Bruna Marques

Mercury cycling and sequestration in salt marshes sediments: An ecosystem service provided by Juncus maritimus and Scirpus maritimus

In this study two time scales were looked at: a yearlong study was completed, and a 180-day decay experiment was done. Juncus maritimus and Scirpus maritimus have different life cycles, and this seems to have implications in the Hg-contaminated salt marsh sediment chemical environment, namely Eh and pH. In addition, the belowground biomass decomposition rates were faster for J. maritimus, as well as the biomass turnover rates. Results show that all these species-specific factors have implications in the mercury dynamics and sequestration. Meaning that J. maritimus belowground biomass has a sequestration capacity for mercury per square metre approximately 4-5 times higher than S. maritimus, i.e., in S. maritimus colonized areas Hg is more extensively exchange between belowground biomass and the rhizosediment. In conclusion, J. maritimus seems to provide a comparatively higher ecosystem service through phytostabilization (Hg complexation in the rhizosediment) and through phytoaccumulation (Hg sequestration in the belowground biomass).

Impact of sampling depth and plant species on local environmental conditions, microbiological parameters and bacterial composition in a mercury contaminated salt marsh.

We compare the environmental characteristics and bacterial communities associated with two rushes, Juncus maritimus and Bolboschoenus maritimus, and adjacent unvegetated habitat in a salt marsh subjected to historical mercury pollution. Mercury content was higher in vegetated than unvegetated habitat and increased with sampling depth. There was also a significant relationship between mercury concentration and bacterial composition. Habitat (Juncus, Bolboschoenus or unvegetated), sample depth, and the interaction between both, however, explained most of the variation in composition (~70%). Variation in composition with depth was most prominent for the unvegetated habitat, followed by Juncus, but more constrained for Bolboschoenus habitat. This constraint may be indicative of a strong plant-microbe ecophysiological adaptation. Vegetated habitat contained distinct bacterial communities associated with higher potential activity of aminopeptidase, β-glucosidase and arylsulphatase and incorporation rates of (14)C-glucose and (14)C-acetate. Communities in unvegetated habitat were, in contrast, associated with both higher pH and proportion of sulphate reducing bacteria.

New species for the biomitigation of a super-intensive marine fish farm effluent: Combined use of polychaete-assisted sand filters and halophyte aquaponics

The main objective of this study was to test an innovative biomitigation approach, where polychaete-assisted (Hediste diversicolor) sand filters were combined with the production of Halimione portulacoides in aquaponics, to remediate an organic-rich effluent generated by a super intensive fish farm operating a land-based RAS (Recirculating aquaculture system). The set up included four different experimental combinations that were periodically monitored for 5months. After this period, polychaete-assisted sand filters reduced in 70% the percentage of OM and the average densities increased from ≈400ind.m-2 to 7000ind.m-2. H. portulacoides in aquaponics contributed to an average DIN (Dissolved inorganic Nitrogen) decrease of 65%, which increased to 67% when preceded by filter tanks stocked with polychaetes. From May until October (5months) halophytes biomass increased from 1.4kgm-2±0.7 (initial wet weight) to 18.6kgm-2±4.0. Bearing in mind that the uptake of carbon is mostly via photosynthesis and not though the uptake of dissolved inorganic carbon, this represents an approximate incorporation of ≈1.3kgm-2 carbon (C), ≈15gm-2 nitrogen (N) and ≈8gm-2 phosphorus (P) in the aerial part (76% of total biomass), and an approximate incorporation of ≈0.5kgm-2 carbon (C), ≈3gm-2 nitrogen (N) and ≈2gm-2 phosphorus (P) in the roots (24% of total biomass). In the present study, the potential of the two extractive species for biomitigation of a super-intensive marine fish farm effluent could be clearly demonstrated, contributing in this way to potentiate the implementation of more sustainable practices.

Microcosm Assessment of the Effect of an Acute Mercury Contamination Event on the Structure and Activity of Sediment Bacterial Communities

Objectives: In the present study, the effect of acute mercury contamination on the structure and activity of bacterial communities in intertidal mudflats was assessed through a microcosm experiment simulating the mobilization of highly contaminated sub-surface sediments. Methods: Box-microcosms corresponding to different test conditions were constructed by mixing natural estuarine sediments with high and low concentrations of mercury in defined proportions. The effects on sediment bacteria were characterized by quantifying bacteria using fluorescent in situ hybridization (FISH) technique, assessing the community structural diversity by denaturating gradient gel electrophoresis (DGGE) and analysing descriptors of bacterial activity (extracellular enzymatic activity and leucine incorporation) at the beginning and at the end of a 7-days incubation period. Results: At the end of the experiment, total abundance of Bacteria was significantly higher in the low-Hg microcosms than in the high-Hg and blended-sediment microcosms. DGGE patterns revealed that the structure of sediment bacterial communities responded to the experimental treatment and to the incubation time. Bacterial activity was inhibited by mercury and that the levels of arylsulfatase and biomass productivity were inversely related with the Hg concentration. The proportion sulfate-reducing in relation to total prokaryotes increased at the end of the experiment, which might indicate a differential response of Bacteria and Archaea to confinement and mercury contamination. Conclusion: Mechanical disturbance of sediments historically exposed to mercury contamination, like bottom trawling or dredging, will cause the mobilization of deeper sediments highly contaminated with Hg which will impact the less contaminated surface sediments. These acute events will impact the structure and activity of bacterial communities and their contributions to the associated biogeochemical cycles, with expectable impacts at the ecosystem level.

Ragworm fatty acid profiles reveals habitat and trophic interactions with halophytes and with mercury.

The present study aimed to assess if ragworm fatty acids (FA) profiles could be used to discriminate their spatial distribution in an historically mercury-contaminated estuarine environment, i.e., if it was possible to differentiate ragworms present in salt marsh sediments surrounding plant roots and rhizomes (rhizosediment) from adjacent unvegetated sediment. Additionally, we also tried to determine if ragworms differed in mercury content and if these values could also be used to identify the habitat they occur in. Results show that, within the same area, ragworms can be distinguished using FA profiles and that in halophyte rhizosediment ragworms display more than twice the levels of alpha-linolenic acid (18:3n-3). The ratio cis-vaccenic/oleic acids (18:1n-7/18:ln-9) in ragworms suggests higher carnivory in unvegetated sediments. Our study indicates that ragworm FA profiles can be used to identify their habitat, their trophic interaction with halophytes and reveal a spatially contrasting feeding behaviour, which also reflects mercury accumulation.