Contribution of benthic blue-green algal recruitment to lake populations and phosphorus translocation

1. A two-season investigation was undertaken to determine the contribution of benthic recruitment to the population development of several species of blue-green algae. 2. Gloevtrichia echinulata populations were shown to be heavily subsidized by benthic recruitment, deriving on average 40% of their planktonic colonies from the benthos. 3. Benthic recruitment of Aphanizomenon flos-aquae, Anabaena flos-aquae and a second Anabaena species contributed less than 2% to planktonic increases, while Microcystis aeruginosa recruitment was negligible. 4. Phosphorus translocation via migrating G. echinulata accounted for most of the phosphorus (P) in the planktonic colonies, and constituted a significant portion of the internal loading of the lake. 5. Estimated P translocation via Aph. flos-aquae was relatively minor, although there was evidence of luxury uptake in the benthos.     

Factors regulating recruitment from the sediment to the water column in the bloom-forming cyanobacterium Gloeotrichia echinulata

1. The influence of light, temperature, sediment mixing and sediment origin (water depth) on the recruitment of the cyanobacterium Gloeotrichia echinulata was examined in the laboratory. 2. Light and temperature were the most important factors initiating germination in G. echinulata. 3. The extent of germination (recruited biovolume) was mainly regulated by temperature and sediment mixing. Furthermore, sediment mixing significantly enhanced the frequency of observed heterocysts and colonies. 4. Despite the fact that the deep and shallow sediments contained a similar number of akinete colonies, the highest recruitment occurred from shallow sediments, indicating that akinetes from shallow sediments have a higher viability than those from deeper parts of the lake. 5. Our results support the hypothesis that shallow sediments are more important than profundal sediments for the recruitment of G. echinulata to the pelagic zone.     

RECRUITMENT AND PELAGIC GROWTH OF GLOEOTRICHIA ECHINULATA (CYANOPHYCEAE) IN LAKE ERKEN1

Different parameters in the life cycle of the colony forming cyanobacterium Gloeotrichia echinulata (J.E. Smith) Richter was evaluated in Lake Erken, Sweden. Recruitment of colonies from the sediments and pelagic abundance were measured during 2 years. These data were then used in a model to evaluate and estimate parameters of the life cycle. In our study, recruitment alone only contributed to a small part (<5%) of the maximum G. echinulata abundance that occurred during late summer. However, recruitment from shallow sediments forms the important seed for the pelagic population. Together with measured rates of migration from the sediment, variations in either pelagic colony division rate or pelagic residence time could explain variations in the measured abundance of G. echinulata in situ.     

RECRUITMENT OF MICROCYSTIS (CYANOPHYCEAE) FROM LAKE SEDIMENTS: THE IMPORTANCE OF LITTORAL INOCULA1

Recruitment of Microcystis from sediments to the water column was investigated in shallow (1–2 m) and deep (6–7 m) areas of Lake Limmaren, central Sweden. Recruitment traps attached to the bottom were sampled on a weekly basis throughout the summer season ( June–September). A comparison between the two sites showed that the recruitment from the shallow bay was significantly higher over the entire season for all three Microcystis species present in the lake. Maximum rates of recruitment were found in August, when 2.3 × 10⁵ colonies m ^{? 2}·day ^{? 1} 1 Received 18 April 2002. Accepted 29 October 2002. left the sediments of the shallow area. Calculated over the entire summer, Microcystis colonies corresponding to 50% of the initial abundance in the surface sediments were recruited in the shallow bay, whereas recruitment from the deep area was only 8% of the sediment colonies. From these results we conclude that shallow areas, which to a large extent have been overlooked in studies of recruitment of phytoplankton, may be crucial to the dynamics of these organisms by playing an important role as inoculation sites for pelagic populations.     

富营养化山仔水库沉积物微囊藻复苏的受控因子

山仔水库作为福建省福州市重要的饮用水水源地之一,从2000年起每年都周期性爆发蓝藻门微囊藻属(Microcystis)水华现象,特别是在温暖的季节。对于这个富营养化水库,是否在沉积物中存在蓝藻门微囊藻的"种源"？假设山仔水库底泥中存在蓝藻门微囊藻休眠体,一定的环境条件能够促进蓝藻门微囊藻的复苏。研究于2009年12月采集水库大坝断面5根柱状沉积物,采用正交试验的方法,模拟了温度、光照、pH值、营养盐、物理扰动和浮游动物(膨大肾形虫)等环境因子对山仔水库沉积物中蓝藻门微囊藻的复苏响应。结果表明,底泥中存在着一定数量的底栖动物和硅藻、蓝藻和绿藻等微藻,从实验结束后沉积物中微囊藻数量的减少和上覆水体中微囊藻数量的增加,可以判断在适宜的环境条件下,蓝藻门微囊藻能够复苏并上浮到上覆水体中。正交实验显著性分析表明,温度是沉积物蓝藻门微囊藻复苏的重要影响因子,光照次之,上覆水体的pH值、营养盐、物理扰动和浮游动物干扰对沉积物蓝藻门微囊藻的复苏影响作用不显著,升温有利于沉积物中微囊藻的复苏。     

Diurnal variations in the auto- and heterotrophic activity of cyanobacterial phycospheres (Gloeotrichia echinulata) and the identity of attached bacteria

1. We assessed the role of cyanobacterial–bacterial consortia (Gloeotrichia echinulata phycospheres) for net changes in inorganic carbon, primary production (PP) and secondary production in Lake Erken (Sweden). 2. At the time of sampling, large colonies of G. echinulata formed a massive bloom with abundances ranging from 102 colonies L^?1 in the pelagic zone to 5000 colonies L^?1 in shallow bays. These colonies and their surrounding phycospheres contributed between 17 and 92% of total PP, and phycosphere‐associated bacteria contributed between 8.5 and 82% of total bacterial secondary production. PP followed a diurnal cycle, whereas bacterial production showed no such pattern. Over a 24 h period, carbon dioxide measurements showed that the phycospheres were net autotrophic in the top layer of the water column, whereas they were net heterotrophic below 2 m depth. 3. Sequencing and phylogenetic analysis of 16S rRNA genes of attached bacteria revealed a diverse bacterial community that included populations affiliated with Proteobacteria, Bacteriodetes, Acidobacteria, Fusobacteria, Firmicutes, Verrucomicrobia, and other Cyanobacteria. 4. Compared with their planktonic counterparts, bacteria associated with cyanobacterial phycospheres had lower affinity for arginine, used as a model compound to assess uptake of organic compounds. 5. Extrapolation of our data to the water column of lake Erken suggests that microorganisms that were not associated with cyanobacteria dominated CO₂ production at the ecosystem scale during our experiments, as CO₂ fixation balanced CO₂ production in the cyanobacterial phycospheres.     

Bloom formation of Gloeotrichia echinulata and Aphanizomenon flos-aquae in a shallow,eutrophic, Danish lake

Over a period of four years, the seasonal periodicity of dominant phytoplankton species in a shallow, eutrophic Danish lake changed markedly. Cyanophytes prevailed during the summer period of all four years. In the first three years, species of Microcystis, Anabaena and Aphanothece dominated, whereas in the fourth year of investigation, these algae were replaced by Gloeotrichia echinulata (J. E. Smith) Richter and Aphanizomenon flos-aquae (L.) Ralfs. The most striking environmental differences in the fourth year as compared with the previous three years, were an increase in tranparency, from about 0.5 meter in 1989–1991 to more than 2 metres preceding the summer maximum in 1992, and a simultaneous occurrence of low oxygen concentrations. A collapse of the fish population was followed by an increased proportion of large Cladocerans in the zooplankton. Improved light conditions at the bottom and grazing pressure from large Cladocerans favoured growth of the large colony forming blue-green algae, Gloeotrichia echinulata and Aphanizomenon flos-aquae. These species germinate from resting spores in the sediment and are able to sustain some growth there before migration to the lake water. The transfer of algal biomass from the bottom sediment to the water phase was accompanied by a marked increase in concentrations of particulate phosphorus and nitrogen in the entire lake.     

Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainment

1. Wind‐induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas‐tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light‐limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light‐limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity.     

The viability of akinetes of blue-green algae recovered from the sediments of Rostherne Mere

Akinetes from species of blue-green algae were recovered from the recent sediments of Rostherne Mere. Gas vacuolate populations of Aphanizomenon and Anabaena were cultured from sediment up to 18 and 64 years old respectively. Akinetes of blue-green algae may not only have a temporary, or overwintering, function but may also ensure long term survival.     

RECRUITMENT OF BENTHIC MICROCYSTIS (CYANOPHYCEAE) TO THE WATER COLUMN: INTERNAL BUOYANCY CHANGES OR RESUSPENSION?1

In some lakes, large amounts of the potentially toxic cyanobacterium Microcystis overwinter in the sediment. This overwintering population might inoculate the water column in spring and promote the development of dense surface blooms of Microcystis during summer. In the Dutch Lake Volkerak, we found photochemically active Microcystis colonies in the sediment throughout the year. The most vital colonies originated from shallow sediments within the euphotic zone. We investigated whether recruitment of Microcystis colonies from the sediment to the water column was an active process, through production of gas vesicles or respiration of carbohydrate ballast. We calculated net buoyancy, as an indication of relative density, using the amounts and densities of the major cell constituents (carbohydrates, proteins, and gas vesicles). Carbohydrate content of benthic Microcystis cells was very low throughout the year. Buoyancy changes of benthic Microcystis were mostly a result of changes in gas vesicle volume. Before the summer bloom, net buoyancy and the amount of buoyant colonies in the sediment did not change. Therefore, recruitment of Microcystis from the sediment does not seem to be an active process regulated by internal buoyancy changes. Instead, our observations indicate that attachment of sediment particles to colonies plays an important part in the buoyancy state of benthic colonies. Therefore, we suggest that recruitment of Microcystis is more likely a passive process resulting from resuspension by wind‐induced mixing or bioturbation. Consequently, shallow areas of the lake probably play a more important role in recruitment of benthic Microcystis than deep areas.     

Recruitment of Total Phytoplankton,Chlorophytes and Cyanobacteria from Lake Sediments Recorded by Photosynthetic Pigments in a Large,Shallow Lake (Lake Taihu,China)

Recruitment of total phytoplankton, chlorophytes and cyanobacteria from lake sediments to the water column was studied using photosynthetic pigments at one site (1.5 m) in Lake Taihu, a large shallow lake in China. Samples were taken weekly from the migration traps installed on the bottom from March to May 2004. Abundance of total phytoplankton, chlorophytes and cyanobacteria were represented by Chlorophyll (Chl) a, b, and phycocyanin (PC), respectively. Over the three months, total phytoplankton, chlorophytes, and cyanobacteria corresponding to 48.9%, 68.9% and 316.2% of their initial concentrations in surface sediments were recruited in Lake Taihu. However, compared with their increase in pelagic abundance over the same period, the recruitment accounted for a rather small inoculum. Accompanying the recruitment, total phytoplankton and chlorophytes declined and cyanobacteria increased in the upper 0–2 cm sediments; colonies of Microcystis aeruginosa in the water column enlarged from small size with several cells to large colonies with hundreds of cells. Thus, overwintering and subsequent growth renewal of pelagic phytoplankton merits further study and comparison with benthic survival and recruitment. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The role of Gloeotrichia echinulata in the transfer of phosphorus from sediments to water in Lake Erken

The abundance of Gloeotrichia echinulata colonies in the sediments of Lake Erken and their phosphorus content were investigated to determine the contribution of Gloeotrichia colonies to total sediment phosphorus. Moreover, the potential size of the algal inoculum and the migration to the water during summer were estimated.The surplus phosphorus content of the resting colonies in the sediment was about 45% of total phosphorus, which maximized at 8.5 µg P (mg dw)^–1 or 81 ng P colony^–1. The C:P ratio (by weight) in the early colonies appearing in the lake water was 50:1, while the ratio stabilized at 150 during the major migration period. The internal supply of surplus phosphorus was used during the pelagic growth of the colonies.The internal phosphorus loading to the epilimnion of Lake Erken due to Gloeotrichia migration could, from the measurements of the increase in particulate epilimnetic phosphorus, be estimated at 40 mg P m ^–2 or 2.5 mg P m^–2 d^–1 in late July and early August. Determination of the number of colonies in the sediment before and during the migration verified this value to be a conservative estimate of the internal phosphorus loading due to Gloeotrichia migration to the epilimnion in Lake Erken.The sediment P content calculated from the P concentration in early epilimnion colonies resulted in a value of 35 µg P (g dw)^–1 as a maximum. This corresponds to only 3% of the total phosphorus content in Lake Erken sediment.     

Algal nitrogen fixation in the tropics

Summary a)Nitrogen fixation in rice fields. Nitrogen-fixing blue-green algae grow abundantly in tropical regions and are particularly common in paddy fields. Their possible role in the nitrogen accumulation of soil has been studied. The most vigorous nitrogen-fixing blue-green algae have been assessed for use as green manure in rice fields and favorable effects have been reported in India and other countries. b)Nitrogen fixation by algae in water. The planktonic blue-green algae occur abundantly at certain time of the year in sea water and lake water, and some of them are known to be nitrogen fixers. Certain Japanese species of blue-green algae can withstand high temperatures including ten nitrogen-fixing species from hot-spring waters. c)Nitrogen fixation by symbiotic blue-green algae. Certain species of blue-green algae form associations with other organisms such as fungi, liverworts, ferns and seed plants. The relationship between these two organisms is on one occasion commensal and on others symbiotic. Certain symbiotic blue-green algae are provided with the ability to fix the atmospheric nitrogen.     

Is food availability the main factor controlling the abundance of Euchlanis dilatata lucksiana Hauer in a shallow,hypertrophic lake?

Visual observations and experiments on food preference of Euchlanis dilatata lucksiana show that this euchlanid can feed on blue-green algae not consumed by the most planktonic animals. Nevertheless, even in lakes with blooms of blue-green algae, E. d. lucksiana occur infrequently and generally in low numbers. The paper is an attempt to explore into the causes for the rare occurrence of Euchlanis in the pelagial. A comparison of threshold food concentrations calculated from N and P excretion rates (Gulati et al., this volume) with the concentrations of seston in the Lake Loosdrecht shows that the latter were several times higher during study period in 1984. This implies that the food requirements of Euchlanis were always satisfied in this lake. The time needed for the consumption of the total food fraction in a liter of lake water by a concentration of 50 Euchlanis l^–1 was also calculated. This time varied from 70 to 200 days, so a Euchlanis population even at its maximum density will not cause major changes in blue-green algae biomass by grazing. Thus, food limitation cannot be viewed as a factor controlling the Euchlanis densities in Loosdrecht Lakes. There is some evidence that Euchlanis is heavily predated in Loosdrecht Lakes, losses in its biomass accounting for 126% of the production. Adaptation of this species to the littoral zone, as expressed by the deposition of eggs on plants, can also limit the occurrence of the lucksiana form to water bodies with blooms of blue-green algae.     

Available phosphorus in lake sediments in The Netherlands

The amount of phosphorus available to algae in the sediments of four lakes in the western part of the Netherlands has been assessed by means of chemical extraction and bioassay techniques. In addition to direct chemical sediment analyses, extractions were carried out with an NTA column method and a stepwise NH₄ Cl-NaOH-HCI shaking method, the latter supposedly separating the weakly bound, the Fe- and Al-bound and the Ca-bound phosphates in the sediments. Bioassays, with sediment as the sole source of P, were made withScenedesmus quadricauda in modified Skulberg's 28 medium to determine the amount of phosphates available to algae.The average total P concentration of the sediments varied from 0.8 to 3.6 mg P g^–1 dry wt and correlated well with the net external P loading of the lakes. Uptake of P by algae in the bioassays varied from 0.4 to 36% — while NTA extracted 36–69% of the total P. The ratio NH₄Cl extracted/ NaOH extracted/ HCI extracted phosphates is different from lake to lake, although in all lakes the highest extractions (27–62% of total P) are found in the NaOH fraction. However, in the peaty sediments of these lakes, the NaOH step extracted not only the Fe- and Al-bound phosphates but, also, large amounts of humus compounds. Hence, this fraction also contains non-available organic P.The results are related to soil type and chemical characteristics of the sediments, and compared with data from other authors. A positive correlation was found between phosphate available to algae and NTA- and NaOH-extractable P, but the correlation with total phosphorus was higher. Moreover, algal-extractable P proved to be positively correlated with total iron and clay content and negatively with the amount of organic matter.It is concluded that the sediments in the investigated lakes show great variability and that the chemical extraction techniques cannot replace the bioassays to assess the amount of phosphorus available to algae.     

Pelagic growth and colony division of Gloeotrichia echinulata in Lake Erken

Gloeotrichia echinulata colony development was monitored inLake Erken, Sweden and studied in enclosure experiments. Significantcolonial division did not occur in mesh bags, although the abundanceof the pelagic population in the lake increased during the experimentalperiods. On the basis of these findings, it is suggested thatcirculation of G. echinulata to deeper nutrient rich water supportspelagic growth. In support of this, a large part of the buoyantG. echinulata colonies in Lake Erken was found at several metersdepth. In an experiment with nutrient additions, the only treatmentthat favoured G. echinulata development was additions of phosphate,nitrate and iron. Trace element additions had a negative effecton the development of G. echinulata. On the basis of these findings,the nutritional requirements of G. echinulata are discussed.     

The hypolimnetic protozoan plankton of a eutrophic lake

The seasonal distribution of benthic species in the water column above and below the thermocline in a small eutrophic lake is described. During summer stratification populations of Spirostomum spp, Loxodes spp., Plagiopyla and Deltopylum become established in the plankton on or below the oxycline/thermocline. At shallow sites no migration occurred and populations of the migratory species in the benthos were sparse, with the exception of Plagiopyla which occurred in high densities in the sediment. Two distinct planktonic populations are established during stratification: an epilimnetic community of obligate planktonic ciliates and a hypolimnetic community of benthic migrants.     

太湖梅梁湾水华蓝藻复苏过程的研究

采用在底泥表面设置藻类细胞捕捉器的方法,测定其中的色素含量变化,并与水柱和底泥中的色素含量变化相比较.结果表明,藻类复苏与底泥环境中的温度、光照、溶解氧、氧化还原电位均有密切关系,叶绿素a、b和藻蓝素所表征的总藻类、绿藻以及蓝藻的上浮率分别为59.84%、76.83%和466.98%,3种藻的上浮量分别占相应浮游藻类最大生物量的7.18%、3.71%和9.33%.蓝藻复苏对太湖水华的形成具有很重要的意义.     

Influence of outbreak of macroalgal blooms on phosphorus release from the sediments in Swan Lake Wetland,China

Macroalgal blooms have occurred worldwide frequently in coastal areas in recent decades, which dramatically modify phosphorus (P) cycle in water column and the sediments. Rongcheng Swan Lake Wetland, a coastal wetland in China, is suffering from extensive macroalgal blooms. In order to verify the influence of macroalgal growth on sediment P release, the sediments and filamentous Chaetomorpha spp. were incubated in the laboratory to investigate the changes of water quality parameters, P levels in overlying water, and sediments during the growth period. In addition, algal biomass and tissue P concentration were determined. In general, Chaetomorpha biomasses were much higher in high P treatments than in low P treatments. Compared with algae+low P water treatment, the addition of sediments increased the algal growth rate and P accumulation amount. During the algal growth, water pH increased greatly, which showed significant correlation with algal biomass in treatments with high P (P < 0.05). P fractions in the sediments showed that Fe/Al–P and organic P concentrations declined during the algal growth, and great changes were observed in algae+low P water+sediment treatment for both. As a whole, the sediments can supply P for Chaetomorpha growth when water P level was low, and the probable mechanism was the release of Fe/Al–P at high pH condition induced by intensive Chaetomorpha blooms.     

WATER-BLOOMS

1. Peculiarities in the ecology of planktonic blue-green algae are reviewed in relation to recent advances in understanding their physiological characteristics. 2. Dense water-blooms are always the result of buoyant migration of existing populations to the lake surface under calm weather conditions. The size of the population is the direct result of photoautotrophic growth, and is dependent upon light and the availability of inorganic nutrients; it is apparently enhanced by moderately high water temperatures, high pH, low oxygen tensions and possibly, the presence of organic solutes. The relative effectiveness of these factors is untested. 3. Buoyancy is imparted by gas vacuoles whose principal function is to regulate the position of the alga in the water column. Control is effected by two mechanisms: (i) ‘dilution’ of newly produced vacuoles during active cell division; (ii) changes in cell turgor-pressure acting on the gas-vacuole structure. Gas-vacuole production is greatest at low light intensities and the alga becomes more buoyant; at higher light intensities, increased turgor-pressure collapses the weaker vacuoles causing the alga to lose buoyancy. 4. Potentially, algae are able to poise themselves at an optimum point in the light gradient, usually towards the bottom of the euphotic zone, where the algae are likely to encounter the conditions most favouring their growth. 5. Different species of blue-green algae differ in the typical sizes of their colonies and, hence, in their rates of controlled movement. These differences are interpreted as hydrodynamic adaptations to the variations in turbulent water movements to which the algae are subject. 6. Populations of single-filamentous Oscillatoria agardhii and O. rubescens come to occupy the stable metalimnia of stratified lakes, provided that they are located within the euphotic zone. 7. The large stream-lined colonial forms occur mainly in polymictic lakes and in the unstable epilimnia of stratified lakes where light penetration is restricted to the superficial layers. These algae are adapted to sink or float rapidly to the optimum depth when turbulence subsides. Because of their potentially high rates of movement, it is the large colonial forms that commonly form blooms. 8. Bloom formation can occur when most of the algae possess excess buoyancy. Excess buoyancy is acquired when the photosynthetic rate is insufficient to develop the necessary turgor-pressure to cause collapse of the vacuoles. Photosynthesis may be sufficiently impaired under four circumstances: (i) during turbulent circulation of the population over a depth that significantly exceeds the euphotic depth; (ii) in the absence of light (e.g. at night): (iii) at limiting concentrations of carbon dioxide: and (iv) when the algal population is senescent. 9. Because bloom-formation depends upon the coincidence of persistent algal overbuoyancy with calm weather, its occurrence is incidental, and serves no vital function in the biology of blue-green algae. 10. Some possible causes for the occurrence of blue-green algal blooms in a relatively restricted range of water bodies are discussed. Large bloom-forming populations are probably restricted to moderately rich, mildly alkaline, thermally unstable lakes in all regions, except those which are permanently cold. Extremes of poverty or richness of nutrients, short water-retention times and low pH seem to be factors which select against planktonic blue-green algae.