Experimental Ecological Research On Shellfish-Macroalgae Ecological Restoration And Amplify Carbon Sink In Eutrophic Water

In response to the problem of Eutrophication in coastal waters,a systematic research method of on-site water quality survey—physiological characteristic experiment of shellfish and macroalgae—indoor small volume quantitative experiment-indoor large volume ecological simulation experiment was used to study the physiological characteristics of Crassostrea gigas and Mytilus edulis,Gracilaria lemaneiformis and Gracilaria lichenoides,and the Nutrient absorption and carbon sink changes under different shellfish-macroalgae ratios.Provide reference for ecological restoration of eutrophic seawater.The main conclusions and results of this paper are as follows:(1)The results of bay water quality investigation:According to monitoring,the concentration of DIN in Xipu Bay,Dongshan County,Fujian Province was distributed in 0.648?2.396 mg/L,the DIP was in 0.31?0.496 mg/L,and the concentration of Chl-a was distributed in 2.86?29.30?g/L.In Maluan Bay,Xiamen City,Fujian Province,the DIN distribution was 1.231?5.146 mg/L in July,DIP was 0.136?0.151mg/L,and Chl-a concentration was 4.23?27.83?g/L;in December,DIN was distributed in 0.137?4.252?g/L,DIP was in 0.001?0.381?g/L,and Chl-a concentration was in 0.884?79.15?g/L,most of the stations showed severe eutrophication in July and December.The monitoring results show that the two enclosed bays are in a severe eutrophication state.(2)Physiological characteristics of macroalgae:The absorption rate of Gracilaria lemaneiformis and Gracilaria lichenoides had a good positive correlation with nutrient concentration.The higher the nutrient concentration was,the faster the absorption rate was.Gracilaria lemaneiformis in Xipu Bay,Dongshan County,Fujian Province is more tolerant to high temperature,and has a higher specific growth rate(SGR),of 4.464%to 4.592%at 20-25?.Gracilaria lemaneiformis and Gracilaria lichenoides can grow in salinity between 10 and 30,but their SGR is lower at low salinity.But in low salinity environment such as 10 and 15,Gracilaria lemaneiformis and Gracilaria lichenoides can still absorb nutrients rapidly.(3)Physiological characteristics of shellfish:Crassostrea gigas and Mytilus edulis did not die in large numbers when the concentration of NH₄⁺-N was 9?12mg/L and DO as low as 1?1.5 mg/L,which indicated that they had strong tolerance to high NH₄⁺-N and low DO,and the tolerance of Mytilus edulis was stronger than that of Crassostrea gigas.The average oxygen consumption rate of Crassostrea gigas was0.023±0.0034 mg/(g·h)(wet weight with shell,the same below),and the ammonia excretion rate was 0.0337±0.0003 mg/(g·h);The average oxygen consumption rate of Mytilus edulis was 0.0627±0.0049 mg/(g·h),and the ammonia excretion rate was0.0913±0.0007 mg/(g·h).(4)Indoor small-volume quantitative experiment:Monoculture of Gracilaria lemaneiformis and Gracilaria lichenoides can rapidly reduce nutrients in water,and manifested as a strong sink of CO₂.In the monoculture oyster experimental group,the water DIN,DIP concentration and p CO₂in the water all increased,and the DO concentration and p H decreased.It is manifested as a source of nutrient emissions and carbon sources.Different ratios of large seaweeds and oysters have different absorption effects on nutrients and CO₂.The ratio higher than 3:25 can reduce the nutrients in seawater,and has a carbon sink effect.(5)Large-volume ecological simulation experiments:The concentration of DIN,DIP and p CO₂in the experimental group of Crassostrea gigas monoculture showed an overall upward trend,which was the emission source of nutrients and carbon source.When the ratio of Crassostrea gigas and Gracilaria lemaneiformis was 5:1and 2.5:1,the concentrations of DIN,DIP and p CO₂decreased,while the concentrations of p H and DO increased,indicating that the ratio of oyster and Gracilaria lemaneiformis could effectively reduce the nutrient concentration,and manifested as a carbon sink.(6)The study shows that the higher the proportion of macroalgae in shellfish-macroalgae polyculture system,the faster the consumption rate of nutrients and DIC,and the faster the increase of DO and p H in water.However,high proportion of macroalgae will rapidly consume nutrients and DIC in the water,which will have adverse effects on the growth and Photosynthesis of macroalgae.Therefore,the appropriate ratio of shellfish-macroalgae polyculture should also be adjusted according to the actual eutrophication situation in the sea area.In natural sea areas with heavy or continuous nutrient input,the proportion of large seaweeds can be appropriately increased,which can achieve the purpose of quickly improving the eutrophication environment and increasing carbon sinks;If it is polycultured in light or moderate eutrophication sea areas,the proportion of macroalgae should be reduced appropriately.In conclusion,through on-site water quality survey and indoor experiment,this study provides a suitable ratio of shellfish and macroalgae that can reduce the concentration of nutrients and DIC in water,which can provide a reference for ecological restoration and carbon sink expansion of eutrophic seawater.