| Marine ranching is the creation of a fishing ground environment suitable for the reproduction,habitat and growth of aquatic organisms through engineering means,which has the role of restoring biological habitats and conserving biological resources.This paper investigates the ecological environment before the construction,follow-up survey and completion of the Yangtze River Estuary Marine Ranch Demonstration Zone(hereinafter referred to as the"Yangtze River Estuary Marine Ranch Demonstration Zone"),and evaluates the ecological enhancement effect of the Yangtze River Estuary Marine Ranch on ecology,with a view to laying a foundation for the subsequent quantification of the ecosystem of the marine ranch:(1)Evaluation of water quality effectIn 2020,the water environmental quality chemical oxygen demand(COD)of each station in Yangtze Estuary Marine Pasture Demonstration area was similar to that of the previous two years,basically meeting the class Ⅰ water quality standard.The concentration of DIN in the Marine pasture demonstration area ranged from 0.129 to0.336 mg.L-1,and the single factor quality index P_iof inorganic nitrogen ranged from0.645 to 1.678.Inorganic nitrogen was always at a relatively low level.Meet the requirements of class Ⅱ seawater specification.Overall,the water quality standard of Yangtze Estuary Marine Pasture demonstration area is basically the same as that of the previous two years.According to the pollution degree classification of the comprehensive quality index,the water quality of about 80%of the stations in the Yangtze Estuary Marine Pasture Demonstration Zone is in the state of light pollution,and 20%of the stations are in the state of pollution.Compared with the water pollution situation in 2018,the water quality has greatly improved.In 2020,the nitrogen phosphorus atomic ratio(N/P)of the Yangtze Estuary Marine ranching demonstration area was between 6.23 and 12.13,which was similar to that in2018,while the N/P in 2019 was significantly higher than that in 2018 and 2020,and the active phosphate content in 2019 was significantly lower,which may be due to the fact that the artificial reef was in the construction period at that time.Based on the content of inorganic nitrogen and active phosphate,active phosphate is the limiting factor of eutrophication in changjiangkou region from 2018 to 2020.In 2020,the eutrophication index of water body is between 1.37～3.35,and the eutrophication index of all stations is greater than 1,indicating that there is a large risk of eutrophication in this area.Looking at the change of N/P in 2019,it is likely that the engineering construction in 2019 will lead to the increase of active phosphate in the water area.The construction of artificial reefs will reduce the risk of water eutrophication to a certain extent.However,after the completion of the project,this continuous project may bring some adverse effects in the later stage,so it is necessary to maintain continuous monitoring.(2)Effect evaluation of primary productivityIn 2020,the monitoring and investigation results of the sea area of the Yangtze River Estuary Marine ranching demonstration area show that the concentration of chlorophyll a at 70%of the stations is above 5.00 mg/L,and only the concentration of chlorophyll a at D2 and D8 stations in the north of the tidal flat is relatively low.Compared with 2018 and 2019,the chlorophyll a content of each site of Marine ranching in 2020 is higher,and the chlorophyll a concentration in artificial reef area and its downstream area is significantly higher.From the perspective of spatial distribution,there are obvious differences in the distribution of chlorophyll a from 2018 to 2020.In2020,it shows the distribution law of high in the South and low in the north.The chlorophyll a in fish reef beach area and downstream area is much higher than that in upstream area.The upwelling generated in the artificial reef area of the Yangtze River Estuary marine ranch demonstration area makes the upper and lower water bodies in the area mix,and the lower nutrients float to the upper water body,which effectively promotes the primary productivity of the water body.(3)Evaluation of aquatic biological effectsThe aquatic organisms in the Yangtze River Estuary were evaluated unilaterally from the aspects of biological composition,biological density and biodiversity.In 2020,a total of 83 species of 5 phyla of phytoplankton were identified,including 53 species of diatom,accounting for 63.85%of the total species;The second is 10 species of Chlorophyta,10 species of dinoflagellate,accounting for 12.05%of the total species.The rest are 8 species of Cyanophyta and 2 species of golden algae.Compared with2018 and 2019,in 2020,the number of phytoplankton communities in the Yangtze Estuary Marine ranching demonstration area and adjacent waters was the largest,with a basic increase of about 20 species over the previous two years.Diatom was the main species,and other phyla were secondary.The overall biological density of phytoplankton in 2020 is slightly higher than that in 2018.The most significant increase is still YJ station and its nearby D1 station,which is consistent with the survey results in 2019.The phytoplankton density of YJ station has increased by 43.29%compared with 2018,and that of D1 station near the reef has increased by 181.54%compared with 2018.There is little change among other stations.This shows that the Yangtze River Estuary Marine ranching demonstration area has a significant increase in primary productivity in local sea areas,and has an obvious biological effect on the improvement of primary productivity in YJ station represented by fish reef area and D1 station near fish reef area.In August 2020,the voyage survey identified 9 categories and 50 species of zooplankton.Among crustaceans,copepods are dominant,and the overall biomass of zooplankton has increased to a certain extent compared with the previous two years.The most significant increase is the artificial reef YJ station and nearby D1 and D3stations.The biomass of zooplankton at YJ station has increased by 84.13%compared with the background,which is a typical significant increase;D1 station near the reef increased by 41.09%compared with the background,while D3 station increased by20.17%.The range of zooplankton biodiversity index in 2020 is 1.013～1.277,with an average of 1.135;Among them,YJ station has the highest biodiversity,followed by D3station and D1 station,and the lowest value appears in D8 station.The biodiversity difference of other stations is small.The biodiversity of zooplankton at each station is relatively uniform,and the biodiversity of surrounding waters is significantly better than that investigated in the previous two years,It shows that the construction of artificial reef in Marine ranching has a certain positive effect on the secondary productivity of the surrounding waters.In 2020,the species,biomass and biodiversity of benthos in the artificial reef area of the marine ranch demonstration area will increase significantly.In 2020,52 species of benthos in 6 categories were monitored in the fish reef beach area,8 species more than that in 2019,with an increase rate of 18.2%,23 species more than that in 2018,with an increase rate of 79.3%.After the completion of fish reef construction,the larvae of fish,shrimp and crab have increased significantly,indicating that the beach marine ranching in the Changjiang Estuary has played the effect of biological species agglomeration and settlement.In 2020,the benthic biomass(mean 694.54 g/m~2)in the artificial reef area of marine ranch was significantly higher than that in other areas,which was 3 times that of the beach near the reef area and 20 times that of the peripheral waters,reflecting that the artificial reef of beach marine ranch has a good conservation effect on benthos,but also showing that the peripheral radiation effect of marine ranch is still limited.Each survey station in the fish reef area and its adjacent beach area showed a significant increasing trend of biomass.In 2020,the average biomass increased to 254.33g/m~2,218.77%higher than that in 2019 and 290.06%higher than the background in 2018.The average biodiversity index increased from 0.6429 in 2018to 0.75634 in 2019,and finally increased to 2.216 in 2020,3.45 times that of the background period.Compared with the peripheral waters outside the reef area,the benthic species,biomass and biodiversity show a relatively stable or slightly increased state.In 2020,a total of 20 species of swimming organisms were identified in the trawl,gill net and cage survey catches in the marine ranch demonstration area,which was1.33 times that of 2019 and 2.86 times that of 2018,including 11 species of fish and 2species of crustaceans.On the whole,the total biomass of catch also increased slightly compared with the previous two years.The emergence of adult Coilia was first monitored in 2020,and it has advantages in quantity,indicating that the Yangtze River Estuary Marine ranching demonstration area provides a good habitat for the restoration of Coilia resources.According to the bottom trawl survey in the peripheral waters of the marine ranch,there were 12 kinds of catch in 2020,2 more than 2019 and 5 more than 2018.The number of species showed a continuous growth trend,and the total catch weight was 1.8 times that of the background survey in 2018.According to the cage net survey in the artificial reef area,a total of 12 species of organisms were monitored in2020,four more than that in 2019.The main species increased by Macrobrachium nipponense and long snake,and the total catch weight was higher than that in 2019.The gill net survey in the artificial reef area shows that there are two new species of fish in2020 than in 2019.The species investigated in the two years are basically similar.The total biomass in 2020 is 1.4 times that in 2019,and the dominant species captured are larger individuals.The biodiversity index results show that the species diversity index,richness index and evenness index of the summer survey in 2020 are better than those in 2019. |
PDF Full Text Request