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

Abstract

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 (R_tot), soil CO₂ emission (R_soil), and heterotrophic respiration (R_het) were 26 ± 5, 14 ± 3 and 12 ± 3 mg C m^–2 h^–1, respectively, The annual cumulative fluxes R_tot, R_soil and R_het equal to 234, 127 and 103 g C m^–2 y^–1, respectively. The contribution of R_soil to R_tot, and R_het to R_soil 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.