Effects of nitrate contamination and seasonal variation on the denitrification and greenhouse gas production in La Rocina stream (Doñana National Park, SW Spain)
Climatic influence (global warming and decreased rainfall) could lead to an increase in the ecological
and toxicological effects of the pollution in aquatic ecosystems, especially contamination from agricultural
nitrate (NO3
−) fertilizers. Physicochemical properties of the surface waters and sediments of four
selected sites varying in NO3
− concentration along La Rocina Stream, which feeds Marisma del Rocio in
Do˜nana National Park (South West, Spain), were studied. Electrical conductivity, pH, content in macro
and microelements, total organic carbon and nitrogen, and dissolved carbon and nitrogen were affected
by each sampling site and sampling time. Contaminant NO3
− in surface water at the site with the highest
NO3
− concentration (ranged in 61.6–106.6mgL−1) was of inorganic origin, most probably from chemical
fertilizers, as determined chemically (90% of the total dissolved nitrogen from NO3
−) and by isotopic analysis
of ı15N-NO3
−. Changes in seasonal weather conditions and hydrological effects at the sampling sites
were also responsible for variations in some biological activities (dehydrogenase, -glucosidase, arylsulphatase,
acid phosphatase and urease) in sediments, as well as in the production of the greenhouse gases
CO2, CH4 and N2O. Both organic matter and NO3
− contents influenced rates of gas production. Increased
NO3
− concentration also resulted in enhanced levels of potential denitrification measured as N2O production.
The denitrification process was affected by NO3
− contamination and the rainfall regimen, increasing
the greenhouse gases emissions (CO2, CH4 and especially N2O) during the driest season in all sampling
sites studied.This work was supported by grants CGL2006-06870 and
CTM2009-1473-C02-02 from Ministerio de Ciencia e Innovación
(Spain) and RNM-4746 from Consejería de Innovación, Ciencia y
Empresa de la Junta de Andalucía (Spain), all of them co-financed by
the European Regional Development Fund (ERDF). Support of Junta
de Andalucía to Research Group BIO-275 is also acknowledged. D.
David Correa thanks Ministerio de Educación for predoctoral grant
AP2007-03967.Peer reviewe