СО2 and СН4 Fluxes in Wetland Ecosystems of the Mezquital Valley, Central Mexico

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We measured dark CO2 fluxes and CH4 emissions from two naturally vegetated ecosystems of the Mezquital Valley irrigated with wastewater from Mexico City. The ecosystems were characterized by high groundwater levels; the vegetation was represented mainly by saltgrass in the first plot and chairmaker’s bulrush in the second. A dark chamber technique was used for the study from August 2008 to June 2009. For the two studied plots, mean values (mean ± SE) for dark ecosystem CO2 fluxes (Rtot), soil CO2 emission (Rsoil), and heterotrophic respiration (Rhet) were 26 ± 5, 14 ± 3 and 12 ± 3 mg C m–2 h–1, respectively, The annual cumulative fluxes Rtot, Rsoil and Rhet equal to 234, 127 and 103 g C m–2 y–1, respectively. The contribution of Rsoil to Rtot, and Rhet to Rsoil varied significantly over the study period, with no clear relationship to seasonal dynamics. The observed low CO2 fluxes may be due to soil salinization resulting from wastewater flooding. The fluxes of CH4 were observed in the flooded plot, with peaks up to 370 µg C m–2 h–1. The fluxes of CH4 were significantly higher when plants were present in the measurement chamber than when there were no plants, confirming the important role of plant cover in CH4 transport. Unlike CH4 fluxes, CO2 fluxes show seasonal dynamics, mainly due to their strong dependence on temperature. The observed results may be useful for properly estimating the global C budget and the contribution of saline soils to C fluxes.