| Copper seine net culture is an emerging aquaculture form,this form uses a new type farming facility which uses copper alloy materials as nets and steel pipe as piles,the area surrounded by the copper seine net can reach tens of thousands of square meters.In order to assess the impact that using this facility to culture large yellow croaker,we select a large yellow croaker farm in Dachen island as the research object,Dachen island locates in Taizhou city,Zhejiang province,and it's in the offshore area.According to a fish farming cycle of the large yellow croaker?April to December?,10voyages were conducted during the spring tide period to collect water samples and sediment samples from the aquaculture area in February,June,August,October 2017,May,October,December 2018,June,October,December 2019.We collected samples from four areas,including the central area of the fish fence,the peripheral area of the fish fence,the peripheral area of the small cage,the control area?350-700 meters from the breeding facility?.We analysis and evaluates the content change,regional distribution,pollution level of the copper,zinc,inorganic nitrogen?DIN?,active phosphate(PO43-)in the seawater and the copper,zinc,organic carbon,sulfide in the sediment,and the Nemerow index is used to comprehensively evaluate the quality of the water samples and sediment samples in the surveyed sea area.IMTA is the abbreviation of integrated multi-trophic aquaculture,this mode advocates culturing different trophic levels of organisms in the same system to enhance the utilization of aquaculture waste.Therefore,integrated aquaculture is a more environmentally friendly aquaculture mode than monoculture.Due to long-term wind and waves in Dachen Island,Large yellow croakers have a higher energy consumption.Therefore,we intend to cultivate some Myltilus coruscus near the fish fence to reduce the seawater velocity and reduce the energy consumption of fish,this study conducted an experiment that making Myltilus coruscus and Gracilaria lemaneiformis culture in the same system under laboratory condition,and we choose a better ratio of shell and algae according to the water quality and the growth rate of Gracilaria lemaneiformis,the main research results are as follows:?1?During the survey period,the copper content in the seawater ranges from 0.22?9.9?g/L,with a total average value of 3.2±2.4?g/L.The copper contents in the seawater at each station meet with the standard of second class of seawater quality for fisheries in China,the annual average of copper content in the seawater is 5.9±2.0?g/L in 2017,1.0±0.4?g/L in 2018,1.5±0.9?g/L in 2019,and the copper content in the seawater in the first year is significantly higher than that in the next two years,it means that the copper alloy mesh releases more copper into the seawater in the initial stage,the release rate decreases in the later stage.The zinc content in the seawater during the survey period ranged from 0 to 33.7?g/L,with a total average value of 5.9±3.4?g/L.The zinc contents in seawater at each station meet with the standard of second class of seawater quality for fisheries in China,the annual average of zinc content in the seawater is 6.1±2.9?g/L in 2017,5.7±4.3?g/L in 2018,8.4±7.7?g/L in 2019.The content of inorganic nitrogen in the central area of the fish fence during the non-cultivation period is 0.199mg/L,which meets the standard of first class of seawater quality for fisheries in China.The content of the central area of the fish fence during the cultivation period ranges from 0.233 to 0.989mg/L,with an average value of0.503±0.253mg/L,the inorganic nitrogen contents of the seawater during the cultivation period all exceed the standard of second class of seawater quality for fisheries in China,and half of the voyage surveys exceed the standard of fourth class of seawater quality.The contents of the active phosphate in the central area of the fish fence during the non-cultivation period is 0.03mg/L,which meets the standard of second class of the seawater quality for fisheries in China.The content of active phosphate in the central area of the fish fence during the cultivation period is 0.009?0.104mg/L,and the average content is 0.054±0.033mg/kg,more than half of the voyage surveys exceed the standard of fourth class of seawater quality.The evaluation results of Nemerow index indicate that the comprehensive quality of seawater during the non-cultivation period meet with Class I?clean?or Class II?relatively clean?status,the comprehensive quality of seawater in the central area of the fish fence is below the Class III?light pollution?status in most cases,and the control area can reach Class I?clean?or Class II?relatively clean?status in most cases.?2?The copper contents in the sediments in different regions have no significant difference?P>0.05?,the copper contents in the sediments range from 15.3 to 35.5mg/kg,the copper contents in the sediments all mostly meet with the standard of first class of marine sediment quality for fisheries in China except for one site in October2019.The annual average copper content of the sediments is 25.2±4.7mg/kg in 2017,28.3±3.0mg/kg in 2018,31.9±2.3mg/kg in 2019,and the sediment content in the sediments tends to accumulate slightly between the years;the zinc contents in the sediments in different regions have no significant difference?P>0.05?,the zinc contents in the sediments range from 73.2?136.6mg/kg,these datas all meet with the standard of first class of sediment quality for fisheries in China,with a total average of97.5±14.6mg/kg.The annual average of zinc content in the sediments is 100.4±17.9mg/kg in 2017,96.5±13.5mg/kg in 2018,94.5±9.4mg/kg in 2019.The zinc content in the sediments has no obvious cumulative trend between years.The organic carbon contents in the sediments range from 0.14 to 2.76%,all the organic carbon contents in the sediments meet with the standard of the first class of marine sediment quality for fisheries in China except for a station in October 2018 and a station in December 2019.The organic carbon contents in the sediments in different regions have no significant difference?P>0.05?.The total average organic carbon mass of sediments in the central area of the fence is the largest,which is 1.34±0.68%.The total average value of other regions ranges from 0.83 to 1.06%;The annual average of the organic carbon content in the sediments is 0.76±0.34%in 2017,1.10±0.57%in2018,1.20±0.40%in 2019.During the investigation,the sulfide contents in the sediments range from 0 to 260 mg/kg,these datas all meet with the standard of first class of marine sediment quality for fisheries in China.The sulfide content in the sediment in the center area of the fish fence is significantly higher than that of the other three areas?P<0.05?,the total average content of the sulfide in the central area of the fish fence is 60.8±92.1 mg/kg,and the total average contents in the other three regions range from 4.1 to 12.2 mg/kg.The evaluation results of Nemerow index indicate that the comprehensive quality of sediment all meet with Class I?clean?or Class II?relatively clean?status except for one station in October 2018.?3?The polyculture experiment of culturing Myltilus coruscus and Gracilariopsis lemaneiformis in the same system under indoor conditions shows that Gracilariopsis lemaneiformis can absorb the nutrients such as nitrogen and phosphorus excreted by the Myltilus coruscus well,and the Gracilariopsis lemaneiformis significantly improves the water environment.When the wet weight ratio of Myltilus coruscus and Gracilariopsis lemaneiformis is 2.6:1,the growth of the algae and the improvement effect of water quality can reach a good balance. |
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