Methane emissions from aqueous sediments are influenced by complex interactions among microbes and environmental...

Methane fluxes from aqueous sediments strongly influence global atmospheric methane. However, many questions still puzzle researchers; for example, why are some unstable sediments atmospheric methane sinks? In this study, a biofilm model originally developed for wastewater treatment was modified to simulate the microbial kinetics and substance conversions in aqueous surface sediments. The model was validated by the experimental data and could predict chemical profiles and microbial distributions in sediments. The model revealed complicated interactions between different microbial communities and environmental factors, including competition between aerobic methane-oxidizing bacteria, nitrite-dependent anaerobic methane-oxidizing bacteria, and anaerobic ammonia-oxidizing bacteria. The results of model simulations showed that the effects of environmental factors, especially dissolved oxygen and ammonia in overlying water, on methane fluxes are very complicated. Rapid environmental changes (which can be caused by tide, day-night alternation, or zoobenthic and human activity) and intensive competition between microbes greatly affected methane fluxes and resulted in alternation between atmospheric methane source and sink in unstable sediments. This study extends the application of a wastewater treatment model to ecological studies of microbial interactions in natural sediments and explains some problems that might be difficult to resolve by using experimental methods.