Effects of multi-scale landscape pattern changes on seasonal water quality: a case study of the Tumen River Basin in China

Landscape patterns affect river water quality by influencing hydrological processes. However, with changes in spatial scale and season, landscape factors may have different effects on water pollution. Therefore, quantitative analysis of the scale effect of each landscape index was carried out to determine the mutation point of river water quality and its index relationship, which is of great significance to landscape planning and water quality protection. Based on the water quality monitoring data of 19 sampling points in the Tumen River Basin, we used redundant methods to quantify the spatial scale effects and seasonal dependencies of various landscape indicators on river water quality, then determined the mutation point of the water quality along the landscape-scale gradient. The results showed that different types of landscape indicators have different effects on river water quality, and the spatial-scale effect of landscape composition affects a river's water quality, while landscape configuration indicators had the highest sensitivity. The landscape characteristics of river straps better explained the overall water quality, a phenomenon that is more obvious in the wet season than the dry season. We identified a key landscape indicator of urban area proportion (Urban%) and a contagion index (CONTAG) as the river strap scale. An Urban% < 30% and a CONTAG > 70% suggest effective landscape planning parameters that effectively protect water quality. The results indicated that, to protect water quality, landscape regulation should follow scale-adaptability measures and consider landscape thresholds, which cause abrupt changes in water quality.