Impact Of Land Use/Landscape Pattern On Hydrochemical Characteristics In Binggou River Basin

In the context of global change,land use or cover change has received widespread attention.The landscape pattern of land use is a comprehensive reflection of the spatial structure and quantitative compositions of land use or cover types.It is affected by various natural and human factors,which in turn affects various ecological processes.And the hydrochemical characteristics of rivers are comprehensively affected by various ecological processes and human activities.Therefore,it is of great significance to study the relationship between landscape patterns of land use and the chemical characteristics of river water.In this paper,the relationship between the landscape pattern of land use and the hydrochemical characteristics of the river water in the Binggou River Basin in the northern part of the Qilian Mountains and the upper reaches of the Shiyang River Basin is studied.Based on the land use data of August 2019 and the river water chemistry data from April to October 2019,the sub-catchment scales,riparian scales,and fan-shaped buffer zones with 1000 m radiation radius were taken from the river sampling points as control points,respectively.Scale analysis of land use or cover type structure and landscape pattern characteristics in each region;the entire river water sampling period is divided into before the rainy season(April to June),the rainy season(July to August)and after the rainy season(September to(October),the spatial and temporal distribution of hydrochemistry in Binggou River was analyzed from the three periods before,during and after the rainy season,and the main ion sources and controlling factors were analyzed during each period.Finally,the relationship between land use types and landscape indices and the hydrochemical characteristics of rivers at different spatial scales was analyzed by redundant analysis,and the impact of land use landscape patterns on hydrochemical characteristics of rivers was discussed.The results show that:(1)On the whole,the distribution of land use or cover types in the Binggou River Basin is significantly different.Deserts,grasslands,woodlands,alpine meadows,and alpine deserts are distributed in order from the lower reaches to the upper reaches.There is a small amount of glaciers and snow in the upstream area,the water area is mainly the river surface and the cultivated land and construction land are concentrated on the banks of the middle and lower reaches.According to the patch density(PD),the maximum patch density(LPI),the landscape shape index(LSI),and the landscape fragmentation index(DIVISION),it can be seen that the landscape within each scale of the XCL,JZGD,and HLQ sampling points in the middle reaches is relatively fragmentation;The landscape in the upstream area and SKRK is relatively complete;The landscape fragmentation is highest in the riparian zone,and the landscape is relatively complete in the sub-watershed scale.The Contagion index(CONTAG)and patch Cohesion index(COHESION)show that QSH,QSHZY and SKRK have a higher degree of landscape aggregation,with different scales showing higher trends in sub-watersheds than riparian zones and fan-shaped buffer zones.The Shannon's Evenness Index(SHDI)and Shannon's Evenness Index(SHEI)show that the distribution of land use or cover types at each scale of LKS,JZGD,XCL,and HLD is relatively balanced,and the types are most uniformly distributed at the riparian scale,and the spatial difference is most obvious at the buffer scale.(2)The river water in the Binggou River Basin was weakly alkaline fresh water,and the overall water chemical type was Ca2?-SO?2?-HCO??.The average TDS was 88.46 mg/L,the concentration was relatively low,and the water quality was good.From the perspective of spatial distribution,from the upstream to the downstream,except that the concentration of water chemical parameters in XG is obviously higher,the concentration of main water chemical parameters of samples at other sampling points generally shows a gradually increasing trend.From the perspective of time,the concentrations of NO?? and K? during the rainy season are the highest,and the concentrations before the rainy season are the lowest.The other main water chemical parameters are the highest before the rainy season,and the lowest during the rainy season.(3)There are significant spatial and temporal differences in the effects of land use/cover types and landscape patterns on hydrochemical characteristics in the watershed.The results of comparative analysis among different spatial scales show that the riparian zone scale has the highest explanation for the impact of land use/cover on hydrochemical characteristics.Among them,water,woodland,alpine meadows,and alpine deserts play the role of "sink" landscape,while construction land and cultivated land play the role of "source" landscape,and grassland and desert have no obvious impact on hydrochemical characteristics.The landscape pattern has a higher degree of interpretation of the water chemical characteristics at the sub-basin scale.The more fragmented the landscape,the smaller the species diversity,and the lower the patch connectivity,the more conducive to the collection of hydrochemical elements.The results of comparative analysis in different seasons show that the land use/cover type has the most significant effect on the hydrochemical characteristics during the rainy season,and the effect is the smallest before the rainy season.The landscape pattern had a significant effect on the hydrochemical characteristics before the rainy season;the landscape fragmentation was positively related to the main hydrochemical parameters;the landscape aggregation and the diversity and uniformity of landscape type were negatively related to the main hydrochemical parameters.(4)The land use/landscape pattern of the Binggou River Basin has a significant impact on water chemical characteristics.In order to protect the water environment,the landscape pattern of the watershed must be optimized.It is necessary to strictly control the cultivated land and construction land in the watershed,protect woodland,alpine meadows,alpine deserts and waters,protect the integrity of landscape patches,and reduce landscape fragmentation.In addition,according to the characteristics of the landscape pattern at different spatial scales and its impact on the water environment,targeted land use adjustment and optimization of the landscape pattern must be carried out.