Periphyton development during summer stratification in the presence of a metalimnetic bloom of Planktothrix rubescens

Authors

Ivana Trbojević, Ana Blagojević, Dušan Kostić, Prvoslav Marjanović, Jelena Krizmanić, Slađana Popović, Gordana Subakov Simić

Cyanobacterial blooms have become common all over the world, negatively affecting various ecosystem components. Planktothrix rubescens is a planktonic cyanobacterium that frequently causes blooms in temperate (mostly mesotrophic) lakes in Europe and, unlike other cyanobacteria, it is usually associated with ecosystem re-oligotrophication. The potential effects of P. rubescens on periphyton development have not been estimated in any recently published studies. The objective of the present paper was to assess how a Planktohrix rubescens bloom affects periphyton development in a temperate freshwater reservoir. A field study was performed in the Vrutci reservoir (western Serbia), where P. rubescens blooms have occurred since December of 2013. Periphyton was grown on glass slides that were incubated following lake stratification and sampled monthly from July to October of 2015. Dry mass, ash free dry mass and content of chlorophyll a, as well as composition of the community of developed periphyton, were estimated, together with P. rubescens biomass in the water column at the particular depths where substrates for periphyton were incubated. The metalimnetic bloom of P. rubescens induced calcite precipitation on the incubated substrates, which was reflected in obstructed colonization. The periphyton community composition was mainly determined by the depth gradient, which was potentially related to reduced light availability driven by shading effects caused by the P.rubescens bloom. Our results provide a significant update on periphyton ecology in relation to cyanobacterial blooms, elucidating complex interactions in the ecosystem. They also represent a stimulus for further studies on the capacity of P. rubescens for induction of calcium carbonate precipitation in lakes.

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.

Precipitation of calcium carbonate mineral induced by viral lysis of cyanobacteria: evidence from laboratory experiments

Authors

Hengchao Xu, Xiaotong Peng, Shijie Bai, Kaiwen Ta, Shouye Yang, Shuangquan Liu, Ho Bin Jang, and Zixiao Guo

Viruses have been acknowledged as being important components of the marine system for the past 2 decades, but their role in the functioning of the geochemical cycle has not been thoroughly elucidated to date. Virus-induced rupturing of cyanobacteria is theoretically capable of releasing intracellular bicarbonate and inducing the homogeneous nucleation of calcium carbonate; however, experiment-based support for virus-induced calcification is lacking. In this laboratory study, both water carbonate chemistry and precipitates were monitored during the viral infection and lysis of host cells. Our results show that viral lysis of cyanobacteria can influence the carbonate equilibrium system remarkably and promotes the formation and precipitation of carbonate minerals. Amorphous calcium carbonate (ACC) and aragonite were evident in the lysate, compared with the Mg(OH)₂ (brucite in this paper) precipitate in noninfected cultures, implying that a different precipitation process had occurred. Based on the carbonate chemistry change and microstructure of the precipitation, we propose that viral lysis of cyanobacteria can construct a calcification environment where carbonate is the dominant inorganic carbon species. Numerous virus particles available in lysate may coprecipitate with the calcium carbonate. The experimental results presented in this study demonstrate both the pathway and the outcome with respect to how viruses influence the mineralization of carbonate minerals. It is suggested that viral calcification offers new perspectives on mechanisms of CaCO₃ biomineralization and may play a crucial role within the Earth system.

Approaches for phosphorus removal with calcium hydroxide and floating macrophytes in a mesocosm experiment: impacts on plankton structure

Authors

D. Frau, M. E. Spies, Y. Battauz, J. Medrano, R. Sinistro

Cultural eutrophication has promoted the application of several mitigation strategies in the last 50 years. In this study we tested the combined effects of two techniques: calcium hydroxide [(Ca(OH)₂), lime] and a free-floating macrophyte (Salvinia rotundifolia Willd) to examine the soluble reactive phosphorus removal capability and the effects on plankton (phytoplankton and zooplankton) structure in a in situ lake mesocosms experiment. The experiment lasted 10 days (n = 12, 500 l each) with a control and three treatments (lime (CH), plants (FM), and the combination of both (CH + FM)). Samples of several physical and chemical variables (including nutrients) and phytoplankton were taken at the beginning, 2 days after, 4 days, and 10 days (end of the experiment). Zooplankton was sampled at the beginning and at the end. The highest depletion effect of soluble reactive phosphorus (SRP) was observed in presence of lime. Phytoplankton biovolume was highly and negatively affected in lime treatments (CH and CH + FM). Zooplankton changed from Rotifera to Cladocera and Copepoda in presence of macrophytes. We conclude that lime + plants reduces more effectively SRP, phytoplankton biovolume and promotes herbivorous zooplankton development; becoming by this way, in a suitable mitigation strategy to be explored in future field manipulation studies.

Cyanobacteria–phosphate–calcite interactions in limestone (hardwater) streams of England

Author

Allan Pentecost

Hardwater streams often contain deposits of calcium carbonate (travertine, tufa) supporting well-defined communities of cyanobacteria. Deposition of carbonate crusts is inhibited by moderate levels (c.100 μg/l) of dissolved orthophosphate phosphorus that can result in their loss, along with their cyanobacteria. Thirteen English cyanobacterium crust communities were investigated and in all but one, orthophosphate levels were too low to influence carbonate deposition. At one site, inhibitory levels of orthophosphate were found, and here, crusts have not been recorded for over 40 years. Phosphorus was detected in both the inorganic (CaCO₃) and organic fractions of the crusts, and in the latter, it was highest in the living cyanobacterium mat. No interaction between the phosphorus in these two fractions was observed. Levels of total phosphorus in the crusts were positively correlated with orthophosphate in the water. The great majority of English lowland waters currently contain inhibitory levels of dissolved orthophosphate preventing the development of these communities over large tracts of the country. Estimates of the uptake of phosphorus by the cyanobacteria suggested that their growth would not significantly influence the inhibition of precipitation of the associated calcium carbonate.