An Experimental Approach to Assessing the Roles of Magnesium, Calcium, and Carbonate Ratios in Marine Carbonates

Marine biomineralization is a globally important biological and geochemical process. Understanding the mechanisms controlling the precipitation of calcium carbonate [CaCO3] within the calcifying fluid of marine organisms, such as corals, crustose coralline algae, and foraminifera, presents one of the most elusive, yet relevant areas of biomineralization research, due to the often-impenetrable ability to measure the process in situ. The precipitation of CaCO3 is assumed to be largely controlled by the saturation state [Ω] of the extracellular calcifying fluid. In this study, we mimicked the typical pH and Ω known for the calcifying fluid in corals, while varying the magnesium, calcium, and carbonate concentrations in six chemo-static growth experiments, thereby mimicking various dissolved inorganic carbon concentration mechanisms and ionic movement into the extracellular calcifying fluid. Reduced mineralization and varied CaCO3 morphologies highlight the inhibiting effect of magnesium regardless of pH and Ω and suggests the importance of strong magnesium removal or calcium concentration mechanisms. In respect to ocean acidification studies, this could allow an explanation for why specific marine calcifiers respond differently to lower saturation states.

Effect of Inorganic Carbon Concentration on the Development of Subaerial Phototrophic Biofilms on Granite

Organisms living at the stone–air interface are expected to be affected by changes in the atmospheric composition due to greenhouse gases emissions. Increased CO2 concentrations may particularly affect phototrophic microorganisms that colonize stone cultural heritage and form subaerial biofilms. However, little is known about the effects of the environmental changes on microorganisms that colonize stone and the consequences for cultural heritage conservation. In the present study, we investigated how an increase in inorganic carbon concentration affected the development of a subaerial biofilm composed by the cyanobacterium Synechocystis sp. PCC 6803 grown on granite. For this purpose, we established two experiments on biofilm formation, with and without addition of inorganic carbon to the growth medium. Higher concentrations of carbon promoted biofilm growth and increased the concentrations of the photosynthetic pigments chlorophyll a and carotenoids on granite surface, potentially exacerbating the aesthetic impact of these biofilms on stone-made cultural heritage. However, the extracellular polysaccharides produced were not significantly affected by carbon availability, so that physical stone biodeterioration might not be increased by the cyanobacterial matrix. The findings provide valuable data on how the existing global change scenario might affect organisms inhabiting stone cultural heritage and encourage to develop new sustainable treatments and methodologies to prevent biodeterioration and thus preserve stone cultural heritage.

Short-term effect of shock ammonium nitrogen load on activated sludge properties

The activated sludge process suffers from rapid load changes of ammonium (NH4), which may result in process failure during wastewater treatment. In this study, the response of activated sludge properties in terms of microfauna composition and sludge volume index (SVI5 and SVI30) on short-term increase of NH4 concentration (from 55 mg/l to 105 mg/l) was evaluated in batch scale reactors over 72 h. The results show that the first-step nitrification (NH4 transformation to nitrite (NO2)) was inhibited after 24 h, whereas the second-step nitrification (NO2 transformation to nitrate (NO3)) was not significantly affected. Sludge volume indices (sedimentation ability characteristics) SVI5 and SVI30 in the reactor with NH4–N shock concentration increased, whereas microfauna diversity decreased (Shannon-Weaver index decreased from 2.12 at 48 h to 1.23 at 72 h) leading to dominance of stalked ciliate Epistylis sp. Notable changes in inorganic carbon concentration (IC) were observed, indicating that rapid decrease of IC concentration leads to nitrification inhibition and challenges the overall process recovery. To conclude, short-term exposure of about two times higher concentration of NH4 caused significant changes in activated sludge properties by inhibiting NH4-oxidizing bacteria, reducing sludge microfauna diversity and deteriorating sludge sedimentation ability.