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.