Sources of atmospheric methane (CH4) are naturally occurring and anthropogenic. However, these sources are not mutually exclusive, and anthropogenic activities may drive the production of CH4 from natural sources, such as lakes. As the human population continues to grow and expand, so does our demand for agricultural crops to feed and fuel our society. With intensification of agriculture and heavy use of synthetic fertilizers, eutrophication has become a major concern for aquatic ecosystems. The aesthetics of noxious algal blooms are often cited as the largest human concern surrounding eutrophication. However, greater carbon substrate supply, from enhanced algal production, available to methanogens in the anoxic sediments of lakes, may enhance CH4 production rates as well as shape methanogen abundance and community structure.
Our study sought to examine the effects of enhanced algal growth on CH4 production rates, methanogen community composition, and abundance within temperate lake sediment. To do this, we measured CH4 production rates in sediments amended with algal carbon. We utilized quantitative PCR and terminal restriction fragment length polymorphisms (T-RFLP) to measure methanogen abundance and community composition differences amongst the incubations.
Results/Conclusions
Multiple lines of evidence indicate that algal biomass significantly enhanced CH4 production. However, the observed increases in CH4 production rates were not the result of changes in abundance or community composition. Overall, increased CH4 production rates, due to carbon inputs, may be the result of a change in per cell transcriptional and translational activity and not due to methanogen community composition or abundance changes within lake sediments. Together our results suggest the indirect implications of eutrophication on lake greenhouse gas production must be considered when evaluating the net benefits of food and biofuel crop production.