A Study Of Plankton Communities And Food Web Structures In Lake Dajiuhu Of Shennongjia Alpine

Dajiuhu wetland,consisting mainly of nine basins,is a rare subtropical alpine in the central China.The Dajiuhu wetland is the source of the Du river,a first-grade tributary of the Han River,and the wetland also serves as one of the important water conservation area of the middle routes of South-to-North Water Diversion Project..The human activities such as ditches digging,holes dredging and bog draining have led to severe degradation of ecological function and the shrinking of lake surface area in Dajiuhu wetland since 1986.After the implementation of‘the Dajiuhu wetland protection and ecological restoration project'from 2005 until present,we conducted a field survey on the lake trophic status,plankton and fish community from November2016 to November 2017to reveal the status quo post the restoration project.We also combined food web studies using stable isotope and lipid biomarker with gut content analyses of the most dominant fish species to elucidate fish carbon source.The main findings are bellow:?1?Trophic Status Indice?TLI?indicates the water quality was light eutrophication in July and September,and wasmesotrophyin May and November.The water eutrophication level decreased along the water flow direction.?2?The dominant phytoplankton species was Scenedesmus quadricauda??-mesosaprobity?in November 2016,Melosira granulata??-mesosaprobity?and Scenedesmus quadricaudain May 2017,Anabaena sp.??-mesosaprobity?and Aphanizomenon??-mesosaprobity?in July and September 2017,while Achnanthes exigua?oligosaprobity?was the dominant species in November 2017.The highest abundance was 18.13⁶31.8×10⁶cells·L^-1 in July,and the highest biomass was1.64¹3.09mg·L^-1 in September.The dominant species were mainly the?or?-mesosaprobity.Chlorophyta was the dominant groupin November 2016,May 2017,and July 2017,Cyanophyta in September 2017 and Pyrroptatain in November 2017.However,diatom was the dominant group during the sampling period according to biomass results.Both of the abundance and biomass decreased along the direction of water flow.?3?The zooplankton dominant species was Synchaeta sp.?oligo-?-mesosaprobity?of in November 2016,Brachionus angularia??-mesosaprobity?in May 2017,Diaphanosoma brachyurum??-mesosaprobity?in July 2017,and Polyarthra vulgaris??-mesosaprobity?in September 2017,and Synchaeta sp.in November 2017.RDA analysis revealed that temperature and Chl-a are important factors determining zooplankton abundance.In addition,small zooplankton was dominant group such as rotifers,indicating high prey pressure.?4?A total of 1 order,1 family,6 genera,6 species of fish were identified during the whole investigation,which were Carassius auratus,Cyprinus carpio specularis,Abbottina rivularis,Psendorasbora parva,Hypophthalmichthys molitrix and Rhodeus sinensis.Carassius auratus was dominant species.?5?Stable isotope technique and fatty acid biomarkers with gut content analyses were used to determine the extent to which main organic carbon sources support Carassius carassius.The diet consisted mainly of phytoplankton,zooplankton and plant debris in the fishes gut content.IsoSource Mixing models showed the organic carbon sources of consumers were mainly derived from periphyton in the D1 and D2 basins,while basal food sources from particulate organic matter?POM?in D5 basins.The content of C18:1n-9 was high in fatty acid content,suggesting that zooplankton was an important food component.Furthermore,the content of C18:2n-6+C18:3n-3 fatty acids were higher than 2.5%which indicated weak terrestrial organic matter contribution to the carbon source of Carassius auratus.Our results showed water quality of Dajiuhu wetland was between mesotrophy and light eutrophication.Carassius auratuscould maintain a high predation pressure on zooplankton in spite of low biomasses of true zooplanktivorous fish,resulting in small rotifers and zooplankton larvae dominateding Dajiuhu wetland.The results indicated removal of Crucian carpas a tools to create a trophic cascade mediating increasing grazing by large-bodied zooplankton on phytoplankton and higher water clarity increase.