[Impact Analysis of Different Buffer Scale Landscape Patterns on Water Quality of the Fourth Drainage Ditch in...

Landscape patterns at specific spatial scales can respond to the sources of non-point source pollutants in water bodies and the surface landscape's ability to absorb them. To investigate the influence of landscape patterns on the water quality of the drainage ditch at different circular buffer scales， the fourth drainage ditch of the Ningxia Yellow River Irrigation Area （YDIA） was taken as the research object， and based on the land-use data in 2022 and the dynamic water quality monitoring data of 26 sampling points from 2021 to 2022， five circular buffer scales， including 100， 200， 500， 1 000， and 2 000 m， were set up， and three methods. Landscape pattern analysis， Spearman rank correlation analysis， and redundancy analysis were used to filter the water quality of the drainage ditch. Landscape pattern analysis， Spearman rank correlation analysis， and redundancy analysis were used to screen out the optimal buffer scales and corresponding key landscape indicators to explain the changes in water quality and to analyze the response relationship between the water quality of the drainage ditch and landscape features. The results showed that： ① The fourth drainage ditch in Ningxia Huang Irrigation Area was mostly polluted by high nitrogen， and more than 70% of the TN indexes exceeded the standard limit for Class V water throughout the year， while the TP indexes did not exceed the standard limit for Class III water， which was less polluted. ② The landscape characteristics at the scale of the 200 m circular buffer zone had a close relationship with the water quality indexes of the two periods， and the explanation rates of the fallow period and the cultivation period at that scale were the highest， 45.76% and 44.14%， respectively， and the explanation rate was the highest， 47.63% and 45.83%， respectively， which was the best buffer scale for discriminating the water quality of the fourth drainage ditch. ③ Cultivated land was the main 'source' land use type within the optimal buffer zone， which was the main factor affecting the change of pollutants in the drainage ditch. Followed by the spreading index， aggregation index， scattering and juxtaposition index， and fragrance uniformity， which were the main landscape factors affecting the change of water quality. Therefore， when optimizing the landscape pattern method for monitoring and controlling water pollution in drainage ditches， it is recommended to strictly control the proportion of arable land and other 'source' land-use types within the 200 m circular buffer zone， and at the same time， improve the diversity， connectivity， and aggregation of the landscape. The results of this study can provide new ideas and solutions for monitoring and analyzing the water quality of drainage ditches in Ningxia's Yellow River Irrigation District.