Different impacts of landscape pattern and industrial structure on water quality in Yellow River's mainstream and tributary in Gansu, China

The water quality of rivers is usually influenced by landscape patterns and industrial structures, but the impact of the COVID-19 pandemic has received less attention. Taking the mainstream and tributary rivers of the Yellow River in Gansu Province as the study area, the correlation between water quality indicators and landscape pattern index, as well as the social and economic factors were analyzed to explain the driving forces of the differences in water quality from 2018 to 2021, moreover, the impact of the COVID-19 pandemic on water quality were investigated. The water quality of the mainstream and tributary rivers was improving, except the Taohe River; however, the monthly nitrogen source pollution in the Weihe River (3.58-11.19 mg/L for TN and 0.25-1.88 mg/L for NH 4 + -N), Jinghe River (2.66-8.18 mg/L for TN and 0.25-1.69 mg/L for NH 4 + -N) and Zhuanglang River (1.20-6.75 mg/L for TN and 0.18-0.65 mg/L for NH 4 + -N) still had high levels, and the average values of TN even fall within the Class V standard. Water quality is positively correlated with the aggregation degree and connectivity of landscape, but the risk of water pollution increased with the increase of the degree of landscape fragmentation and dispersion. The NH 4 + -N, TP, CODMn and COD are influenced by rural domestic and agricultural activities, while TN and DO are affected by urban domestic and industrial production. The COVID-19 pandemic has affected river water quality by impacting production and daily life. These findings provide a foundation for managing the water quality of Yellow River Basin. • Water quality of the main and tributary streams improved, but with serious total nitrogen pollution. • The aggregation and connectivity can improve water quality, but the fragmentation and dispersion are opposite. • River water quality varies with the rural and urban life as well as agricultural and industrial production. • The COVID-19 pandemic affected water quality by influencing pollutant emissions of production and daily life.