Implications of agriculture for lake contributions to the global methane cycle

Background/Question/Methods

Watershed land use is known to influence aquatic ecosystems and water quality.  As a result of the link between watershed activities and lake ecosystem processes, land use management, governmental policy, and economics can all influence the intensity and extent of agriculture in a region.  For example, governmental and economic commitment to biofuel technologies has influenced the production of corn in the Midwest United States.  To truly evaluate the benefits of renewable energy sources, the indirect environmental implications, including land use effects on lake greenhouse gas production, must be evaluated.  Runoff from intensive agriculture is known to enhance lake production and it is thought that enhanced algal carbon supply to lake sediments may increase methanogenesis activity in lake sediments and therefore lake contributions to the global methane cycle.  We evaluated the effect of watershed land use and lake productivity on lake methanogenesis rates using a regional lake survey in southern Michigan and northern Indiana. 

Results/Conclusions

Our eighteen-lake survey indicated positive relationships between percent cultivated crop watershed land cover, lake total phosphorus (a common proxy for lake productivity), and lake methanogenesis rates.  Using statistical relationships generated between watershed characteristics and lake methanogenesis rates, we made regional estimates of lake methanogenesis and atmospheric flux of methane from lakes.  Integration of our survey results with GIS analysis of the region enables estimation of regional lake methanogenesis rates and prediction of these rates under a variety of land use scenarios.