Effect of juvenile omni-benthivorous fish (Carassius carassius) disturbance on the efficiency of lanthanum-modified bentonite (LMB) for eutrophication control: a mesocosm study

Lanthanum-modified bentonite (LMB) is widely used for eutrophication control and has demonstrated good efficiency in some eutrophic lakes. However, the efficiency of LMB on eutrophication control in some eutrophic lakes, where the structure of food webs is mainly dominated by omni-benthivorous fish, remains ambiguous. Omni-benthivorous fish usually disturbs sediment and promotes the release of internal nutrients, the effect of which on the efficacy of LMB remains to be studied. Thus, a 30-day mesocosm experiment was conducted to determine whether omni-benthivorous fish disturbance and LMB would cause antagonistic responses. LMB significantly reduced dissolved P concentration in overlying water, converting mobile P to bound P in the surface layer of sediment in the absence of crucian carp (Carassius carassius). However, there were significantly negative interaction effects between LMB and crucian carp. Although LMB still effectively reduced the total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP) concentrations of overlying water in the presence of crucian carp, it had limited efficacy on inhibiting the increased concentrations of suspended solids, particulate nutrients, and chlorophyll a (Chl a) due to crucian carp disturbance. Furthermore, the crucian carp disturbance also increased the risk of mobile P releasing from surface sediment, whether with or without LMB application. The results indicated that the efficacy of LMB was insufficient to offset the negative effect of omni-benthivorous fish disturbance on eutrophication control. Hence, the omni-benthivorous fish also need to be considered for eutrophication control in shallow eutrophic lakes. Some measures need to be taken to control the biomass of omni-benthivorous fish.