The consequences for stream water quality of long-term changes in landscape patterns: Implications for land use management and policies

Abstract

The preservation of water resources is a worldwide goal that requires continuous research to support the action of decision-makers. The learning about water quality is paramount in that regard to assess the complex interactions between surface waters and pollution sources. To assess the impact of diffuse pressures, many authors established nexus between landscape metrics and surface water quality. The present study used that approach in a Portuguese urban catchment, the Ave River Basin. The relation between landscape metrics and eight surface water quality parameters was studied during 26 hydrological years, based on the Spearman's rank correlation analysis. The correlation analysis exposed strong relationships between water quality and parameters that describe land use composition or configuration. During the studied period, even in recent years, the water quality parameters reached concentrations above the legally recommended limits. The most concerning parameters were ammoniacal nitrogen, chemical oxygen demand and total orthophosphate. Among the analysed metrics, Shannon's diversity index, percentage of urban areas, and the percentage of agricultural edges that are shared with artificial areas were the most preoccupying land use characteristics that indicate degradation of water resources. Besides the correlations, the study calculated the variation rates of land use maps relative to the years of 1995, 2007, 2010, 2015 and 2018. The results of correlation analysis and land use changes identified actions for the short-term that could improve water quality in the Ave River, namely a reduction in agricultural fields and an increase of forest edges density. In the long-term, water quality improvements could be accomplished through the decrease of artificial surfaces, the increase of forested areas and edges surrounding agricultural fields.