Modeling cyanobacterial blooms in tropical reservoirs: The role of physicochemical variables and trophic interactions

Authors

Cihelio Alves Amorim, Ênio Wocyli Dantas, Ariadne do Nascimento Moura

Understanding the importance of environmental variables on the dominance of cyanobacteria is crucial for appropriately managing water resources. Although studies about temperate and subtropical regions show a high influence of nutrients and temperature on blooms, this relationship is still unclear for the tropics. Accordingly, we hypothesized that nutrients and temperature are the main factors driving cyanobacterial blooms in tropical reservoirs, and those relationships are intensified by the zooplankton. To test these hypotheses, we constructed a structural equation model based on the monitoring of ten reservoirs from Northeast Brazil. We analyzed the effects of physicochemical variables and zooplankton on cyanobacterial blooms and the biomass of four morphotypes. Cyanobacterial biomass varied within the reservoirs, with bloom records (0.2–268.4 mg L⁻¹) in all of them, primarily constituted by the colonial morphotype, followed by picocyanobacteria, heterocyted, and non-heterocyted filaments. The cyanobacterial community was driven mainly by chemical variables (55.14% of the variation), followed by physical (48.28%), and zooplankton (39.47%). Through the structural equation model, we demonstrated that total cyanobacterial biomass, as well as the morphotypes, were mainly influenced by omnivorous crustaceans and total dissolved phosphorus. Solar radiation, air temperature, mixing zone, and salinity were important to explain the biomass of the morphotypes. The model explained most of the variation in the picocyanobacterial blooms (79.8%), followed by total cyanobacteria (62.4%), heterocyted filaments (59.1%), non-heterocyted filaments (58.2%), and coccoids (55.1%). Zooplankton groups were also influenced by the physicochemical variables, which presented direct and indirect effects on cyanobacteria. Given the predictions of increased eutrophication, warming, and salinization, cyanobacterial blooms will become more intense in tropical reservoirs. Thus, restoring measures must be adopted to reduce bloom development, such as external phosphorus and salt loadings, and biomanipulation.

Phytoplankton in extreme environments: importance and consequences of habitat permanency

Authors

Judit Padisák & Luigi Naselli-Flores

There is hardly any sunshine exposed surface on this Earth, be it water or terrain, which would not support some biota. Still, many habitats offer harsh conditions requiring specialized physiological adaptations to survive. These environments are referred to as extremes; often inhabited by extremophilic organisms. In this review, characteristic species and assemblage properties of phytoplankton inhabiting extreme environments (especially lakes and pools where planktic life is potentially possible and independently of their origin) in terms of alkalinity, acidity, DOC, salinity, temperature, light and mixing regime will be outlined. Lakes characterized by more than a single extreme are common (e.g. saline + alkaline; acidic + high DOC + high metal content + low light). At the edge of extremes (e.g. pH of 1; salinity over ~ 100–150 g l⁻¹) single species with appropriate physiological adaptation are selected and the phytoplankton is often dominated by a single species (monodominant) setting compositional diversity to zero. Under less extreme conditions permanent equilibria may persist; in many cases over several years in contrast to „average” lakes where equilibria are rare and ephemeral. Food webs depending on „extreme phytoplankton” are often atypical for example because the microbial loop is of prior importance or because birds are top predators.

 

Physiological responses of Raphidiopsis raciborskii (Cyanobacteria) strains to water conductivity: effect of sodium and magnesium ions

Authors

Daniel Vinícius Neves de Lima, Ana Beatriz Furlanetto Pacheco, Carolina Lage Goulart & Sandra Maria Feliciano de Oliveira e Azevedo

Cyanobacterial blooms dominated by Raphidiopsis raciborskii, a potential producer of saxitoxin (STX), are commonly reported in continental water bodies of semiarid regions with high conductivity (> 1000 µS cm⁻¹). STX production is proposed as a cellular protection mechanism against salt stress. Here, we test the hypothesis that high conductivity favors R. raciborskii growth and that STX is advantageous under this condition. We included four tropical strains (two STX⁺ and two STX⁻) cultured for 12 days in control (450 µS cm⁻¹) or in media with NaCl (10 mM) or MgCl₂ (5 mM) (1500 µS cm⁻¹). High conductivity (either NaCl or MgCl₂) had neutral or positive effects on growth for all strains. Total STX content did not differ in response to salt concentrations. All strains could tolerate higher conductivity without signals of stress, as noted for stable photosynthetic parameters and protein expression profiles. For the strain with higher growth in salt, accumulation of intracellular carbohydrates occurred in early times (3 days). In conclusion, high conductivity is a favorable condition for R. raciborskii, with no clear relation with the ability to produce STX. Pronounced intraspecific variability was observed, a fact that must be considered for a better understanding of this species.

Microbial mat contribution to the formation of an evaporitic environment in a temperate-latitude ecosystem

Authors

Vanesa Liliana Perillo, Lucía Maisano, Ana María Martinez, Isabel Emma Quijada, Diana Graciela Cuadrado

An evaporitic environment is characterized by having high salinity, climatic, and hydrological factors that promote a negative water balance; however, biological factors may also influence their development. Modern coastal flat Paso Seco (40°33′S; 62°14′W) is located in a semi-arid region with low precipitation and dry winds coming mainly from the NW. The site is an old tidal channel, which nowadays behaves like a shallow coastal saline-like basin, separated from the sea by a sand barrier, which the sea periodically overcomes, flooding the flat with eventual water evaporation. Microbial mats of up to 1 cm thick colonize the sandy sediments of this evaporitic environment. Water samples were taken during five field trips (2017–2018) from interstitial water of the flat, a tidal creek that crosses the flat, and two shallow tidal depressions (TDs) within the flat with different degrees of evaporation. In comparison to the sea, the maximum salinity values measured in Austral spring (September 2017) in the tidal creek were doubled, tripled in interstitial water, and 5.9 to 8 times higher in TDs. Ionic concentration denotes that evaporite chemical divides are followed as water evaporates, corresponding to the presence of CaCO₃, gypsum and halite found in TDs. On-site permeability of microbial mat-covered surfaces presented semi-pervious properties. Microbial mat presence is condition for CaCO₃, gypsum, and halite precipitation as they allow for water retention and its consequent evaporation due to the impermeability they confer to the sedimentary surface. Thus, microbial mats are a biological factor affecting the development of an evaporitic environment.

Understanding the effect of salinity tolerance on cyanobacteria associated with a harmful algal bloom in Lake Okeechobee, Florida

Authors

Barry H. Rosen, Keith A. Loftin, Jennifer L. Graham, Katherine N. Stahlhut, James M. Riley, Brett D. Johnston, and Sarena Senegal

In an effort to simulate the survival of cyanobacteria as they are transported from Lake Okeechobee to the estuarine habitats that receive waters from the lake, a bioassay encompassing a range of salinities was performed. An overall decline in cyanobacteria health in salinity treatments greater than 18 practical salinity units (psu) was indicated by loss ofcell membrane integrity based on SYTOX® Green staining, but this loss varied by the kind of cyanobacteria present.
Microcystis aeruginosa was tolerant of salinities up to 18 psu; however, higher salinities caused leaking of microcystin from the cells. Dolichospermum circinale, another common bloomformer in this system, did not tolerate salinities greater than 7.5 psu. Stimulation of mucilage production was observed and is likely a mechanism used by both species to protect organism viability. At 7.5 psu, microcystin increased relative to chlorophyll-a, providing some evidence of biosynthesis when M. aeruginosa is exposed to this salinity. This study indicates that as freshwater cyanobacteria are transported to brackish and marine waters, there will be a loss of membrane integrity which will lead to the release of cellular microcystin into the surrounding waterbody. Additional research would be needed to determine the exact effect of salinity on this relationship.

Functional and Compositional Responses of Periphyton Mats to Simulated Saltwater Intrusion in the Southern Everglades

Authors

Viviana Mazzei, Evelyn E. Gaiser, John S. Kominoski, Benjamin J. Wilson, Shelby Servais, Laura Bauman, Stephen E. Davis, Steve Kelly, Fred H. Sklar, David T. Rudnick, Joseph Stachelek, Tiffany G. Troxler

Periphyton plays key ecological roles in karstic, freshwater wetlands and is extremely sensitive to environmental change making it a powerful tool to detect saltwater intrusion into these vulnerable and valuable ecosystems. We conducted field mesocosm experiments in the Florida Everglades, USA to test the effects of saltwater intrusion on periphyton metabolism, nutrient content, and diatom species composition, and how these responses differ between mats from a freshwater versus a brackish marsh. Pulsed saltwater intrusion was simulated by dosing treatment chambers monthly with a brine solution for 15 months; control chambers were simultaneously dosed with site water. Periphyton from the freshwater marsh responded to a 1-ppt increase in surface water salinity with reduced productivity and decreased concentrations of total carbon, nitrogen, and phosphorus. These functional responses were accompanied by significant shifts in periphytic diatom assemblages. Periphyton mats at the brackish marsh were more functionally resilient to the saltwater treatment (~ 2 ppt above ambient), but nonetheless experienced significant shifts in diatom composition. These findings suggest that freshwater periphyton is negatively affected by small, short-term increases in salinity and that periphytic diatom assemblages, particularly at the brackish marsh, are a better metric of salinity increases compared with periphyton functional metrics due to functional redundancy. This research provides new and valuable information regarding periphyton dynamics in response to changing water sources in the southern Everglades that will allow us to extend the use of periphyton, and their diatom assemblages, as tools for environmental assessments related to saltwater intrusion.

Cyanobacterial diversity in the alkaline Lake Khilganta during the dry and wet periods

Authors

Z. B. Namsaraev, T. V. Kolganova, E. O. Patutina, D. D. Tsyrenova, O. S. Samylina

Clone libraries and morphological analysis were used to investigate cyanobacterial diversity in the cyanobacterial mat and dry crust at the bottom of the shallow, saline, alkaline Lake Khilganta (Southern Siberia, Russia). Filamentous cyanobacteria belonging to Phormidiumgenus and Coleofasciculus chthonoplastes were found to predominate during the dry period (2006) and the wet periods (1995 and 2012), respectively. Community composition during the dry and wet periods differed significantly. While 11 operational taxonomic units of cyanobacteria were revealed, only 3 occurred during both dry and wet periods. Occurrence of cosmopolitan C. chthonoplastes, which is common in neutral saline environments, is not typical of a continental alkaline lake and may be explained by the similarity of the dominant ions composition in lake water and in seawater.

Characterization of phototrophic microorganisms and description of new cyanobacteria isolated from the saline-alkaline crater-lake Dziani Dzaha (Mayotte, Indian Ocean)

Authors

M Cellamare, C Duval, Y Drelin, C Djediat, N Touibi, H Agogué, C Leboulanger, M Ader, C Bernard

The saline-alkaline crater-lake Dziani Dzaha (Mayotte, Indian Ocean) is dominated by the bloom-forming cyanobacterium Arthrospira. However, the rest of the phototrophic community remains underexplored because of their minute dimension or lower biomass. To characterize the phototrophic microorganisms living in this ecosystem considered as a modern analog of Precambrian environments, several strains were isolated from the water column and stromatolites, and analyzed using the polyphasic approach. Based on morphological, ultrastructural and molecular (16S rRNA gene, 18S rRNA gene, 16S-23S ITS region, cpcBA-IGS locus) methods, seven filamentous cyanobacteria and the prasinophyte Picocystis salinarum were identified. Two new genera and four new cyanobacteria species belonging to the orders Oscillatoriales (Desertifilum dzianense sp. nov.) and Synechococcales (Sodalinema komarekii gen. nov., sp. nov., Sodaleptolyngbya stromatolitii gen. nov., sp. nov. and Haloleptolyngbya elongata sp. nov.) were described. This approach also allowed to identify Arthrospira fusiformis with exclusively straight trichomes instead of the spirally coiled form commonly observed in the genus. This study evidenced the importance of using the polyphasic approach to solve the complex taxonomy of cyanobacteria and to study algal assemblages from unexplored ecosystems.

Spatial variation of above-ground carbon storage in temperate coastal wetlands

Authors

Christopher J. Owers, Kerrylee Rogers, Colin D. Woodroffe

Carbon mitigation services provided by coastal wetlands are not spatially homogeneous. The scale of assessment at which above-ground biomass is measured will directly influence carbon storage estimates. Greater confidence in estimates is obtained with approaches that describe more variation. There is a need to improve accuracy while optimising assessment effort efficiency. Accurate quantification of carbon storage is dependent upon accurate assessment of biomass, carbon content and the extent of vegetation for which carbon storage is being assessed. This study demonstrates that vegetation structure influences above-ground biomass of mangrove and saltmarsh, resulting in considerable variability in biomass estimates and associated carbon storage of temperate coastal wetlands in southeast Australia. For mangrove, variability in above-ground biomass (Mg ha−1 ± SE) was best described by measuring height, stem diameter, crown area and vegetation density, whereby tall mangrove (3–8 m in height; 71.50 ± 12.53 Mg ha−1) had higher biomass than both shrub (1.3–3 m in height; 53.06 ± 6.94 Mg ha−1) and dwarf mangrove (<1.3 m in height; 10.68 ± 1.77 Mg ha−1). Saltmarsh above-ground biomass was best described by height, species and vegetation density, which demonstrated significant differences between rush saltmarsh (15.97 ± 2.35 Mg ha−1) and herbs, grasses and sedges saltmarsh (7.51 ± 0.91 Mg ha−1). The effect of this variation was compounded by carbon content (% C), which varied markedly between vegetation structural form and species (30.9–49.8% C). Maintaining accuracy when assessing carbon storage requires mapping units that correspond to the scale of biomass assessments. Results from this study suggest that recognition of variation in biomass and carbon content of mangrove and saltmarsh vegetation structure will enhance the accuracy of estimates of carbon storage, and provide the confidence necessary for carbon storage inventories.

Dissolved carbon in a large variety of lakes across five limnetic regions in China

Authors

Kaishan Song, Zhidan Wena, Yijun Xu, Hong Yang, Lili Lyu, Ying Zhao, Chong Fanga, Yingxin Shang, Jia Du

Dissolved carbon in lakes play a vital role in the global carbon cycling. The concentration and dynamics of lake dissolved carbon can be influenced by both the surrounding landscape and a combination of physical, chemical and biological processes within the lakes themselves. From 2009 to 2016, we conducted a large-scale assessment of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in 249 lakes across a diverse range of climatic, geopedologic, topographical and hydrological conditions in five Chinese limnetic regions: the East Limnetic Region (ELR), the Northeast Limnetic Region (NLR), the Inner Mongolia-Xinjiang Limnetic Region (MXR), the Yungui Limnetic Region (YGR), and the Tibet-Qinghai Limnetic Region (TQR). We found that the density of the organic matter in the soil in the surrounding landscape plays an important role in the DOC and DIC in lake water, as was evidenced by the high DOC and DIC levels in the NLR, where the soil is respectively organically rich. Conditions in the arid and semi-arid environments (i.e. TQR and MXR) have created a number of brackish/saline lakes and here we found that, DOC and DIC levels (median: 21.79 and 93.72 mg/L, respectively) are significantly higher than those in the freshwater lakes (median: 5.80 and 29.38 mg/L). It also appears to be the case that the trophic state of freshwater lakes influences the spatial variation of DOC. This can be seen in the relationships between DOC and trophic state index (TSI) in agriculturally-dominated regions such as the ELR (R2 = 0.59, p < 0.01), NLR (R2 = 0.65, p < 0.001), and YGR (R2 = 0.78, p < 0.001). Additionally, a close relationship between DOC and DIC can be found in lake waters with different trophic states (eutrophic: slp = 0.63, R2= 0.69; mesotrophic: slp = 1.03, R2 = 0.65; oligotrophic: slp = 1.00, R2 = 0.64). This indicates that human activities influence the quantity and quality of dissolved carbon in inland water across China. This study is able to provide insights regarding the potential effects of climate change and changes in land-use upon the amount of dissolved carbon in lake water.