Effect of Wetlands on water quality of an agricultural catchment in a semi-arid area under land use transformation

The reduction of nutrients and sediments from agriculturalrunoff by natural wetlands has been commonly accepted, buttheirrole in water quality improvement at the catchmentscale has been seldom studied, especially in irrigated catchments. This study aims to elucidate the effect of natural and recently created wetlands on stream water quality after the conversion of a catchment for irrigation purposes.Water quality andmorphometrical andvegetation-related variables weremeasured in 19 wetlands on a 750-ha agricultural catchment under semi-arid conditions in the Ebro basin(NE Spain). A pollution gradient was found, increasing from the wetlands located in the upper catchment to those in the lower catchment.Wetlands with the lowest degree of artificiality, measured asthe amount of human createdstructures(e.g., channel excavation, dikes), and higher plant richness hadthepoorest water quality, probablybecause they were in the lower catchment and their water contained more pollutants carried from agricultural and salinesoils upstream. Some of these wetlands also had the highest rates of sediment and N-NO3 retention, incontrast to more artificial wetlands, which exported nutrients and sediments. Less artificial wetlands could also provide ancillary benefits such as biodiversity enhancement or landscape heterogeneity improvement.