A Comparison Of Community Structure Of Macrozoobenthos In Two Different Lakes In Yunnan Province

The plateau lakes play an extremely important role in the water storage and flood discharge,agricultural irrigation,domestic water and aquatic products supply.In recent decades,due to intensive disturbance of human activities,the water quality has been deteriorating,and the ecosystem health has been greatly threatened in these plateau lakes.As an important component of aquatic ecosystem,the tolerance of macrozoobenthos to different environmental factors is significantly different.Moreover,the changes of water environment quality can be reflected by the dynamic and the succession of macrozoobenthos communities.At present,most investigations of macrozoobenthos in plateau lakes focused on the short-term investigation of several taxonomic groups or their community structures.There are only a few studies working on long-term historical evolution.In this study,we investigated the community dynamics of macrozoobenthos in Yangzonghai Lake and Luguhu Lake and the relationship between macrozoobenthos and environmental factors.Firstly,we analyzed the community structure of macrozoobenthos and its influencing factors in the two lakes.Secondly,so as to provide scientific support for monitoring,protection and management of plateau lakes,through comparisons of the macrozoobenthos community structures in the two lakes,we analyzed the main processes and mechanisms that explains how community dynamics and spatial variation of macroinvertebrates were driven by the increasing deterioration of aquatic environment.The main results are as following:1.Community structure of macrozoobenthos and its influencing factors in Yangzonghai Lake were analyzed.20 taxa were recorded in Yangzonghai Lake including 9 oligochaetes,4aquatic insects,and 5 molluscs.In addition,2 taxa of Nematoda and Platyhelminthes were also collected,respectively.Annual mean density and biomass in Yangzonghai Lake were 675±115ind./m~2 and 1.49±0.98 g/m~2,respectively.Density and biomass were dominated by oligochaetes and molluscs,respectively.The dominant species in Yangzonghai Lake were Tubifex tubifex,Limnodrilus hoffmeisteri,Procladius sp.,Physa acuta and Hippeutis umbilicalis.The taxa richness and standing crops of macrozoobenthos varied greatly in different regions of the whole lake.In summary,the taxa richness and standing crops in the northwest of lake was much higher than in the southeast.Water depth and total nitrogen were the main factors affecting the abundance of macrozoobenthos in Yangzonghai Lake.The taxa richness,total standing crops of macrozoobenthos and standing crops of oligochaetes were negatively correlated with water depth and positively correlated with total nitrogen.2.Community structure and its influencing factors of macrozoobenthos in Luguhu Lake were analyzed.27 taxa were recorded in Luguhu Lake including 12 oligochaetes,8 aquatic insects and 4 molluscs.In addition,3 taxa of Nematoda,Arthropoda and Hirudinea were also collected,respectively.Annual mean density and biomass in Luguhu Lake were 1045±538 ind./m~2and 6.58±4.32 g/m~2,respectively.Density and biomass were contributed by chironomid larvae and molluscs,respectively.The dominant species in Luguhu Lake were mostly consisted of Tubifex tubifex,Branchiura sowerbyi,Limnodrilus hoffmeisteri,Polypedilum sp.,Procladius sp.,Hippeutis umbilicalis and Corbicula flumineaumbilicalis.There were significant spatial differences in the taxa richness and standing crops across the whole lake.In summary,the taxa richness and standing crops were higher in the southeast and northeast lake than in other regions.Water depth,transparency and chlorophyll a were the key environmental factors,determining the species distribution and the dynamic of macroinvertebrate community structure.Total standing crops of macrozoobenthos and standing crops of molluscs were negatively correlated with water depth and transparency and positively correlated with chlorophyll a.3.Spatial and temporal dynamics of macrozoobenthos community structure in Yangzonghai and Luguhu Lake were compared.Since 1980s,58 taxa of macrozoobenthos belonging to 5 phyla,7 classes and 18 families were recorded.In five investigations,6 taxa(only Molluscs),19 taxa,20 taxa,16 taxa and 20 taxa(only Molluscs)were recorded,respectively.The numbers of taxa richness increased firstly and then decreased.Compared with 2003-2004,the density and biomass of macrozoobenthos in Yangzonghai Lake decreased by 84.1%and 82.7%respectively.The results of three spatial distribution investigations showed that the number of taxa richness maintained a high value near Tangchi town in the northern lake,Shijiazui in the northwestern lake and Tangeying in the southern lake,while it was lower in the east and the center of the lake.Since 2004,59 taxa of macrozoobenthos belonging to 4 phyla,7 classes and 16families were recorded in Luguhu Lake.In the three investigations,27 taxa,18 taxa(only Mollusca),27 taxa were recorded,respectively.The total number of taxa richness kept an stable trend,but community structure changed greatly.Compared with 2004-2005,the mean density of macrozoobenthos in Luguhu Lake increased by 55.9%and the mean biomass decreased by 45.4%.The spatial distribution pattern of macrozoobenthos in Luguhu Lake was stable.The preverious studies showed that the taxa richness was relatively higher in the east of the southern lake and the east of the northern lake,while it remained at a low level in the western part and the central part of the northern lake.