Impact of high Fe-concentrations on microbial community structure and dissolved organics in hydrothermal plumes: an experimental study.

Iron (Fe) is an essential trace element for life. In the ocean, Fe can be exceptionally scarce and thus biolimiting or extremely enriched causing microbial stress. The ability of hydrothermal plume microbes to counteract unfavorable Fe-concentrations up to 10 mM is investigated through experiments. While Campylobacterota (Sulfurimonas) are prominent in a diverse community at low to intermediate Fe-concentrations, the highest 10 mM Fe-level is phylogenetically less diverse and dominated by the SUP05 clade (Gammaproteobacteria), a species known to be genetically well equipped to strive in high-Fe environments. In all incubations, Fe-binding ligands were produced in excess of the corresponding Fe-concentration level, possibly facilitating biological Fe-uptake in low-Fe incubations and detoxification in high-Fe incubations. The diversity of Fe-containing formulae among dissolved organics (SPE-DOM) decreased with increasing Fe-concentration, which may reflect toxic conditions of the high-Fe treatments. A DOM-derived degradation index (IDEG) points to a degradation magnitude (microbial activity) that decreases with Fe and/or selective Fe-DOM coagulation. Our results show that some hydrothermal microbes (especially Gammaproteobacteria) have the capacity to thrive even at unfavorably high Fe-concentrations. These ligand-producing microbes could hence play a key role in keeping Fe in solution, particularly in environments, where Fe precipitation dominates and toxic conditions prevail.

Copper-binding ligands in deep-sea pore waters of the Pacific Ocean and potential impacts of polymetallic nodule mining on the copper cycle.

The release of potentially toxic metals, such as copper (Cu), into the water column is of concern during polymetallic nodule mining. The bioavailability and thus toxicity of Cu is strongly influenced by its speciation which is dominated by organic ligand (L) complexation in seawater, with L-complexes being considered less bioavailable than free Cu2+. The presence of CuL-complexes in deep-sea sediments has, however, not been systematically studied in the context of deep-sea mining. We thus analyzed the Cu-binding L concentration ([L]) in deep-sea pore waters of two polymetallic nodule provinces in the Pacific Ocean, the Peru Basin and the Clarion-Clipperton-Zone, using competitive ligand equilibration-adsorptive stripping voltammetry. The pore-water dissolved Cu concentration ([dCu]) ranged from 3 to 96 nM, generally exceeding bottom water concentrations (4-44 nM). Based on fitting results from ProMCC and Excel, Cu was predominantly complexed by L (3-313 nM) in bottom waters and undisturbed pore waters. We conclude that processes like deep-sea mining are unlikely to cause a release of toxic Cu2+ concentrations ([Cu2+]) to the seawater as > 99% Cu was organically complexed in pore waters and the [Cu2+] was < 6 pM for 8 of 9 samples. Moreover, the excess of L found especially in shallow pore waters implied that even with a Cu release through mining activities, Cu2+ likely remains beneath toxic thresholds.

Parameters Governing the Community Structure and Element Turnover in Kermadec Volcanic Ash and Hydrothermal Fluids as Monitored by Inorganic Electron Donor Consumption, Autotrophic CO2 Fixation and 16S Tags of the Transcriptome in Incubation Experiments.

The microbial community composition and its functionality was assessed for hydrothermal fluids and volcanic ash sediments from Haungaroa and hydrothermal fluids from the Brothers volcano in the Kermadec island arc (New Zealand). The Haungaroa volcanic ash sediments were dominated by epsilonproteobacterial Sulfurovum sp. Ratios of electron donor consumption to CO2 fixation from respective sediment incubations indicated that sulfide oxidation appeared to fuel autotrophic CO2 fixation, coinciding with thermodynamic estimates predicting sulfide oxidation as the major energy source in the environment. Transcript analyses with the sulfide-supplemented sediment slurries demonstrated that Sulfurovum prevailed in the experiments as well. Hence, our sediment incubations appeared to simulate environmental conditions well suggesting that sulfide oxidation catalyzed by Sulfurovum members drive biomass synthesis in the volcanic ash sediments. For the Haungaroa fluids no inorganic electron donor and responsible microorganisms could be identified that clearly stimulated autotrophic CO2 fixation. In the Brothers hydrothermal fluids Sulfurimonas (49%) and Hydrogenovibrio/Thiomicrospira (15%) species prevailed. Respective fluid incubations exhibited highest autotrophic CO2 fixation if supplemented with iron(II) or hydrogen. Likewise catabolic energy calculations predicted primarily iron(II) but also hydrogen oxidation as major energy sources in the natural fluids. According to transcript analyses with material from the incubation experiments Thiomicrospira/Hydrogenovibrio species dominated, outcompeting Sulfurimonas. Given that experimental conditions likely only simulated environmental conditions that cause Thiomicrospira/Hydrogenovibrio but not Sulfurimonas to thrive, it remains unclear which environmental parameters determine Sulfurimonas' dominance in the Brothers natural hydrothermal fluids.

Aqueous copper bioavailability linked to shipwreck-contaminated reef sediments.

Pollution from the grounding or sinking of ships can have long lasting effects on the recovery and dynamics of coastal ecosystems. Research on the impact of copper (Cu) pollution from the 2011 MV Rena shipwreck at the Astrolabe Reef (Otaiti), New Zealand, 5 years after the grounding, followed a multi-method and multi-disciplinary approach. Three independent measures of aqueous Cu using trace-element-clean-techniques substantiate the presence of high total, total dissolved (<2 µm) and elevated bioavailable Cu in the water column immediately above the aft section of the wreck where the highest sedimentary load of Cu was located. Intermittently elevated concentrations of strong Cu-binding ligands occurred in this location, and their binding strength was consistent with ligands actively produced by organisms in response to Cu induced stress. The recruitment of benthic invertebrates was modified at the high-Cu location. Taxonomic groups usually considered robust to pollution were restricted to this site (e.g. barnacles) or were the most abundant taxa present (e.g. foraminifera). Our results demonstrate that Cu-contaminated sediments can impose a persistent point source of Cu pollution in high-energy reef environments, with the potential to modify the composition and recovery of biological communities.

Investigating the fate of copper in a laboratory-based toxicity test with embryos of Mytilus galloprovincialis: Copper mass balance of a closed bioassay.

The production of accurate and reliable data on metal toxicity during ecotoxicological bioassays is important for credible environmental risk assessments and management in aquatic environments. Actual measurements and reporting of contaminant concentrations in bioassays are, however, often disregarded; and potential contaminant loss attributable to adsorption processes (e.g., wall adsorption) in bioassays is widely omitted, which can have detrimental effects on calculated metal toxicity thresholds. In the present we assessed copper (Cu) mass balance during a standard 48-h bioassay test with blue mussel (Mytilus galloprovincialis) embryos to evaluate effects on calculated toxicity endpoints. We demonstrated that measured Cu concentrations at the test conclusion need to be used to quantify the risk of Cu toxicity because nominal Cu and initial Cu concentrations underestimate overall Cu toxicity by up to 1.5-fold, owing to Cu loss in solution attributable to adsorption and bioaccumulation processes. For the first time we provide evidence that extracellular adsorption to the biological surface of the embryos is the most important sink for total dissolved Cu in a bioassay. We also established that adsorbed extracellular Cu accumulation reduces Cu toxicity to embryos, potentially by inhibiting Cu from entering the cell of the mussel embryo. Environmental factors (e.g., salinity and dissolved organic carbon) did not influence the partitioning of Cu within the laboratory-based bioassay. The present results 1) demonstrate the importance of differentiating extra- and intracellular Cu pools to improve our understanding of Cu toxicity and associated processes, 2) reveal the potential for bias with respect to calculated Cu toxicity thresholds when results are based on nominal and initial Cu concentrations, and 3) point out the need to follow current guidelines for the testing of chemicals to standardize toxicity tests and data reporting. Environ Toxicol Chem 2019;38:561-574. © 2019 SETAC.

Copper toxicity to blue mussel embryos (Mytilus galloprovincialis): The effect of natural dissolved organic matter on copper toxicity in estuarine waters.

Copper (Cu) is a naturally occurring micronutrient of eco-toxicological concern in aquatic ecosystems. Current knowledge of Cu-speciation and bioavailability in natural saline environments is insufficient to adequately inform environmental protection policy for estuarine systems. We assessed the combined effect of two of the main drivers of metal bioavailability, salinity and natural dissolved organic carbon (DOC), on Cu-speciation and associated Cu-toxicity to blue mussel (Mytilus galloprovincialis) embryos in a standard 48-h bioassay. We placed special emphasis on measurement of Cu-speciation rather than modelling. Cu-toxicity was found to be a function of DOC and salinity. The varying protective effect of different DOC-types suggests that estuarine DOC is more protective against Cu-toxicity than oceanic DOC. Salinity was negatively correlated with [Cu48-h-EC50], indicating a salinity-induced alteration in the physiology of the exposed mussel embryos and/or Cu-DOC-reactivity. These two assumptions were supported by (1) the relative uniformity of bioavailable copper ([Cu']) across similar salinity treatments despite considerable variation in [Cu48-h-EC50] and DOC-concentrations, and (2) the fact that Cu-toxicity and [Cu'] were slightly higher in the 35 salinity treatment compared to the 25 salinity treatment. Stripping voltammetry studies determined the presence of only one strong Cu-binding ligand class (i.e., L1), either actively or passively released by the exposed embryos. [L1] was found to be proportional to the total dissolved Cu-concentration ([CuT]), suggesting a protective effect of Cu-binding-ligands, in addition to the protective effect of DOC. There was also a strong positive correlation between [L1] and [Cu48-h-EC50], implying that electrochemically defined ligand concentrations along with measurements of [Cu'], DOC-quality, and salinity can be used as proxies for 48-h-EC50 Cu-values in estuarine waters, which may result in a significant improvement to risk assessments of Cu in estuarine systems.