Freshwater food webs control carbon dioxide saturation through sedimentation

Carbon cycling in lakes has been studied both in terms of the magnitude and global significance of carbon released to the atmosphere and carbon stored in the sediments. Interestingly, to the best of our knowledge there have been no studies examining whether instantaneous measures of carbon flux are directly related to how much carbon is being drawn down to the sediments. Here, we show that the saturation of CO2 in the water column is negatively related to the sedimentation rate. We, therefore, suggest that sedimentation should be explicitly considered as a factor directly controlling CO2 flux from freshwaters. Furthermore, we show that food webs and nutrients can alter CO2 flux by changing sedimentation. Oceanographers have long recognized the interaction between biota and sedimentation in the carbon dynamics of the ocean, a mechanism referred to as the biological pump. Our experiments rigorously test sedimentation and food web structure as factors controlling CO2 saturation and suggest a common framework for freshwater and marine systems.