Chen Feizhou

Mechanism and control of lake eutrophication

A review about lake naturally eutrophicating, the internal loading of nutrients from lake sediment as well as the mechanism of algal blooms and the control practices was made, especially the eutrophication problem of shallow lakes since seventy percent of fresh water lakes in China are shallow lakes. It was found that shallow lakes are apt toward eutrophication than deep lakes. Without any influences of human activity, shallow lakes in the middle and lower reaches of Yangtze River are still easily eutrophicated, which may be owing to the effects of flood in this area. In shallow lakes, sediments are frequently disturbed by wind-wave and resuspended, which result in huge nutrients release to overlying water. This may be the major reason for higher internal loading of nutrients in shallow lakes than in deep lakes. Algal bloom is an extreme response of lake ecosystem to the eutrophication. Appearance of algal blooms is related to physical condition of lakes, such as underwater radiation (or transparency), temperature, and hydrodynamic conditions, or related to geochemical conditions of lakes, like concentrations of nutrients and ratio of nitrogen to phosphorus, as well as the physiological advantage of cyanobacteria such as vacuole for moving towards the radiant energy-rich zone and the mycosporine-like amino acids (MAAs) for resisting the harm of ultraviolet radiation. In shallow lakes, these advantages of cyanobacteria are favorable in the competition than in deep lakes. Also being the shallowness, it is more difficult to reduce nutrient loading and to control algae blooms in shallow lakes. For the control of eutrophication, people should follow the sequence from pollution sources control, ecological restoration to catchment management. To control the internal nutrient release, physical, chemical, biological techniques, and even bionic techniques could be selected. The idea of ecological restoration for a eutrophic lake is to shift the ecosystem from phytoplankton-dominant state to macrophyte-dominant state. To realize the shift of ecosystem state, environmental condition improvement is the fundamental work. Nowadays, we should do more work on environmental condition improvement than on planting of macrophytes since we are lack of the knowledge about the relationship between macrophyte and lake ecosystem. Emphasizing the macrophyte planting, therefore, has blindness at present. Because all lakes have different characteristics of environment and ecosystem, applicable lake harness techniques should be selected based on the distinct ecosystem types and environmental problems.

Reflections on the theory and practice of shallow lake ecosystem restoration

Aquatic ecosystem restoration is a wide-used term at present, and it has gradually aroused the attention of the public and government due to serious environmental problem of lake in China. In fact, as a systematic work, ecosystem restoration makes the ecosystem towards the good state or prestine status. It comes true through the decreasing or amelioration of environmental press combining with single or multi introduced measures of plants and animals. At present, lake ecosystem restoration is usually considered as simple planting grass and cultivating fish etc. or explained as the man-made re-arrangement or incrustation of biocommunity. These bias in cognition result in less successful examples during the long time of the ecosystem restoration practices. Here we put forward an alternative technological way to purify the lake water in part area of Lake Taihu through ecosystem restoration, including three mutual-connected phases, viz,improving the lake condition→restorating aquatic macrophyte→ecosystem transformating from algae-typed to grass-typed lake→improving water quality. Whether this idea directing the restoration of aquatic macrophyte and lake ecosystem is successful will be tested by future practice.

Effects of colonial Microcystis spp.on the growth and reproduction of large-sized cladoceran Daphnia similis in Lake Taihu

Cyanobacterial blooms in eutrophic lakes have significant influence on population and community structures of cladoceran,but the impacts of natural colonial Microcystis spp.on the growth and reproduction of Daphnia remain controversial.Two 10-day experiments were conducted separately to simulate the impacts of the colonial Microcystis spp.(20-100μm and 100-200μm) on population characteristics of D.similis,which were cultivated in filtered water from Lake Taihu.The results show that colonial Microcystis spp.has no significantly negative effect on the survivorship of D.similis.The growth rate and reproductive capacity of D.similis differed among different concentrations and sizes of colonial Microcystis spp.,which was significantly higher in groups with Microcystis than the control group.Our results indicate that there is no significant inhibition from cellular microcystins on the population of D.similis in natural conditions.D.similis can coexist with Microcystis blooms and its population characteristics are mostly affected by the size composition and biomass of colonial Microcystis spp.Cyanobacterial blooms in eutrophic lakes have significant influence on population and community structures of cladoceran,but the impacts of natural colonial Microcystis spp.on the growth and reproduction of Daphnia remain controversial.Two 10-day experiments were conducted separately to simulate the impacts of the colonial Microcystis spp.(20-100μm and 100-200μm) on population characteristics of D.similis,which were cultivated in filtered water from Lake Taihu.The results show that colonial Microcystis spp.has no significantly negative effect on the survivorship of D.similis.The growth rate and reproductive capacity of D.similis differed among different concentrations and sizes of colonial Microcystis spp.,which was significantly higher in groups with Microcystis than the control group.Our results indicate that there is no significant inhibition from cellular microcystins on the population of D.similis in natural conditions.D.similis can coexist with Microcystis blooms and its population characteristics are mostly affected by the size composition and biomass of colonial Microcystis spp.

Fish stocking quantities and structures of the fishery resources enhancement in Lake Taihu

According to the investigations of biological resources in Lake Taihu during 2006-2007,we calculated that total fishery yield potential of phytoplankton,zooplankton,zoobenthos and aquatic macrophytes in Lake Taihu was about 78494t.In order to increase fish yields and inhibit cyanobacteria bloom in Lake Taihu,stocking number of silver carp(Hypohthalmichthys molitrix Richardson) and bighead carp(Aristichthys nobilis Cuvier) should be increased to 10 million and 3 million tails,respectively,and the specification should be 20 tails per kilogram.To protect resources of aquatic macrophytes and zoobenthos,the reasonable stocking number of grass carp(Ctenopharyngodon idellus Cuvier),blunt snout bream(Megalobrama amblycephala Yih),black carp(Mylopharyngodon piceus Richardson) and common carp(Cyprinidae carpio Linnaeus)should be 1.5 million,1.65 million,80-100 thousand and 25 million tails,respectively.As topmouth cutler such as cutler alburnus could play important roles in controlling miniaturization and singleness of fishery structure and increase added-value of fishery economy,its stocking quantity should be increased to 5 million tails.

Seasonal variations in the diets of Coilia ectenes taihuensis Yen et Lin in Gonghu Bay of Lake Taihu

Coilia ectenes taihuensis Yen et Lin(C.ectenes) is the dominant fish species in Lake Taihu,and the catch has been increasing with the eutrophication of Lake Taihu.In this study,in order to investigate the seasonal diets variations of C.ectenes in Gonghu Bay of Lake Taihu,we sampled the fish by gill net and analyzed bimonthly the gut contents of C.ectenes from April to December,2009.Meanwhile,selectivity for different food items was also analyzed for the purpose to study the food preference of the fish.The results showed that the food composition of C.ectenes varied from month to month.Zooplankton,fish larvae,shrimp and insects were found in the stomach contents of the fish,but zooplankton was the dominant food.Among the zooplankton species,Copepod was the main food in April with close mean percentages diet composition of Copepodite,Sinocalanus dorrii Brehm and Cyclops spp.In June,August and October,C.ectenes fed mainly on cladoceran with Moina spp.as the dominated mean percentage diet composition in June and Bosmina spp.in August and October,respectively.Small zooplankton composed the main percentage diet composition,such as Bosmina spp.and Moina spp.,in all sampling months.However,C.ectenes negatively selected Bosmina spp.for their food,but positively selected Moina spp.and other large-sized zooplankton species.But when Daphnia spp.and Leptodora kindti Focke were present in the sampling months,C.ectenes showed high selectivity for them.From this investigation,we can conclude that C.ectenes feed mainly on planktonic crustaceans,and showed high selectivity for large-sized zooplankton.Moreover,fish larvae,shrimp and insects may be their potential food for the fish when its total length is longer than 130mm.Different food items varied largely in fish food composition among different seasons.Studying on the diet composition of C.ectenes can help us understand the seasonal effects of C.ectenes on zooplankton community structures better,and provide evidences and foundations for making rational plans of fisheries and lake management.Coilia ectenes taihuensis Yen et Lin(C.ectenes) is the dominant fish species in Lake Taihu,and the catch has been increasing with the eutrophication of Lake Taihu.In this study,in order to investigate the seasonal diets variations of C.ectenes in Gonghu Bay of Lake Taihu,we sampled the fish by gill net and analyzed bimonthly the gut contents of C.ectenes from April to December,2009.Meanwhile,selectivity for different food items was also analyzed for the purpose to study the food preference of the fish.The results showed that the food composition of C.ectenes varied from month to month.Zooplankton,fish larvae,shrimp and insects were found in the stomach contents of the fish,but zooplankton was the dominant food.Among the zooplankton species,Copepod was the main food in April with close mean percentages diet composition of Copepodite,Sinocalanus dorrii Brehm and Cyclops spp.In June,August and October,C.ectenes fed mainly on cladoceran with Moina spp.as the dominated mean percentage diet composition in June and Bosmina spp.in August and October,respectively.Small zooplankton composed the main percentage diet composition,such as Bosmina spp.and Moina spp.,in all sampling months.However,C.ectenes negatively selected Bosmina spp.for their food,but positively selected Moina spp.and other large-sized zooplankton species.But when Daphnia spp.and Leptodora kindti Focke were present in the sampling months,C.ectenes showed high selectivity for them.From this investigation,we can conclude that C.ectenes feed mainly on planktonic crustaceans,and showed high selectivity for large-sized zooplankton.Moreover,fish larvae,shrimp and insects may be their potential food for the fish when its total length is longer than 130mm.Different food items varied largely in fish food composition among different seasons.Studying on the diet composition of C.ectenes can help us understand the seasonal effects of C.ectenes on zooplankton community structures better,and provide evidences and foundations for making rational plans of fisheries and lake management.

不同碳磷比的斜生栅藻(Scenedesmus obliquus)对同型溞(Daphnia similis)生长和繁殖的影响

食物质量会影响浮游动物的生长和繁殖，表征食物质量的指标包括食物大小、元素比、生物化学组成和毒性有无等.用斜生栅藻（Scenedesmus obliquus）的碳磷比（C/P）表征食物质量，分析不同C/P斜生栅藻对同型溞（Daphnia similis）生长和繁殖的影响.研究中4个处理组斜生栅藻C/P分别为881.8、512.3、124.3和42.4.培养9 d后不同处理组同型溞的生长速率分别为0.15、0.27、0.47和0.44 d-1.C/P比为881.8的处理组同型溞在整个培养过程中没有产仔，其余3个处理组的同型溞第1成龄期的产仔量分别为1.2±1.3、9.8±2.3和9.5±2.5 ind./female.结果表明，与斜生栅藻C/P为124.3处理条件相比，斜生栅藻C/P过高（512.3和881.8）及C/P过低（42.4）处理条件下同型溞生长速率和产仔量均降低.本研究表明食物C/P的高低会影响溞的生长和繁殖，从而影响其在湖泊中的生存.Food quality can influence the growth and reproduction of zooplankton in freshwater systems. Food size, element ratios, biochemical composition and toxicity are indicative of food quality. The C / P ratios of Scenedesmus obliquus was used to represent the food quality in this experiment. We analyzed the effects of S. obliquus with different C / P ratios on the growth and reproduction of Daphnia similis. The C / P ratios of S. obliquus in four treatments were 881.8, 512.3, 124.3 and 42.4, respectively. The growth rates of D. similis in four treatments were 0.15, 0.27, 0.47 and 0.44 d-1, respectively. D. similis did not release any offspring dur⁃ ing this period of growth in treatment with C / P = 881.8. The average numbers of offspring of first adult instar of D. similis in other three treatments were 1.2±1.3, 9.8±2.3 and 9.5±2.5 ind. / female, respectively. The results showed that the growth rate and off⁃ spring number of D. similis decreased when the C / P ratio of S. obliquus was too high (512.3 and 881.8) or too low (42.4) com⁃ pared with C / P = 124.3. Our study indicated that different C / P ratios of food could affect the growth and reproduction of Daphnia, thus determining their survival in freshwater lakes.

Characteristics of community structure of plankton in the Lake Taihu basin during the dry season of 2012

A detailed field survey of zooplankton and phytoplankton was conducted in the Lake Taihu basin during the 2012 dry season. Community structure of zooplankton and phytoplankton,and their relationships with environmental factors were studied by species diversity index and canonical correspondence analysis( CCA). Totally 139 species of phytoplankton from 7 phyla and 71 genera have been identified. In Lake Taihu,Cyanophyta was the dominant population,accounted for 95. 8% of the density of phytoplankton. Notably the density of Microcystis aeruginosa,the predominant species,was 86. 7% of the density of phytoplankton. In the river systems discharging into Lake Taihu,92. 2% density of the phytoplankton belonging to Cyanophyta,Bacillarophyta and Chlorophyta,which constructed the dominant populations. Cyclotella sp. and Microcystis wesenbergii were the dominant species,accounted for 17. 4% and 10. 3% of the numbers of phytoplankton,respectively. Twenty-seven species of zooplankton have also been identified,including Cladocera( mainly Bosmina sp. and Ceriodaphnia sp.) and Copepoda( mainly Sinocalanus dorrii and Limnoithona sinenesis). In Lake Taihu,the biomass of zooplankton was 265. 1 μg /L,Bosmina sp.,Ceriodaphnia sp.,Sinocalanus dorrii and Limnoithona sinenesis accounted for 48. 7%,5. 1%,15. 9% and 22. 5% of the total biomass,respectively; whilein river systems discharging into Lake Taihu,the biomass of zooplankton was only 21. 8 μg /L. Bosmina sp.,Sinocalanus dorrii and Limnoithona sinenesis were the dominant species. Diversity index showed that Lake Taihu have the highest phytoplankton biodiversity,followed by the Yili River system,the Yunhe River system,the Chuhu River system and the Shaoxi River system successively. The highest zooplankton diversity was also found in Lake Taihu,followed by the Shaoxi River system,and then the Yili River system,the Chuhu River system and the Yunhe River system. CCA analysis showed that phytoplankton community was significantly associated with nitrate,total nitrogen and total phosphorus while the distribution of zooplankton was related significantly to nitrate,dissolved oxygen and temperature. There was a significant correlation between phytoplankton and zooplankton. Bacillariophyta was significant positively related to Diaphanosoma sp.,Bosminopsis sp. and Mesocyclops sp.. Cyanophyta was significantly associated with Bosmina sp.,Ceriodaphnia sp. and Sinocalanus dorrii.

Simulated research on anti-predation reaction of Daphnia similis to Chaoborus larvae

Daphnia exhibits diverse morphological,behavioral and life-history responses to the kairomones of predators.A 10-day simulated experiment was conducted on anti-predation reaction of Daphnia similis,a dominant species in Lake Taihu,to invertebrate predator Chaoborus larvae.The experiment had three treatments: the presence of Chaoborus larvae(CL),control without Chaoborus larvae or filtered water(CK) and no Chaoborus larvae but with the filtered water that had cultured Chaoborus larvae the day before(FL).The results showed that the average body length,average number of offspring and cumulative number of offspring of D.similis in the CL and FL treatments were significantly higher than those in the CK treatment,which suggested that the release of kairomones from Chaoborus larvae can alter the life history traits of D.similis.These alterations can reduce the predation risk of D.similis.Our results indicate that invertebrate predator can affect the cladoceran population through both direct predation and release of the kairomones in the field.Daphnia exhibits diverse morphological,behavioral and life-history responses to the kairomones of predators.A 10-day simulated experiment was conducted on anti-predation reaction of Daphnia similis,a dominant species in Lake Taihu,to invertebrate predator Chaoborus larvae.The experiment had three treatments: the presence of Chaoborus larvae(CL),control without Chaoborus larvae or filtered water(CK) and no Chaoborus larvae but with the filtered water that had cultured Chaoborus larvae the day before(FL).The results showed that the average body length,average number of offspring and cumulative number of offspring of D.similis in the CL and FL treatments were significantly higher than those in the CK treatment,which suggested that the release of kairomones from Chaoborus larvae can alter the life history traits of D.similis.These alterations can reduce the predation risk of D.similis.Our results indicate that invertebrate predator can affect the cladoceran population through both direct predation and release of the kairomones in the field.

Effects of Daphnia carinata grazing on the phytoplankton of Lake Xuanwu,Nanjing

Daphnia carinata is a large zooplankter in many eutrophic lakes and has a high efficiency to graze phytoplankton. The effects of Daphnia carinata on chlorophyll-a and the community structure of phytoplankton of Lake Xuanwu in Nanjing was studied experimentally. The results showed that the density of phytoplankton decreased 83% and the chlorophyll-a decreased 81% in the Daphnia carinata treatment comparing with the control. There is no significant relationship between nitrogen, phosphorus and chlorophyll-a in the Daphnia treatment. When Daphnia presented, the community structure of phytoplankton had changed. The proportion of Cyanophyta, Chlorophyta and Bacillariophyta obviously increased and the proportion of Cryptophyta obviously decreased. The Chrysophyta, Pyrrophyta, and Euglenophyta were not found at the end of the experimentation. Our experiments showed that Daphnia carinata can efficiently control the biomass of phytoplankton and change the community structure of phytoplankton.Daphnia carinata is a large zooplankter in many eutrophic lakes and has a high efficiency to graze phytoplankton. The effects of Daphnia carinata on chlorophyll-a and the community structure of phytoplankton of Lake Xuanwu in Nanjing was studied experimentally. The results showed that the density of phytoplankton decreased 83% and the chlorophyll-a decreased 81% in the Daphnia carinata treatment comparing with the control. There is no significant relationship between nitrogen, phosphorus and chlorophyll-a in the Daphnia treatment. When Daphnia presented, the community structure of phytoplankton had changed. The proportion of Cyanophyta, Chlorophyta and Bacillariophyta obviously increased and the proportion of Cryptophyta obviously decreased. The Chrysophyta, Pyrrophyta, and Euglenophyta were not found at the end of the experimentation. Our experiments showed that Daphnia carinata can efficiently control the biomass of phytoplankton and change the community structure of phytoplankton.