial variation of water quality,water pollution in the mean-flow period is the most serious,followed by the low-flow period,and water quality in the high-flow is the best;the water quality shows a declining trend from upstream to downstream,and the downstream water quality is relatively serious.(3)The influence of area percentage of landscape typies on water quality: Pearson’s correlation analysis and multivariate linear stepwise regression analysis showed that the correlation between landscape types and water quality indicators(COD,TP,Turbidity,NH4+-N,EC and DO)is more obvious in the mean-flow water period and the whole basin scale.Redundancy analysis shows that in the whole basin scale,landscape types are more significant impact on water quality indicators: forest land,grassland and water body(reservoirs and ponds,and canals)has positive effect on water quality,while construction land,cultivated land has negative effects on water quality.Furthermore,construction land is the main contributors of organic pollutant(COD),physical index(Turbidity,EC)and nutrients(TP)during the study time,the nitrogen and phosphorus pollutants of low-flow and mean-flow period in water body mainly comes from cultivated land.(4)The influence of landscape pattern on water quality: At the class level,there was a significant positive correlation between water quality indicators except DO and the largest patch index(LPI)and cohesion index(COHESION)of construction land and cultivated land.The water quality indicators have significantly negative correlation and weak negative correction with the LPI and COHESION of forest and grassland respectively.The LPI of canal and the COHESION of reservoir are negatively correlated with most of the water quality indicators in the middle reaches of the river basin,and have a postive correlation within the scale of the whole basin.At the landscape level,Pearson’s correlation analysis and multivariate linear stepwise regression analysis indicated that the respond of water quality indicators to PD,FRAC_AM,SHDI and DIVISION gradually increased from low-flow to high-flow period,from upstream to downstream of the river basin,and most of them are positive relation.RDA analysis showed that PD,FRAC_AM and SHDI in the whole basin scale are weak negatively correlated with COD,Turbidity,NH4+-N and TP in the high-flow period,while DIVISION has no correlation with water quality indicators.(5)Increase the landscape patch number of “source” landscape such as construction land or decrease “sink” landscape such as forest,sited in key position which especially along the both sides of river,adjust the “source and sink” landscape patches in Yihe River Basin and the relative position,relative distance,relative slope,relative height and space configuration of water,as well as raising public awareness and action on public participation in water environmental protection in the basin so as to reduce the output of non-point pollution in the basin,improve the water quality and promote the sustainable development of Yihe River Basin.