Extreme Sensitivity of Greenhouse Gas Production in Mineral Wetland Sediments under Multiple Salinization Regimes.

Wetlands and small inland waters are atmospheric sources of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). Human activities are inducing the salinization of inland aquatic habitats, with unclear implications for greenhouse gas (GHG) emissions. Here, we show that GHG production is extremely sensitive to multiple salinization regimes (NaCl or MgSO4 amendments from 0.2 to ∼5 ppt salinity) in a mineral soil wetland sediment slurry incubation experiment. Production of CH4 decreased nonlinearly in both treatments, with more pronounced declines in MgSO4 treatments. Production of CO2 had contrasting patterns, increasing with MgSO4 but decreasing with NaCl additions, signaling divergent responses of sediment geochemistry and microbial respiration between treatments. Both treatments inconsistently stimulated N2O production. Overall, we have shown that even small increases in salinity (<1 ppt) induce major shifts in wetland GHG production, but that responses depend heavily on salinization chemistry, a factor requiring consideration in future salinization research.