Influence Of Landscape Pattern On Water Quality And Ecological Risk Assessment In Dongjiang River Source Watershed

Dongjiang River source watershed is the guarantee of safe water supply for production and living in the Guangdong-Hong Kong-Macao Greater Bay Area.The health of its ecological environment is related to the construction of the strategic pattern and water quality development in Guangdong-Hong Kong-Macao Greater Bay Area.Therefore,it is important to pay attention to Dongjiang River source landscape pattern construction and improve the ecological environment quality.Based on water quality monitoring data,using the water comprehensive pollution index method to analyze Dongjiang River source watershed water quality from 2017 to 2019.Arc GIS and FRAGSTATS were used as processing platforms to obtain landscape indices in different years to analyze landscape pattern long-term change characteristics.The effect of landscape pattern on water quality in Dongjiang River source watershed was studied through correlation analysis and redundancy analysis by SPSS and CANOCO software.Constructing Dongjiang River source watershed landscape ecological risk assessment model in different years and exploring the temporal and spatial variation characteristics and spatial aggregation degree of Dongjiang River source watershed landscape ecological risk by Geo Da and geographic detector.Driving factors affecting the changes of landscape ecological risk in the Dongjiang source watershed from topography and socioeconomics were analyzed.The main research results are as follows:(1)Dongjiang River source watershed water quality has improved as a whole,but the total nitrogen pollution is still serious.As of 2019,the annual average concentration of total nitrogen at all monitoring sites has exceeded the limit of Class III water quality standards.The average annual concentration of other water quality indicators has reached the Class II water quality standards.The results of water quality assessment spatial distribution show that water quality of Dongjiang River source watershed is the best in the upper reaches of Dingnan,followed by upper reaches of Xunwu,the lower reaches of Xunwu,and the worst in the lower reaches of Dingnan.The results of water quality evaluation time changes show that compared with 2017 and 2018,more water quality monitoring points in 2019 are basically qualified or above.The water quality is the best in winter.The Dingnan water monitoring site showed poor water quality in spring and summer and better water quality in autumn;Xunwu water monitoring site shows poor water quality in summer and autumn and better water quality in spring.(2)From 1980 to 2018,cultivated land,grassland and water area had largest mutual transfer area with woodland.Construction land was mainly transferred to cultivated land.From1980 to 2000,gravity center moving distance of water in the Xunwu watershed was the largest and gravity center moving distance of construction land in the Dingnan watershed was the largest.At landscape level,the Shannon’diversity index and Shannon’evenness index of Dongjiang River source watershed both increased.The aggregation index did not change much.Maximum patch index and number of patches decreased.At type level,the number of patches in forest and grassland decreased.The proportion of construction land and the largest patch index increased.The water aggregation index and the number of patches increased and decreased respectively.The number of patches in paddy fields and dry land were much higher than the number of patches in other land types.(3)At landscape level,water quality was positively correlated with number of patches,Shannon’s Diversity index and Shannon’s Evenness Index,but negatively correlated with largest patch index and aggregation index.At type level,construction land was the main source of total nitrogen and total phosphorus output.Forest and grassland played an active role in water purification.The greater the fragmentation and complexity of arable land patches,the higher the risk of water pollution.The reasonable allocation of urban sewage centralized treatment facilities,strengthening management of abandoned mining areas,improvement of intensive treatment of cultivated land and construction of shelterbelt in areas where cultivated land is concentrated are beneficial for the water quality of Dongjiang River source watershed.(4)The Dongjiang River source watershed was dominated by low ecological risk and intermediate ecological risk.Except the area of low ecological risk area increased,the area of other ecological risk areas decreased.Higher and high ecological risk areas are mainly distributed in the three major town centers.The low and medium ecological risk areas are mainly distributed in the low hilly areas and marginal mountainous areas at the junction of the Xunwu and Dingnan watersheds.The Dongjiang River source watershed landscape ecological risk value had obvious agglomeration effect with high-high aggregation and low-low aggregation.Geographical detection results showed that population density,elevation,human disturbance,vegetation index and urbanization level had obvious effects on the spatial distribution of ecological risks in the Dongjiang River source watershed.The interaction of any driving factor had a greater impact on the ecological risk of the Dongjiang River source watershed landscape than a single driving factor.