Influence of sea ice on the composition of the spring phytoplankton bloom in the northern Baltic Sea

During the late winter and spring of 1994, the influence of sea ice on phytoplankton succession in the water was studied at a coastal station in the northern Baltic Sea. Ice cores were taken together with water samples from the underlying water and analysed for algal composition, chlorophyll a and nutrients. Sediment traps were placed under the ice and near the bottom, and the sedimented material was analysed for algal composition. The highest concentration of ice algae (4.1 mmol C m⁻²) was found shortly before ice break-up in the middle of April, coincidental with the onset of an under-ice phytoplankton bloom. The ice algae were dominated by the diatoms Chaetoceros wighamii Brightwell, Melosira arctica (Ehrenberg) Dickie and Nitzschia frigida Grunow. Under the ice the diatom Achnanthes taeniata Grunow and the dinoflagellate Peridiniella catenata (Levander) Balech were dominant. Calculations of sinking rates and residence times of the dominant ice algal species in the photic water column indicated that only one ice algal species (Chaetoceros wighamii) had a seeding effect on the water column: this diatom dominated the spring phytoplankton bloom in the water together with Achnanthes taeniata and Peridiniella catenata. Received: 9 May 1997 / Accepted: 15 February 1998     

着生藻类和浮游藻类在三峡库区河流健康评价中的适宜性比较研究

藻类对水体环境变化敏感,其种类和数量与环境因素有密切联系并因环境的变化而发生变化,因此藻类常作为河流健康评价的指示生物。水体中的藻类根据生活习性不同分为着生藻类和浮游藻类,在河流健康评价中,以往的工作中有的采用浮游藻类用于河流健康评价,有的采用着生藻类用于评价,但浮游藻类和着生藻类究竟何者用于河流健康评价更适宜,抑或是二者在用于评价的适宜性上没有明显差别,迄今为止未开展过深入研究。选择三峡库区内的两条河流嘉陵江和乌江作为研究对象,于2015年9月,在两条河流上共布设11个研究断面,对嘉陵江、乌江的水环境理化因子、着生藻类和浮游藻类群落进行调查研究,应用着生藻类生物完整性指数(Periphytic algal index of biological integrity,Pe-IBI)和浮游藻类生物完整性指数(Phytoplankton index of biological integrity,Ph-IBI),并结合水体综合污染指数(Comprehensive pollution index,CPI),对嘉陵江、乌江的健康状况进行评价。研究结果表明,采用着生藻类生物完整性评价(Pe-IBI)能筛选出7个核心生物参数(藻类总分类单元数、蓝藻总分类单元数、绿藻总分类单元数、菱形藻比例、优势分类单元比例、香农多样性指数、均匀度)用于河流健康评价,着生藻类生物完整性指数(Pe-IBI)与水体综合污染指数(CPI)具有极显著的负相关关系,并且与水体中总氮、铅含量也有极显著的负相关关系,表明水环境质量越低则着生藻类的生物完整性越差;当采用浮游藻类生物完整性(Ph-IBI)用于河流健康评价时却只能筛选出1个核心生物参数(藻类密度),而且浮游藻类生物完整性指数(Ph-IBI)与水体综合污染指数(CPI)及12个水体环境指标并无明显的相关性。本研究表明,在河流水体中,与浮游藻类相比,着生藻类更能反映水体环境的状况,对河流水体环境的反映更为准确。因此,在以流动水体为特征的河流的健康评价中,采用着生藻类比采用浮游藻类更为适宜。     

Implications of rapid changes in chlorophyll-<Emphasis Type="Italic">a</Emphasis> of plankton,epipelon, and epiphyton in a Pampean shallow lake: an interpretation in terms of a conceptual model

Biomass assessments of algae in wetlands usually include only the phytoplankton community without considering the contribution of other algal associations to total algal biomass. This omission prevents an accurate evaluation of the phytoplankton community as an integral part of the total ecosystem. In the present work, the biomass contributions (expressed as chlorophyll-a content per m² of lake) of phytoplankton, epiphyton on both submerged and emergent macrophytes, and epipelon were measured in Lacombe Lake, Argentina, for the purpose of (1) establishing the relative importance of the phytoplankton and (2) evaluating the entire contribution of algal biomass within the context of the Goldsborough & Robinson conceptual model. Our sampling was carried out monthly for a year in sites representative of different conditions with respect to water depth and type of macrophytes. Physicochemical analyses of water were performed following standard methods. Plankton was collected in a five-level profile at deeper stations and in subsurface samples at the shallow one. Samples of sediment obtained with corers were collected for epipelon sampling and segments of plants were cut at different levels, so as to obtain the epiphytes by scraping. Pigment was extracted with aqueous acetone and calculations were made by means of the Lorenzen equation. According to the Goldsborough & Robinson model, a Lake State developed here during the winter (phytoplankton maxima: 150 mg chlorophyll-a per m²). Then, through the subsequent growth of the submerged macrophytes, an Open State was observed, characterized by a maximum epiphyton biomass (at 3,502 mg chlorophyll-a per m²) along with lower levels of phytoplankton biomass. The epiphytic algae on the emergent macrophytes were always present but attained only relatively low biomass values (maximum: 120 mg of chlorophyll-a per m² in February). The epipelon biomass varied between 50 and 252 mg chlorophyll-a per m², registering a considerable contribution of settled algae from the water column (phytoplankton). This study contributes to our knowledge of wetland dynamics through its assessment of the rapid changes in the relative contributions of both planktonic and attached algae to the total algal biomass within the context of specific environmental factors. Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira Plankton Studies     

水色及其与藻类的关系

水色是水环境质量评价中一个重要的综合性指标,不同的水色反映水质的营养状况;藻类群落是水体营养状况的生物表征,对水色具有重要影响作用。本文通过分析不同水色中的藻类优势种群及其作用,认为藻类优势种群是决定水色的主要生物因子;阐明了藻类与水色之间的相互关系以及施肥改变水色的内在机理,水体营养状况决定了水体藻类群落结构进而决定不同的水色;并结合实践对如何判断不同藻类种群引起的不同水色提出了看法,同时对改变和调控水色的方法和途径进行了论述,为相关生产和水环境管理提供理论依据和技术指导。     

Effects of acidic pH and phytoplankton on survival and condition of Bosmina longirostris and Daphnia pulex

The effects of pH, algal composition and algal biomass on abundance, size, reproduction and condition of Daphnia pulex and Bosmina longirostris were tested in a field experiment using water and natural phytoplankton assemblages from a circumneutral (pH 6.43) and a moderately acidic (pH 5.75) lake in south-central Ontario. Both species were affected by pH and phytoplankton composition, with decreased egg production, lipid reserves, body size or abundance in treatments containing algae and/or water from the more acidic lake compared to treatments containing water and phytoplankton from the circumneutral lake. This result was unexpected for Bosmina, which often increases in relative and/or absolute abundance in acidified lakes. The negative effect of acidic conditions on Bosmina suggests that the population increase observed in most acidified lakes is not due to a positive response to low pH or ambient phytoplankton, but to altered biotic interactions possibly involving reduced competition.     

Impact of chronic and pulse dilution disturbances on metabolism and trophic structure in a saline Mediterranean stream

Non-diatom benthic algae from 104 streams in southern California were studied. We present a novel method for quantification of non-diatom algae that seeks to improve upon two important aspects of existing methods: separate processing of macroalgae and microalgae to avoid sample blending and consequent loss of macroalgal integrity, and for better viewing, counting a well-mixed microalgal subsample on a standard microscope slide instead of using a counting chamber. Our method provided high-quality taxonomic and quantitative data with low uncertainty. A total of 260 algal taxa were recorded, 180 of which were identified to species level. The median total algal biovolume per site was 22.7 mm³ cm⁻² (range: <0.001–836.9 mm³ cm⁻²), the median species number was 11 (range: 2–43). Total algal biovolume and species number correlated with canopy cover (negative) and water temperature (positive), but not with measured water chemistry constituents. The proportion of heterocystous cyanobacteria and Zygnemataceae were strongly negatively correlated with nitrate concentrations and TN. The proportion of red algae was negatively correlated with TP. Species optima calculations combined with indicator species analysis identified >40 algal species as potential indicators of nutrient conditions. Proposed here is a practical tool for non-diatom algal quantification that enhances its application to stream bioassessment.     

毛乌素沙地南缘沙丘生物结皮对凝结水形成和蒸发的影响

在水分极度匮乏的荒漠生态系统,凝结水是除降雨之外最重要的水分来源之一,它对荒漠生态系统结构、功能和过程的维持产生重要的影响。为探明半干旱沙区生物结皮表面的凝结水形成和蒸发特征,采用自制的微型蒸渗计(直径7 cm、高5 cm的PVC管)实验观测了不同类型地表(裸沙、浅灰色藻类结皮、黑褐色藻类结皮和苔藓结皮)对凝结水形成和蒸发的影响。结果表明:(1)观测期间共有20次凝结水形成记录,除降雨天气外,几乎每天都能观测到水分凝结现象;(2)不同类型地表凝结水总量依次为(1.998±0.075),(2.326±0.083),(2.790±0.058)和(3.416±0.068) mm,生物结皮表面的凝结水总量显著大于裸沙(P < 0.05);随生物结皮的发育,不同类型生物结皮表面的凝结水总量呈增加的趋势,凝结水总量之间差异显著(P < 0.05);观测期间不同类型地表日平均凝结水量依次为(0.100±0.003),(0.116±0.004),(0.140±0.002)和(0.171± 0.003) mm,不同类型地表日平均凝结水量之间差异极显著(P < 0.01);(3)凝结水形成过程的观测结果显示,凝结水19:00开始形成,23:00-凌晨1:00形成不明显,1:00-7:00继续形成,除浅灰色藻类结皮外,太阳升出后在黑褐色藻类结皮和苔藓结皮表面继续形成少量的凝结水;凝结水7:30开始蒸发,10:30到11:00之间结束蒸发,凝结水在裸沙和浅灰色藻类结皮中的保持时间显著大于黑褐色藻类结皮和苔藓结皮中的保持时间(P < 0.05);(4)凝结水的形成受大气温度、地表温度、空气相对湿度和大气地表温度差等气象因素的影响,但其形成过程不与某一个气象因素呈简单的线性关系。     

Experimental formation of sea ice: importance of water circulation and wave action for incorporation of phytoplankton and bacteria

The efficiency of physical concentration mechanisms for enrichment of algae and bacteria in newly formed sea-ice was investigated under defined conditions in the laboratory. Sea-ice formation was simulated in a 3,000 l tank under different patterns of water movement. When ice formed in an artificially generated current pattern, algal cells were substantially enriched within the ice matrix. Enrichment factors for chlorophyll a calculated from the ratio between the concentrations in ice and underlying water reached values of up to 53. Repeated mixing of ice crystals into the water column, as well as flow of water through the new ice layer, contributed to the enrichment of algae in the ice. Wave action during ice formation revealed lower phytoplankton enrichment factors of up to 9. Mixing of floating ice crystals with underlying water and pumping of water into the ice matrix by periodical expansion and compression of the slush ice layer were responsible for the wave-induced enrichment of algal cells. Physical enrichment of bacteria within the ice was negligible. Bacterial biomass within new ice was enhanced only when the concentration of algae was high. At low algal biomass, bacteria experienced substantial losses in the ice, most likely due to brine drainage, which were not observed for the microalgae. Bacterial cells are therefore not scavenged by ice crystals and the observed enrichment and sustainment of bacterial biomass within newly formed ice depend on their attachment to cells or aggregates of algae. Division rates of bacteria changed only slightly during ice formation. Received: 21 October 1997 / Accepted: 9 April 1998     

Halogenating activities detected in Antarctic macroalgae

 Halogenating activities were determined in samples of 18 cultivated species of brown, red and green macroalgae from the Antarctic. Activities for the halogenating organic compounds with bromide, iodide and chloride were found. Investigated red algae (rhodophytes) showed higher brominating and iodinating activities compared to brown (phaeophytes) and green (chlorophytes) algae. The highest brominating and iodinating activities were measured in the red algae Plocamium cartilagineum (1.11±0.01 U g^-1 wet algal weight and 0.18 U g^-1 wet algal weight, respectively) and Myriogramme mangini (3.62±0.17 U g^-1 wet algal weight and 4.5 U g^-1 wet algal weight, respectively). Chlorinating activities were detected in the red alga Plocamium cartilagineum only (0.086 U g^-1 wet algal weight). Received: 12 February 1996/Accepted: 20 June 1996     

Copper adsorption kinetics of cultured algal cells and freshwater phytoplankton with emphasis on cell surface characteristics

Comparative studies were carried out on the adsorption of copper by a range of laboratory-cultured algae and freshwater phytoplankton samples. The level of surface mucilage associated with the cultured algae ranged from high (Anabaena spiroides, Eudorina elegans) to moderate (Anabaena cylindrica, Microcystis aeruginosa) to complete absence (Chlorella vulgaris, Asterionella formosa, Aulacoseira varians, Ceratium hirundinella). With laboratory cultures, the rapid uptake, EDTA release and quantitative similarity between living and dead (glutaraldehyde-fixed) algae were consistent with physical binding of Cu at the cell surface. The higher Cu adsorption per unit surface area and longer adsorption time of mucilaginous algae in the time-course study, and the relatively high level of Cu bound to mucilage found by X-ray microanalysis suggest that mucilage played an important role in metal binding. For all species examined, Cu adsorption kinetics (external Cu concentrations 1 to 1000 mg L⁻¹) showed a clear fit to the Freundlich, but not the Langmuir isotherm, indicating a monolayer adsorption model with heterogenous binding sites. The Freundlich adsorption capacity constant (K_f) was higher in mucilaginous (3.96–12.62) compared to nonmucilaginous (0.36–3.63) species, but binding intensity (Freundlich constant 1/n) did not differ between the two cell types. The results suggest that mucilaginous algal species may have potential as biosorbents for treatment of industrial effluents containing heavy metals. Investigation of the Cu adsorption behavior of four mixed phytoplankton samples also revealed a good fit to the Freundlich, but not the Langmuir, isotherm. Freundlich constants were in the range 2.3–3.2 for samples dominated by Chlorophyta, Bacillariophyta and Cyanophyta, but recorded a value of 7.4 in the sample dominated by Dinophyta. Comparison with data from laboratory monocultures suggested that the adsorption kinetics of mixed environmental phytoplankton samples cannot be predicted simply in terms of the major algal species.     

The structure and dynamics of the phytoplankton assemblages in Lake Kinneret, Israel

The phytoplankton of Lake Kinneret, a warm monomictic lake,is dominated by a Pyrrhophyta-Chlorophyta assemblage. Four stagesof succession of planktonic algae occur in the lake, startingwith thermal and chemical destratification and ending with stratification. The index of diversity of the phytoplankton communities is highduring the destratification and mixed periods. The index reachesminimal values during late summer, when the ecosystem is subjectto strong physical, chemical and biological stresses. The diversityin Lake Kinneret increases with the increase in nutrients andnot with the increase in temperature. During most of the year, the nanoplanktonic forms are in greaternumbers than the netplankton species. This fact is correlatedwith the amounts of available nutrients in the lake. The annual averages of the wet autotrophic biomass in Lake Kinneretare very high in comparison with other warm lakes. The contributionof the nanoplanktonic species to the total algal biomass isvery small during the Peridinium bloom, but represents approximatelyhalf of the total algal biomass during the rest of the year. The concentration of nutrients in the water, together with theadverse competitive effect of Peridinium on other algae, areto a large extent responsible for the composition, successionand abundance of the phytoplankton assemblages in Lake Kinneret.     

Limitations of using extracellular alkaline phosphatase activities as a general indicator for describing P deficiency of phytoplankton in Chinese shallow lakes

Extracellular phosphatase can be produced by phytoplankton to utilize organic phosphorus under phosphorus (P) deficiency. However, there is a controversy about its use as an indicator of P deficiency in natural phytoplankton community inferred by such an “induction–repression” mechanism. Size-fractionation of alkaline phosphatase activity (APA), soluble reactive phosphorus (SRP) concentration, algal density, and composition were determined in six Chinese shallow lakes ranking in gradient of trophic status, where a positive relationship between SRP concentration and algal density was observed. Enzyme-labeled fluorescence (ELF) method was used to localize phosphatase on cell membrane of algae. The so-called algal APA that associated with coarser particle (>3.0 μm) accounted for the largest part of total APA. Within a lake with lower SRP concentration, the “induction–repression” mechanism held true. Contrastingly, both algal and total APA were positively related to SRP concentration based on the data across all study lakes with statistical significance, which may be explained firstly by algal composition. The lakes with higher SRP concentration were dominated by diatoms and green algae, while they easily produced extracellular phosphatases as evidenced by ELFA labeling. In parallel, the lakes with lower SRP concentration were dominated by cyanobacteria, while it was never ELFA-positive; secondly, ELFA-positive dots or structures suggested that, in lakes with higher trophic status, attached bacteria or heterotrophic microorganisms could substantially contribute to extracellular phosphatases for hydrolyzing organophosphoric compounds but probably utilizing the organic moiety as an organic carbon source. This process simultaneously produces inorganic P, leading to the co-occurrence of high phosphate concentration and APA. So, the contributor of APA are complex, which may produce extracellular phosphatase species-specific or not exclusively for P nutrient and consequently make it difficult to normalize APA with the exact biomass estimators. Therefore, it is not reasonable to use APA, normalized or not, as a general indicator for describing P deficiency of phytoplankton in shallow lakes especially eutrophic ones.     

Food concentration and temperature effects on the demography of <Emphasis Type="Italic">Latonopsis</Emphasis> cf. <Emphasis Type="Italic">australis</Emphasis> Sars (Cladocera: Sididae)

This study has two main objectives, the first being the determination of net phytoplankton primary production to explain the phytoplankton’s function in a wetland carbon cycle, while the second objective is to relate this function with the phytoplankton assemblage composition. The annual variation in the phytoplankton production was monitored monthly for more than a year (2007–2008) in the semiarid eutrophic, hydrologically-perturbed “Tablas de Daimiel” National Park wetland. The phytoplankton fraction considered in this study comprised all organisms between the size 3 and 100 μm. The total biomass of phytoplankton was obtained by counting algae and calculating their volume, while net primary production and respiration were quantified by in situ incubations with the Winkler method. The respiration ranged from undetectable to 0.07 mgO₂ l⁻¹ h⁻¹; net photosynthesis reached 0.20 mgO₂ l⁻¹ h⁻¹. Net primary production was maximum at the end of the warm period (October 2007), and other peaks occurred at the start of summer (July 2007) or spring (March 2008). When maximum production took place, phytoplankton was mainly composed of small fast-growing chlorophytes (Tetraselmis cf. fontiana or Chlamydomonas sp.), in addition to some of the large, S-strategist algae (Peridinium umbonatum, Microcystis flos-aquae, Euglena sp.). The phytoplankton metabolism in “Tablas de Daimiel” was autotrophic as a whole due to changing contributions of algal groups. Only chlorophyte biomass was statistically related to net primary production. The conclusion reached is that this shallow eutrophic semiarid wetland possessed an annual net autotrophic production of phytoplankton fraction resulting from the small, fast-growing algae enhanced by hydrological perturbations that interrupted the autogenic course of S strategists.     

Long term study on the influence of eutrophication, restoration and biomanipulation on the structure and development of phytoplankton communities in Feldberger Haussee (Baltic Lake District, Germany)

Feldberger Haussee provides a classic example of eutrophication history of hardwater lakes in the Baltic Lake District (Germany) and of changes in their algal flora during the 20th century. The lake originally was regarded as slightly eutrophic. A process of drastic eutrophication from the 1950s until the end of the 1970s caused mass developments of blue-green and green algae. A restoration program was started in the 1980s to improve the water quality of the lake using both diversion of sewage outside the catchment area, and biomanipulation by altering the fish community. This restoration program led to positive changes in the lake ecosystem. Direct effects of biomanipulation resulted in an increase of herbivorous zooplankton, a decrease of phytoplankton biomass, and an increase of water transparency. The recovery of Feldberger Haussee also may have been indirectly enhanced by an increase in nutrient sedimentation as a consequence of intensified calcite precipitation, decrease in phosphorus remobilization due to a pH-decrease, increased NIP-ratio, and recolonization of the littoral zone by macrophytes. This paper concentrates on the long term development of the phytoplankton community as a response to changes in the food web structure as well as to alterations in the chemical environment of the algae. Both are reflected in four major stages passed by the algal assemblage between 1980 and 1994: (1) From 1980-summer 1985 dense green algal populations were found indicating similar conditions as in the 1970s during the period of maximum eutrophication. (2) A diverse phytoplankton community during summer 1985–1989 showed the first effects of a recovery. (3) From 1990–1992 the phytoplankton was characterized by ungrazeable filamentous blue-green algae first of all as a response to increased herbivory of zooplankton on edible species and to increasing N/P-ratios. (4) Finally, the algal species diversity increased in 1993 and 1994 whereas the phytoplankton biomass decreased showing the success of the combined restoration measures.     

Preliminary investigation of the contribution of fast-ice algae to the spring phytoplankton bloom in Ellis Fjord,eastern Antarctica

 Algae released from fast-ice in Ellis Fjord, eastern Antarctica, made little contribution to subsequent phytoplankton growth. Dominant taxa in the interior ice community included Nitzschia cylindrus (Grun) Hasle, Navicula glaciei V.H. and a dinoflagellate cyst. Diatom mortality within the ice was high. The algal contribution to the phytoplankton from the fast ice was estimated by calculating the difference between algal biomass in ice cores taken on 14 November with those taken on 18 December 1992. The biomass of sedimenting phytoplankton was estimated using sediment traps; weekly cell counts of water were used to monitor net phytoplankton growth. The low contribution from the fast-ice of Ellis Fjord to the phytoplankton is similar to results from other Antarctic fast-ice communities but is not necessarily reflective of processes occurring within either Antarctic or Arctic pack ice communities. An algal mat growing on the base of the fast-ice had a carbon standing crop of between 0.231 gC m^-2 and 0.022 gC m^-2. Much of this was delivered to the water column as the ice melted while the remainder was exported. Received: 15 March 1995/Accepted: 4 September 1995     

Responses of spring phytoplankton communities to their habitats in the Xiangxi Bay of Three Gorges Reservoir,China

Since the water storage was initiated in 2003, the environment of Three Gorges Reservoir (TGR) has changed significantly. Algal blooms and eutrophication have been a frequent occurrence, with serious eutrophication in the tributary bays. To provide some theoretical evidence for the prevention and control of algal blooms, the goal of this study is to elucidate factors that influence algal blooms at different sections of the Xiangxi Bay (XXB). Using field data from the XXB, the responses of phytoplankton communities to their habitats were investigated from March to May, 2010. The results indicated a significant spatial and temporal heterogeneity in phytoplankton composition, cellular abundance, and habitats in the spring. Fifty-four genera representing 6 phyla were monitored. Redundancy analysis indicated that the variation in water temperature and relative water column stability (RWCS) contributed greatly to the succession of spring phytoplankton. Due to different physiological adaptabilities and mechanisms of competition among the algae species, significant succession of the community structure had been observed. The predominant species appears to have changed from those adapted to low temperatures and strong mixing (dinoflagellates and diatoms) to those adapted to high temperatures and weak mixing (green algae and cyanobacteria). The lack of silicate resulted in the succession from diatoms to green algae. Due to the influence of the Yangtze River, there is a low potential for algal blooms at lower reaches of the bay because of frequent water exchange. In contrast, the potential is high at middle and upper reaches where the water temperature increases gradually. The hierarchical status of the two sections is significantly different. Precipitation would inhibit algal blooms somewhat, and heavy rainfall would eliminate algal blooms throughout the bay. Phytoplankton are sensitive to their changing habitat in XXB. For a bloom to occur, sufficient nutrients, a lower flow velocity, and appropriate temperature and light conditions are necessary. As an artificial regulating reservoir, proper ecological regulation could not only significantly affect the dynamic conditions of the water body tributaries, but it could also change the transfer characteristics of light and heat, abolishing the algae habitats and thereby inhibiting the water bloom.     

Light environment within dense algal populations: cell size influences on self-shading

The influence of algal cell size on the light environment withindense phytoplankton populations was analysed in cultures of11 freshwater algae (mostly Chlorophyta) varying widely in cellsize and growing at saturated (220 µM m² s^–1) andlimited (11 µM m^–2 s^–1) irradiances Chlorophyll-a-specificabsorbance coefficients did not bear any obvious relationshipto cell size and, as expected from previous analyses, were stronglyinfluenced by the light intensity at which the algae were grown.However, biomass (fresh weight)-specific absorbance coefficientsdecreased as algal cell volume increased regardless of the incomingirradiance Intracellular chlorophyll a concentration (c₁), whichdecreased as algal cell size increased, explained a substantialfraction of the variance in biomass (fresh weight)-specifjcabsorbance coefficients. Thus, this study supports the notionthat reduced serf-shading allows large algae to support greatermaximal biomass than smaller algae.     

放养鲢鱼(Hypophthalmichys molitrix C et V)对水库围隔浮游生物群落的影响

本文研究在水库围隔实验生态系统中鲢鱼对浮游生物群落的影响。结果表明,放养鲢鱼后,浮游动物生物量、浮游植物生物量、叶绿素a和浮游植物毛产量分别下降了58.7％、63.6％、52.5％和65.0％;透明度、浮游植物群落多样性指数分别提高了18.2％、32.5％;铜绿微囊藻数量减少了90.6％“水华”得到明显抑制。但小型绿藻(<20μm)数量未出现显著变化,因而其在藻类生物量中所占比例反而提高了82.3％。围隔内可被鲢鱼滤食的大型藻类(硅藻、甲藻、隐藻和绿藻(>20μm))占藻类生物量的85.8％,因此鲢鱼的存在能明显限制浮游植物的生物量。此外,放养鲢鱼还显著降低了水体中的COD,TP,DO和pH值,这表明鲢鱼对水质有净化作用。     

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

Excitation–emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450–470 nm) with high accuracy (R ² = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590–650 nm range (R ² = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65–0.7.     

A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Algal Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of phytoplankton communities, and to evaluate the effectiveness of various sediment treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutrophic Akanoi Bay, Lake Biwa, Japan, 7–11 species of phytoplankton seeded from the sediments grew during the 3-week assay indicating that sediment resuspension has the potential to increase both phytoplankton biomass and species diversity. Treatment of sediments with Ca(NO3)2 substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays with sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, among various oxidation treatments of sediments, Ca(NO3)2 was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytoplankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment. This revised version was published online in June 2006 with corrections to the Cover Date.