Effects Of Common Carp(Cyprinus Carpio)on Water Quality In An Aquatic Ecosystem Dominated By Submerged Plants:a Mesocosm Study

Submerged plants are the primary producers of aquatic ecosystems,which play an important role in the structure and function of aquatic ecosystems and maintain the health and stability of ecosystems.Common carp has been widely introduced into aquatic systems in the world.Being benthivorous,the decrease of transparency in water caused serious water quality problem of ecosystems invaded,such as deterioration of water quality and degradation of submerged plants.Mesocosm experiments（control,common carp）were conducted to evaluate the effects of common carp（Cyprinus carpio）on water quality in an aquatic ecosystem dominated by submerged plants.Results showed that:relative to the controls,the presence of carp decreased water clarity by increasing total suspended solids（TSS）and light attenuation.However,levels of total nitrogen（TN）,total dissolved nitrogen（TDN）,nitrate nitrogen（NO₃^--N）,nitrite nitrogen（NO₂^--N）,total phosphorus（TP）,total dissolved phosphorus（TDP）and soluble reactive phosphorus（SRP）in the water column were reduced.No significant change in phytoplankton biomass（measured as chlorophyll a）and total biomass of submerged plants was observed between fish treatment mesocosms and controls,but the fish did reduce the biomass of the submerged macrophyte Vallisneria denseserrulata.We conclude that removal of common carp is likely to improve water quality in aquatic ecosystems dominated by submerged plants primarily by decreasing TSS and improving water transparency.