Nutrient excretion by fish in wetland ecosystems and its potential to support algal production

We used both direct measurement and bioenergetic methods to examine nitrogen and phosphorus (P) excretion by fathead minnows in two wetlands over 2 yr. We also assessed the potential importance of nutrient flux from fish by comparing excretion estimates to empirically derived estimates of algal P demand. Population-level estimates of P excretion across the four lake-years were high relative to other published studies, peaking at 11.7 mg m^-3 d^-1 and occurring when fish densities exceeded 69 fish m^-3. Excretion rates peaked in late summer during maximal algal demand, and P excretion by fish exceeded algal demand in two of the four wetland-years. Detritus was a major diet component (up to 90% by mass), making fish excretion a major nutrient flux from wetland sediments to the water column. Consumer-driven effects could have strong influences on nutrient dynamics in prairie wetlands, ecosystems historically thought to be constrained largely by abiotic factors.