The Effects Of Freshwater Snail On Wetland Methane Emission

Due to the special flooded condition, wetland sediment can sequester large amount of organic carbon. Therefore, wetland ecosystem carbon cycle has caused worldwide concern with global warming. As an important component of the wetland ecosystem, benthic fauna play a key role in the sediment-water interface due to their high frequency and intensity bioturbation. They can alter sediment texture, modify sediment properties, and trigger nutrition cycle. This process can, therefore, stimulate microbial growth and activity and shift their community. Consequently, benthic fauna may have potentially profound effects on carbon cycling. In the present study, we performed a field experiment in combination with laboratory incubations to address whether freshwater snail (a ubiquitous component of benthic fauna) can affect CH4emission in the biggest freshwater lake in China. Then, characterized the soil chemistry of the top layer of sediment and used real-time PCR to quantify the abundance of microorganisms that metabolized CH4. Furthermore, sediment samples were incubated in the laboratory to determine the ability of the microorganisms to produce and oxidize CH4. The major findings are summarized as follow:1. The presence of freshwater snail could significantly increase CH4fluxes. And the CH4flux was significantly increased with the increasing snail abundance.2. Our results suggested that snails’ habitats are a strong source of CH4in freshwater lake. The CH4emission (23.98mg CH4-C m-2d-1) emitted from the habitats with snail abundance more than1750Ind m-2were comparable to CH4emission (24.72mg CH4-C m-2d-1) from Spartina alterniflora dominated coastal marsh.3. The significant effect of snails on CH4emission was not produced by the anaerobic methanogens in their guts.4. In the wetland with rich nutrition, CH4flux might be affected by snail through changing NH4+concentration. NH4+is known as the dominant and preferred nitrogen source for microbial metabolism, especially for heterotrophic bacteria. Proper addition of NH4+can also stimulate microbial activities. In the present study, we observed that NH4+concentration was positively correlated with potential CH4production rate and the abundance of mcrA gene. Although the abundance of pmoA gene also significantly increased across these sediments, potential CH4oxidation rate was significantly decreased, possibly because of sediment NH4+which can compete for CH4oxidation due to the similar molecular size and structure of CH4. As a result, CH4emission might be increased.5. In the experimental microcosms, the feces and bioturbation of snails might increase the concentration of dissolved organic carbon (DOC). Previous studies have indicated that dissolved nutrition, such as acetate, was the substrate of methanogenesis. Thus, CH4emission was significantly correlated with increasing DOC.