Effects of nitrate contamination and seasonal variation on the denitrification and greenhouse gas production in La Rocina stream (Doñana National Park, SW Spain)

摘要

Climatic influence (global warming and decreased rainfall) could lead to an increase in the ecological\udand toxicological effects of the pollution in aquatic ecosystems, especially contamination from agricultural\udnitrate (NO3\ud−) fertilizers. Physicochemical properties of the surface waters and sediments of four\udselected sites varying in NO3\ud− concentration along La Rocina Stream, which feeds Marisma del Rocio in\udDo˜nana National Park (South West, Spain), were studied. Electrical conductivity, pH, content in macro\udand microelements, total organic carbon and nitrogen, and dissolved carbon and nitrogen were affected\udby each sampling site and sampling time. Contaminant NO3\ud− in surface water at the site with the highest\udNO3\ud− concentration (ranged in 61.6–106.6mgL−1) was of inorganic origin, most probably from chemical\udfertilizers, as determined chemically (90% of the total dissolved nitrogen from NO3\ud−) and by isotopic analysis\udof ı15N-NO3\ud−. Changes in seasonal weather conditions and hydrological effects at the sampling sites\udwere also responsible for variations in some biological activities (dehydrogenase, -glucosidase, arylsulphatase,\udacid phosphatase and urease) in sediments, as well as in the production of the greenhouse gases\udCO2, CH4 and N2O. Both organic matter and NO3\ud− contents influenced rates of gas production. Increased\udNO3\ud− concentration also resulted in enhanced levels of potential denitrification measured as N2O production.\udThe denitrification process was affected by NO3\ud− contamination and the rainfall regimen, increasing\udthe greenhouse gases emissions (CO2, CH4 and especially N2O) during the driest season in all sampling\udsites studied.