不同水源补给对景观水体水质及浮游动物的影响

通过定期监测由再生水补给的桃花潭和由地表水补给的兴庆湖两个景观水体中水质和浮游动物的历时变化,探究不同水源补给对水体水质和浮游动物的影响及其相关性。结果表明,桃花潭水体中TN、TP、TCOD和Chl-a浓度年均值分别为4.65、0.22、29.24 mg/L和92.81μg/L,分别为兴庆湖对应值的1.95、2.29、1.49和2.30倍,分析可知再生水补给水体TP浓度增加引起浮游藻类增加,最终导致水体TCOD浓度上升。两水体检测到轮形动物门和节肢动物门共27种,其中轮虫类21种、枝角类和桡足类各3种;桃花潭浮游动物年均生物量为0.70 mg/L,且该水体中浮游动物种数、富营养型指示种种数及生物量均大于兴庆湖的对应值。冗余分析(RDA)和Pearson相关性分析结果表明,两水体中轮虫、枝角类的生物量与水质中的磷酸盐和TP相关性强,藻类的暴发性增长对枝角类的贡献比对轮虫的贡献更大,而桡足类受影响较小。总之,TP是影响再生水补给的水体中浮游动物生物量的主导因子。     

Changes in the Crustacean Communities of the Central Basin of Lake Erie during the First Full Year of the Bythotrephes longimanus Invasion

The exotic predatory cladoceran Bythotrephes longimanus was first observed in Lake Erie on 19 September, 1985. During the early summer immediately prior to its appearance, the cladoceran community in the central basin of Lake Erie was characterized by large populations of Bosmina longirostris, Eubosmina coregoni, Daphnia mendotae, and Daphnia retrocurva, with the latter three species persisting throughout August and September, along with Diaphanosoma spp. Community composition during early summer 1986 was similar to that of the previous year, but densities of all cladocerans decreased dramatically coincident with the appearance of Bythotrephes in mid-July, and remained suppressed throughout August and September. Only D. mendotae was present in appreciable numbers during this period; from mid-July through the end of August, 86-98% of cladoceran biomass (exclusive of Bythotrephes and Leptodora) was contributed by D. mendotae. Densities of Leptodora and Bythotrephes showed a strikingly inverse relationship, both temporally and spatially, during 1986. Size frequency distributions of D. mendotae exhibited an immediate shift towards extremely large ( > 2.5 mm) individuals coincident with Bythotrephes’ appearance in 1986, suggesting an upper size limit to efficient prey utilization by Bythotrephes. These results suggest that Bythotrephes can have substantial impacts both on cladoceran community composition, and on the size distributions of individual species.     

Analysis of self-overlap reveals trade-offs in plankton swimming trajectories

Movement is a fundamental behaviour of organisms that not only brings about beneficial encounters with resources and mates, but also at the same time exposes the organism to dangerous encounters with predators. The movement patterns adopted by organisms should reflect a balance between these contrasting processes. This trade-off can be hypothesized as being evident in the behaviour of plankton, which inhabit a dilute three-dimensional environment with few refuges or orienting landmarks. We present an analysis of the swimming path geometries based on a volumetric Monte Carlo sampling approach, which is particularly adept at revealing such trade-offs by measuring the self-overlap of the trajectories. Application of this method to experimentally measured trajectories reveals that swimming patterns in copepods are shaped to efficiently explore volumes at small scales, while achieving a large overlap at larger scales. Regularities in the observed trajectories make the transition between these two regimes always sharper than in randomized trajectories or as predicted by random walk theory. Thus, real trajectories present a stronger separation between exploration for food and exposure to predators. The specific scale and features of this transition depend on species, gender and local environmental conditions, pointing at adaptation to state and stage-dependent evolutionary trade-offs.     

Benefits to 0+ fishes of connecting man‐made waterbodies to the lower River Trent,England

Floodplain waterbodies are reputed to enhance recruitment of riverine fish populations via provision of spawning and nursery habitat, refuge from floods, and increased availability of planktonic food resources compared with main river channels. Notwithstanding, there have been few parallel studies of fishes and their food resources at both main river and floodplain sites. Thus, this study investigated the 0+ fishes, zooplankton and phytoplankton (chlorophyll a) at four main river and four (man‐made) floodplain sites on the lower River Trent, England, between May 1999 and October 2004 inclusive. All sites shared the same key fish species, and there were no consistent differences in the densities, growth or condition of 0+ fishes from main river and floodplain sites. Similarly, all sites shared the same key zooplankton taxa. However, zooplankton densities, notably of large‐bodied cladocerans, and chlorophyll a concentrations, were significantly higher at floodplain sites than at main river sites. Thus, connection of man‐made waterbodies has the potential to enhance recruitment of riverine fish populations via provision of important spawning and nursery habitat, and superior feeding opportunities for 0+ fishes compared with main river channels. Copyright © 2007 John Wiley & Sons, Ltd.     

Seasonal water level fluctuations: Implications for reservoir limnology and management

With the purpose of finding out whether seasonal water level fluctuations could affect water quality in a reservoir subjected to those changes, trends in environmental variables and in phytoplankton and zooplankton assemblages were analysed. The reservoir's hydrological cycle was characterized by three regimes. The maximum level phase lasted from January to the beginning of June, the emptying phase existed between mid‐June to the beginning of September and the minimum level phase lasted from mid‐September to the beginning of the first autumn/winter rain events. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. The phytoplankton assemblage was dominated by taxa typical of meso‐eutrophic environments during the emptying and minimum level phases. However, during the maximum level phase, taxa generally found in more oligotrophic systems were observed here also. Similar to other disturbed systems, the zooplankton assemblage was dominated by Rotifera, except in summer and autumn when the cladoceran Ceriodaphnia quadrangula and/or the copepod Tropocyclops prasinus became dominant. Although those shifts seem to be related to water level variations, further research is needed to evaluate to what extent they might also be induced by other seasonal factors acting independently of water fluctuations. Based upon the obtained data, suggestions for reservoir management are proposed.     

Limnological variations of a reservoir during two successive years: One wet, another dry

Changes in environmental variables, as well as in planktonic algae and in crustacean zooplankton abundance, were investigated in a meso‐eutrophic reservoir during two successive years: one wet, another dry. In the wet winter, both total phosphorus and soluble reactive phosphorus reached their maxima, whereas water transparency achieved the minimum during the same period. The obtained data suggest that total phosphorus and soluble reactive phosphorus peaks were related to the increase in nutrient loading as a consequence of the intense rainfall which occurred during this period. Phytoplankton composition was dominated by Cyclotella spp., except during the dry winter when Anabaena became dominant. The dominance of this alga seemed to be related to nitrate depletion. The establishment of more stable environmental conditions (e.g. low water turbulence, longer water retention time) and the increase of irradiance during the dry period (summer 2001 and winter 2001/2002) also favoured growth of this cyanobacterium. Concomitant to Anabaena dominance, Ceriodaphnia abundance decreased while nauplii increased. Although variation between the two years of study seemed to be related to the sequence of a pluvial and a dry year, further research is needed to evaluate whether variations in precipitation intensity influence reservoir ecological processes.     

采煤塌陷塘浮游动物群落结构研究

以大通南塌陷塘为主要研究对象,通过为期一年的采样、监测,鉴定出浮游动物123种,共计75个属,主要优势种为臂尾轮属和秀体漫属,得出该塘由八十年代以寡营养型针眼虫为优势种转变为现以臂尾轮属的优势种,在一定程度上说明塌陷塘有机污染的加重。本研究可为矿区塌陷塘生态环境状况的改善提供理论基础。     

Evidence for biotic control of Australian reservoir phytoplankton communities and the potential for applied biomanipulation

Although some concerns have been expressed with respect to the applicability of biomanipulation to Australian reservoirs and other inland waters, no major obstacles were found in this review. The previous doubts stimulated research, which has provided evidence for unexpected mechanisms of food web interactions, such as positive effects of small copepods on planktonic algae, higher than usual grazing potential of cladoceran communities, and direct positive effects of planktivores on phytoplankton. Further research into zooplankton-cyanobacteria interactions should indicate how widespread is the previously reported ability of some southern hemisphere crustaceans to benefit at a population level from feeding on cyanobacteria. Quantitative fisheries acoustics, which has not been widely used in biomanipulation trials before, is a promising new tool in the assessment of the biomass of planktivorous fish in the pelagic zone of reservoirs.     

Limnological features of Funil Reservoir (R.J., Brazil) and indicator properties of rotifers and cladocerans of the zooplankton community

Funil Reservoir receives inflow from a highly industrialized region and acts as a natural sink to pollutants. Among the consequences of the uncontrolled nutrient loading is the constant presence and periodic heavy blooms of Microcystis aeruginosa . This study verified limnological features and zooplankton assemblage of the Funil Reservoir focusing on the environmental-indicator properties of rotifers and cladocerans. The summer bloom of M. aeruginosa caused reductions in water transparency, nitrate and orthophosphate concentrations and raises in chlorophyll a , pH, dissolved oxygen and chemical oxygen demand values. All zooplankton species presented spatial and temporal variations with the exception of the copepods, which were present in all samples. According to canonical correspondence analysis, ammonium was the variable most related to zooplankton variability and different Rotifera and Cladocera assemblages indicated distinct environment conditions. Rotifer taxa associated with increases of water temperature and chlorophyll a concentration were found with high densities during M. aeruginosa blooms. Species of rotifer and cladocerans are suggested as indicators that can be used to identify different physical and chemical gradients or eutrophic increases in Funil Reservoir.