Anthropogenic effects on greenhouse gas (CH4 and N2O) emissions in the Guadalete River Estuary (SW Spain)

Abstract

Coastalareasaresubjecttoagreatanthropogenicpressurebecausemorethanhalfoftheworld'spopulationlives in its vicinity causing organic matter inputs, which intensifies greenhouse gas emissions into the atmosphere. Dissolved concentrations of CH4 and N2O have beenmeasuredseasonallyduring 2013intheGuadaleteRiver Es tuary, which flows into the Cadiz Bay (southwestern Spanish coast). It has been intensely contaminated since 1970. Currently it receives wastewater effluents from cities and direct discharges from nearby agriculture crop. Eight sampling stations have been established along 18 km of the estuary. CH4 and N2O were measured using a gas chromatograph connected to an equilibration system. Additional parameters such as organic matter, dis solved oxygen, nutrients and chlorophyll were determinate as well, in order to understand the relationship be tween physicochemical and biological processes. Gas concentrations increased from the River mouth toward the inner part, closer to the wastewater treatment plant discharge. Values varied widely within 21.8 and 3483.4 nMforCH4andbetween9.7and147.6nMforN2O.Greenhousegasseasonal variationswere large influ enced by the precipitation regime, masking the temperature influence. The Guadatete Estuary acted as a green house gas source along the year, with mean fluxes of 495.7 μmol m−2 d−1 and 92.8 μmol m−2 d−1 for CH4 and N2O, respectively.