Longitudinal Changes in Water Quality to Landscape Gradients Along Sha River Basin

Both lateral and longitudinal scales are critical to understand the response of stream ecosystem to landscape changes. After acknowledged the most effective lateral scale in previous study, the aim of our study was to investigate the characteristic reaches explaining water quality most and construct dose-response curves to predict water quality changes along the longitudinal scale of Sha River Basin. Results showed that most water quality values at headwater sites were apparently better than those at middle and lower reaches (p<0.05). Sites at middle or lower reaches are more responsible for water quality deterioration, especially those reaches where towns and cities located. Urbanization is the primary cause, in spite of that the dominant land type in Sha River Basin is agriculture. Response curves of the two major water eutrophication variables (total nitrogen and ammonium) at Sha River Basin both exhibited obvious positive relationships with increasing urbanization, and the response to urbanization gradients was more profound (parabolic curve). According to the Chinese State Standard max permissible limit for drinking and surface water, lower urban land percentage (<20%) was appropriate for keeping water quality from further degradation. All results indicate that quantifying the relationship between water quality and landscape pattern at longitudinal scale may provide a useful tool for determining thresholds where stream health declines and offer constructive suggestions for effective stream restoration.