Inorganic Nutrient Concentrations and Chlorophyll in the Euphotic Zone of Lake Tanganyika

Large benthic accumulations of cyanobacteria occur in sheltered embayments within Myall Lake, New South Wales, Australia. The lake is shallow, with the entire bottom within the euphotic zone, and it is generally considered pristine, having low nutrient concentrations. The accumulations are highly organic and contain a mix of species mainly from the order Chroococcales, with two forms of Aphanothece being dominant. However polymerase chain reaction (PCR) analysis indicates a close similarity to Microcystis flos-aquae. The cells appear to lack aerotopes and form sticky mucilaginous amalgamations, which may enhance their benthic habit. Although Chroococcales also dominate the planktonic cyanobacterial community, the benthic species are seldom, if ever, found entrained within the water column. Some hepatotoxicity was indicated by mouse bioassay, protein phosphatase inhibition assay, enzyme-linked immuno-sorbent assay (ELISA) for microcystins, PCR and by chromatographic evidence for a microcystin. Ecological aspects of the distribution, gross morphology of the organisms and management implications for recreational water-users are discussed.

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Trichome Lengths of the Heterocystous N2-Fixing Cyanobacteria in the Tropical Marginal Seas of the Western North Pacific

Frontiers in Marine Science ◽

10.3389/fmars.2021.678607 ◽

2021 ◽

Vol 8 ◽

Author(s):

Sing-how Tuo ◽

Margaret R. Mulholland ◽

Yukiko Taniuchi ◽

Houng-Yung Chen ◽

Wann-Neng Jane ◽

...

Keyword(s):

North Pacific ◽

Western North Pacific ◽

Euphotic Zone ◽

Nutrient Concentrations ◽

Gas Vesicles ◽

Filamentous Cyanobacteria ◽

Cool Season ◽

Free Living ◽

Marginal Seas ◽

Tropical Oceans

Calothrix rhizosoleniae and Richelia intracellularis are heterocystous cyanobacteria found in the tropical oceans. C. rhizosoleniae commonly live epiphytically on diatom genera Chaetoceros (C-C) and Bacteriastrum (B-C) while R. intracellularis live endosymbiotically within Rhizosolenia (R-R), Guinardia (G-R), and Hemiaulus (H-R); although, they occasionally live freely (FL-C and FL-R). Both species have much shorter trichomes than the other marine filamentous cyanobacteria such as Trichodesmium spp. and Anabaena gerdii. We investigated the trichome lengths of C. rhizosoleniae and R. intracellularis in the South China Sea (SCS) and the Philippine Sea (PS) between 2006 and 2014. On average, H-R had the shortest trichome lengths (3.5 cells/trichome), followed by B-C and C-C (4.9–5.2 cells/trichome) and FL-C (5.9 cells/trichome), and R-R, G-R, and FL-R had the longest trichome lengths (7.4–8.3 cells/trichome). Field results showed the trichome lengths of C-C and B-C did not vary seasonally or regionally. However, FL-C and H-R from the SCS and during the cool season had longer trichomes, where/when the ambient nutrient concentrations were higher. R-R, G-R, and FL-R also showed regional and seasonal variations in trichome length. Ultrastructural analysis found no gas vesicles within the C. rhizosoleniae cells to assist in buoyancy regulation. Results suggest that the trichome lengths of C. rhizosoleniae and R. intracellularis might be regulated by their diatom hosts’ symbiotic styles and by ambient nutrients. Short trichome length might help C. rhizosoleniae and R. intracellularis to stay in the euphotic zone regardless as to whether they are free-living or symbiotic.

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Diazotrophic Cyanobacteria are Associated With a Low Nitrate Resupply to Surface Waters in Lake Tanganyika

Frontiers in Environmental Science ◽

10.3389/fenvs.2021.716765 ◽

2021 ◽

Vol 9 ◽

Author(s):

Benedikt Ehrenfels ◽

Maciej Bartosiewicz ◽

Athanasio Stephano Mbonde ◽

Kathrin B.L. Baumann ◽

Christian Dinkel ◽

...

Keyword(s):

Surface Waters ◽

Phytoplankton Community ◽

Lake Tanganyika ◽

Euphotic Zone ◽

Convective Mixing ◽

Nitrate Supply ◽

Upward Transport ◽

Diazotrophic Cyanobacteria ◽

Nitrate Depletion ◽

Productive Surface

In Lake Tanganyika, blooms of nitrogen-fixing (diazotrophic) cyanobacteria emerge, when the upper water column re-stratifies after a period of upwelling and convective mixing. During this seasonal transition, diazotrophic cyanobacteria exploit the abundant phosphate and fix nitrogen after other phytoplankton taxa have consumed the available nitrate. However, it remains less clear, which mechanisms favour diazotrophic cyanobacteria under more heavily stratified conditions with lower levels of excess phosphate and persistent nitrate-depletion. Here, we collected profiles of physicochemical parameters, nutrients and photo-pigments, as well as the medium- to large-sized phytoplankton community during two lake-wide cruises to elucidate to what extent the abundance of diazotrophic cyanobacteria in Lake Tanganyika may be controlled by the nitrate resupply through the thermocline into the euphotic zone. At stations where nitrate was depleted, but phosphate remained available near the surface, high densities of diazotrophic cyanobacteria were associated with a low nitrate supply to surface waters. Our data provide first support for two conceptual scenarios, where the relative position of the thermocline and the euphotic depth may create a functional niche for diazotrophic cyanobacteria: when the upward transport of nitrate into the euphotic zone is reduced by a subjacent thermocline, diazotrophic cyanobacteria, comprising Dolichospermum and Anabaenopsis, are key players in the medium-to large-sized phytoplankton community. By contrast, a thermocline located within the euphotic zone allows for a rapid vertical transport of nitrate for a thriving nitrate-assimilating phytoplankton community that evidently outcompetes diazotrophic cyanobacteria. This study highlights that, under nitrogen-depleted conditions, diazotrophic cyanobacteria can also grow in response to a reduced nutrient resupply to the productive surface waters.

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Variable particle size distributions reduce the sensitivity of global export flux to climate change

Biogeosciences ◽

10.5194/bg-18-229-2021 ◽

2021 ◽

Vol 18 (1) ◽

pp. 229-250

Author(s):

Shirley W. Leung ◽

Thomas Weber ◽

Jacob A. Cram ◽

Curtis Deutsch

Keyword(s):

Climate Change ◽

Particle Size ◽

Euphotic Zone ◽

Nutrient Concentrations ◽

Biogeochemical Model ◽

Size Distributions ◽

Earth System ◽

Particle Size Distributions ◽

System Models ◽

Earth System Models

Abstract. Recent earth system models predict a 10 %–20 % decrease in particulate organic carbon export from the surface ocean by the end of the 21st century due to global climate change. This decline is mainly caused by increased stratification of the upper ocean, resulting in reduced shallow subsurface nutrient concentrations and a slower supply of nutrients to the surface euphotic zone in low latitudes. These predictions, however, do not typically account for associated changes in remineralization depths driven by sinking-particle size. Here we combine satellite-derived export and particle size maps with a simple 3-D global biogeochemical model that resolves dynamic particle size distributions to investigate how shifts in particle size may buffer or amplify predicted changes in surface nutrient supply and therefore export production. We show that higher export rates are empirically correlated with larger sinking particles and presumably larger phytoplankton, particularly in tropical and subtropical regions. Incorporating these empirical relationships into our global model shows that as circulation slows, a decrease in export is associated with a shift towards smaller particles, which sink more slowly and are thus remineralized shallower. This shift towards shallower remineralization in turn leads to greater recycling of nutrients in the upper water column and thus faster nutrient recirculation into the euphotic zone. The end result is a boost in productivity and export that counteracts the initial circulation-driven decreases. This negative feedback mechanism (termed the particle-size–remineralization feedback) slows export decline over the next century by ∼ 14 % globally (from −0.29 to −0.25 GtC yr−1) and by ∼ 20 % in the tropical and subtropical oceans, where export decreases are currently predicted to be greatest. Our findings suggest that to more accurately predict changes in biological pump strength under a warming climate, earth system models should include dynamic particle-size-dependent remineralization depths.

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Phytoplankton and bacterioplankton dependencies on dissolved organic matter (DOM) and inorganic nutrient concentrations in lake enclosures

SIL Proceedings 1922-2010 ◽

10.1080/03680770.2005.11902892 ◽

2006 ◽

Vol 29 (3) ◽

pp. 1301-1305

Author(s):

Erinn H. Radomske ◽

P. Jefferson Curtis ◽

Ellen L. Petticrew

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Inorganic Nutrient ◽

Nutrient Concentrations

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Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity

Applied and Environmental Microbiology ◽

10.1128/aem.71.9.5029-5037.2005 ◽

2005 ◽

Vol 71 (9) ◽

pp. 5029-5037 ◽

Cited By ~ 60

Author(s):

Aaike De Wever ◽

Koenraad Muylaert ◽

Katleen Van der Gucht ◽

Samuel Pirlot ◽

Christine Cocquyt ◽

...

Keyword(s):

Bacterial Community ◽

Community Composition ◽

Lake Tanganyika ◽

Denaturing Gradient Gel Electrophoresis ◽

Bacterial Community Composition ◽

Latitudinal Variation ◽

Nutrient Concentrations ◽

Water Column Stratification ◽

16S Rna ◽

Gradient Gel Electrophoresis

ABSTRACT Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.

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Variable phytoplankton size distributions reduce the sensitivity of global export flux to climate change

10.5194/bg-2020-156 ◽

2020 ◽

Author(s):

Shirley W. Leung ◽

Thomas Weber ◽

Jacob A. Cram ◽

Curtis Deutsch

Keyword(s):

Climate Change ◽

Particle Size ◽

Global Climate ◽

Euphotic Zone ◽

Nutrient Concentrations ◽

Biogeochemical Model ◽

Earth System ◽

Export Production ◽

System Models ◽

Earth System Models

Abstract. Earth System Models predict a 10–20 % decrease in ocean carbon export production by the end of the 21st century due to global climate change. This decline is caused by increased stratification of the upper ocean, resulting in reduced shallow subsurface nutrient concentrations and a slower supply of nutrients to the surface euphotic zone. These predictions, however, do not account for associated changes in sinking particle size and remineralization depth. Here we combine satellite-derived export and particle size maps with a simple 3-D global biogeochemical model to investigate how shifts in sinking particle size may buffer predicted changes in surface nutrient supply and therefore export production. We show that higher export rates are correlated with larger phytoplankton and sinking particles, especially in tropical and subtropical regions. Incorporation of these empirical relationships into a global model shows that as circulation slows, a decrease in export and associated shift toward smaller phytoplankton yields particles that sink more slowly and are thus remineralized shallower; this in turn leads to greater recycling of nutrients in the upper water column and faster nutrient recirculation into the euphotic zone, boosting productivity and export to counteract the initial circulation-driven decreases. This negative feedback mechanism (termed the particle size-remineralization feedback) slows export decline over the next century by ~14 % globally and by ~20 % in the tropical and subtropical oceans, where export decreases are currently predicted to be greatest. Thus, incorporating dynamic particle size-dependent remineralization depths into Earth System Models will result in more robust predictions of changes in biological pump strength in a warming climate.

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Supplementary material to "Thermocline depth and euphotic zone thickness regulate the abundance of diazotrophic cyanobacteria in Lake Tanganyika"

10.5194/bg-2020-214-supplement ◽

2020 ◽

Author(s):

Benedikt Ehrenfels ◽

Maciej Bartosiewicz ◽

Athanasio S. Mbonde ◽

Kathrin B. L. Baumann ◽

Christian Dinkel ◽

...

Keyword(s):

Lake Tanganyika ◽

Euphotic Zone ◽

Thermocline Depth ◽

Diazotrophic Cyanobacteria ◽

Supplementary Material

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Projected 21st century decrease in marine productivity: a multi-model analysis

Biogeosciences ◽

10.5194/bg-7-979-2010 ◽

2010 ◽

Vol 7 (3) ◽

pp. 979-1005 ◽

Cited By ~ 389

Author(s):

M. Steinacher ◽

F. Joos ◽

T. L. Frölicher ◽

L. Bopp ◽

P. Cadule ◽

...

Keyword(s):

Carbon Cycle ◽

21St Century ◽

Climate Models ◽

Net Primary Productivity ◽

Net Primary Production ◽

Mixed Layer Depth ◽

Euphotic Zone ◽

The Arctic ◽

Nutrient Concentrations ◽

Model Average

Abstract. Changes in marine net primary productivity (PP) and export of particulate organic carbon (EP) are projected over the 21st century with four global coupled carbon cycle-climate models. These include representations of marine ecosystems and the carbon cycle of different structure and complexity. All four models show a decrease in global mean PP and EP between 2 and 20% by 2100 relative to preindustrial conditions, for the SRES A2 emission scenario. Two different regimes for productivity changes are consistently identified in all models. The first chain of mechanisms is dominant in the low- and mid-latitude ocean and in the North Atlantic: reduced input of macro-nutrients into the euphotic zone related to enhanced stratification, reduced mixed layer depth, and slowed circulation causes a decrease in macro-nutrient concentrations and in PP and EP. The second regime is projected for parts of the Southern Ocean: an alleviation of light and/or temperature limitation leads to an increase in PP and EP as productivity is fueled by a sustained nutrient input. A region of disagreement among the models is the Arctic, where three models project an increase in PP while one model projects a decrease. Projected changes in seasonal and interannual variability are modest in most regions. Regional model skill metrics are proposed to generate multi-model mean fields that show an improved skill in representing observation-based estimates compared to a simple multi-model average. Model results are compared to recent productivity projections with three different algorithms, usually applied to infer net primary production from satellite observations.

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