The Influence of Eutrophication Status on the Kinetics of Methane Oxidation in Soils from a Subtropical Freshwater Wetland.

Microbial methane (CH4) oxidation has potential to reduce up to 90% of CH4 emissions fluxed from wetland soils. Therefore, a greater understanding of the process of is essential to improve strategies to reduce CH4 emissions from wetland systems. A laboratory manipulation study was performed using microcosms containing soils which were collected from the eutrophic (F1) and oligotrophic ridge (U3R) and slough (U3S) sites of WCA-2A in Florida Everglades. The rates of CH4 oxidation were measured for each site along the depth profile at 0-5, 5-10, and 10-20 cm increments to determine the Michaelis-Menton kinetics. Significant differences were found in the maximum oxidation rate (Vmax) and oxidation affinity (Km) among the sites and with soil depth. The Vmax (20.1±4.7 µg CH4 g-1 h -1) at 0-5 cm in F1 was significantly lower than deeper depths. The Vmax of F1 at 5-10 cm was significantly higher than U3R and U3S. The Km at 0-5 cm in F1 (684 ± 313 µg CH4 g-1) and U3R (1380 ± 230 µg CH4 g-1) showed significantly higher affinity than deeper depths. The Km values below 5 cm of U3S were significantly lower than both F1 and U3R. Significant positive correlations with total phosphorus (TP) suggest that TP may be influencing the oxidation activity. Correlations with nitrate (NO3-) suggest varying influence of NO3- on oxidation activity, with higher NO3- concentrations having an inhibitory effect on CH4 oxidation rates. In addition, phospholipid fatty acid analysis was performed to determine the fingerprint of the microbial community structure.