Riparian zones can serve as a critical interface to regulate the river water quality. However, it is still lacking in the influence of the riparian zone landscape patterns on the river water quality. Targeted strategies of water pollution control have been hindered in optimizing the riparian zone landscape. This study aims to quantify the spatial scale effects of the riparian zone landscape patterns on the river water quality. Key indicators of the landscape patterns were also identified to obtain the optimal sizes of the riparian buffer. Accordingly, the Dongting Lake basin was selected as the study area due to the intensive agriculture and rapid urbanization in recent years. The dataset was collected from the high-resolution land use and surface water quality in 2023. The recursive feature elimination-random forest model was integrated with the redundancy analysis. The key indicators of the riparian landscape were identified for the specific and composite water quality variables. The results showed that the total nitrogen (TN) was first identified as the predominant pollutant, with the elevated concentrations primarily distributed in the Dongting Lake area and Chang-Zhu-Tan urban agglomeration, which was driven by the combined agricultural non-point source pollution and urban emissions. Secondly, the most significant influence of the riparian landscape patterns on the dissolved oxygen (DO) occurred at a buffer scale of 25 m. In contrast, the optimal buffer scale was 200 m for the total nitrogen (TN), total phosphorus (TP), and the chemical oxygen demand by manganese (COD_Mn), while the most effective buffer scale was 100 m for the ammonia nitrogen (NH₃-N). Thirdly, the explanatory power of the landscape pattern of the riparian zones to the composite river water quality demonstrated a nonlinear trend of initially decreasing, then increasing, and finally decreasing. With the maximum explanatory power of 41.87% at the 200 m buffer zone, the landscape pattern of the riparian zone was thus identified as an effective predictor of the composite river water quality variations. Fourthly, the dominant influencing indicator of the landscape on the composite water quality also shifted at the different scales: Patch density of cultivated land at 25 m, contagion index at 100 m, patch density of construction land at 200 m, and Shannon's diversity index at 800 m. The 50 and 400 m buffers were both characterized by the edge density of the construction land. The landscape patterns of the cultivated and construction land were the key influencing factors on the composite river water quality. A great contribution was made to the landscape patterns' influence on the river water quality at the different spatial scales in riparian zones. The 200 m riparian zone was recommended to optimize the landscape strategies for the spatially precise regulation. A hierarchical regulatory framework was integrated with the "source reduction–process interception–end purification". The proportion of the cultivated and construction land was reduced to increase that of the forest land. The interface of the cultivated land, construction, and forest land was significantly expanded for the optimal landscape pattern of the riparian zone. The finding can also provide a strong reference to improve the river water quality.

A major interdisciplinary issue can be the interaction between the supply and demand of ecosystem services, as well as the welfare of residents in the natural and socioeconomic system. Frequent contradictions need to be balanced in the research on the ecosystem and residents' welfare. However, previous studies have focused only on the contribution rate of the supply of ecosystem services to residents' welfare. A tradeoff can consider the demand and supply-demand balance of ecosystem services. Particularly, there has been a dramatic change in the relationship between the supply-demand balance of ecosystem services and welfare residents in recent years. The rapid economic growth and dramatic land use have led to a decrease in supply while an increase in demand for ecosystem services. The spatial heterogeneity of supply-demand levels can also lead to the deterioration of the supply-demand of ecosystem services, even the ecological environment and damage to residents' well-being. This study aims to focus on the middle reaches of the Yangtze River (MRYR) in the period from 2000 to 2018. A quantitative matrix was established to measure the supply-demand balance of ecosystem services. The annual combined empowerment and linear function weighting were employed to accurately assess the score of residents' welfare. The elasticity coefficient model was then used to determine the coupling relationship between the supply-demand balance of ecosystem service and the welfare of residents. Four types were divided for the coupling relationship between supply-demand balance on the ecosystem services and welfare of residents: supply-demand improving and welfare increases, deteriorated supply-demand but welfare increases, supply-demand improving but welfare decreases, as well as the deteriorated supply-demand and welfare decreases, representing by the optimal, sub-optimal, sub-poor, and worst relationships, respectively. A tradeoff relationship was dominated gradually over time. The proportion of county units with deteriorated supply-demand but welfare increase increased from 81.99% in 2000-2010 to 91.57% in 2010-2018. However, both stability and fluctuation were also observed. The former was dominated by the vast majority of counties that remained the deteriorated supply-demand but welfare increases; the latter was a significant contraction of counties with supply-demand improving and welfare increases. The feedback depended mainly on the welfare type, services type, spatial scale, time scale, and economic-social development level. The socioeconomic development was transitioned from the primary product production stage II to the late industrialization stage from 2000 to 2018. However, there were outstanding spatial differences in the socioeconomic development. The rapid urbanization and industrialization zones continued to allocate excessive resources and energy toward economic growth without environmental protection. Economic growth showed the potential to enhance the material prosperity and life quality of residents, offsetting the adverse effects of the supply-demand deterioration in the ecosystem services on residents' safety and health welfare. Consequently, the comprehensive welfare of residents can be enhanced for the coordinated development between the ecological environment and residents' welfare in the rapidly urbanizing and industrializing areas. The findings can also provide a strong reference for the decision-making on regional development.