CONSUMPTION OF ORGANIC CARBON FROM LAKE SEDIMENTS BY DETRITIVOROUS FISH: IMPLICATIONS FOR CARBON SEQUESTRATION IN SHALLOW LAKES

Shallow lakes have the potential to sequester large amounts of organic carbon in their sediment, but sequestration rates may be reduced by consumption of detritus by detritivorous fish and aquatic invertebrates. The fathead minnow (Pimephales promelas) is a detritivorous fish common in shallow lakes in North America and Canada, and can reach high densities (107 fish m²) and biomass (252 kg ha^-1) in these systems. We used bioenergetics models to estimate consumption and assimilation of carbon from lake detritus by fathead minnow populations in three shallow Minnesota lakes, and compared these rates to estimates of carbon sequestration rates in sediments from similar lakes. Results showed the three fish populations on average consumed 2.0 kg ha^-1 day^-1 of detritus (dry weight) from May through August of 2005 and 2006. This represents 0.86 kg ha^-1 day^-1 organic carbon consumed from lake detritus, with 0.43 kg ha^-1 day^-1 carbon assimilated by the fish. Estimates of organic carbon sequestration in sediments from similar lakes averaged 1.6 kg ha^-1 day^-1 (range 0.8 - 2.9). The similarity in fish consumption and sequestration rates indicates fathead minnows may have strong influences on carbon burial rates in shallow lakes, and management activities that change the distribution and abundance of these fish may also change sequestration rates.