The Influence Of Landscape Pattern On River Water Quality

The relationship between river and human life is inseparable.As one of the indispensable resources for the development of human society,water resources have become the restrictive factors in many developing areas.The causes of river water pollution come from all aspects.With the effective control of point source pollution,non-point source pollution has become a major issue worthy of attention at this stage.By analyzing the influence of landscape pattern on river water quality and summarizing its law,it is helpful to provide basis and reference for river water quality improvement.In this study,based on the GF-2 remote sensing image in 2017,Arc GIS 10.4 and e Cognition9.0 were used to interpret the study area and get the land use distribution.The landscape pattern index in the basin was obtained through Fragstats 4.2.At the same time,based on Digital Elevation Model,combined with drainage map,the sub-watersheds of the upper reaches of Dongtiaoxi were extracted and divided.Water quality sampling was carried out in 2019,and four phases?March,June,September and December?of water quality data were obtained.By using the methods of correlation analysis,redundancy analysis and stepwise regression analysis,the relationship between landscape pattern and water quality was systematically studied on sub-watershed,riparian corridor and reach buffer.The main conclusions are as follows:?1?The main landscape type in the upper reaches of Dongtiaoxi was forest land,accounting for 68.2% of the study area,followed by farmland,which accounting for 15% of the total area.In terms of spatial distribution,the construction land showed a trend of aggregation and distribution;meanwhile,the forest land was distributed in the mountain area on the west side of the basin,while farmland was mainly distributed in the plain area and the east side of the study area.?2?The TN content in the upper reaches of Dongtiaoxi was far beyond the Standard for Grade ? in the environmental quality standard of surface water,and NH₄⁺-N and TP in some monitoring sections in the source area could reach Standard for Grade ?.In terms of time,the water pollution in March and December was relatively serious.From the perspective of space,the high values of NH₄⁺-N and TP were distributed in the areas where the urban construction land was concentrated,while the most seriously polluted areas of NO3--N and TN was Nanxi,the main tributary of Nantiaoxi,where bamboo was planted intensively.?3?NH₄⁺-N and TP were positively correlated with the percentage of construction land and negatively correlated with the landscape index PAFRAC.The TP in June also showed a significant negative correlation with IJI.In the riparian corridor and reach buffer,when the buffer radius reached 300 m and 1000 m respectively,the correlation was the strongest,and then decreased with the increase of buffer radius.NO3--N and TN showed a very significant positive correlation with the percentage of farmland,and had a good correlation with the five landscape indexes of LPI,PAFRAC,CONTAG,DIVISION and SHDI.Among them,there was a significant negative correlation with LPI,PAFRAC and CONTAG,and a significant positive correlation with DIVISION and SHDI.?4?The results of redundancy analysis demonstrated that the best scale was not sub-watershed when studying the contribution of various landscape indexes to water quality.At the scale of riparian corridor and reach buffer,the explained variance was higher.It was also found that the contribution of landscape indexes to water quality was more prominent when analyzing on reach buffer.?5?The results of stepwise regression analysis of water quality were similar to those of correlation analysis.The regression equation reflected the key role of the percentage of construction land in the control of NH₄⁺-N and TP in water quality.But the NO3--N mainly came from the contribution of farmland,because the nitrogen pollution mostly came from the non-point source pollution of farmland.The regression equation of TN had great seasonal difference,which reflected the purification effect of forest land on water quality and the influence of landscape shape complexity on its content in different seasons.