The effects of benthivorous smallmouth buffalo (ictiobus bubalus) on water quality and nutrient cycling in a shallow floodplain lake

Experimental mesocosm studies revealed that the presence of benthivorous smallmouth buffalo (Ictiobus bubalus) significantly enhanced turbidity, phytoplankton biomass, ammonium (NH₄⁺), and total nitrogen (N) and phosphorus (P) concentrations in a shallow, aerobic, hypereutrophic oxbow lake. The effects of Ictiobuson water quality are similar to the results of experiments performed on other benthivorous fish species. Prior studies have suggested that enhanced phytoplankton biomass in the presence of benthivorous fishes is a result of P excretion by fish and physical relocation of sediment P to the water column. However, our results revealed that enhanced microbial NH₄⁺ regeneration and subsequent uptake by phytoplankton may also be an important factor causing increased phytoplankton biomass levels in the presence of benthivorous fishes. Net sediment plus water column particle NH₄⁺ fluxes were over six times higher in the presence of Ictiobus, relative to the control. Increased biological demand for phosphate, as well as adsorption to resuspended sediments, resulted in a significant increase in water column particle phosphate demand in the presence of Ictiobus, relative to the control. Furthermore, we estimated that approximately 60% of the increase in water column total N in the presence of Ictiobus, relative to the control, was attributed to increases in phytoplankton and bacterial biomass, while 77% of the P increase could be explained by physical resuspension of sediment P.