Life under ice in the perennial ice‐covered Lake Glubokoe in Summer (East Antarctica)

This study focuses on hydrological and biotic variables in Lake Glubokoe, which is located in Thala Hills of Enderby Land (East Antarctica). Water and sediment samples and physical measurements were collected once a week in the austral summer (19 December 2010 – 6 February 2011). This lake exhibits perennial ice cover that reached a thickness of 2.5–2.7 m during the study period. A very low concentration of planktonic chlorophyll‐a (0.06–0.45 μg L^?1) was measured in the lake, indicating its ultra‐oligotrophic status. The water was poorly populated by algae and metazoans, especially in upper waters below ice cover to a depth of 2 m. Small planktonic organisms (2–5 μm) were observed throughout the study period, but larger organisms (>8 μm) such as the cyanobacteria Planktolyngbya limnetica occurred only during the warmest period (January). Only few individuals of metazoans (rotifers) were found in planktonic samples. Due to deep light penetration (10–15% of incoming active solar radiation reached the depth of 30 m), thick cyanobacterial mats (30 cm) cover all the bottom surface (grey silts) in the lake. Abundant benthic biota associated with these mats was found (up to 1000 ind. m^?2). Among the benthic metazoans, bdelloid rotifers and tardigrades were the dominating taxa. The results of this study suggest a typical ecological feature of most subglacial lakes in East Antarctica is that metazoans are very poor in the pelagic zone, preferring instead to occupy an area near the lake bottom because of a favourable constant temperature of 4 °C, good level of dissolved oxygen and available food resources as the bacterial detritus.     

阳宗海浮游生物群落结构研究

采用生物多样性指数方法,对2013年阳宗海湖泊的浮游生物群落结构进行研究。结果表明,阳宗海湖泊共检出浮游植物7门39属,蓝藻门的拟鱼腥藻和泽丝藻为优势种群;浮游动物鉴定出33种,轮虫为优势种;浮游植物和浮游动物的香浓多样性指数在1.10~2.83之间,均匀度指数在0.37~0.88之间,属于中度污染,阳宗海湖泊已处于中营养状态,并有向富营养化过渡的趋势。     

晋阳湖夏季浮游生物调查及水质分析

2009年5-9月,对晋阳湖的浮游生物及水质进行了调查,结果表明:晋阳湖共有浮游植物47种,浮游植物生物量为100.63 mg/L,浮游动物30种,生物量0.304 mg/L,水质类型为SCⅡa型。晋阳湖处于富营养化状态。     

Algal ecology and composition in the Garmat ali river,Iraq

Planktonic, epipelic and epiphytic algae were studied monthly, during the period from January to December 1985 in the Garmat ali river, a naturally regulated river draining to the al-Hammar marsh, Iraq. Chlorophyll-a, primary productivity and water quality variables were also measured. High light penetration was noticed during the winter and spring. The water is oligohaline, alkaline and very hard. Reactive nitrate was found in higher concentrations than nitrite, and there were low concentrations of reactive phosphate. Two peaks were noticed for chlorophyll-a concentrations during spring and autumn, whereas only one occurred during autumn for primary productivity. The study area may be characterized as typically mesotrophic. A total of 154 species of algae was identified, including 65, 89, 98 and 77 species of plankton, epipelic and epiphytic algae on Potamogeton lucens and on Ceratophyllum demersum, respectively. Only 25 species were common to all the different communities. Diatoms were the dominant group in the epipelic and epiphytic algae during the study period, as well as in the plankton during spring and autumn. Seasonal variations were clear in the total cell numbers of algae from different habitats.     

Longitudinal Plankton Dynamics in the Rivers Rhine and Elbe

We compared the longitudinal plankton development in the two large rivers Rhine and Elbe by means of four Lagrangian sampling campaigns performed within the time span 2009–2011. The campaigns revealed low chlorophyll concentrations in the Rhine along a long river stretch (Rhine‐km 170 to 854) with maximum values below 5 µg L^?1 in 2010. In contrast, the Elbe (Elbe‐km 4 to 582) showed high and longitudinally increasing chlorophyll concentrations with maximal values of 174 µg L^?1 in 2009 and 123 µg L^?1 in 2011. Additional samples of the benthic bivalves along the river stretches revealed high densities of the filter feeders in the Rhine that could potentially explain losses of plankton production. Their densities in the Elbe were significantly lower, making important losses to benthic filter feeders unlikely. However, strong phytoplankton growth was observed during the sampling campaign in 2011 in the Rhine coinciding with a low discharge event. This resulted in an exceptionally high chlorophyll value of up to 244 µg L^?1 in the lower river sections, a value that was not reached in the last two decades of continuous water quality monitoring in the Rhine. Even though we cannot fully explain this phenomenon, it shows that phytoplankton has a high growth potential in the Rhine but is usually controlled by other mechanisms. Tributaries represented an additional and important source of plankton biomass and suspended substances in the Rhine, whereas they primarily diluted the plankton concentrations in the Elbe. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling and prediction of phyto- and zooplankton dynamics in Lake Kasumigaura by artificial neural networks

An artificial neural network model was developed for Lake Kasumigaura to predict timing and magnitudes for chlorophyll a, five species of blue-green algae and three zooplankton groups. The model was trained by 8 years of limnological time series and validated by two independent years. The validation showed the potential of neural networks as predictive tools for highly non-linear phenomena such as blue-green algal blooms in freshwater lakes.     

Food of Young-of-the-Year Lake Trout (Salvelinus Namaycush) in Presque Isle Harbor,Lake Superior

The food habits of young lake trout (Salvelinus namaycush) were studied by examining the digestive tracts of 293 young-of-the-year collected in Presque Isle Harbor, Lake Superior. Lake trout in the 25 to 27-mm length range started to eat food organisms before all of their yolk material was absorbed. Organisms consumed by the 25 to 27-mm young-of-the-year included Chironomidae, Copepoda (Harpacticoida, Calanoida, Cyclopoida), and Cladocerea (Daphnia spp., Bosmina sp., Chydorus sp.). Chironomid pupae and chironomid larvae accounted for 74% and 5%, respectively, of the total volume of food eaten by the young lake trout in Presque Isle Harbor. Although copepods, cladocerans, and mysids were present in many stomachs, their contribution to the total volume of food was only 15%. Some lake trout in the 32 to 54-mm length range had consumed fry of sculpin (Cottus spp.) or rainbow smelt (Osmerus mordax), but the overall contribution of fish fry to the total volume of food was only 4% (frequency of occurrence, 10%). The lake trout in Presque Isle Harbor fed heavily on planktonic organisms, sparingly on benthic organisms, and were opportunistic feeders that appeared to prey on whatever forage organisms were available in the shallow nearshore waters.     

天津北大港水库渔业生态环境调查与评价

运用熵权模糊综合评价法和浮游生物多样性指数及优势种等方法,分析评价了天津北大港水库2013年5月、7月和9月的检测数据。结果表明:北大港水库2013年5、7和9月的水质都属于Ⅳ类水,浮游生物多样性指数较高,但是优势种中已出现耐污种类。北大港水库的水质评价结果和浮游生物分析结果都表明其已处于富营养化状态。最后针对这一结果提出了改善建议。     

三峡库区试验性蓄水期间浮游生物群落特点研究

蓄水改变了三峡水库的水文情势,使得浮游生物密度及群落结构出现明显改变,在不同蓄水阶段呈现不同的特点。根据2009年三峡水库试验性蓄水期间分季节实地监测结果,分析了浮游动植物在不同季节、不同蓄水位以干流与支流河口的分布变化情况。结果表明：就季节变化而言,秋季浮游植物种类最多、夏季次之、冬春较少;浮游生物密度整体不高,且时空分布不均,为春夏秋冬依次递减,支流河口密度高于干流;与蓄水前相比,蓄水后浮游生物密度显著增加,但与135 m及156 m蓄水位相比,试验性蓄水期间有下降趋势。库区营养盐水平较高,对浮游生物的生长不形成限制,浮游生物分布的时空显著差异是由流量、流速及浊度造成的。     

Climate change does not explain historical changes in the pelagic ecosystem of Lake Kariba (Zambia–Zimbabwe)

Recent studies on the pelagic ecosystem of Lake Kariba identified a number of changes in its thermal regime, planktonic communities and fishery production, concluding they were the result of climate change, particularly warming. This study re‐examines these conclusions and suggests alternative explanations for these changes. Historical data suggest there was no warming of the lake until at least the 1990s. Furthermore, lack of recent data makes it difficult to conclude that the lake’s temperature has increased by 2 °C. It is also not clear that the pattern of thermal stratification has changed, or that the thermocline has risen and become more stable. Although one of the suggested effects of climate change was a decreased number of larger zooplankton, this change occurred in the 1970s, when there had been no change in the lake temperature. Rather, there is strong evidence that the zooplankton composition changed as a result of selective predation by the introduced clupeid, Limnothrissa miodon. Furthermore, the loss of large grazing zooplankton species could have affected the composition of the phytoplankton, although this phenomenon also has been attributed to climate change. Although the phytoplankton communities in the lake are not as well documented as the zooplankton communities, it is clear that many changes in the lake actually began in the 1970s. Finally, the decline in the pelagic fishery for Limnothrissa was also linked to temperature changes. However, because the fisheries on the Zambian and Zimbabwean sides exhibited very different behaviours, there is little evidence to support this conclusion. It is concluded that the impacts of climate change on Lake Kariba are likely to be complex and that possible over‐simplification in identifying these impacts will not facilitate our understanding of these complexities.