Study On Zooplankton Community In Land Water Ecotone Of Songhua River (Harbin)

The land water ecotone is an important ecological transition zone for energy,material and information exchange between aquatic ecosystems and terrestrial ecosystems.It is an important part of the ecosystem and plays an important role in climate regulation,soil and water conservation and river bank stability.As the primary consumption in the land water ecotone ecosystem,zooplankton can respond quickly to environmental changes and further affect the function of aquatic ecosystems through the food chain,so it is often used for water environment monitoring.In order to explore the influence of Harbin city on the water of Harbin section of Songhua River Basin,four representative sample sites were selected in the main urban area of Harbin,and zooplankton samples were collected during the flat water period（May）,abundant water period（September）and dry water period（October）in 2021,and the samples were identified and counted,and the spatial and temporal characteristics of the water quality factors and zooplankton community and the composition and spatial and temporal dynamics of the dominant zooplankton species in the four sample sites were analyzed by combining 15 water quality factors.The spatial and temporal characteristics of the dominant zooplankton species were analyzed.Pearson correlation matrix,BIO-ENV analysis and redundancy analysis（RDA）were used to investigate the relationship between zooplankton community and water quality factors during the survey period,in order to identify the key factors driving the spatial and temporal dynamics of zooplankton community.The single-factor evaluation method and diversity index evaluation method were used to assess the water quality at the four sample sites to provide reference for the protection of ecological environment and improvement of water ecological quality in the Songhua River basin.The main study results are as follows:（1）The variation range of WT during the investigation was 7.4～25.2°C;the range of p H was 6.52～8.44.The range of DO was 4.09-16.45 mg/L;the SD ranged from 12.5to 29.17 cm.The range of Spc was 0.018-0.042 S/m.ORP ranged from 342.74 to 556.37mv;the variation range of SS was 32.67-394.00 mg/L;the variation range of COD_Mnwas 6.24～13.12 mg/L;BOD₅ranged from 0.50 to 9.65 mg/L;TP ranged from 0.11 to0.74 mg/L;the variation range of TN was 1.16～6.71 mg/L;the range of NO₃-N was0.27～3.57 mg/L;the range of NO₂-N was 0.003～0.019 mg/L;the range of NH₄-N was0.13～2.19 mg/L;the range of Chl-a was 4.22-42.24μg/L.The results of principal component analysis showed that water temperature（WT）,nitrate nitrogen（NO₃-N）,nitrite nitrogen（NO₂-N）,ammonium nitrogen（NH₄-N）,suspended solids（SS）,total nitrogen（TN）and total phosphorus（TP）were the main factor affecting the four sample sites.（2）A total of 46 species of zooplankton（excluding rotifers eggs）were identified,belonging to 3 phyla and 36 genera,of which protozoans were the main components of zooplankton community,including 22 genera and 26 species,accounting for 56.52%of the total species of zooplankton.Followed by rotifers,including 12 genera and 16 species,accounting for 36.96%of the total number of zooplankton;Cladocerans included 1 genus and 2 species,accounting for 4.35%of the total zooplankton species.Copepods included two species,Nauplius and Cyclops vicinus,accounting for 4.35%of the total zooplankton species.The average abundance of zooplankton in the four sample sites was 31320.83ind/L,of which the abundance of protozoans accounted for 94.72%,and the abundance of rotifers accounted for 4.99%.The average biomass of zooplankton was 4.25 mg/L.The biomass of rotifers accounted for the largest proportion of 44.16%,the biomass of protozoans accounted for 34.94%,the biomass of copepods accounted for 13.74%,and the biomass of cladocerans accounted for 7.16%.The species composition,abundance and biomass of zooplankton community showed significant spatiotemporal heterogeneity.A total of 14 dominant species（Y≥0.02）were screened,including 8 protozoans and 6rotifers.There were differences in the number of dominant species in different hydrological periods,and the number of dominant species in the wet season was up to 10.（3）The results of rating the health status of the Songhua River water bodies based on physicochemical parameters during the survey period were consistent on temporal and spatial scales,but the water quality evaluation results of the four sample sites by the diversity index evaluation method showed strong spatial and temporal heterogeneity of the diversity index.The evaluation results based on dissolved oxygen（DO）and permanganate index(COD_Mn)show that the water body health is excellent;the evaluation results based on total phosphorus（TP）show that the water body health is moderately polluted;the evaluation results based on total nitrogen（TN）show that the water body health is heavily polluted;the evaluation results based on five-day biochemical oxygen demand（BOD₅）show that the water body health is lightly polluted.The results of rating the health status of the Songhua River water bodies based on the diversity index evaluation method show that the Pielou uniformity index（J）is consistent in evaluating the water quality status at the spatial and temporal levels,and the Shannon-Wiener diversity index（H’）shows that the water bodies are lightly polluted during the flat water period and moderately polluted during the abundant and dry water periods;S1 and S4 are moderately polluted Margalef richness index（D）evaluation of water quality status results show that the three hydrological periods are medium-fouling water bodies;except for S4water quality status for heavy pollution,the rest of the sample sites are medium-fouling type.（4）The results of redundancy analysis（RDA）showed that SD,COD_Mn,NO₃-N,NO₂-N and WT were the main water quality factors affecting the spatio-temporal dynamics of zooplankton in four sample sites;according to Pearson correlation analysis,there was a certain correlation between zooplankton abundance and environmental factors.Margalef richness index（D）and Shannon Wiener diversity index（H’）showed a significant positive correlation with Spc,and Spc showed a significant positive correlation and a significant negative correlation with TP and total zooplankton abundance,respectively.Spc showed a significant positive correlation with zooplankton biomass and species number.BIO-ENV analysis showed that the optimal water quality factors affecting zooplankton community structure included SD,NO₃-N,ORP,Chl-a,TP and COD_Mn.（5）Due to the influence of Harbin city,the pollution level of sample site S2 is higher than that of sample site S1,which is reflected in the increase of nitrogen and phosphorus nutrient content and the decrease of dissolved oxygen content;the wetland ecosystem has a purifying effect on the water quality of sample site S3;the p H of sample site S4 tends to be weakly alkaline due to the discharge of sewage and domestic water from Harbin city.The zooplankton abundance at sample site S2 in the city increased compared with S1;the wetland ecosystem increased the zooplankton community diversity at sample site S3.