Effects Of Crucian Carp On Light,Temperature Distribution And Water Quality In An Aquatic Ecosystem Dominant By Submerged Plants

Eutrophication has become a widespread water environment problem today.Omnivorous fish is widely distributed and omnivorous,which has a profound impact on aquatic ecosystem and may increase the eutrophication of aquatic ecosystem when invasion.In order to evaluate the impact of omnivorous fish on the light and temperature distribution of aquatic ecosystem and its water quality,mesocosms with submerged plant Valsneria denseserrulata as the main primary producer outdoors were constructed.Mesocosm experiments with crucian carp as fish group and fish-free group as controls were conducted.Meanwhile,a group by shading was also conducted.Nitrogen,phosphorus and chlorophyll a concentrations were measured.In addition,transparency,dissolved oxygen,pH and some other indicators such as light and temperature were also measured to evaluate the effects of omnivorous fish on light,temperature distribution and water quality.The main results are as follows:1.In average,the concentration of dissolved oxygen in the crucian carp group was 7.47 mg/L and there was no significance as in the controls(p> 0.05);the transparency of the water body in the crucian carp group was 20.37 cm,which was 19.13 cm lower than the control group,about 48.4% reduction as in the controls,so the presence of the fish significantly reduced the water transparency(p <0.05);however,the pH of the water in the crucian carp group 8.59 was similar as in the controls(p> 0.05).2.The total nitrogen concentration was 4.44 mg/L and the ammonia nitrogen was 0.16 mg/L in the crucian carp,which was similar concentrations as in the controls(p> 0.05);the total phosphorus in the crucian carp group was 0.16 mg/L,which was 0.08 mg/L higher than in the control group,about 100% increase,and the total phosphorus concentration in the crucian carp group was always higher than that in the control group.In addition,the phosphate content in the fish group was higher than in the controls(p <0.05).3.In average,the chlorophyll a concentration in the fish group 10.15 ?g/L was about 57.6% higher than that in the control group,indicating that the crucian carp promoted the growth of phytoplankton(p <0.05).Crucian carp reduced the water transparency,but the light and temperature distribution was similar in both treatments(p> 0.05).4.In average,the concentration of dissolved oxygen in the shading group was 7.90 mg/L,which was similar concentration as in the controls.The transparency was 41.39 cm and pH was 8.41 in the shading group and no significant difference was found between the treatment group and the controls.The concentration of total nitrogen was 5.2 mg/L and which was 1.55 mg/L about 42.5% higher than that in the controls.The ammonia nitrogen was 0.17 mg/L,which was 0.07 mg/L or 70% higher than in the controls and total phosphorus was 0.1 mg/L,which was about 25% high as compared with the controls;the chlorophyll a concentration was 6.9 ?g/L,which was 0.46 ?g/L higher than that in the controls.No significant difference was found of surface and bottom temperatures between the control and the fish group(p>0.05).However,The light intensity was lower in the treatment group than in the controls(p <0.05).Therefore,reducing or removing omnivorous fish,such as crucian carp,in the water body dominated by submerged plants will reduce the total phosphorus,decrease the phytoplankton biomass,and increase the water transparency and improve water quality and alleviate the degree of eutrophication.This study can provide a reference for aquatic meteorology or fish regulation.