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Item-typ:Veröffentlichung, Geochemical characteristics, speciation and size-fractionation of iron (Fe) in two marine shallow-water hydrothermal systems, Dominica, Lesser AntillesMarine shallow-water hydrothermal systems have so far largely been neglected with respect to trace metal fluxes and possible stabilizing complexation processes, even though they emit their fluids directly into the photic zone. The impact of stabilized dissolved metal input by shallow vents into surface waters as well as the effect on the transport and bioavailability of bioactive trace metals within the area of highest primary production rates in the world oceans is therefore, at present, mostly unknown. In this study, we investigated the concentration, size fraction distribution (colloidal and soluble) as well as redox speciation and labile concentrations of the limiting micronutrient iron (Fe) at two marine shallow-water hydrothermal systems (Champagne Hot Springs and Soufriere) off the coast of Dominica, Lesser Antilles Island Arc, Caribbean. Geochemical characterization of the two different vent sites showed that both are affected by meteoric and seawater influence, with a stronger meteoric influence at Soufriere than at Champagne Hot Springs. Measurements of soluble and labile Fe were performed using a modified competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) with salicylaldoxime (SA) as the artificial ligand. Our results show that focused fluids discharging at the seafloor, as well as hydrothermal pore fluids are, despite a calculated theoretical oxidation half-life of only 6.4 min, highly enriched in Fe(II), indicating a strong complexation of Fe(II), strong enough to prevent Fe(II) from oxidation and precipitation. Since these fluids show enriched dissolved organic carbon (DOC) concentrations, and very low fractions of chemically labile Fe, complexation may occur by organic carbon, which was recently suggested to also be a factor in stabilizing particulate Fe(II) in deep-sea hydrothermal non-buoyant plumes. Our results indicate that shallow-water hydrothermalism off the coast of Dominica releases high concentrations of stabilized, bioavailable Fe(II) into the photic zone, which influences the biogeochemical cycle of Fe in surface waters. Considering the abundance of marine shallow-water hydrothermal systems in many regions, such processes may even play a role in the global oceanic dFe cycle.Wissenschaftlicher ArtikelBand:45447 42 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic occurrence and speciation in Cyclope neritea, a gastropod inhabiting the arsenic-rich marine shallow-water hydrothermal system off Milos Island, GreeceAround Milos Island marine shallow-water hydrothermal activity can be found and in Paleochori Bay, where high arsenic concentrations were reported for the hydrothermal fluids. There the gastropod Cyclope neritea was present at high densities despite the extreme conditions associated with hydrothermal venting, feeding on white microbial mats. Surprisingly, C. neritea collected from the hydrothermal vent area accumulated comparatively less arsenic in its tissues than specimens of the same species collected from an area not affected by hydrothermal activity. Inorganic arsenic was found at high percentages with respect to the sum of arsenic species both in the gut and muscle of C. neritea and the amount of arsenobetaine (AB) was less than in specimens collected at an area away from hydrothermal activity. Trimethylarsoniopropionate (TMAP) was found at relatively high percentages in C. neritea and in the surrounding environment (sediment and plankton) in Paleochori Bay. Tetramethylarsonium ion (TETRA) was found at high percentages in the gut and muscle of C. neritea. It was most likely biosynthesized in the gastropod gut, and accumulated in the muscle, because it was not found in any other compartment studied. Based on these observations we conclude that C. neritea is arsenic tolerant. The data suggests that arsenic species distribution is strongly influenced by arsenic species exposure and/or different detoxifying mechanisms, although the exact metabolic pathways could not be completely resolved.Wissenschaftlicher ArtikelBand:34896 108 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Enhanced bioaccumulation and biotransformation of As in coral reef organisms surrounding a marine shallow-water hydrothermal vent system(Elsevier Science, 2013-06-19); ; ; ; The marine shallow-water hydrothermal system in Tutum Bay, Ambitle Island, Papua New Guinea discharges as much as 1.5 kg of arsenic (As) per day into a coral reef ecosystem. Despite the amount of As released, coral reef organisms do not seem to be affected. We investigated the uptake and bioaccumulation of geothermally-derived inorganic As by the soft coral Clavularia sp., the calcareous algae Halimeda sp., and the sea squirt Polycarpa sp., by measuring the total As concentration (TAs) in tissues from each organism and comparing it to the same type of organism collected from a nearby control site. All organisms collected from the hydrothermal area displayed distinctly higher (2 to 20 times) TAs compared to the control site. Concentrations were typically higher in samples collected closer to the focused hydrothermal venting, which is the first direct evidence for enhanced bioaccumulation of As in organisms living within an area of hydrothermal influence. To assess As biotransformation to organoarsenicals, anionic and cationic As species were determined by IC-ICP-MS in methanol/water tissue extracts. The concentrations of several of the organoarsenic species were much higher at the hydrothermal vent site compared to the control site, and several organoarsenic species were present only in the hydrothermal samples, including some unidentifiable species. While intriguing, these speciation results cannot be interpreted robustly due to poor extraction efficiencies. Future researchers should attempt to improve the extraction efficiency to closer to 100%, which would allow a more accurate description of As biosynthesis pathways for the marine organisms living in these environments.Wissenschaftlicher ArtikelBand:34889 100 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic in marine hydrothermal fluidsHydrothermal fluids emerging at the seafloor near mid-ocean ridges (MOR) or in back-arc basins (BAB) and island arc (IA) settings are known to contain a considerable amount of dissolved metals (e.g. Fe, Zn, Cu, Cd) due to water–rock interaction at elevated temperatures and potentially magmatic degassing. The chemical input from these fluids plays an important role for ocean chemistry and the cycling of elements. Despite its notoriety as an environmental toxin and its abundance in hydrothermal ore deposits in combination with gold, arsenic (As) is one of the few elements, which has been rarely investigated. Compared to the amount of As in open ocean seawater of around 1.7 μg L− 1, hydrothermal fluids can have significantly higher concentrations. Fluids from MOR hydrothermal systems such as the East Pacific Rise can contain up to 80.5 μg L− 1 As and at the Mid-Atlantic Ridge the highest values were around 24 μg L− 1. Those values, although elevated are surpassed by As concentrations in BAB and IA hosted hydrothermal systems, which can be as high as 1386 µg L− 1 in BAB settings and even higher with values up to 5850 µg L− 1 (~3900-times seawater) in IA shallow-water settings, occurring near shore hydrothermal systems. The most important factors controlling the amount of As in hydrothermal fluids are the different – mostly physicochemical – conditions at and beneath the seafloor. These include temperature (controlling phase separation of the fluids and leaching processes in the host rock), pressure as a function of depth, pH directly influencing leaching processes, As mobility and speciation, reaction time and maturity of the system in combination with redox reactions and diverse chemical reactions like adsorption and desorption. The concentration of As in the underlying host rock may also play a role, although its mineralogical association may be more important than bulk rock concentration. Additional input of As could be caused by degassing magmatic metal-rich volatiles or sediment-fluid interaction in sediment covered hydrothermal systems. The contribution from magmatic volatiles is hard to quantify and therefore often neglected in calculations and discussions. Of the two As redox species, arsenate (AsV) and arsenite (AsIII), arsenite is easier transported in the vapor phase. However, As speciation has not been traditionally part of chemical analyses. Prior to discharge at the seafloor, the concentration of As in hydrothermal fluids may decrease rapidly, if precipitation of As-bearing and As-scavenging minerals, such as pyrite, orpiment, claudetite and hydrous ferric/manganese oxides, occurs in the shallow subsurface as shown by thermodynamic calculations. This is consistent to the observation that those hydrothermal fluids high in Fe and Mn are often low in As. Arsenic concentrations in fluids from shallow BAB/IA hydrothermal systems are higher than those in deep situated MOR hydrothermal systems most likely due to their different physicochemical conditions. Basaltic host rocks (MOR) and dacitic/andesitic host rocks (BAB/IA) have As concentrations which are more or less identical and cannot account for the huge differences in fluid As concentration. Arsenic is one of the few trace elements whose concentration in seawater is higher than in river water, which could be caused by the flux of As from hydrothermal systems. Estimating that between 3.0 × 103 and 1.25 × 108 kg As could be discharged at the MOR annually, which is a substantial amount compared to 53.9 × 106 kg transported annually by rivers. Higher flux can be expected at BAB and IA settings, however data is sparse. A single IA system, confined to a very small area of 60 by 100 m (Tutum Bay, Papua New Guinea), discharges around 5.5 × 102 kg As annually.Wissenschaftlicher ArtikelBand:34866 144 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic in marine hydrothermal systems: Source, fate and environmental implications-Wissenschaftlicher ArtikelBand:34860 55 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Long-term performance of a constructed wetland/filter basin system treating wastewater, Central FloridaThis study investigated the efficiency of a constructed wetland/filter basin (CW/FB) treatment system to improve the chemical composition of waste and surface waters. The system was constructed in closed phosphate mines used for clay settling and sand tailings. Monitoring was carried out for 18 months to evaluate the CW/FB performance under a variety of climatic conditions. Water samples were taken bi-monthly. To evaluate possible groundwater input into and water leaking out of the wetland 6 monitor wells were installed along the flow path and sampled monthly. In order to estimate the change of water chemistry along the wetland flow path, water samples along a transect were taken during the dry and rainy seasons. The samples were analyzed for pH, T, oxidation–reduction potential (ORP), conductivity, total dissolved solids (TDS), dissolved oxygen (DO), Fe(II), H2S, major anions, major cations, arsenic, fecal and total coliform. The study showed the following changes in water quality between the input and output: (1) Substantial decrease of water temperature (up to 10 °C); (2) Significant change in pH from about 9 to 6.5–7; (3) Negative ORP confirming the reducing conditions of the treatment system; (4) Substantial increase of H2S (up to 1060 µg/L); (5) Reduction of As from 5 to <2 µg/L (mostly <0.5); (6) Substantial reduction of SO4, F, Cl, NO3, NO2, Br, Na, K, Ca, and Mg; (7) Reduction of fecal and total coliform from 30–730 and 1000–7000 to <2 and <100 count/100 mL, respectively. In general, the performance of the CW/FB treatment system showed great potential to improve the water quality of industrial and municipal wastewater. Despite significant seasonal variations with respect to temperature, rainfall and humidity, the chemical/microbiological composition of the wetland output remained relatively constant.Wissenschaftlicher ArtikelBand:269Heft:1-265 71 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Abundance and mineralogical association of arsenic in the Suwannee Limestone (Florida): Implications for arsenic release during water–rock interactionArsenic (As) is being released from the Suwannee Limestone, Upper Floridan aquifer, during aquifer storage and recovery (ASR) cycle testing with concentrations of up to 130 μg/L in the recovered water. To determine the abundance and mineralogical association of As in the Suwannee Limestone matrix we have conducted a detailed mineralogical and geochemical study of 306 core samples. In addition to random sampling of core material, we also collected “targeted” samples of core material that contained organic material, hydrous ferric oxide, pyrite, phosphate minerals and clays. Bulk As concentrations were determined by acid digestion followed by hydride generation-atomic fluorescence spectrometry (HG-AFS). Specific mineral phases were analyzed using scanning electron microscopy (SEM) and electron-probe microanalyses (EPMA). The average As concentration for all 306 samples is 3.5 ppm, but only 1.7 ppm after exclusion of the “targeted” samples. The average for the “targeted” samples is 9.5 ppm. The detailed lithologic, mineralogical, and geochemical study of As in the Upper Floridan aquifer, Suwannee Limestone shows that: (1) Arsenic is present in the Suwannee Limestone in low concentrations, but is concentrated in minor mineral phases, particularly pseudo-framboidal pyrite. (2) Pyrite is generally As-rich and can contain concentrations between 100 and 11,200 ppm As (average 2300 ppm, n = 25). (3) Compared to pyrite, other trace minerals contain much less As. (4) Pyrite is ubiquitous throughout the Suwannee Limestone, but is most abundant in high porosity zones. (5) Previously suggested hydrous ferric oxide, clay minerals and apatite are not an important source of As. This study also provided some insight into the question whether the interaction (reaction) of water with an aquifer matrix that contains only a few part per million As is capable of producing high-As concentrations in groundwater. Our findings indicate that it can be relatively easy to generate a high-As groundwater despite a low bulk As concentration in the aquifer matrix. A change in physico-chemical conditions that selectively affects the stability of As-bearing minerals is sufficient to increase As concentrations by several orders of magnitude.Wissenschaftlicher ArtikelBand:228Heft:1-388 95 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Geochemistry of Champagne Hot Springs shallow hydrothermal vent field and associated sediments, Dominica, Lesser AntillesThe Champagne Hot Springs (CHS) shallow submarine hydrothermal system is located along the submerged flank of the Plat Pays volcanic system on the southwest section of the island of Dominica, Lesser Antilles. We have conducted a detailed geochemical study of the hydrothermal system, with the objectives to investigate the source of the hydrothermal fluids and gases, their effect on sediment and precipitate chemistry, as well as comparing the submarine vent chemistry with nearby on-land hydrothermal vents. Finally, we compare our findings to previous preliminary data from CHS, and compare sediment chemistry to that of average Caribbean sediments. We also report on a newly discovered area of submarine hydrothermal venting, located approximately 40 m to the north of CHS. This area consists of hydrothermally altered areas of sand that contain abundant coatings of hydrous ferric oxides (HFO) on sediment grains. Geochemical and mineralogical analyses of vent waters, pore waters, gases, sediments and precipitates reveal that the vent fluids consist of a mixture of entrained seawater and meteorically derived hydrothermal fluid in varying proportions. Vent fluids are depleted in Br−, SO42−, Cl−, Na+, K+, and Sr2+ relative to ambient seawater. These species are all positively correlated with Mg2+, which is also depleted relative to seawater. Boron, Fe, As, Sb, Mn, Si and Li are all enriched relative to ambient seawater. Pore waters in the hydrothermally altered sand patches have essentially the same chemistry. Mixing between Fe2+ rich vent fluids and seawater causes rapid oxidation of Fe2+ to insoluble Fe3+ and leads to precipitation of HFO at the vent site and subsequent formation of hydrothermally altered sand patches. The elevated concentrations of As and Sb in the precipitates and sediments relative to average Caribbean seafloor sediments reflect adsorption by HFO. Gas samples from the vent site are typical arc-type gases and have both meteoric and magmatic signatures.Wissenschaftlicher ArtikelBand:224Heft:1-361 53 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Distribution, speciation and bioavailability of arsenic in a shallow-water submarine hydrothermal system, Tutum Bay, Ambitle Island, PNGShallow-water hydrothermal vent systems can introduce large amounts of potentially toxic elements, such as arsenic (As), into coastal marine environments. The first step in understanding and describing the potential impact of these elements throughout hydrothermally influenced coastal ecosystems is to determine the element's distribution and speciation, which in turn influences the availability of the toxin for biological uptake. Shallow submarine hot springs near Ambitle Island, Papua New Guinea, are discharging as much as 1.5 kg per day of arsenic directly into a coral-reef ecosystem. We have investigated the bioavailability of the As throughout Tutum Bay by studying vent fluid, seawater, pore water, precipitates, and sediments. In addition to measuring As abundance, As speciation (As(III), As(V), and the methylated species DMA and MMA) was determined in various waters. The As concentration for discrete mineral phases in vent precipitates and sediments was determined by sequentially extracting arsenic from the easily extractable, carbonate, Fe-oxyhydroxide or hydrous ferric oxide (HFO), and residual fractions, each of which have a different bioavailability. Diffuse venting seems to play a critical role on the distribution of As throughout Tutum Bay surface sediments, which have a mean As concentration of 527 ppm while excluding the vent precipitates (range = 1483 to 52 ppm). Up to 54 ppm As were extracted from the easily extractable fraction of surface sediments (mean = 19.7 ppm), using a K2HPO4/KH2PO4 buffer at pH = 7.2. Arsenic from this fraction is considered to be the most available for biological processes, and therefore the most dangerous for biota. However, sequential extraction shows that 98.6% of the As in vent precipitates, and a mean of 93.3% in surface sediments (range = 88.2% to 96.3%), is coprecipitated with the hydrous ferric oxide (HFO) fraction. Thus, the bulk of the As being discharged into Tutum Bay is scavenged by the HFO, and should remain stable unless the physicochemical conditions surrounding the oxides change. In surface seawaters of Tutum bay, we found as much as four times the average seawater concentration of As (8.4 μg/L compared to ∼2 μg/L). The abundance of As in seawater just above the sediment/water interface is near normal, although As(III) in both surface and bottom seawater throughout Tutum Bay is substantially enriched compared to average seawater. Hydrothermal venting therefore provides bioavailable As by two major pathways throughout Tutum Bay: 1) easily-exchangeable As from hydrothermally influenced sediments to as far away as 200 m from focused venting, and 2) in surface seawaters, which may allow for biological uptake by phytoplankton and transfer up the food web.Wissenschaftlicher ArtikelBand:224Heft:1-3405 113 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The precipitation of aragonite from shallow-water hydrothermal fluids in a coral reef, Tutum Bay, Ambitle Island, Papua New GuineaThe fringing reef in Tutum Bay on the west side of Ambitle Island, Papua New Guinea is the only presently known coral reef exposed to the extensive discharge of a hot, mineralized hydrothermal fluid. There, aragonite and ferrihydrite, a hydrous ferric oxide, are the prominent hydrothermal precipitates. Aragonite forms two distinct crystal habits, (a) euhedral (pseudo-hexagonal) crystals up to 2 cm long and (b) micro-crystals similar in appearance to “feather dendrite”. Aragonite encrusts dead coral fragments, volcaniclastic boulders and pebbles, and fills secondary fracture and remaining primary intergranular porosity within volcaniclastic arenite. The hydrothermal aragonite has a distinctively different isotopic composition when compared to “normal” shallow-water marine inorganic and organic carbonate that precipitated from seawater. This difference arises from precipitation at high temperature from a mixture of seawater and hydrothermal fluid that has lower 87Sr/86Sr and δ18O values than seawater. Based on a 87Sr/86Sr mixing model, aragonite precipitated from a hydrothermal fluid–seawater mixture of approximately 9:1. Precipitation from the hydrothermal solution is mainly caused by CO2 degassing, but mixing between hydrothermal fluid and seawater may have enhanced precipitation due to an increase in pH. The δ13C of Tutum Bay hydrothermal aragonite ranges from 1.9‰ to 2.2‰ (VPDB). This range of values is in good agreement with experimental data [J. Phys. Chem. 72 (1968) 800; Geochim. Cosmochim. Acta 61 (1997) 3461], indicating that C-13-equilibirum has been reached during its formation. Values for δ18O range from 14.2‰ to 14.7‰ and calculated isotopic equilibrium temperatures are approximately 20 °C lower than directly measured vent fluids and those temperatures obtained from fluid inclusion experiments and the 87Sr/86Sr mixing model. This indicates that either oxygen isotope equilibrium was not attained or that the calcite–water fractionation factor for oxygen isotopes is not applicable for the precipitation of Tutum Bay hydrothermal aragonite. Trace element concentrations, except for the REEs, Y and Sr are low. The REE patterns of aragonite are similar to those of Tutum Bay vent water, indicating the hydrothermal origin of the aragonite. Rare earth element concentrations are higher in the coarse than in the fine-grained aragonite, which might be caused by a change in precipitation rate and seawater mixing.Wissenschaftlicher ArtikelBand:207Heft:1-262 106