Sediment-to-water blue-green algal recruitment in response to alum and environmental factors

The sediment-to-water recruitment of blue-green algae was investigated in a shallow lake following treatment with aluminum sulfate and sodium aluminate to control sediment phosphorus (P) release. A comparison of results from two summers each before and after treatment indicates that the treatment did not universally impact the recruitment of either sporulating or non-sporulating forms of blue-green algae. Blooms of Anabaena, Aphanizomenon, and Coelosphaerium resulted predominantly from growth in the water column following strong recruitment episodes lasting up to two weeks, while Microcystis populations were relatively insensitive to periodically high inputs from recruitment. The development of planktonic populations of Gloeotrichia echinulata, by contrast, were largely dependent on sustained recruitment in response to adequate light and temperature regimes at the sediment surface.The cellular P content of recruited G. echinulata colonies was unaffected by the accumulation of aluminum floc to the lake sediments. Both G. echinulata and C. naegelianum showed elevated levels of cellular P in newly recruited colonies as compared to planktonic colonies, indicating P transport from the sediments to the water column. Total P translocation by blue-green algae was negligible in the absence of a substantial recruitment of G. echinulata. The recruitment of G. echinulata, and hence the magnitude of P translocation, was therefore more responsive to environmental conditions prevalent at the sediments than to direct effects of the treatment itself.     

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 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 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.     

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.     

Fouling mussels (Dreissena spp.) colonize soft sediments in Lake Erie and facilitate benthic invertebrates

• 1 We conducted survey and transplant studies to determine whether colonization and residency on soft sediments by introduced, fouling mussels (Dreissena polymorpha and D. bugensis) were affected by physical disturbance, and whether Dreissena presence in turn influenced the diversity and population densities of other benthic invertebrates. Surveys revealed that colony density was typically higher at moderate depths than at shallower and greater ones. However, the largest, midsummer colonies and greatest coverage of sediments by mussels occurred at deeper sites.
• 2 Disturbance of transplanted colonies varied by depth and colony size, with deeper and larger colonies experiencing the lowest destruction rates. Colony destruction rate was positively correlated with current velocity adjacent to the lakebed.
• 3 Absence of mussel colonies at shallow sites was not determined by recruitment or substrate limitation, as recruit density was higher and sediment characteristics more suitable for postveliger settlement at shallow than at deeper sites. Rather, seasonal storms have much stronger effects in shallow than in deep water.
• 4 Mussel residency on soft sediment has profound effects on invertebrate biodiversity. Invertebrate species (taxon) richness and total abundance were positively correlated with mussel colony area. Mussel‐sediment habitat supported between 462 and 703% more taxa, and between 202 and 335% more individuals (exclusive of Dreissena) than adjacent soft‐sediment lacking mussels.
• 5 Results from this study illustrate that physical disturbance directly limits the distribution of mussels on soft sediments, and the diversity and abundance of other benthic invertebrates in consequence.

     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.     

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.     

Seed germination traits of Trapella sinensis (Trapellaceae), an endangered aquatic plant in Japan: Conservation implications

We investigated the effects of cold stratification, temperature, light, and oxygen conditions on seed germination of Trapella sinensis Oliver, an endangered aquatic plant in Japan. Seeds had physiological dormancy, and final germination rate increased with an increasing period of cold stratification. Seeds of T. sinensis had an almost absolute requirement for aerobic conditions to germinate. Also, alternating temperatures significantly promoted germination regardless of light conditions, although final germination percentage was twice to four times higher in light under constant temperature conditions. Suitable sites for germination of T. sinensis appear to be shallow water with alternating temperatures and sufficient oxygen and sediment anoxia, caused by eutrophication of water bodies, may have prevented recruitment of T. sinensis from seed.     

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.     

Effects of salinity and source of inocula on germination of Anabaena akinetes from a tidally influenced lake

1. Sedimentary akinetes (resting stages) may represent significant potential inocula for nuisance blooms of cyanobacteria. We studied the effects of salinity and sediment source on the germination and subsequent growth of Anabaena flos‐aquae akinetes from a shallow, tidally influenced lake. 2. Surface sediments collected from littoral and open‐water sites were used as inocula to culture A. flos‐aquae akinetes in four salinities (0.1, 2.2, 4.4 and 6.5) over 22 days. Akinete germination and development was followed by counting developmental stages every second day. 3. Filament growth, but not akinete germination, was inhibited by salinity and there were significantly fewer filaments at 6.5 than at 0.1 and 2.2. Cultures inoculated with littoral sediment had more akinetes, germlings and filaments than those inoculated with open‐water sediment. 4. Sediment is a potential source of inocula for Anabaena blooms in the lake, which potentially could develop solely from this source because germination and subsequent filament growth do not depend on the existence of an initial pelagic Anabaena population.     

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.     

THE IMPORTANCE OF SHALLOW SEDIMENTS IN THE RECRUITMENT OF ANABAENA AND APHANIZOMENON (CYANOPHYCEAE)1

Recruitment of Anabaena and Aphanizomenon from the 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 weekly throughout the summer season (June through September). A comparison between the two sites shows that the largest part of the recruited cells originated from the shallow site, although recruitment occurred at all depths in the lake. There were also differences between the species, regarding the site as well as the timing of the recruitment. The contribution of the inoculum to the pelagic population was calculated to vary between 0.003% and 0.05% for the different species. From these results we conclude that shallow sediments are more important than deep ones for the recruitment and that the inoculum in Lake Limmaren is small but may still be an important factor in the population dynamics.     

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)     

ROLE OF ENCYSTMENT AND EXCYSTMENT OF PERIDINIUM BIPES F. OCCULATUM (DINOPHYCEAE) IN FRESH WATER RED TIDES IN LAKE KIZAKI,JAPAN1

The encystment flux of Peridinium bipes f. occulatum (Dinophyceae) was investigated with sediment traps from 1968 to 1990 in Lake Kazki. Cysts of P. bipes were formed throughout the blooms, Encystment flux of P. bipes in the pelagic zone was usually lower than those at shallow sites, and the density of P. bipes cysts in lake sediment was higher in the shallow region than in the pelagic zone. However, in the shallower region, The concentration of P. bipes cysts varied widely, possibly due to high rates of encystment and excystment. Peridinium bipes encystment occurred between 15° and 25° C in the laboratory, with very little cyst formation below 10°C. Though cyst formation was observed in continous darkness, the rate increased with irradiance. Under continuous darkness, no excystment was observed at any temperature from 5° to 25° C. Eighty-one percent of the cysts illuminated at 105 μE m^?2 s^?1 excysted after 13 days incubation at 15° C, and lower irradiances decreased germination success. Results from laboratory experiments suggest that light is a critical factor in the germination of P. bipes cysts. Bottom depth thus can have a significant effect on germination because cysts only can excyst from depths where light is sufficient. The shallow region of the lake is thus very important as a seed bed for P. bipes during early spring. Cyst deposited in deeper waters may not ever germinate unless they are resuspended and transported to shallow areas where light reaches the bottom.     

Temporal changes in biomass specific photosynthesis during the summer: regulation by environmental factors and the importance of phytoplankton succession

Measurements of phytoplankton photosynthesis vs. irradiance relationships have been made at 3–7 day intervals in Lake Erken (central Sweden) for three years during summer stratification. Both the rate of light-limited (^B) and light-saturated (P_max ^B) photosynthesis per unit chlorophyll a showed distinct and similar temporal trends in each year. Seasonal trends were especially evident for P_max ^B, which increased in value for several weeks following the onset of thermal stratification, and then declined in the presence of the large colonial blue-green alga, Gloeotrichia echinulata. By late summer, when the biomass of G. echinulata had decreased, P_max ^B again rose to its early summer value. The covariation of biomass-specific photosynthesis with the blooming of G. echinulata was the one clear seasonal (week-month) pattern which emerged in each of 3 years. Over short (day-week) time scales, changes in ^B were related to changes in irradiance exposure on the day of sampling. However, the relationship between these two parameters was variable in time, since it was superimposed upon longer term trends controlled by changes in phytoplankton species composition. Increases in G. echinulata biomass corresponded with a deepening of the thermocline, which both increased internal phosphorus loading and the transport of resting G. echinulata colonies into the epilimnion. The timing and magnitude of the yearly G. echinulata bloom was as a result related to the seasonal development of thermal stratification. These results illustrate the importance of seasonal changes in the phytoplankton community as a factor regulating rates of biomass specific photosynthesis, particularly when the successional changes involve species with very different life strategies.     

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.     

Inhibition of Chara vulgaris oospore germination by sulfidic sediments

The germinability of Chara vulgaris oospores collected from the sediments of four Ontario lakes varies considerably, ranging in germination percentage from 7% to 54%. Chemical analysis of the interstitial water of the sediments indicated that oospores with low germination occurred in lakes which have high acid volatile sulfides (H₂S, FeS, HS⁻) and high soluble Fe²⁺. The inhibitory effects of sediment on oospore germination were demonstrated by transplant experiments, and suggested that sulfide was the toxic agent. Exposure of high-germinating sedimentary oospores to free sulfide concentrations greater than 2.0 mM caused a greater than 30% reduction in oospore germination. The presence of sulfide in sediments was shown to result from sulfate reduction by bacteria in sediment pore water of those lakes where oospore viability was lowest. Differences in oospore germination percentage appear, therefore, to be due to the toxicity of H₂S produced in the sediment, either by a direct effect on the oospore, or on the parent plants.     

Microbial activity and phosphorus dynamics in eutrophic lake sediments enriched with Microcystis colonies

1. Sediments from hypereutrophic Lake Vallentunasjön were enriched with Microcystis colonies from the lake water, thereby simulating the conditions after the autumn sedimentation. Release of phosphorus to the overlying lake water was followed during 2–3 weeks in the laboratory. X-ray microanalysis of individual Microcystis and bacterial cells, and chemical phosphorus fractionation, were used to assess the phosphorus pool size in different fractions of the sediment. 2. Benthic Microcystis colonies, most of these having survived within the sediment for 1 year or more, were less susceptible to decomposition, and the specific growth rate of bacteria in their mucilage was lower than for other sediment bacteria. 3. Pelagic Microcystis colonies from late August were resistant to decomposition, when placed on the sediments. When Microcystis colonies from a declining pelagic population in October were added to the sediments, however, a substantial fraction of these colonies was decomposed. The specific growth rate of mucilage bacteria was five times higher than for other sediment bacteria. 4. Release of molybdate-reactive phosphorus to the overlying lake water was larger from sediment cores enriched with Microcystis colonies than from control cores. Chemical phosphorus fractionation showed a decrease in organic-bound phosphorus (residual P). 5. X-ray microanalysis showed that the phosphorus bound in Microcystis cells decreased by -0.300 mg g^?1 DW in the October experiment, due both to a decrease in biomass (i.e. mineralization) and to a decrease in phosphorus content in the remaining cells. Heterotrophic bacteria increased their cellular concentration of phosphorus. The net release of phosphorus from the Microcystis and bacterial pools corresponded to 74% of the decrease of organic-bound phosphorus in the chemical phosphorus fractionation, and to 65% of the decrease of total phosphorus in the upper 0–1 cm of the sediment. 6. Benthic bacteria and cyanobacteria may thus contribute significantly to changes in phosphorus content and turnover of the sediment by changes in their biomass, turnover rate and cellular phosphorus content.