| Yanhe River is one of the important tributaries of the Yellow River,and it plays an important role in the maintenance of biodiversity and ecological conservation in the middle reaches of the Yellow River.As an important component of aquatic biological resources,phytoplankton respond rapidly to changes in the water environment and play an important role in maintaining the stability and integrity of the aquatic ecosystem.Therefore,in this study,a systematic aquatic ecological survey of the Yanhe River Basin was conducted in spring(April-May)and autumn(SeptemberOctober)of 2021,using phytoplankton as indicator organisms.A total of 33 sampling sections were deployed for sample collection in the main stream,five first-order tributaries and impounded water bodies(reservoir and silt dam water bodies)of the Yanhe River Basin to investigate the distribution characteristics and influencing factors of the phytoplankton community,assess the comprehensive quality of the water environment of the basin based on the phytoplankton characterization index,and then establish the phytoplankton biological integrity index to evaluate the water ecological health of the Yanhe River Basin.The research results provide basic data and scientific basis for the rational use of water resources and water ecology protection in the Yanhe River Basin.The main results of this study are as follows:(1)A total of 253 species of phytoplankton in 7 families and 91 genera were detected in the spring and autumn surveys,among which diatoms and green algae prevailed in the spring(168 species)and diatoms and cyanobacteria in the autumn(179 species).The average values of phytoplankton density and biomass in spring and autumn were 316.07×104 cells/L,6.41 mg/L and 69.56×104 cells/L,1.59 mg/L.On the temporal scale,the abundance of phytoplankton in spring was higher than that in autumn;on the spatial scale,the abundance of phytoplankton in the middle and lower reaches of the main stream was higher than that in the upper reaches,and the abundance of phytoplankton in the impoundment formed by damming was higher than that in the upper reaches.The phytoplankton abundance in the impounded water bodies remained at a high level and was significantly higher than that in the main stream and tributary waters in autumn.The phytoplankton diversity was greater in spring than in autumn,and the phytoplankton diversity in the main stream and tributary water bodies was greater than that in the impounded water bodies.The results of redundancy analysis showed that:flow velocity,dissolved oxygen,nitrite nitrogen and water depth were the key factors affecting the phytoplankton community structure in spring;nitrate nitrogen,water depth and dissolved oxygen were the key factors affecting the phytoplankton community structure in autumn.(2)The phytoplankton in the Yanhe River Basin were divided into 26 functional groups,and the common dominant functional groups in spring were C,D,LO,MP,TB and W1,and the common dominant functional groups in autumn were C,D,LO and MP,and the functional groups D and MP were dominant in both spring and autumn in the Yanhe River Basin.The Qr index can combine phytoplankton with its habitat habitat,thus effectively reflecting the quality of water environment.The biological evaluation results of water quality based on Qr index and Shannon diversity index show that the water quality of Yanhe River basin in spring is better than that in autumn,and the water quality of the basin is in light to moderate pollution.Comparing the evaluation results of the two indices,it was found that the evaluation results of Qr index were closer to the actual situation of the water body than those of Shannon diversity index.The results of redundancy analysis showed that the distribution of phytoplankton functional groups in spring was influenced by flow rate and nitrite nitrogen,and dissolved oxygen and water depth influenced the spatial and temporal distribution of phytoplankton functional groups in autumn.(3)P-IBI was constructed based on seven core parameters:total number of phytoplankton species,relative diatom abundance,diatom genus index,diatom quotient,percentage of dominant functional groups,Shannon diversity index and total phytoplankton biomass.The percentage of sections with "subhealthy and above" status was 94%and 93.4%,respectively.The ecological health of main stream and tributary water bodies is better than that of impounded water bodies,and the ecological health of tributary water bodies is better than that of main stream,and the ecological health of main stream shows a decreasing trend from upstream to downstream. |
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