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

Water resources,as the source of human life,play an important role to ecological environment and social development.River water quality is affected by many natural and social factors,while landscape types and their spatial structure are the most significant manifestation of human's effect on river ecology.Exploring the response relationship between landscape pattern and water quality is a hot topic in the field of river ecology.Dongjiang River,an important tributary of the Pearl River,its middle and lower reaches is one of the representative areas of rapid urbanization in the southeast coastal areas of China.In recent years,urbanization has led to dramatic changes in the landscape of the basin,which has a profound impact on the ecological environment of the basin.This paper study on the water quality survey data and the land use data obtained from remote sensing interpretation in January(dry season),March(normal season),and July(wet season)of 2018.Correlation analysis and redundancy analysis are used to analyze different hydrological periods and more data,so as to study the response relationship between the landscape pattern of the Dongjiang River Basin and the output of the nitrogen and phosphorus on two scales of spatial unit.The main research results are as follows:(1)The spatial distribution characteristics of the nitrogen and phosphorus in the Dongjiang River are obviously different.The total nitrogen concentration in the upstream and downstream areas is relatively high,and the total nitrogen concentration in the middle of the basin is relatively low.During the dry and normal season,the total nitrogen concentration in the basin does not change much,but in the wet season the total nitrogen concentration is lower.For the concentration of total phosphorus,the downstream area is higher than that in the upstream area.The main stream is also higher than that of the tributaries.In normal season,The concentration of total phosphorus is relatively higher,and the second is in dry season,and the last one is wet season.(2)The landscape characteristics of Dongjiang River Basin are as follows: the landscape types are diverse,and the proportion of medium density forest land is the largest,with the smallest proportion of unused land.The distribution of land use types in the buffer zone is relatively uniform,with low dominance and poor agglomeration.With the increasing buffer distance,landscape similarity and spatial connectivity increases,increases,and patch types tend to be homogenized and simplified.In the catchment area,the patches are relatively complete,with simple patch types and good landscape integrity,high degree of agglomeration and low degree of fragmentation.(3)Towns,paddy fields,water areas and unused land has negative effects on the nitrogen and phosphorus pollution in Dongjiang River,while woodland and grassland has a positive effect.Among them,towns and woodlands are the dominant factors affecting the output of nitrogen and phosphorus in the Dongjiang River Basin.(4)Patch Density(PD),Edge Density(ED)and Shannon's Evenness Index(SHEI)of landscape pattern index has negative effects on the nitrogen and phosphorus pollution in the Dongjiang River.,but Proportion of Like Adjacencies(PLADJ)and Contagion(CONTAG)are the opposite.Patch Density(PD)plays a leading role in the output of the nitrogen and phosphorus in Dongjiang River Basin.(5)In different hydrological periods,the correlation between landscape pattern and the nitrogen and phosphorus output of Dongjiang River Basin is the highest in normal season,followed by dry season,and in normal season is the lowest.(6)At different spatial scales,the response of landscape pattern at catchment scale to the nitrogen and phosphorus output was more sensitive than that at buffer scale.In the three riparian zone buffers,the relationship between landscape pattern at 500 m buffer scale and total nitrogen and total phosphorus output of Dongjiang River can represent the response of landscape characteristics at riparian scale to water quality in this region.In addition,the factors affecting the total phosphorus in the study area are more complex and diverse than the total nitrogen.