Study On The Community Structure Characteristics Of Aquatic Organisms In The Ganjiang River System

The scientific assessment of aquatic community status is an important measure to improve freshwater ecological protection,essentially significant to water resources protection and water environment governance.Fish,benthic macroinvertebrate and phytoplankton,widely distributed in freshwater ecosystems,were important groups of freshwater organisms,and bioindicators in environmental monitoring.Based on fish,benthic macroinvertebrate and phytoplankton survey data collected in the Ganjiang River System from 2016-2017,the species composition,biodiversity and community structure were analyzed.Indices of biotic integrity（IBIs）were applied to evaluate the health status of the aquatic ecosystem.And the following results were obtained:（1）In the Ganjiang River System,a total of 159 fish species were identified from27 sampling sites,belonging to nine orders,24 families and 87 genera.Among these,Acrossocheilus parallens,Saurogobio dabryi and Squalidus argentatus were the dominant species.229 benthic macroinvertebrate species belonging to five phyla,10classes,25 orders and 81 families were recorded.Among these,Limnodrilus hoffmeisteri and Corbicula fluminea were the dominant species.A total of 185phytoplankton species belonging to eight phyla were recorded.Among these,Navicula simplex,Ankistrodesmus angustus,Crucigenia apiculata and Cyclotella meneghiniana were the dominant species.（2）The seasonal fluctuation of species composition of the three groups was different.Phytoplankton species composition and community structure has significant seasonal fluctuations（P<0.05）,while fish（P>0.05）and benthic macroinvertebrate（P>0.05）were basically stable.The spatial distribution was large different in fish community structure,followed by benthic macroinvertebrate,while relatively small in phytoplankton.The seasonal difference of phytoplankton community structure was large,followed by benthic macroinvertebrate,while fish was relatively small.（3）The species diversity of the three groups had strong spatial heterogeneity,and the spatial change trend was different.Fish’s Shannon-Wiener diversity index were0.49-3.26;Simpson index were 0.24-0.93;Pielou’s species evenness index were0.26-0.90;and Margalef index were 1.29-7.05.Overall,Shannon-Wiener index and Margalef index were relatively high,while Simpson index and Pielou index were general;There were areas with high Margalef index in the upper,middle and lower reaches,while other indexes in the lower reaches were significantly higher than those in the middle and upper reaches.Shannon-Wiener index of benthic macroinvertebrate was 0-2.28,and higher areas mainly occurred in tributaries;Simpson index was0-0.85,and the upstream tributaries and midstream tributaries were relatively high;Pielou index was 0-0.91,higher in upstream tributaries and significantly higher than in other regions;Margalef index was 0-4.09,and the tributary was significantly higher than the mainstream.Shannon-Wiener index of phytoplankton was 1.52-2.80,and the downstream was slightly higher than the middle and upstream,but the difference was not obvious;Simpson index was 0.61-0.92,and the spatial difference was not obvious;Pielou index was 0.64-0.93,the middle and lower reaches of the mainstream and some tributaries were slightly higher than those in other regions;Margalef index was0.44-1.83,only the upstream tributaries and downstream estuaries were relatively high.（4）There were some differences in environmental factors affecting the distribution of the three groups.The main environmental factors affecting the fish community structure were elevation（m.a.s.l.）,NH₃-N and DO;those affecting benthic macroinvertebrates were elevation,p H,Cond and DO;and those affecting phytoplankton were WT,DO,BOD and TP.（5）The annual average ecosystem health assessment results obtained for the Ganjiang River System based on the F-IBI,B-IBI and P-IBI indicated good,fair and healthy conditions,respectively.Ecosystem health assessments performed based on different biological groups exhibited significant differences（P<0.05）.（6）The F-IBI,B-IBI and P-IBI developed in this study can serve as tools for aquatic ecosystem health assessments and resource management in the Ganjiang River System.Fish and benthic macroinvertebrates were suitable for annual monitoring,while the P-IBI was more effective in real-time monitoring or continuous monitoring.