Spatiotemporal Distribution Of Epipelic Algae And Its Impact Factors In Lake Taihu

Epipelic algae as a primary producer is very important in the ecosystem of freshwater lakes. In this paper, Taihu Lake was used as the study area. The spatial distribution of the epipelic algae in Taihu Lake was sampled four times in June and October in 2015 and April and August in 2016, combined with the indoor analysis. Liquid chromatography, elemental analyzer and conventional physical and chemical methods were used to analyze biomass, community composition of epipelic algae, and physical and chemical indicators of water and sediments. The temporal and spatial distribution of the epipelic algae in Taihu Lake and its influencing factors were explored. The results provide a theoretical basis for further understanding the effect of the epipelic algae on the release of endogenous phosphorus. The main results are as follows:1.The biomass and community composition of epipelic algae in Taihu Lake have significant temporal and spatial variation rule. The heterogeneity of the epipelic algae biomass ( characterized by chlorophyll a ) in Taihu Lake is obvious, the minimum is 0.07?g/g org, and the maximum is 2.38?g/g org. The biomass of epipelic algae is higher in the northwestern part of Taihu Lake and east of Taihu Lake, followed by the Gonghu Bay, Meiliang Bay and the eastern part of the lake, which is lower in the southwest lake. The biomass of epipelic algae in Taihu Lake is obviously changed with time, it is the lowest in June, but there are differences in the biomass of epipelic algae in different lake areas.In the eastern part of Taihu Lake, biomass in April is generally higher than in August; In Meiliang Bay and the northwest part of Taihu Lake,biomass in August is generally higher than in April. The composition of the epipelic algae community in Taihu Lake is different in different lake areas, but it has obvious time variation. In April, the epipelic algae in Taihu Lake was generally dominated by cyanophyta ( zeaxanthin content ), followed by chlorophyta ( chlorophyll b content), and bacillariophyta ( fucoidan content)was relatively few. In August, Taihu Lake with epipelic algae generally dominated by bacillariophyta, followed by cyanophyta and chlorophyta. The contents of the components in the epipelic algae community decreased significantly in the vertical direction. The composition of the epipelic algae community was significantly different in the surface sediments, but with the increase of the depth, the community composition difference gradually narrowed and gradually same at a certain depth In agreement.2.The spatial distribution of water and sediment physical and chemical factors in Taihu Lake is obvious. The content of nitrogen and phosphorus in water also has obvious spatial changes. The contents of nitrogen and phosphorus in Zhushan Bay, Meishan Bay and western part of Taihu Lake are significantly higher than other lake area. The spatial heterogeneity of nitrogen and phosphorus and total organic carbon ( TOC ) in surface sediments of Taihu Lake was obvious, and the distribution characteristics of total phosphorus in surface sediments were similar to those in water. the distribution characteristics of TN and TOC in surface sediments were similar to the biomass of epipelic algae, which is higher in the northwestern part of Taihu Lake ( including Zhu Shan Wan ), Meiliang Bay and East Lake(including East Taihu Lake and Xukou Bay) and lower in the middle and the southwestern part of Taihu Lake. The nutrients of sediments show a significant decrease with depth in the vertical direction, but there are different changes in different lake areas.3.Biomass and community composition of epipelic algae are closely related to environmental factors. There was a positive correlation between the biomass of sediments and the TN, TP, TOC and porosity ( R?0.039 ), and significant positively correlated with TN ( R=0.554, p<0.01 ). The biomass was negatively correlated with water pH and positively correlated with other factors, and there was a significant positive correlation with NH4+-N(R=0.713, p<0.01 ). The TN, TP and TOC of sediments ( p<0.01 ) were significantly correlated with cyanophyta and chlorophyta in epipelic algae except bacillariophyta( R? 0.236, p<0.01 ). There was a significant negative correlation between epipelic cyanophyta and planktonic cyanophyta(R=-0.415, p<0.05 ). There was no significant correlation between epipelic chlorophyta and planktonic chlorophyta. There was no significant correlation between epipelic bacillariophyta and planktonic bacillariophyta.