Effects Of Anodonta Woodiana On Water Quality In Shallow System

The filtration rate on phytoplankton and excretion rate of nutrients by mussels are key processes affecting water quality.Experiments on characteristics of mussel filtration rate,nutrients excretion and effect of mussels on water quality were conducted with and without Anodonta woodiana.Results showed that in clear water,the filtration rate by the mussels was low with limited effect on improving water quality,while in eutrophic conditions,the filtration rate was high,the concentrations of nutrient and phytoplankton biomass in water decreased significantly,the transparency increased,thus improving water quality.In addition,the filtration rate of young mussels was generally higher than that of adults.Furthermore,the filtration rate appeared high in spring(0.132±0.018 L/g/h)and low in summer for both the young and adult mussels.In the experiment of nutrient excretion of the mussels,A.woodiana increased the total nitrogen,ammonium and total phosphorus significantly,but did not change the concentrations of soluble reactive phosphate.In a mesocosm experiment,though the mussels increased the concentrations of ammonium and did not changed the concentrations of total nitrogen,the filter-feeding mussels decreased the TSS,total phosphorus,nitrate,nitrite and planktonic algal biomass in the water,improved the light conditions and increased the benthic algae biomass.This study indicates that filter-feeding mussels can be useful in improving water quality at early stages of the degraded ecosystem restoration due to the eutrophication.But,mussel alone may have limited effect on improving water quality in clear water due to the nutrient excretion.