Aquatic Biodiversity Assessment And Environmental Impact In Hongan Section Of The Daoshui River

As one of the important tributaries in the middle reaches of the Yangtze River,the Daoshui River is the mother river of the Hong’an County with vita function of water source.It also serves local agricultural cultivation and industrial porduction.However,these human activities in turn cause strong disturbances to the river ecosystem.That is,water resources,water environment and ecosystem diversity are threatened.In this study,we systematically investigated the current status of aquatic organisms and water environment of the Daoshui River Basin in the Hong’an section.We explored the spatial and temporal differences of aquatic community structure,as well as the mechanisms responding to environmental changes.We were committed to providing theoretical basis for the comprehensive management of this mother river.Main findings were as follows:1.The water temperature of the Daoshui River Basin in the Hong’an Section annually ranged from 3.3℃ to 37.0℃,while the ranges of p H,dissolved oxygen,total nitrogen content,total phosphorus,electrical conductivity,total dissolved solids,salinity,REDOX potential,ammonia nitrogen,permanganate index,and chemical oxygen demand were6.5～9.59,1.03 mg/L～11.92 mg/L,0.11 mg/L～11.96 mg/L,0.04 mg/L～1.14 mg/L,81.5 ms/cm～550.2 ms/cm,73.1 mg/L～557 mg/L,0 mg/L～0.42 mg/L,-3.2 m V～236.2m V,0.00 mg/L ～ 8.02 mg/L,0.16 mg/L ～ 8.18 mg/L,5.00 mg/L ～ 36.00 mg/L,respectively.According to the national standard "Surface Water Environmental Quality Standard"(GB 3838-2002),the water quality were mostly class Ⅰ to Ⅲ,which meets the target of water quality.2.We detected a total of 303 species of phytoplankton,belonging to 8 phyla,11 classes,23 orders,40 families and 89 genera.The majorities were diatoma(37%)and Chlorophyta(30%).Among the 17 dominant species detected,the density of cyanobacteria was the largest,while the biomass of Diatoma was the largest.The variation trend of abundance ranked with the order as autumn > summer > spring > winter,of which the species composition and distribution were significantly different.A total of188 zooplankton species were detected,belonging to 18 orders,56 families,88 genera,The majorities were rotifers(52%)and protozoa(36%).Among the 17 dominant species detected,the density of protozoa was the largest,while the biomass of copepods was the largest.The variation trend of abundance was similar to that of phytoplankton,with significant spatial and temporal differences in composition and distribution.The results of water quality evaluation based on the plankton diversity index were mostly moderate to good.We detected a total of 82 species of zoobenthos,belonging to 8 classes,13 orders,31 families,50 genera.The species composition was mainly Arthropoda(58%).The arthropoda had the highest density,while the Mollusca had the largest biomass.And the species composition and distribution were significantly different.3.A total of 44 fish species were identified in the Daoshui River Basin in the Hong’an Section,belonging to 3 orders,9 families and 38 genera.The main species composition was small cypriniidae,accounting for 71% of the total species.Fish catches were significantly higher in autumn than in summer,and higher in main stream than in tributaries.The dominant species in summer were Abbottina rivularis,Rhodeus sinensis and Carassius auratus,while the dominant species in autumn was Rhodeus sinensis only.There were two dominant species in summer and three in autumn in the main stream,but only one in both summer and autumn in tributaries.4.A total of 35 aquatic higher plant species were detected,belonging to 2 phyla,3classes,21 orders,23 families,and 30 genera.There were 10 emergent species,2submerged species,4 floating leaf species,1 floating species,18 associated species,and 4invasive species.The overall species richness was relatively high,while that of main stream was significantly higher than that of tributaries.The species genetic relationships were distant with obvious differences.5.There was a significant correlation between phytoplankton community structure and water total solid dissolved matter,as well as permanganate index,chemical oxygen demand,water temperature,and salinity.The zooplankton community structure was significantly correlated with ammonia nitrogen,as well as permanganate index,chemical oxygen demand,water temperature and salinity.The community structure of zoobenthos was significantly correlated with salinity,as well as oxidation-reduction potential,total nitrogen,dissolved oxygen,total phosphorus,orthophosphorus and ammonia nitrogen in water.In conclusion,the water quality of the Daoshui River Basin in the Hong’an Section was basically Ⅰ to Ⅲ class,namely medium state.The content of nitrogen and phosphorus was high.Though the aquatic biodiversity was improved compared with previous years,but still at a poor level.Environmental changes significantly affected the community structure of plankton and zoobenthos.The plankton density was significantly correlated with water temperature and chemical oxygen demand,while that of zoobenthos was significantly correlated with total nitrogen content,total phosphorus and some other factors.