| The sea area of Xiangyun Bay is the area where artificial reefs were put in earlier in Hebei Province.Tangshan Xiangyun Bay Marine Ranching has invested a total of 140 million yuan since 2005,focusing on the restoration of marine ecological environment and marine ranching industrialization.In 2017,Tangshan Marine Ranching Industrial The Co.,Ltd.began to plan to reef in the 0.57 km2 sea area,and the artificial reef was placed in early 2018.In order to understand the restoration of marine ranches,from August 2019 to June 2020,a survey of the 14 km2 area of Xiangyun Bay was conducted to understand the water quality and biological changes of the marine ranches,and the principal component analysis method was used to evaluate the environmental changes of the marine ranches,Concluded as follow:(1)The pH,salinity,and temperature within and outside the reef fluctuate slightly,with a pH of about 8 and a salinity of about 30.The temperature of the upper and lower layers does not exceed 2℃.The average transparency within the reef varies from 0.53 to 1.4 m.The concentration of dissolved oxygen in the reef area was higher than that in the control area in August,April,and June,and the range of dissolved oxygen in the reef was 8.00～8.71 mg/L.Compared with the same period of the background survey,the COD concentration in the reef area was higher than that in the background survey,with an average concentration of 1.24 mg/L.The DIN content of inorganic nitrogen in the reef area was lower than that in the background survey,and the concentration range was 0.48～0.67.The content of active phosphate does not change much inside and outside the reef,with an average value of 0.01 mg/L.The overall quality of seawater is at the potential eutrophication level of medium phosphorus restriction.(2)The content of chlorophyll a was the highest in August,followed by June,and the lowest in November.The content of chlorophyll a changed the most in August,with the surface content ranging from 4.95 to 13.44 mg/m3,and the lower chlorophyll a content ranging from 7.23 to 11.33 mg/m3.The overall chlorophyll a in the sea area showed a tendency that the upper layer content was higher than the lower layer.Primary productivity in the reef area is generally higher than that in the control area,5-10 times that of the control area.(3)The species of phytoplankton in the reef area are mainly diatoms.After artificial reefs are put into use,the density and biomass of phytoplankton increase.In August,the overall phytoplankton density in the reef was the highest,with an average of 131.11 ×104 ind./m3,which was 2.5 times that of the control area.The overall phytoplankton density in the reef area was higher than that in the control area.The phytoplankton diversity index in the reef area varies from 3.54 to 4.44,and the evenness index varies from 0.56 to 0.79.(4)The species of zooplankton in the reef area are mainly plankton larvae and arthropod species.The species,density,biomass,etc.of zooplankton have all increased compared with before the reefs were cast,and during the same period,the marine pasture area was higher than the control area.During the survey period,the biomass was the highest in June,with an average of 1419.51 mg/m3,and the biomass of zooplankton in November was the lowest 0.16 mg/m3.The Shannon-Wiener diversity index(H’)of zooplankton in the reef area was the highest in August,with a range of 1.37～3.61;the Pielou evenness index(J’)in the artificial reef area showed the highest in November The lowest change trend in April,the change range is 0.25～0.70.(5)The benthic animals in the reef area are mainly Mollusca and Annelid.A total of 44 benthic species have been found.Compared with the control area,the biomass of benthic animals in the artificial reef area is relatively high.The change level of benthic biomass in the reef area was 1.05～56.09 g/m2,the change range of diversity index was 0.41～4.34,and the change range of uniformity was 0.18～0.85,which was higher than the control area during the same period.(6)The types of fishery resources in the reef area are mainly chordates and arthropods.The types and biomass of swimming organisms have increased.A total of 41 biological species have been found,such as Japanese snails,Rhododendron spp.Other economic species have become the main dominant species of marine ranches.The swimming animal diversity in the marine pasture varied from 1.74 to 3.77,and the uniformity varied from 0.49 to 0.94.The swimming animal species in the artificial reef area and the control area were generally at a moderately similar level.(7)Analyze the three principal components of ocean pastures by principal component analysis.The first principal component has an eigenvalue of 4.354,accounting for 48.383%of the total eigenvalues,and the second principal component’s eigenvalue is 1.955,accounting for features 21.728%of the total value,the cumulative contribution rate reached 70.111%,the eigenvalue of the third principal component was 1.605,accounting for 21.728%of the total eigenvalue,and the cumulative contribution rate reached 87.939%.The principal component factor scores were lower than the control area as a whole,and the comprehensive scores were 0.66,0.73,0.67,and 0.62,respectively. |
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