Preliminary assessment of microbial mats in seawater metal remediation.

Microbial mats have a special role in the removal of metals in marine environment. This study aimed to experimentally determine the efficiency of Cr removal from seawater by microbial mats. The effect of Cr on the microphytobenthic community and the influence of an aerated condition on the removal of metal and microorganisms were also considered. Hence, microbial mat samples were subdivided in 4 groups: submerged in Cr (chromium 2 mg/L without aeration), Cr + O2 (chromium 2 mg/L with aeration), SW + O2 (filtered seawater with aeration), and a control: SW (filtered seawater with neither chromium nor aeration). Water and microbial mat subsamples were used to determine Cr concentrations, organic matter content, granulometry, physicochemical parameters, chlorophyll a, phaeopigments, and quantitative analysis of the microphytobenthic community. Cr removal efficiency from seawater was 95% for the Cr treatment and 99% for the Cr + O2 treatment. The abundance of cyanobacteria tended to decrease between the initial and final days of the assay, whereas the opposite trend was observed for diatoms. Two aspects are worth noting in the paper: microbial mats efficiently removed Cr from seawater at a concentration of 2 mg Cr/L and the removal of Cr by microbial mats was more efficient with water aeration.

Epibenthic microbial mats behavior as phosphorus sinks or sources in relation to biological and physicochemical conditions.

Microbial mats are complex microecosystems that have shown promise as possible green filters to remediate polluted seawater. This usage would possibly require changing the natural conditions under which these microbial mats prosper in order to maximize their contact with the water. Thus, it is necessary to evaluate the adaptation of the mats to different environmental conditions, while monitoring their short-term efficiency at nutrient removal. To that aim, epibenthic microbial mats collected from a tidal flat in the Bahía Blanca Estuary, were incubated under different flooding conditions (periodically exposed to the air or continuously flooded), with and without the addition of a high phosphorus concentration (5 mg PO43- L-1), and with and without the presence of penicillin. This last condition was added to understand the influence of penicillin-sensitive microbes on cyanobacteria and diatom communities and their importance for P remediation. The presence of high P concentrations as well as the continual flooding of the mats resulted in the decrease of the dominant cyanobacterium, Coleofasciculus (Microcoleus) chthonoplastes, giving rise to the dominance of other genera such as Arthrospira sp. Or Oscillatoria sp., depending on the presence or absence of the antibiotic, respectively. Water P removal was highly efficient (60-87%) when the mats were treated with the high-P water. However, microbial mat behavior changed from P sink to source when mats where incubated in seawater with no P addition, suggesting that mats can both function as P sinks and sources, depending on the condition of the water they come in contact with.

Short-term efficiency of epibenthic microbial mat components on phosphorus sorption.

Microbial mats may be an alternative tool for phosphorus (P) remediation of eutrophic coastal waters. The main objective of this work was to determine the importance that the living and non-living components of the mats have on P short-term sorption. Microbial mats were collected in the Paso Seco coastal flat, Argentina (40°38'3.32″S; 62°12'24.85″W), and incubated under controlled conditions in the lab. An adsorption curve was performed with the microbial mats. Active mats had a Freundlich constant 8.9-fold higher than underlying sandy sediments. Collected samples were then treated as follows: maintaining and disturbing their structural integrity (natural and autoclaved, respectively), and both conditions were incubated with filtered seawater, without and with phosphate addition (0 and 5 mg P L-1, respectively). Natural mats had a significantly-higher phosphate removal percentage than autoclaved ones, suggesting that living microorganisms increase P short-term sorption efficiency by ~25%, while non-living matter may account for the rest.