Evaluation Of Water Quality In The Wei River Basin Based On Landscape Pattern

The landscape pattern reflects the distribution,structure,and quantitative changes of land use types.In the context of intensifying global human activities,scientific understanding of the impact of landscape pattern on water quality and the mechanism of action is the key to watershed land planning and water environment management.As the largest tributary of the Yellow River,the rapid urbanization of the Wei River basin and human activities such as the reforestation and grassland restoration projects have significantly changed the landscape pattern and land use patterns of the basin.In this context,it is important to study the characteristics of multi-scale watershed landscape patterns and their impact mechanisms on water quality for water quality improvement and landscape planning.In this study,water samples were collected from the Wei River basin during the abundant water period(August 2021)and the dry water period(May 2022),and several water chemistry indicators,mainly nitrogen,were measured.The response of water quality indicators to the landscape pattern,focusing on the scale effect of landscape pattern on water quality.The main findings of this study are as follows:(1)There is significant spatial and temporal variability in the water quality characteristics of surface waters in the Wei River basin.Seasonally,nitrate-nitrogen and total nitrogen concentrations are significantly higher in the dry period than in the rich period,while nitrite nitrogen concentrations are significantly higher in the rich period than in the dry period;there is no significant seasonal difference in ammonia nitrogen concentrations.Spatially,the concentrations of total nitrogen and nitratenitrogen were higher in the middle and upper reaches than in the lower reaches,while there was no spatial difference in ammonia nitrogen concentrations.(2)There is significant spatial variation in the landscape characteristics of the Wei River basin.The main land use types in the Wei River basin are cropland,grassland and forest land,accounting for 40.4%,38.3% and 16.5% of the total area of the study area,respectively.At the sub-basin scale,the coefficients of variation of the maximum patch index,landscape shape index and segmentation index were all greater than 70.0%,while the coefficients of variation of the remaining landscape indices were all less than 25.0% in space.At the scale of riparian zone,the patch density and segmentation index showed a decreasing trend with the increase of buffer zone distance;the maximum patch index,spreading index and aggregation index showed an increasing trend;the edge density showed an increasing and then decreasing trend;the landscape shape index showed a decreasing and then increasing trend;the diversity index tended to be stable.(3)There are seasonal differences in the correlation between landscape pattern and water quality indexes.At the sub-basin scale,the proportion of arable land area was positively correlated with nitrate-nitrogen in the water-abundance period,the proportion of arable and forest land area,landscape shape index and partition index were significantly and positively correlated with ammonia-nitrogen in the waterabundance period,the proportion of building land area was significantly and positively correlated with nitrite-nitrogen in the water-abundance period,the proportion of grassland area was significantly and negatively correlated with nitratenitrogen in the water-abundance period,the proportion of grassland area and maximum patch index were significantly and negatively correlated with ammonianitrogen in the water-abundance period,the landscape The proportion of grassland area and the maximum patch index were negatively correlated with ammonia nitrogen in the abundant water period,the landscape shape index was negatively correlated with nitrite nitrogen in the abundant water period,and the patch density was negatively correlated with ammonia and nitrite nitrogen in the dry water period.At the riparian zone scale,the spreading index was negatively correlated with water quality index,and the diversity index was positively correlated with nitrate-nitrogen.The proportion of unused land area and edge density were significantly and positively correlated with nitrate-nitrogen in the water-abundant period,while the proportion of grassland area and arable land area were significantly and negatively correlated with nitrate-nitrogen and nitrite nitrogen,respectively;the proportion of building land area,patch density and edge density were significantly and positively correlated with ammonia nitrogen in the water-abundant period,while the proportion of arable land area was significantly and negatively correlated with ammonia nitrogen in the waterabundant period.(4)There are spatial differences in the response relationship of water quality to landscape patterns,with the explanation degree of riparian zone scale being higher than that of sub-basin scale,the explanation degree of landscape index being higher than that of land use type,and the explanation degree of remote buffer being higher than that of proximate buffer.On the sub-basin,the explanation degree of land use type on water quality in the abundant period is higher than that in the dry period,the explanation degree of landscape index on water quality in the abundant period is lower than that in the dry period,and the explanation degree of landscape index on river water quality on the sub-basin scale is higher than that of land use type.On the riparian zone buffer,the land use type has a higher degree of interpretation of water quality in the abundant period than in the dry period,and the best scale is the 300 m riparian zone buffer in the abundant period;the landscape index has a lower degree of interpretation of water quality in the abundant period than in the dry period,and the best scale is the 2000 m riparian zone buffer in the dry period.The interpretation of water quality by landscape pattern at riparian zone scale is higher than that at subbasin scale,and the interpretation of water quality by landscape index at riparian zone buffer scale is higher than that by land use type,so the best buffer scale is 2000 m riparian zone buffer.It can be seen that,in order to protect water quality,landscape pattern regulation should follow scale-adaptive measures and consider the non-linear effects of landscape pattern on water quality.This study provides practical ideas for watershed landscape pattern management and regulation,and provides reference thresholds for multi-scale landscape patterns,providing a scientific basis for water environment management and landscape pattern optimization in the Wei River basin and even in arid and semi-arid regions.