Spatial And Temporal Distribution Of Phytoplankton In Hanfeng Lake And Its Relationship With The Environmental Factors

In the reservoir ecosystem,phytoplankton is the basic link of the food chain which greatly affects the material recycling and energy conversion of the reservoirs.The phytoplankton not only plays an important role to maintain the balance of aquatic ecosystems,but also is an important biological indicator for water quality of these reservoirs.Hanfeng Lake,which is located at Pengxi River upstream near Kaixian city,was constructed to reduce the adverse effects of the Riparian Zone on the ecological environment of the Three Gorges Reservoir.It’s ecological and environmental quality has a great impact on the development of Kaixian city and the ecological and environmental quality of Pengxi River and Yangtze River.Therefore,it is of great importance to evaluate the community structure of phytoplankton and its influencing factors of this lake.In this study,the spatial and temporal distribution of phytoplankton and its influencing factors were investigated from April 2013 to December 2014.According the principles of water sampling,we set up eight sampling points,including the dam(HF1),downstream of the dam(HF2),the interchange of Donghe river and Nanhe river(HF3),the entry of Donghe river(HF4),the Donghujun(HF5),the interchange of Nanhe river and Toudao Ditch(HF6),the Shilongchuan Bridge(HF7)and the entry of Nanhe river(HF8).The physiochemical properties,concentrations of nutrient and phytoplankton community structure of water samples were determined and main environmental factors affecting the distribution of phytoplankton were analyzed.The main results are as follows:1.The physiochemical properties of Hanfeng Lake and its nutrient varied significantly with the changes of time.Water temperature follows the trends of atmospheric temperature.The pH values in the third quarter are higher than those in other quarters.The minimum concentration of dissolve oxygen(DO)was found in November.The concentrations of total suspended solid(TSS)in the discharge period are higher than those in the storage period,but the transparency shows a different trend.The concentrations of CODMn index,ammonia nitrogen(NH4+-N),total phosphorus(TP)and dissolved phosphorus(DP)had the maximum values in the beginning of the storage period and discharge period.The concentrations of total nitrogen(TN),soluble nitrogen(DN)and nitrate nitrogen(NO3--N)in the storage period increased gradually,but in the discharge period,they gradually decreased and then kept constant.The physiochemical properties of water sampled at different points were not significantly,but the difference of nutrient concentration is significant,with the values in Nanhe River(HF5-HF8)being higher than those in Donghe River to dam(HF1～HF4).In the vertical direction,pH values,TP,DP and NO3--N were not significant different,but water temperature,DO and SS in the surface layer and bottom layer were significantly higher than that in the middle level.The CODMn,TN,NH4+-N in the water followed the order of surface layer>bottom layer>middle layer.The differences for CODMn and phosphorus in the vertical direction were more obvious in Donghe River and Nanhe River than other sampling sites.2.A total of 292 species belonged to 7 phyla(including varieties and forms)were identified of Hanfeng Lake in 2014,among which Bacillarophyta and Chlorophyta were the most important components,followed by Euglenophyta and Cyanophyta.Pyrrophyta,Chrysophyta and Cryptophyta were the smallest components.The common species had 12 species which belonged to 3 phyla.Of the species,seven belonged to Bacillarophyta,three belonged to Cyanophyta and two belong to Cryptophyta.The dominant species,which varied significantly with the changes of quarter,had 40 species belonging to 6 phyla.There are 12,15,22 and 18 dominant species in the four quarters.The spatial and temporal changes of phytoplankton density and chlorophyll concentrations followed the same trend,and the maximum values were in observed in February and October.The Chlorella vulgaris Beij and Chroomonas acuta Uterm were the main contributors to phytoplankton density in the river.3.The diversity analysis results of Hanfeng Lake showed that the diversity of the first quarter and the Donghe River(HF4)is the worst and the second quarter and the Nanhe River on the contrary.The overall evaluation result of water quality wasβ-ms—os.4.The results of the influence factors of phytoplankton community structure in Hanfeng Lake which based on Pearson correlation analysis and Redundancy analysis(RDA)were as follow:in the first quarter,the TN,DN,TP and NO3--N were the greatest impact.In the second quarter,the influence of environmental factors on phytoplankton was not obvious except some algae of Bacillariophyta which affected by TP and SS.In the third quarter,the main influence factors were water temperature,TN,DN and NO3--N.In the fourth quarter,the main influence factors were water temperature,DO,CODMn,DP and NH4+-N.