Consumption of organic carbon from lake sediments by detritivorous fish: Implications for carbon sequestration in shallow lakes

Background/Question/Methods

Shallow lakes have the potential to sequester large amounts of organic carbon in their sediment and play a disproportionately large role in the global carbon cycle. However, the sequestration rates in these lakes are highly variable. The consumption of detritus by detritivorous fish and aquatic invertebrates may reduce sequestration rates and contribute to this variability. 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) in these systems. We assessed fathead minnow population dynamics and prey consumption in three shallow Minnesota lakes during summers of 2001 and 2002. We used bioenergetics computer models to estimate fathead minnow consumption and respiration of organic carbon from lake detritus. We then compared the consumption and respiration rates from the fish to estimates of organic carbon sequestration rates in sediments via sediment cores from similar lakes.

Results/Conclusions

Results showed the three fish populations on average consumed 5.8 kg ha^-1 d^-1 of detritus (dry weight) from May through August of both 2001 and 2002. This represents 2.5 kg ha^-1 d^-1 organic carbon consumed from lake detritus, with 1.1 kg ha^-1 d^-1 of the organic carbon converted to CO₂ via respiration of the fish. Larval fathead minnows played a disproportionately large role consuming on average 69% of the total detritus consumed in each lake. Estimates of organic carbon sequestration in sediments via sediment cores from similar lakes averaged 1.6 kg ha^-1 d^-1 (range 0.8 - 2.9). The similarity in fish consumption and respiration rates compared to lake sequestration rates of organic carbon in sediments indicates fathead minnows, especially larval fathead minnows, may influence carbon burial rates in shallow lakes. This influence could contribute to the high variability observed in the organic carbon sequestration rates in shallow lakes. Management activities that change the distribution and abundance of these fish could also change these shallow lakes’ sequestration rates.