Spatiotemporal Distribution Of Benthic Algae Community In Dongting Lake And Its Relationship With Environmental Variables

Benthic algae are the main primary producers of shallow water lakes.They have the characteristics of relatively fixed habitat,wide distribution,short life cycle,sensitive to environmental changes,and quick community recovery after disturbance.They are important indicators for monitoring and evaluating the environmental health of lakes and rivers.Dongting Lake is an important huff and puff regulation and storage Lake in the Yangtze River.With the rapid development of social economy,over exploitation of water resources and over input of nutrients,the water quality and habitat of Dongting Lake ecosystem are deteriorating.Understanding the impact of natural environmental factors and human activities on the water quality of Dongting Lake through benthic algae,and evaluating the current status and existing problems of the Dongting Lake ecosystem could provide feedback information for water ecosystem protection,health evaluation and adaptive management of land use in the Dongting Lake.It is of great significance for achieving a virtuous cycle of the ecosystem in the Dongting Lake.Benthic diatoms were taken as the research object in this study.Benthic algae samples were collected in 29 representative sites in the littoral zone of Dongting Lake.In spring,summer,autumn and winter from October 2017 to August 2018,the physical and chemical indexes of these samples were dertermined,and the benthic algae community structure characteristics,ecological distribution and seasonal succession were studied.Furthermore,the effects of environmental factors on benthic diatoms community composition and the structural characteristics were explored.The aims in this paper were to find suitable diatom index and diatom traits to evaluate the water quality of Dongting Lake and the health and integrity of water ecosystem.The main results were as follows:1.According to the results of water physical and chemical indexes in the whole year,WT,pH,EC values and phosphorus concentration(TP,TDP,SRP)in summer were significantly higher than those in other seasons;the Eh and DO concentration in winter were significantly higher than those in other seasons;the concentrations of Chl a of planktonic algae were significantly lower than those in other seasons(p<0.05).The results of comparative analysis showed that the highest average total phosphorus concentration was in Qingshan Lake area,and the lowest was in Daxi Lake area.Besides,the concentrations of TN and TDN concentration in most urban samples were significantly higher than those in agricultural samples.The benthic algae Chl a concentration in winter was significantly lower than that in the other three seasons.The difference of benthic algae Chl a concentration between the sites in winter was small and Chl a concentration of most sites distributed between 0.5-3 ?g/cm~2.Benthic algae Chl a concentration was positively correlated with T,pH,phosphorus concentration(p<0.01)and negatively correlated with DO concentration(p<0.05).There were 178 species of benthic diatoms in 26 genera in the littoral zone of Dongting Lake.The indicator species in spring were G.parvulum,Melosira varians,Nitzschia dissipata;the indicator species were C.affinis,G.parvulum and N.recens in summer;the indicator species were Cymbella affinis,Navicula recens and Gomphonema parvulumin autumn;the indicator species were N.recens,G.parvulum and Amphora Montana in winter.RDA analysis of dominant species and environmental factors of benthic diatoms showed that Chl a concentration of planktonic was the main environmental factor affecting the distribution of diatoms in Dongting Lake in winter and summer.EC was one of the main environmental factors affecting the distribution of diatom community in Dongting Lake in spring and autumn.During the experiment,there were about 8 genera and four classes of benthic filamentous algae in the littoral zone of Dongting Lake: Chlorophyta,Bacillariophyta,Xanthophyta and Cyanophyta.The dominant genera in spring were Oedogonium and Lyngbya,while in winter were Vaucheria and Oedogonium.2.The effects of high nutrient loading on the community composition,cell size,functional traits of benthic diatoms were evident.The dominant benthic diatom species in environmemt of high phosphorus concentration were more abundant;the high phosphorus concentration was suitable for the growth of species with larger cells,moving and erect diatoms.The environment of low phosphorus concentration was suitable for the growth of prostrate diatoms.The effect of nitrogen loading was that the area with high nitrogen concentration was more suitable for the growth of large cells and prostrate diatoms,and the moving and erect diatoms chose to grow in low nitrogen concentration environment.3.The benthic algae biomass in wet season was significantly higher than that in dry season.There were also obvious differences in benthic diatom community composition in the dry and wet seasons.The dominant species were more abundant in the wet season.Nitrogen was the main environmental factor affecting the composition of diatoms in the dry season,while the dominant species in the wet season were C.tumida and N.recens.Phosphorus was more important in the composition of diatoms in the wet season,while M.varians and C.placendula var.euglypta were absolutely dominant in the dry season.4.The functional traits distribution of benthic diatoms were affected by major environmental factors such as nutrition,temperature and water transparency,the growth of stalked and motile diatoms were mainly in spring;the stalked diatoms were mainly in summer;motile diatoms were dominant in autumn and winter;the prostrate and closely attached diatoms were suitable in the alkaline water environment;the stalked diatoms were in the area with high water transparency.5.In order to evaluate the water quality of Dongting Lake effectively,the correlation between benthic diatom biodiversity index and 18 diatom indexes and environmental factors were analyzed.The results showed that the diatom indexes of IDAP,DES and CEE were suitable for the evaluation of water quality of Dongting Lake.The water quality of the West Dongting Lake area,which mainly uses agricultural land,was better than that of the East Dongting Lake area,which had a high proportion of urban land.6.The health and integrity of water ecosystem in Dongting Lake were evaluated by cell morphology,ecological guild and eco-morphological characteristics of benthic diatoms.The results showed that the low and motile profile guilds were mainly the species with smaller individual morphology,and the high profile guild had larger individual morphology in Dongting Lake.The correlation between eco-morphological characteristics and environmental factors could reflect the changes of environmental factors comprehensively.It was an effective tool to evaluate the water health and integrity of Dongting Lake.The health and integrity of water ecosystem in West Dongting Lake area was higher than that in East Dongting Lake area.