Phycocyanin-rich Picocyanobacteria Research Articles

A Biogeochemical Comparison of three Representative Lakes of Costa Rica

ABSTRACT Lakes are widely distributed across Costa Rica, from coasts to the highest elevation regions, and located in the main terrestrial biomes. However, updated biogeochemical information about the main types of lakes is still lacking. We present comparative biogeochemistry (water chemistry, stable isotopes, and picoplankton) for a coastal lake (Lake Madre de Dios, LMD), a volcanic lake (Lake Barva, LB), and a glacial lake (Lake Ditkevi, LD). Sampling was conducted between February-November 2022 including dry and rainy seasonal conditions. Hydrological and chemical conditions were evaluated using water and carbon stable isotopes, dissolved organic matter (DOM), major ions, and microbiota analysis. Isotopic data (δ18O, δ13CDIC) confirmed lower evaporative losses for the maar and tarn lakes and productivity response to precipitation inputs. Excitation/Emission matrices confirmed the prevalence of fulvic and humic acids in the coastal and glacial lakes, mainly aromatic proteins and soluble microbial by-products in the volcanic lake. Picophytoplankton (PPP, ∼0.2 to 10 μm) was mainly represented by phycocyanin-rich picocyanobacteria (PC-Pcy) events in the three lakes, but maar and tarn lakes had more representation of phycoerythrin (PE-Pcy) events. We confirmed fluctuations in PPP cell abundance in the lakes lower than in temperate lakes. Like in other eutrophic lakes, Pcy also dominated over picoeukaryotes (Peuk) algae abundance. This work seeks to promote adopting an ecosystem approach to study the biogeochemical functioning of tropical lakes using the combination of chemical, hydrological, and biological data and to provide baseline information for future studies (e.g., climate change and pollution impacts) on tropical lakes of Costa Rica.

Seasonal dynamics in picocyanobacterial abundance and clade composition at coastal and offshore stations in the Baltic Sea

Picocyanobacteria (< 2 µm in diameter) are significant contributors to total phytoplankton biomass. Due to the high diversity within this group, their seasonal dynamics and relationship with environmental parameters, especially in brackish waters, are largely unknown. In this study, the abundance and community composition of phycoerythrin rich picocyanobacteria (PE-SYN) and phycocyanin rich picocyanobacteria (PC-SYN) were monitored at a coastal (K-station) and at an offshore station (LMO; ~ 10 km from land) in the Baltic Sea over three years (2018–2020). Cell abundances of picocyanobacteria correlated positively to temperature and negatively to nitrate (NO3) concentration. While PE-SYN abundance correlated to the presence of nitrogen fixers, PC-SYN abundance was linked to stratification/shallow waters. The picocyanobacterial targeted amplicon sequencing revealed an unprecedented diversity of 2169 picocyanobacterial amplicons sequence variants (ASVs). A unique assemblage of distinct picocyanobacterial clades across seasons was identified. Clade A/B dominated the picocyanobacterial community, except during summer when low NO3, high phosphate (PO4) concentrations and warm temperatures promoted S5.2 dominance. This study, providing multiyear data, links picocyanobacterial populations to environmental parameters. The difference in the response of the two functional groups and clades underscore the need for further high-resolution studies to understand their role in the ecosystem.

Seasonality of Coastal Picophytoplankton Growth, Nutrient Limitation, and Biomass Contribution.

Picophytoplankton in the Baltic Sea includes the simplest unicellular cyanoprokaryotes (Synechococcus/Cyanobium) and photosynthetic picoeukaryotes (PPE). Picophytoplankton are thought to be a key component of the phytoplankton community, but their seasonal dynamics and relationships with nutrients and temperature are largely unknown. We monitored pico- and larger phytoplankton at a coastal site in Kalmar Sound (K-Station) weekly during 2018. Among the cyanoprokaryotes, phycoerythrin-rich picocyanobacteria (PE-rich) dominated in spring and summer while phycocyanin-rich picocyanobacteria (PC-rich) dominated during autumn. PE-rich and PC-rich abundances peaked during summer (1.1 × 105 and 2.0 × 105 cells mL–1) while PPE reached highest abundances in spring (1.1 × 105 cells mL–1). PPE was the main contributor to the total phytoplankton biomass (up to 73%). To assess nutrient limitation, bioassays with combinations of nitrogen (NO3 or NH4) and phosphorus additions were performed. PE-rich and PC-rich growth was mainly limited by nitrogen, with a preference for NH4 at >15°C. The three groups had distinct seasonal dynamics and different temperature ranges: 10°C and 17–19°C for PE-rich, 13–16°C for PC-rich and 11–15°C for PPE. We conclude that picophytoplankton contribute significantly to the carbon cycle in the coastal Baltic Sea and underscore the importance of investigating populations to assess the consequences of the combination of high temperature and NH4 in a future climate.

The spatial distribution of the photosynthetic picoeukaryotes community structure in Lake Hongze.

The spatial dynamics of picophytoplankton were investigated by flow cytometry and high-throughput sequencing in Lake Hongze, a large river-connecting lake. Picophytoplankton were mainly composed of phycocyanin-rich picocyanobacteria (PCY) and photosynthetic picoeukaryotes (PPEs). Picocyanobacteria was the dominant picophytoplankton group since the contribution of PPEs to total picophytoplankton was only 11.78%. However, PPEs were highly diverse and were composed of Chlorophyta, Bacillariophyta and Chrysophyceae. Environmental factors showed spatial differences, particularly in total phosphorus (TP), suspended solids (SS) and chemical oxygen demand (CODMn), which showed relatively high concentrations around the river channel. The abundances of PPEs and PCY showed similar spatial patterns, which were relatively low in the river course since they were negatively related to SS and CODMn. The top 10 OTUs contributed 79.18% of the total PPEs reads and affiliated with main species in PPEs. CCA results showed that, PPEs community composition was significantly impacted by temperature and DO at sites away from river channel, while was only influenced by nitrite at sites around the river channel.

Recurrent pattern of picophytoplankton dynamics in estuaries around the world: The case of Río de la Plata

The picoplankton is an important component of aquatic food webs and plays a significant biogeochemical and ecological role in the environment. Little is known about this fraction of the plankton in temperate estuaries and especially in South America. In this article, we study the absolute and relative importance of the picoplankton along an annual cycle, and their relationship with physical and chemical variables in the Río de la Plata estuary. We also review the existing research in estuaries around the world concerning this community and present our results in a global context. The seasonal variation in the abundance of the different groups analyzed was very noticeable. Phycocyanin-rich picocyanobacteria (Pcy) were the main component (in abundance and in biovolume) of the picophytoplankton (PPP) almost during the whole year, with a maximum abundance of 7.3 × 105 cell mL−1 in summer, three orders of magnitude higher compared to autumn-winter. Picoeukaryotes, larger phytoplankton and heterotrophic bacteria showed the same seasonal trend, although with a lower range of variation than that of the Pcy. Considering all the phototrophic planktonic fractions, in terms of biomass, the PPP reached a maximum of 43% of the total biomass in spring. The dynamics of PPP found in this area are consistent with the observed in other temperate estuaries, where temperature is the main variable that influences its development, and with a high seasonal variation. Additionally, the absolute and relative importance of Pcy showed a consistently increasing trend towards lower latitude estuaries. The review also showed us that there is scarce information related to the picoplankton fraction in the Southern Hemisphere, its sanitary implications due to their potential of toxicity or their ecological role in coastal zones. The results presented here show the importance of this fraction, not only in Río de la Plata, but in many estuaries of the world, with a clear increase of relative abundance as we approach the equator.

New findings on the effect of glyphosate on autotrophic and heterotrophic picoplankton structure: A microcosm approach

Massive use of glyphosate-based herbicides in agricultural activities has led to the appearance of this herbicide in freshwater systems, which represents a potential threat to these systems and their communities. These herbicides can affect autotrophic and heterotrophic picoplankton abundance. However, little is known about glyphosate impact on the whole structure of these assemblages. Herein, we used an 8-day long microcosm approach under indoor controlled conditions to analyze changes in the structure of picoplankton exposed to a single pulse of glyphosate. The analyzed picoplankton correspond to two outdoor ponds with contrasting states: “clear” (chlorophyll-a = 3.48 μg L−1± 1.15; nephelometric turbidity, NTU = 1) and “turbid” (chlorophyll-a = 105.96 μg L−1 ± 15.3; NTU = 48). We evaluated herbicide impact on different picoplankton cytometric populations and further explored changes in bacterial dominant operational taxonomic units (OTUs) fingerprinting. We observed that glyphosate induced a drastic decrease in the abundance of phycocyanin-rich picocyanobacteria. Particularly, in the turbid system this effect resulted in an 85 % decrease in the abundance of the whole autotrophic picoplankton. Glyphosate also changed the structure of the heterotrophic fraction by means of changing bacterial dominant OTUs fingerprinting patterns in both systems and by shifting the relative abundances of cytometric groups in the clear scenario. These results demonstrate that upon glyphosate exposure picoplanktonic fractions face not only the already reported changes in abundance, but also alterations in the composition of cytometric groups and of bacterial dominant operational taxonomic units. This research provides suitable and still little explored tools to analyze agrochemical effects on picoplanktonic communities.

Turbidity matters: differential effect of a 2,4-D formulation on the structure of microbial communities from clear and turbid freshwater systems

We evaluated the effect of AsiMax 50®, a commercial formulation of 2,4-D (2,4-dichlorophenoxyacetic acid), on the structure of both micro + nano phytoplankton (>2 μm; species composition and abundance) and cytometric populations (photosynthetic picoplankton (PPP, 0.2–2 μm), which included prokaryotic phycocyanin-rich picocyanobacteria (PC-Pcy), phycoerythrin-rich picocyanobacteria (PE-Pcy) and eukaryotic phototrophs (PEuk); and bacterioplankton (HB), heterotrophic bacteria), using a microcosms-based approach and a single 7-day exposure. Assays were performed on two different microbial assemblages sampled from freshwater bodies of two contrasting turbidity status: clear (chlorophyll a = 7.6 μgL-1, turbidity = 1 NTU) and organic turbid systems (chlorophyll a = 25.0 μgL-1, turbidity = 9 NTU). For each system, the herbicide was applied to 500 mL-Erlenmeyer flasks, at seven concentration levels of the active ingredient (a.i.): 0 (control = no addition), 0.02, 0.2, 2, 20, 200 and 2,000 mg a.i.L−1. The impact of AsiMax 50® seemed to be greater in the turbid system. In this system, total abundance of living (live) micro + nano phytoplankton showed a significant increase at lower concentrations and data were fitted to a humped-shaped curve. For both clear and organic turbid systems, micro + nano phytoplankton decreased in species richness and abundance at higher herbicide concentrations. These results suggest that 2,4-D may mimic hormonal function. Some species, such as Ochromonas sp. and Chlamydomonas sp., showed different responses to herbicide exposure between water systems. In the turbid system, the increase in abundance of the PPP fraction observed at 7-d exposure was probably due to either an increase in PE-Pcy (thus suggesting the existence of auxin pathways) or a reduction in competitive pressure by micro + nano plankton. Our results provide some evidence of the importance of using community-scale approaches in ecotoxicological studies to predict changes in freshwater ecosystems exposed to a 2,4-D-based formulation. However, caution must be taken when extrapolating these effects to real scenarios, as assays were based on a laboratory microcosm experiment.

Physiological and behavioral responses of phytoplankton communities to nutrient availability in a disturbed Mediterranean coastal lagoon

Short-term bioassays were conducted in Biguglia lagoon (Corsica) to study the physiological and behavioral responses of phytoplankton to N- and P-availability. Natural communities were collected in two stations representative of the two sub-basins, at three periods with contrasting environmental characteristics to address the impact of seasonal variability. These samples were separately enriched with a full N and P enrichment, and with enrichments minus N or minus P. Phytoplankton size structuration, diversity, and growth of the total phytoplankton, the micro-, nano- and ultraphytoplankton were evaluated using spectrofluorimetry, and optical microscopy. Results showed that the communities were fueled by NO3− in the wet periods (autumn and spring) and NH4+ in summer. The phytoplankton communities displayed highest cell size in autumn, with high abundances of nanoflagellates, and smallest cell size in summer with a large dominance of phycocyanin-rich picocyanobacteria. Blooms of dinoflagellates also occurred during the wet periods, coinciding with high N:P ratios. The full enrichment has not stimulated phytoplankton growth in autumn, suggesting the importance of other controlling factors such as light, a possible NH4+ inhibition or the use of mixotrophic abilities. In spring, communities have displayed single P-limitation in the northern basin and different N and P co-limitations in the southern basin. In summer, the full enrichment consistently stimulated the growth of all cell sizes. The communities showed high N and P co-limitations, which is consistent with growing observations in aquatic ecosystems, and reflects the different functional responses of phytoplankton communities to the nutrient availability.

Both lake regime and fish introduction shape autotrophic planktonic communities of lakes from the Patagonian Plateau (Argentina)

Strobel Plateau hosts more than 1,500 shallow lakes displaying different water regimes, which constitute the habitat for many species. Although the region is naturally fishless, many of the lakes were stocked with trout, bearing uncertainty about the possible effects on the ecosystem. The main objective of this study was to analyze the characteristics of planktonic autotrophic communities of lakes differing in regime (phytoplankton turbid, clear vegetated, and clear unvegetated) and presence/absence of fish. During late spring and summer, 14 water bodies were sampled in 2011 and 2013 considering different regimes and presence/absence of fish. Besides limnological variables, the autotrophic communities, from pico to microplankton, were also analyzed. Differences in physical and chemical characteristics observed among the lakes corresponded to their current regime and the presence/absence of trouts. Autotrophic picoplankton and phytoplankton > 20 µm abundances differed among lake types being highest in fish-stocked lakes. Although the three type of lakes presented phycoerythrin-rich picocyanobacteria and picoeukaryotes, only fish-stocked lakes hosted phycocyanin-rich picocyanobacteria. Moreover, fish-stocked lakes were dominated by cyanobacteria, while chlorophytes abounded in fishless systems. Evidences that lake regime and fish occurrence influence planktonic autotrophic communities of Strobel plateau is here provided, highlighting the intra- and interannual dynamism of the aquatic systems.

The effect of elevated CO2 on autotrophic picoplankton abundance and production in a eutrophic lake (Lake Taihu, China)

The effects of elevated CO2 concentrations on the community structure and primary production of the autotrophic picoplankton of a eutrophic lake were studied in Lake Taihu, China. We conducted in situ experiments with three CO2 concentrations (270, 380 and 750ppm) over four seasons during 2012 and 2013. Our results showed that phycocyanin-rich picocyanobacteria were dominant in winter and that photosynthetic picoeukaryotes were prevalent during the other three seasons. CO2 elevation could significantly increase the abundance of photosynthetic picoeukaryotes in all seasons except winter, but did not have any influence on picocyanobacterial abundance. CO2 enrichment caused an increase in the primary production of the picoplankton community in most seasons, and significant differences were observed among the treatments in summer and winter. In addition, the contribution of picoplankton to total primary production significantly increased under higher CO2 concentrations in winter. The increase in the abundance of photosynthetic picoeukaryotes and the primary production of picoplankton under high CO2 concentrations may reduce the transfer of matter and energy to higher trophic levels and increase the importance of the microbial food web.

Diversity and seasonal dynamics of the photoautotrophic picoplankton in Lake Balaton (Hungary)

Lake Balaton, in Hungary, is the largest shallow lake in Central Europe. This fresh water ecosystem has been well studied, including investigations of its photoautotrophic picoplankton (PPP). Previous studies revealed that picoeukaryotes could reach an extremely high abundance in winter, while picocyanobacteria are the predominant picoplankters in warmer periods, as in other lakes in the temperate zone. In addition to epifluorescence microscopy — which allows discrimination only between phycocyanin-rich picocyanobacteria, phycoerythrin-rich picocyanobacteria and picoeu - karyotic algae — we used PCR-based molecular methods to reveal the detailed genetic diversity and seasonal dynamics of the PPP in Lake Balaton for the first time. Our results show that a single inte- grated pelagic sample, taken vertically from the whole water column, may harbor a large number of picocyanobacterial genotypes including previously unidentified groups. Based on length polymor- phism analysis of the phycocyanin operon (which contains a non-coding region of variable size), the composition of picocyanobacterial communities showed significant seasonal changes and spatial variation. The relative importance of some of the operational taxonomic units (OTUs) we detected was correlated with environmental factors, such as temperature and the concentration of available nitrogen forms. The picoeukaryotic algal community of winter PPP was dominated by chlorophytes related to the group Trebouxiophyceae. The results of this study highlight the fine internal structure and dynamics of the PPP community in freshwater ecosystems — a view that is usually blurred by the lower resolution of commonly used methods, such as epifluorescence microscopy and flow cytometry.

Distribution of picophytoplankton and nanophytoplankton along an anthropogenic eutrophication gradient in French Mediterranean coastal lagoons

We explored the role of natural and anthropogenic environmental perturbations in shaping the community structure and dynamics of pico- and nanophytoplankton in coastal waters. The distribution patterns of phycoerythrin-rich picocyanobacteria (PE-CYAN) and phycocyanin-rich picocyanobacteria (PC-CYAN), autotrophic picoeukaryotes (PEUK) and nanophytoplankton (NANO) were examined over a period of 3 yr in 24 Mediterranean coastal lagoons displaying wide trophic gradients (from 0.2 to 630 mu g chlorophyll a [chl a] l(-1)) and salinity gradients (from fresh to marine waters). In summer, picoplanktonic abundances reached 3 x 10(8) cells l(-1), 5 x 10(9) cells l(-1) and 6 x 10(10) cells l(-1) for PE-CYAN, PC-CYAN and PEUK, respectively. PE-CYAN and PC-CYAN showed opposing responses to environmental gradients, resulting in a restricted dominance of PE-CYAN in oligotrophic marine lagoons and a dominance of PC-CYAN in some eutrophic brackish lagoons. Most lagoons exhibited steady-state nutrient conditions, giving competitive advantages to small eukaryotic algae, even in eutrophic and hypertrophic waters. Among the picophytoplankton, picoeukaryotes (ca. 2 to 3 mu m) are the most competitive with increasing nutrient availability; in terms of abundance and biomass, their relative and absolute importance tended to increase with increasing total chl a biomass. Freshwater discharges resulted in large pulses of nutrient and more turbulent systems that altered the structure of the phytoplankton community and stimulated fast-growing NANO composed of phytoflagellates and diatoms (ca. 3 to 6 mu m, up to 1.6 x 10(9) cells l(-1)). Members of the microphytoplankton (ca. 20 to 200 mu m) were rarely observed in eutrophic and hypertrophic lagoons and were composed of harmful dinoflagellates in oligotrophic lagoons. These results show that anthropogenic and meteorological changes are highly influential on the composition and size structure of phytoplankton communities.

Composition of Picocyanobacteria Community in The Great Mazurian Lakes: Isolation of Phycoerythrin-Rich and Phycocyanin-Rich Ecotypes from the System – Comparison of two Methods

The study showed that the picocyanobacteria community of the Great Mazurian Lakes system (GML) was dominated by phycoerythrin-rich (PE) ecotypes and demonstrated a gradual decrease of the ratio between PE and phycocyanin-rich (PC) ecotypes. The Great Mazurian Lakes offer better conditions for the PE ecotype than for the PC one, despite the considerably high trophic status, probably thanks to low turbidity and attenuation of light in the water column. The successful isolation of PE and PC picocyanobacteria was achieved by two methods: the classic plate method and a modified flow-cytometry method. The modified flow-cytometry method proved to be superior: being more selective for PE picocyanobacteria as well as less time consuming and less laborious. The modifications introduced to the method, such us concentration of cyanobacterial cells by centrifugation to the density required by the flow cytometer, did not hinder the isolation while allowing to skip an intermediate phase of enrichment cultures that had been formerly proposed. The first phylogenetic analyses based on cpcBA operon and 16S rRNA gene demonstrated that picocyanobacteria isolates from GML could, with a high bootstrap support, be grouped into five and four clusters, respectively. Based on a cpcBA-IGS analysis and IGS length the study suggests that at least one of the clusters is new and has not been previously described.

Macrophyte influence on the structure and productivity of photosynthetic picoplankton in wetlands

We used multiple approaches to analyze photosynthetic picoplankton (PPP) structure and production in a wetland in the Lower Parana Basin (Argentina). A seasonal field survey was combined with an experimental study to analyze PPP variability under different light conditions. Flow cytometry analyses showed differences in PPP structure among the aquatic environments. Three main picoplankton populations were distinguished: phycocyanin-rich picocyanobacteria (Pcy), picoeukaryote (Peuk) and anaerobic anoxygenic photosynthetic bacteria (AnAnPB). The experimental study revealed important changes in PPP structure in relation to the light conditions imposed by floating plants: enclosures exposed to light showed a higher proportion of Peuk and Pcy over AnAnPB; in mesocosms covered by plants, just as in the highly vegetated relict lakes (ROLs), AnAnPB were dominant. Total picophytoplankton abundances varied from 1.7 × 10 4 to 4.6 × 10 5 cells mL -1 in the shallow lakes, and were lower (0.69 × 10 4 to 2.5 × 10 5 cells mL -1 ) in the ROLs. Annual variations in temperature and hydrological conditions influenced the PPP abundances, observing maximum values during the warm dry phase. The photosynthetic rates per unit area of PPP (P APPP ) and algae >3 μm (P A>3 μm ) were measured in the aquatic environments in winter and summer: P A PPP (1.5 to 100 mg C m -2 h -1 ) was lower than P A >3 μm and was directly affected by light, which was limiting under the dense floating plant cover.

Flow cytometric observation of picophytoplankton community structure in the cascade reservoirs along the Wujiang River, SW China

Picophytoplankton community structure has been seasonally investigated in the cascade reservoirs along the Wujiang River from April 2006 to January 2007. Besides picoeukaryotes, two groups of picocyanobacteria have also been detected by flow cytometry. One is a phycoerythrin-rich picocyanobacteria (PE-rich Pcy), the other is a red-fluorescing cells with lacking orange fluorescence and could be a phycocyanin-rich picocyanobacteria (PC-rich Pcy). The average abundances of PC-rich Pcy, PE-rich Pcy and picoeukaryotes were 103, 104 and 102 cells mL-1, respectively. PE-rich Pcy was the dominant population but showed a reduction with eutrophication, and therefore the community structure of picophytoplankton transformed from dominant PE-rich Pcy to dominant PE-rich Pcy and PC-rich Pcy, which suggested they are excellent indicators for the change of trophic state. Picophytoplankton community structure also presented a seasonal variation, indicating the different response of each picophytoplankton group to water temperature.

Lake Superior Supports Novel Clusters of Cyanobacterial Picoplankton

Very little is known about the biodiversity of freshwater autotrophic picoplankton (APP) in the Laurentian Great Lakes, a system comprising 20% of the world's lacustrine freshwater. In this study, the genetic diversity of Lake Superior APP was examined by analyzing 16S rRNA gene and cpcBA PCR amplicons from water samples. By neighbor joining, the majority of 16S rRNA gene sequences clustered within the "picocyanobacterial clade" consisting of freshwater and marine Synechococcus and Prochlorococcus. Two new groups of Synechococcus spp., the pelagic Lake Superior clusters I and II, do not group with any of the known freshwater picocyanobacterial clusters and were the most abundant species (50 to 90% of the sequences) in samples collected from offshore Lake Superior stations. Conversely, at station Portage Deep (PD), located in a nearshore urbanized area, only 4% of the sequences belonged to these clusters and the remaining clones reflected the freshwater Synechococcus diversity described previously at sites throughout the world. Supporting the 16S rRNA gene data, the cpcBA library from nearshore station PD revealed a cosmopolitan diversity, whereas the majority of the cpcBA sequences (97.6%) from pelagic station CD1 fell within a unique Lake Superior cluster. Thus far, these picocyanobacteria have not been cultured, although their phylogenetic assignment suggests that they are phycoerythrin (PE) rich, consistent with the observation that PE-rich APP dominate Lake Superior picoplankton. Lastly, flow cytometry revealed that the summertime APP can exceed 10(5) cells ml-1 and suggests that the APP shifts from a community of PE and phycocyanin-rich picocyanobacteria and picoeukaryotes in winter to a PE-rich community in summer.

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Short-term bioassays were conducted in Biguglia lagoon (Corsica) to study the physiological and behavioral responses of phytoplankton to N- and P-availability. Natural communities were collected in two stations representative of the two sub-basins, at three periods with contrasting environmental characteristics to address the impact of seasonal variability. These samples were separately enriched with a full N and P enrichment, and with enrichments minus N or minus P. Phytoplankton size structuration, diversity, and growth of the total phytoplankton, the micro-, nano- and ultraphytoplankton were evaluated using spectrofluorimetry, and optical microscopy. Results showed that the communities were fueled by NO3− in the wet periods (autumn and spring) and NH4+ in summer. The phytoplankton communities displayed highest cell size in autumn, with high abundances of nanoflagellates, and smallest cell size in summer with a large dominance of phycocyanin-rich picocyanobacteria. Blooms of dinoflagellates also occurred during the wet periods, coinciding with high N:P ratios. The full enrichment has not stimulated phytoplankton growth in autumn, suggesting the importance of other controlling factors such as light, a possible NH4+ inhibition or the use of mixotrophic abilities. In spring, communities have displayed single P-limitation in the northern basin and different N and P co-limitations in the southern basin. In summer, the full enrichment consistently stimulated the growth of all cell sizes. The communities showed high N and P co-limitations, which is consistent with growing observations in aquatic ecosystems, and reflects the different functional responses of phytoplankton communities to the nutrient availability.

Composition and dynamics of autotrophic picoplankton and spectral light distribution in saline lignite mining lakes of Germany

In two saline turbid mining lakes, the seasonal dynamics of autotrophic picoplankton (APP) were investigated. APP biomass accounted for 10–96% (annual average 48%) of the total autotrophic biomass. Eucaryotic picoplankton was dominant during spring and autumn (0.4–9 10 7 cells l −1). Picocyanobacteria appeared from June to September, reaching abundances of up to 1.3×10 8 cells l −1 . The total phosphorus content varied in the range 7–46 μg P l −1 and chlorophyll a (chl a) in the range 0.5–5.2 μg chl a l −1. The euphotic zone (1%-light level) extended only over the upper part of the epilimnion during the 1997 growing season. Red light (620–720 nm) was available within the water body. Blue or green light (430–580 nm) was mostly absent because of the high contents of suspended particles in lakes. This may be a reason for the occurrence of only phycocyanin-rich picocyanobacteria in the lakes investigated. This study shows that the APP constitutes a significant part of the phytoplankton in these slightly saline (6.5–8‰) turbid mining lakes. Because of their small cell size, higher uptake rates of inorganic nutrients and possibility of efficient utilization of low light intensities, they might have had an advantage for the development in the lakes investigated.

Composition and dynamics of autotrophic picoplankton and spectral light distribution in saline lignite mining lakes of Germany

Abstract In two saline turbid mining lakes, the seasonal dynamics of autotrophic picoplankton (APP) were investigated. APP biomass accounted for 10–96% (annual average 48%) of the total autotrophic biomass. Eucaryotic picoplankton was dominant during spring and autumn (0.4–9 107 cells l-1). Picocyanobacteria appeared from June to September, reaching abundances of up to 1.3 × 108 cells l-1. The total phosphorus content varied in the range 7–46 µg P l-1 and chlorophyll a (chla) in the range 0.5–5.2 µg chla l-1. The euphotic zone (1%-light level) extended only over the upper part of the epilimnion during the 1997 growing season. Red light (620–720 nm) was available within the water body. Blue or green light (430–580 nm) was mostly absent because of the high contents of suspended particles in lakes. This may be a reason for the occurrence of only phycocyanin-rich picocyanobacteria in the lakes investigated. This study shows that the APP constitutes a significant part of the phytoplankton in these slightly saline (6.5–8%) turbid mining lakes. Because of their small cell size, higher uptake rates of inorganic nutrients and possibility of efficient utilization of low light intensities, they might have had an advantage for the development in the lakes investigated.