Assessing the effects of landscape pattern on river water quality at multiple scales: A case study of the Dongjiang River watershed, China

Understanding how land use and land cover change influences the flow and water quality of rivers is critically important for river management and restoration. Human activities have transformed the landscapes in southern China where damaged river systems need to be restored and better managed for achieving environmental sustainability. Toward this end, we quantified the land use and land cover pattern of the Dongjiang River watershed, China between 1990 and 2006 based on remote sensing data and field measurements. We then analyzed how river flow and several water quality variables were related to landscape attributes at three scales: subwatershed, catchment, and buffer. Our results show that the water quality of the Dongjiang River differed among the upper, middle, and lower reaches and also changed significantly during the recent decades. These changes in space and time indicate a trend of accelerating deterioration in water quality. Also, land use and land cover pattern had major impacts on the flow and water quality of the Dongjiang River at multiple spatial scales. In particular, urban land use, although small in percent cover, exerted a disproportionately large influence both locally and over distance. We also found that most water quality variables (Cl ^-, EC, NH ₃-N, and NO ₃-N) were correlated with landscape pattern on all three spatial scales although the correlation was stronger at the subwatershed scale than at the catchment and buffer scales. This scale multiplicity suggests that, while water-monitoring and river restoration need to adopt a multi-scale perspective, particular attention should be paid to the subwatershed scale. In addition, the control of pollution sources associated with socioeconomic activities ought to be explicitly incorporated in landscape management practices.