The phytoplankton community of a eutrophic reservoir

The dynamics of the phytoplankton community of a eutrophic reservoir are described for a two year period. Fifty-eight species were recorded, 25 of them common. Bacillariophyta dominated during the winter and early spring and Chlorophyta during late spring, to be replaced by a bloom of Cyanophyta. The mean and peak biomass of phytoplankton was 8.6 mg 1^–1 and 40.8 mg 1^–1 in 1981, and 8.3 mg 1^–1 and 37.6 mg 1^–1 in 1982. Temperature accounted for 67.3% and pH for 8% of the variation in total phytoplankton biomass over the two year period, using a multiple regression technique.Both horizontal and vertical patchiness, measured as an index of mean crowding, were recorded in the reservoir. Horizontal aggregations were associated with spring blooms of Chlorophyta and summer blooms of Cyanophyta, while vertical aggregations were most marked during the summer bloom of Cyanophyta. Concentrations of phytoplankton were influenced by wind, the prevailing southwesterly wind accumulating algae in the northeasterly arm of the reservoir during much of the year.     

Phytoplankton strategies and time scales in a eutrophic reservoir

Phytoplankton species groups were studied in a eutrophic reservoir at different time scales (daily, weekly, monthly and yearly). Four strategic groups along the r-K continuum were defined and their seasonal time courses were followed. Their temporal distribution of relative biomass reflected resource partitioning because each strategic group dominated the phytoplankton community at different times in the year. However, the relationships between strategic groups changed with the time scale involved. At the daily scale an inverse relationship between r- and K-groups occurred whereas at supradaily scales such relationships did not hold. Species groups reflected strategic groups. No relationship between population growth and losses was found, suggesting that both were not counterbalanced. In the long term (supraannual) the phytoplankton community changed very much in this reservoir, its ecological memory being small as compared with that of lakes.     

Bacterial utilization of algal extracellular products in a southwestern reservoir

Rates of carbon flow from phytoplankton to bacteria were estimated for Lake Arlington, Texas. The lake is a warm (annual temperature range 7 to 35 °C), shallow, monomictic reservoir with limited macrophyte development in the littoral zone. Samples were collected from 6 depths within the photic zone from a site located over the deepest portion of the lake. Primary production and exudate production were calculated from NaH¹⁴CO₃ incorporation. Bacterial production was calculated from [methyl-³H]-thymidine incorporation. Depth averaged primary production ranged from a seasonal low of 9.0 μg C l⁻¹ h⁻¹ in January to a seasonal maximum of 153 μg C l⁻¹ h⁻¹ during holomixis in September. Annual depth-averaged production was 67.8 ± 7.3 μg C l⁻¹ h⁻¹. Exudate production ranged between 21.9 and 54.2% of primary production and annually averaged 30.8%. Bacterial production ranged between 1.7 and 46.0 μg C l⁻¹ h⁻¹ and annually averaged 16.0 ± 1.9 μg C l⁻¹ h⁻¹. Bacteria processed approximately 70% of exudate and incorporated 35% into biomass. Bacterial production was positively correlated with total primary production (r = 0.38, p < 0.003, n = 6), particulate primary production (r = 0.34, p < 0.004, n = 70) and bacterial uptake of exudate (r = 0.43, p < 0.001, n = 68). While exudate was readily utilized by bacteria it dit not appear to be produced in sufficient quantity or at a sufficient rate to serve as the sole or a major source of carbon supporting bacterial growth.     

Flora of planktonic microalgae of Amursky Bay, Sea of Japan

Long-term studies of the species composition of phytoplankton in Amursky Bay (Sea of Japan) carried out during the period from 1991 to 2006 revealed a total of 357 species of planktonic microalgae from eight divisions: Cyanophyta (8 species), Chrysophyta (8), Bacillariophyta (157), Cryptophyta (5), Dinophyta (143), Raphidophyta (3), Euglenophyta (11), and Chlorophyta (22 species). An annotated checklist of species is presented. In comparison with the late 1960s and early 1970s, the species richness of phytoplankton increased markedly; a greater number of bloom-forming species was recorded.     

Carbon isotope ratio and photosynthetic activity of phytoplankton in the eutrophic Mikawa Bay,Japan

Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural carbon isotope ratio (δ ¹³C) and short-term carbon uptake rates (¹³C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates, which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ ¹³C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction (−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more negativeδ ¹³C values (−22 to −18‰). Highδ ¹³C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the nannoplankton fractions with higher POC values have relatively lowδ ¹³C values.     

The effects of disturbance events on phytoplankton community structure in a small temperate reservoir

1 The effects of disturbances, in the form of storm events, on phytoplankton community structure were examined over the course of four years in Eau Galle Reservoir, Wisconsin, USA.
2 Disturbances consistently brought about significant, but highly transient, increases in apparent phytoplankton species richness. It is likely that these resulted from temporary increases in the biomass of previously undetected rare species.
3 Substantial shifts in community dominance were confined to large, early season events, and were seldom long-lived. Later 'climax' communities were highly resistant to any changes in dominance, even when increases in species richness occurred.
4 Regardless of when they occurred, disturbances tended to favour species from a narrow range of the successional sequence.     

Sediment resuspension in a monomictic eutrophic reservoir

During the mixing period sediment traps were placed at 9 different levels of the water column in La Concepción reservoir (Málaga-Spain). During the exposure time a benthic nepheloid layer with high suspended matter was detected. Seston vertical flux profile shows an exponential increase with depth, suggesting that a large fraction of the collected particulate matter comes from bottom resuspension, due to an intermittent complete mixing process. It was estimated that resuspension 1 m above the bottom increased the fluxes of seston, particulate organic carbon, particulate nitrogen and particulate phosphorus by factors of 4.1, 1.5, 2.1 and 4.8 respectively.The, fitting to an exponential function allowed us to obtain a resuspension coefficient and the scale vertical length for this event, 36 m, which is higher than those estimated for other aquatic environments. From the above results the calculated vertical eddy diffusivity, suggesting a high turbulence in the water reservoir during the turnover period. Resuspension is considered important in order to estimate net downward fluxes and to understand different processes such as redistribution of sediment and fertilization of the water column.     

Bacteria–algae association in batch cultures of phytoplankton from a tropical reservoir: the significance of algal carbohydrates

Summary 1. The dissolved organic matter, especially carbohydrates, released by phytoplanktonic organisms may be ecologically important, through its influence on carbon cycling and microbial diversity. Here axenic cultures of three phytoplanktonic species, Cryptomonas tetrapyrenoidosa (Cryptophyceae), Staurastrum orbiculare (Zygnematophyceae) and Thalassiosira duostra (Bacillariophyceae), were inoculated with a microbial community from the same habitat in which the algae had been isolated (a tropical reservoir). Replicate cultures were not inoculated.
2. In both axenic and co-inoculated cultures, phytoplanktonic density and extracellular carbohydrate production were monitored microscopically and by high performance liquid chromatography with a pulse amperometric detector, respectively. Bacterial population density was also monitored by epifluorescence microscope in the microbial co-inoculated cultures.
3. Both bacterial and phytoplanktonic densities increased for 11 days in all cases. The use of extracellular carbohydrates by bacteria was also showed for all phytoplanktonic species. Of the three species of phytoplankton, only T. duostra had a faster population growth in the presence of bacteria, and reached a higher biomass than in axenic culture.     

The seasonal periodicity of planktonic diatoms in a shallow eutrophic lake

The seasonal periodicity of four species of planktonic diatoms in a small eutrophic lake in the Shropshire-Cheshire Plain, England, is examined. Diatoms typically dominate the spring increase; a second period of growth follows in the summer months. The growth phases are considered in relation to environmental factors in the mere. Of these, light levels appear to be critical in determining the onset of growth and the size of the population maxima, whilst stratification and turbulence play a leading role in the vertical distribution of the algae, and hence, of the growth conditions to which they are exposed. The thermocline is believed to provide a reservoir of diatoms in summer, maintaining them in a position where they are able to gain maximum advantage from increased wind-induced turbulence. Relative specific differences in growth requirements and in behaviour under varying physical conditions are important in determining which species dominate. Dominance may be modified by the effect of attacks by fungal parasites. It is also shown that, generally, nutrients are present in relative abundance, and only rarely does their availability become a limiting factor. Tt is concluded that diatom growth in this lake is typically subject to physical rather than chemical control.     

乌伦古河流域克孜赛水库浮游植物群落组成

克孜赛水库是乌伦古河源头的一个小型水库,2008年7月(夏季平水期)、2008年10月(秋季枯水期)和2009年5月(春季丰水期)对水库内浮游植物群落进行了调查分析,共鉴定出浮游植物102种(属),隶属于8个门,以硅藻门和绿藻门为主。3个时期浮游植物密度变化趋势为:枯水期(25.221±3.605×106ind/L)>平水期(12.539±1.064×106ind/L)>丰水期(1.052±0.077×106ind/L)。各季节优势种的组成因气候温度差异而变化,其中以夏季平水期最多,达9种。克孜赛水库温度和水量的变化共同导致了水库浮游植物种类组成、密度、优势种和生物多样性指数的季节变化。Shannon-Weaver多样性指数(H)和Pielou均匀度指数(J)变化趋势较一致:平水期>枯水期>丰水期,而Margalef丰富度指数(D)则于丰水期达最大值。     

广西防城港湾周年浮游植物生态特征

2007年3、6、9和12月,对防城港湾海域浮游植物的种类组成、优势种类、群落结构、丰度分布进行了调查,分析了浮游植物丰度、生物指数及其与环境因子的相关性.共鉴定出浮游植物54属138种.其中硅藻门37属112种;甲藻门12属21种;绿藻门和金藻门各2种,蓝藻门1种.全年浮游植物优势种主要为硅藻门的中肋骨条藻.浮游植物种数呈现湾内低于湾外、由春至冬减少的趋势,浮游植物细胞丰度则呈由湾内向湾外递减的趋势.不同季节调查海区浮游植物细胞丰度平面分布格局具有显著差异,夏季(6月)浮游植物丰度最高,达151.39×104 cells·dm-3,冬季(12月)丰度最低,为0.35×104 cells·dm-3.春季防城港湾海域的浮游植物多样性较高,物种较丰富.相关性分析表明,浮游植物群落分布与营养盐、水温、盐度等环境因子存在一定的相关性.西湾内的S1和S2测站,受防城江径流及潮汐等水动力条件的作用,盐度较低,富营养化程度较高,夏季时中肋骨条藻会大量增殖,甚至具有发生赤潮的隐患.     

Seasonal changes in sedimenting material collected by high aspect ratio sediment traps operated in a holomictic eutrophic lake

Cylindrical sediment traps with an aspect ratio (height (60 cm): diameter (5.1 cm)) of 11.8 were located 1 m above the surface sediment by a rigid metal framework support. Traps were exposed in Lough Neagh for one year, from May 1978. Each trap collected between 11 and 12 cm of faintly laminated sediment. One 12 cm sediment column was examined using conventional palaeolimnological techniques of core extrusion and analysis. The algal record in trapped sediment is shown to correspond with successional changes in phytoplankton abundance in the lake during the year of study. The sediment accumulation rate measured by the traps is an order of magnitude greater than that measured in dated sediment cores and redeposited and inwashed sediment formed the bulk of trapped material. However, the value of these high aspect ratio traps is that they provide a continuous but qualitative account of compositional changes in sedimenting material through time. Their potential as long term biological monitoring devices is emphasized.     

The effects of planktivorous fishes on the plankton community in a eutrophic lake

Stocking silver carp, a phytoplankton feeder, and bighead carp, an omnivorous plankton feeder, into an eutrophic lake at high densities caused a dramatic change in the lake ecosystem.Microcystis, which had been dominant in summer and a main food of the fishes decreased markedly, and green algae smaller than 10 μm then became dominant. Consequently, chlorophyll-a per unit area decreased slightly, while the rate of production was higher than that in the previous years. As the total density of the fishes increased (from 0.09 to 0.11 fish m⁻²), the growth of silver carp was retarded, while that of bighead carp increased.Microcystis, was unable to become dominant due to increased grazing pressure by the fishes, and small green algae became dominant. The lake conditions thus became more favourable for zooplankters which selectively consumed small green algae, and accordingly, the production of zooplankton rose. Bighead carp consumed more animal food, which they assimilate at a higher rate than plant food, and grew better in spite of the fact that the fish density increased. The feeding rate of silver carp was greatly reduced because the green algae were too small to ingest, and the fish therefore grew poorly. Results of a computer simulation of a model consisting of five compartments, representing the blue-green algae, green algae, zooplankton, silver and bighead carp, support the food-web change observed in the lake.     

Seasonal patterns of urea regeneration by size-fractionated microheterotrophs in well-mixed temperate coastal waters

Urea regeneration by size-fractionated plankton was measuredover an annual cycle at a coastal station in the permanentlywell-mixed waters of the western English Channel. Rates of urearegeneration in the <200 µm fraction varied from 0.6to 20.6 nmol N L^–1 h^–1. Regeneration rates werelowest in winter and highest in summer. The ratio of the ratesof regeneration to uptake of urea was close to 1 on all time(seasonal and nycthemeral), and space (vertical) scales indicatingthat regeneration by microheterotrophs supplied the totalityof urea used by phytoplankton. On an annual basis, urea regeneratedby the microheterotrophs (0.98 mol N m^–2 year^–1)was equivalent to 33% of the total regenerated N (urea + ammonium).The major part of urea regeneration was due to the nanoplankton(51%) and microplankton fractions (36%). Regeneration of ureain the picoplankton was detectable only from April to Octoberand represented, on an average, 25% of the total urea regeneratedduring this period. Urea regeneration in micro- and nanoplanktonfractions was mainly associated with ciliates and in the picoplanctonfraction with bacteria.     

Prey utilization by Chaoborus punctipennis Say in a small,eutrophic reservoir

Prey selection by 2nd-, 3rd-, and 4th-instar larvae of Chaoborus punctipennis was evaluated by comparing larval crop contents to the species structure of the zooplankton community in a small, eutrophic lake. The rotifers, Brachionus caudatus and Trichocerca similis, were positively selected by and comprised most of the diet of 2nd- and 3rd-instar larvae. Rotifers comprised 67% of all prey items identified in the crops of even 4th-instar larvae. Whereas 2nd-and 3rd-instar larvae selected the two rotifers with equalfrequency, 4th-instar larvae selected Trichocerca significantly more frequently than they did Brachionus. Although copepods comprised only 8% of all prey identified in 3rd-instar crops, they comprised 33% of the crop contents of 4th-instar larvae. Both 3rd and 4th instars exhibited a positive electivity for Cyclops vernalis significantly more frequently than for Diaptomus pallidus. We conclude that the larvae of Chaoborus punctipennis can, and do, select between Trichocerca and Brachionus and between Cyclops and Diaptomus.The paper by Brooks and Dodson (1965) triggered a flurry of studies on aquatic predators and their ability to discriminate between available prey species. Although the original work dealt with vertebrate predators, it has become increasingly apparent that invertebrate predators may also exhibit considerable selectivity in choosing between prey categories. The larval stages of the various species of Chaoborus are ubiquitous lentic predators, especially in mesotrophic or eutrophic systems. Although there have been a number of recent publications which deal with the food habits and preferences of several species of Chaoborus, only a few studies have included analyses of larval crop contents and none of these have included Chaoborus punctipennis. This species is of particular interest because it is one of the smaller species in the genus, and perhaps for this reason, because it is frequently present in lakes which support large populations of planktivorous fish (von Ende 1979). The purpose of our research was to characterize the food habits and preferences of Chaoborus punctipennis in a small, eutrophic reservoir which supports a rather depauperate number of species of zooplankters.     

长江口北支浮游植物群落结构周年变化特征

2010年10月至2011年9月对长江口北支水域的浮游植物进行周年调查,共采集到183种（包括变种和变型）,隶属于7门60属,其中硅藻门种类最多,有35属137种,占浮游植物总种类数的75%。周年优势种为具槽直链藻、中肋骨条藻、条纹小环藻、两栖颤藻、小伪菱形藻双楔变种、颗粒直链藻和小环藻未定种。本次调查中,季节间浮游植物的丰度差异不显著（P〉0.05）,但各月间浮游植物丰度差异显著（P〈0.05）,全年丰度在2.83×10^3～6.18×10^4cells/L之间,其中6月的丰度最高,1月的丰度最低,全年的平均丰度为1.73×10^4cells/L。Pearson相关性分析显示,浮游植物丰度与硝酸盐浓度显著正相关（P〈0.05）,与氨氮浓度极显著正相关（P〈0.01）,含氮营养盐对浮游植物的影响明显。     

Chemical consequences of oxygenation in a shallow eutrophic lake studied with mesocosms

To assess the effects of oxygenation in a shallow, highly eutrophic lake, an experiment with large enclosures was carried out. From the results two main effects can be expected from the oxygenation of the whole lake: (a) fish mortality and the resulting putrefactive processes would be avoided; (b) an increase in nitrogen and phosphorus concentration and, consequently, in the trophic level of the lake would probably occur.     

Uptake of amino acids by uncultivated bacterioplankton of a eutrophic water reservoir

Water bacterioplankton species (clones) feeding on lysine and glycine were revealed in experimental microecosystems using nonsterile cultivation. The structure of the community was analyzed by separation of amplified fragments of the bacterial 16S rRNA gene of by denaturing gradient gel electrophoresis. The dominant species (clones) of the bacterioplankton were identified by molecular cloning and determining the nucleotide sequence of part of the 16S gene of ribosomal RNA. It was found that glycine, one of the prevalent amino acids of a eutrophic reservoir, and lysine, whose content in natural water is lower, are nutrient substrates for various subdominant bacterioplankton species (clones). Thus, free-living bacterial species are highly specialized for the uptake of individual amino acids.