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William M Berelson - One of the best experts on this subject based on the ideXlab platform.

  • Dissolved oxygen and suspended particles regulate the Benthic Flux of iron from continental margins
    Marine Chemistry, 2020
    Co-Authors: William B Homoky, William M Berelson, Silke Severmann, James Mcmanus, Timothy E Riedel, P J Statham, Rachel A Mills
    Abstract:

    We present ex situ sediment incubation results from the California and Oregon shelves and compare the calculated Benthic Flux of dissolved Fe with those from in situ incubations and pore water concentration profiles. We also examine the influence of oxygen depletion and sediment re-suspension on Benthic Fe exchange. Ex situ incubation of the California and Oregon shelf sites yielded average Benthic Fe Fluxes of 3.5 and 8.3μmolm -2day -1, respectively, compared to 17 and 55μmolm -2day -1 from the in situ Lander determinations, and 73 and 103μmolm -2day -1 from modeling of pore water concentration profiles. Differences between Benthic Fe Flux estimates are primarily accounted for by [1] differences in Fe (II) oxidation kinetics, which result from distinct oxygen consumption rates between incubation methods, and the absence of kinetic considerations in the overlying bottom water in pore water Flux calculations, and [2] the effects of biological sediment irrigation that are best represented by in situ incubations due to their sampling area and preservation of bottom water conditions. Bottom water oxygen concentrations were higher at the California shelf site than that at the Oregon shelf site, and probably accounted for the greater discrepancy between methods used to determine Benthic Fe Flux. The comparison of techniques used to determine Benthic Fe Flux indicates that the concentration of bottom water oxygen exerts a principle control over the fate of dissolved Fe entering the overlying bottom water - supporting the view that the expansion of coastal hypoxia has the potential to enhance the Benthic supply of Fe (II) to shelf waters. An episode of surface sediment re-suspension during ex situ incubation led to a rapid removal of 76-89% of dissolved Fe from seawater, followed by a steady return towards initial seawater concentrations during particle settling, indicating that diffusive inputs of dissolved Fe from sediment pore water are rapidly adsorbed and desorbed by particles during periods of Benthic re-suspension. The findings suggest that dissolved Fe concentrations in bottom waters may reflect an equilibrium concentration of non-stabilized aqueous Fe and particle-adsorbed Fe phases - where the addition of suspended particles to bottom waters leads to scavenging of dissolved Fe into labile particulate Fe phases. Thus we suggest that suspended particles are a significant buffer of dissolved Fe released from shelf sediments, an important transport mechanism for Benthic Fe inputs, and a regulator of dissolved Fe concentrations in seawater. © 2012 Elsevier B.V

  • spatial patterns of Benthic silica Flux in the north pacific reflect upper ocean production
    Deep Sea Research Part I: Oceanographic Research Papers, 2019
    Co-Authors: Douglas E Hammond, William M Berelson, Nathaniel Kemnitz, Jess F Adkins, Abby Lunstrum
    Abstract:

    Diatoms are the dominant algal group that cycles dissolved silicic acid in the ocean; they also play an important role in the oceanic carbon cycle. It is therefore important to quantify the spatial distribution of silica cycling for defining global ocean biogeochemical cycles. On the research cruise CDisK-IV, water samples and sediment cores were collected at 5 stations along a North Pacific transect near 150oW from 22oN to 50oN to evaluate Benthic remineralization rates of biogenic silica (bSi). Two independent methods, core incubation and diffusive transport based on porewater profiles, were utilized to estimate Benthic silicic acid Fluxes, and these independent methods yield Fluxes that agree within uncertainties. The Benthic Fluxes are reported as 0.04 ± 0.01, 0.04 ± 0.01, 0.05 ± 0.01, 0.67 ± 0.14, 0.40 ± 0.08 mmol Si m^(−2) day^(−1) for Stations 1 to 5, south to north, respectively. Burial Fluxes were estimated using measurements of solid phase bSi in sediments and literature values of sediment accumulation rate. Burial efficiencies of bSi at all stations were <5% and show reasonable agreement with previous estimates. When burial rates were added to Benthic Fluxes to calculate rain rates, the rain observed under the subarctic gyre (Stations 4–5), was far larger than in the lower latitudes of the subtropics (Stations 1–3), corresponding to higher surface diatom productivity at higher latitudes. At the two northern stations, the bottom 500 m of the water column shows a near-bottom increase in silicic acid that is consistent with the measured Benthic Flux and the estimated vertical eddy diffusivity. Above this horizon, water column density stratification increases and vertical diffusivity decreases, but the silicic acid gradient decreases. This reduction in gradient indicates that above this horizon, horizontal transport by deep waters, rather than vertical diffusion, becomes the dominant process removing the silicic acid released by Benthic remineralization.

  • vitamin b1 in marine sediments pore water concentration gradient drives Benthic Flux with potential biological implications
    Frontiers in Microbiology, 2015
    Co-Authors: Danielle R Monteverde, William M Berelson, Laura Gomezconsarnau, Lynda S Cutter, Lauren Chong, Sergio A Sanudowilhelmy
    Abstract:

    Vitamin B1, or thiamin, can limit primary productivity in marine environments, however the major marine environmental sources of this essential coenzyme remain largely unknown. Vitamin B1 can only be produced by organisms that possess its complete synthesis pathway, while other organisms meet their cellular B1 quota by scavenging the coenzyme from exogenous sources. Due to high bacterial cell density and diversity, marine sediments could represent some of the highest concentrations of putative B1 producers, yet these environments have received little attention as a possible source of B1 to the overlying water column. Here we report the first dissolved pore water profiles of B1 measured in cores collected in two consecutive years from Santa Monica Basin, CA. Vitamin B1 concentrations were fairly consistent between the two years ranging from 30 pM up to 770 pM. A consistent maximum at ~5 cm sediment depth covaried with dissolved concentrations of iron. Pore water concentrations were higher than water column levels and represented some of the highest known environmental concentrations of B1 measured to date, (over two times higher than maximum water column concentrations) suggesting increased rates of cellular production and release within the sediments. A one dimensional diffusion-transport model applied to the B1 profile was used to estimate a diffusive Benthic Flux of ~0.7 nmol m 2 d-1. This is an estimated Flux across the sediment-water interface in a deep sea basin; if similar magnitude B-vitamin Fluxes occur in shallow coastal waters, Benthic input could prove to be a significant B1-source to the water column and may play an important role in supplying this organic growth factor to auxotrophic primary producers.

  • Benthic Flux of oxygen and nutrients across oregon california shelf sediments
    Continental Shelf Research, 2013
    Co-Authors: William M Berelson, Silke Severmann, James Mcmanus, Clare E Reimers
    Abstract:

    Abstract A free vehicle Benthic chamber has been used to define Benthic nutrient Fluxes on the Southern Oregon and Northern California shelf (90–200 m). We measured Fluxes on two occasions, in the spring and fall of 2007, to assess variability in Fluxes and bioirrigation rates. Chambers were also employed to assess the impact of changing oxygen content on Benthic Fluxes. Oxygen uptake rates are similar to within 30% between sites in Oregon, Northern California and Central California, suggesting that a large portion of the Western US continental shelf experiences the same oxygen demand. Oxygen uptake (−2 to −10 mmol m −2  d −1 ) at S. Oregon/N. California sites is likely responsible for org ) oxidized in these sediments as denitrification and other electron transport processes generate much of the observed TCO 2 Flux (4 to 31 mmol C m −2  d −1 ). Much like other coastal regions, these sediments are generally a net sink of water column fixed N as nitrate uptake rates (−0.6 to −2.2 mmol N m −2  d −1 ) typically exceed ammonium efFluxes (0 to 1.9 mmol N m −2  d −1 ). As chamber oxygen concentrations decline during incubation, the concentration vs. time trends in phosphate, nitrate, and silicate remain linear. We interpret this to signify that there is no short-term change in the Flux of these species as a response to changing oxygen concentration. However, there is a non-linear response for ammonium, with some ammonium Fluxes increasing non-linearly by as much as a factor of 14. This occurs after an incubation period of 5–15 h when oxygen levels are 50%–20% of their ambient values. This change in Flux may be related to rather small changes in chamber oxygen concentration, suggesting that under hypoxic conditions, there could be an enhanced efFlux of ammonia to the water column. This would provide a positive feedback leading to enhanced primary productivity and increasing hypoxia.

  • Benthic Flux of oxygen and nutrients across Oregon/California shelf sediments
    Continental Shelf Research, 2013
    Co-Authors: William M Berelson, Silke Severmann, James Mcmanus, Clare E Reimers
    Abstract:

    Abstract A free vehicle Benthic chamber has been used to define Benthic nutrient Fluxes on the Southern Oregon and Northern California shelf (90–200 m). We measured Fluxes on two occasions, in the spring and fall of 2007, to assess variability in Fluxes and bioirrigation rates. Chambers were also employed to assess the impact of changing oxygen content on Benthic Fluxes. Oxygen uptake rates are similar to within 30% between sites in Oregon, Northern California and Central California, suggesting that a large portion of the Western US continental shelf experiences the same oxygen demand. Oxygen uptake (−2 to −10 mmol m −2  d −1 ) at S. Oregon/N. California sites is likely responsible for org ) oxidized in these sediments as denitrification and other electron transport processes generate much of the observed TCO 2 Flux (4 to 31 mmol C m −2  d −1 ). Much like other coastal regions, these sediments are generally a net sink of water column fixed N as nitrate uptake rates (−0.6 to −2.2 mmol N m −2  d −1 ) typically exceed ammonium efFluxes (0 to 1.9 mmol N m −2  d −1 ). As chamber oxygen concentrations decline during incubation, the concentration vs. time trends in phosphate, nitrate, and silicate remain linear. We interpret this to signify that there is no short-term change in the Flux of these species as a response to changing oxygen concentration. However, there is a non-linear response for ammonium, with some ammonium Fluxes increasing non-linearly by as much as a factor of 14. This occurs after an incubation period of 5–15 h when oxygen levels are 50%–20% of their ambient values. This change in Flux may be related to rather small changes in chamber oxygen concentration, suggesting that under hypoxic conditions, there could be an enhanced efFlux of ammonia to the water column. This would provide a positive feedback leading to enhanced primary productivity and increasing hypoxia.

Stefano Covelli - One of the best experts on this subject based on the ideXlab platform.

  • Mobility of heavy metals from polluted sediments of a semi-enclosed basin: in situ Benthic chamber experiments in Taranto’s Mar Piccolo (Ionian Sea, Southern Italy)
    Environmental Science and Pollution Research, 2016
    Co-Authors: Andrea Emili, Stefano Covelli, Alessandro Acquavita, Lucia Spada, Santina Giandomenico, Nicola Cardellicchio
    Abstract:

    In situ Benthic Flux experiments were conducted at two stations in the Mar Piccolo of Taranto (Italy), one of the most industrialised and contaminated coastal areas of the Mediterranean. Sediments of the two stations are notably different in their trace metal content, with a station closer to a Navy harbour showing higher mean concentrations of almost all investigated metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn). Conversely, both stations are characterised by significant Hg contamination, compared to the local baseline. Results of a sequential extraction scheme on surface sediments suggest a relatively scarce mobility of the examined metals (Zn > Ni > Cr > As > Cu > Pb). A Hg-specific extraction procedure showed that most of the element (93.1 %) occurs in a fraction comprising Hg bound to Fe/Mn oxi-hydroxides. Reduction of these oxides may affect Hg remobilisation and redistribution. Porewater profiles of dissolved trace metals were quite similar in the two sites, although significant differences could be observed for Al, Cu, Fe and Hg. The highest diffusive Fluxes were observed for As, Fe and Mn. Mobility rates of several trace elements (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn) were directly measured at the sediment–water interface. Results from Benthic in situ incubation experiments showed increasing dissolved metal concentrations with time, resulting in higher Fluxes for Cu, Fe, Hg, V and Zn in the most contaminated site. Conversely, Fluxes of Mn, Ni and Pb were comparable between the two stations. The estimated Flux of Hg (97 μg m^−2 day^−1) was the highest observed among similar experiments conducted in other highly contaminated Mediterranean coastal environments. Benthic Fluxes could be partially explained by considering rates of organic matter remineralisation, dissolution of Fe/Mn oxy-hydroxides and metal speciation in sediments. Seasonal and spatial variation of biogeochemical parameters can influence metal remobilisation in the Mar Piccolo area. In particular, metals could be promptly remobilised as a consequence of oxygen depletion, posing a serious concern for the widespread fishing and mussel farming activities in the area.

  • Benthic Flux measurements of hg species in a northern adriatic lagoon environment marano and grado lagoon italy
    Estuarine Coastal and Shelf Science, 2012
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Milena Horvat, Alessandro Acquavita, Neža Koron, Suzana žižek, Vesna Fajon
    Abstract:

    As part of the “MIRACLE” project, the biogeochemical cycling of mercury (Hg) at the sediment–water interface was studied in the field in the Marano and Grado Lagoon (Northern Adriatic Sea). Seasonal investigations were conducted at selected experimental sites, where Manila Clams (Tapes philippinarum) were previously seeded. Measurements were performed seasonally during three campaigns, using two Benthic chambers, one transparent and one dark, to evaluate the effect of light on Hg cycling. Total dissolved Hg (THg), methylmercury (MeHg), and dissolved gaseous Hg (DGM) species were considered. Diurnal Benthic Fluxes were found to significantly exceed the diffusive Fluxes at all stations. The assessment of the annual recycling of Hg species from sediments to the water column showed that up to 99% of MeHg is recycled annually to the water column, while Hg recycling ranges from 30 to 60%. MeHg poses the higher risk for potential bioaccumulation in clams, but it is partially mitigated by Hg reduction, which seems to be an important process leading to evasion losses of Hg from these environments. Estimated Benthic Fluxes suggest that Hg recycling at the sediment–water interface is more active in the Grado sector. Hence, based on the estimated release of MeHg from sediments, it is suggested that the western sector seems to be more suitable for clam farming and the extension of rearing activities.

  • does anoxia affect mercury cycling at the sediment water interface in the gulf of trieste northern adriatic sea incubation experiments using Benthic Flux chambers
    Applied Geochemistry, 2011
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Alessandro Acquavita, Neža Koron, S. Predonzani, Cinzia De Vittor
    Abstract:

    Abstract Coastal areas in the northernmost part of the Adriatic Sea (Gulf of Trieste and the adjacent Grado Lagoon) are characterized by high levels of Hg, both in sediments and in the water column, mainly originating from the suspended material inflowing through the Isonzo/Soca River system, draining the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. Hypoxic and anoxic conditions at the sediment–water interface (SWI) are frequently observed in the Gulf of Trieste and in the lagoon, due to strong late summer water stratification and high organic matter input. Mercury mobility at the SWI was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and in the Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature, using a dark Flux chamber simulating an oxic–anoxic transition. Temporal variations of dissolved Hg and methylmercury (MeHg) as well as O2, NH 4 + , NO 3 - + NO 2 - , PO 4 3 - , H2S, dissolved Fe and Mn, dissolved inorganic C (DIC) and dissolved organic C (DOC) were monitored simultaneously. Benthic Hg Fluxes were higher under anoxic conditions than in the oxic phase of the experiment. Methyl Hg release was less noticeable (low or absent) in the oxic phase, probably due to similar methylation and demethylation rates, but high in the anoxic phase of the experiment. The MeHg Flux was linked to SO4 reduction and dissolution of Fe (and Mn) oxyhydroxides, and formation of sulphides. Re-oxygenation was studied at sampling point CZ, where concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) oxyhydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.

  • Benthic Fluxes of mercury species in a lagoon environment (Grado Lagoon, Northern Adriatic Sea, Italy)
    Applied Geochemistry, 2008
    Co-Authors: Stefano Covelli, Jadran Faganeli, Alessandro Acquavita, Cinzia De Vittor, S. Predonzani, Milena Horvat
    Abstract:

    Abstract The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal Fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive Fluxes from porewater and overlying water concentrations, (2) measurements of Benthic Fluxes using a deployed light Benthic chamber in situ and (3) measurements of Benthic Fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g−1, showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g−1) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L−1, 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive Fluxes (up to 17 ng m−2 day−1) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and Benthic Flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive Fluxes in the lagoon (up to 110 ng m−2 day−1) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg Benthic Fluxes were highest in summer at both sites (41,000 and 33,000 ng m−2 day−1 at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O2 and inversely with DIC, suggesting an important influence of Benthic photosynthetic activities on lagoon Benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the Benthic Flux of MeHg was up to 15-fold higher in sediments overlain by O2 depleted waters. In the anoxic phase, the MeHg Fluxes proceeded in parallel with Fe Fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column.

  • porewater distribution and Benthic Flux measurements of mercury and methylmercury in the gulf of trieste northern adriatic sea
    Estuarine Coastal and Shelf Science, 1999
    Co-Authors: Stefano Covelli, Jadran Faganeli, Milena Horvat, A Brambati
    Abstract:

    The Gulf of Trieste is one of the most mercury-contaminated areas in the Mediterranean Sea. It is characterized by high mercury inputs from the Isonzo River whose tributary, the Idrijca River, drains the mercury mining area of Idrija in Slovenia where extraction activity has taken place for nearly 500 years. This appears, therefore, to be one of the most suitable sites for studying processes that affect Hg cycling in the marine environment and for determining whether sediments might act as secondary sources of mercury species in the water column. Porewater seasonal distributions of total dissolved Hg (HgT) and methylmercury (MeHg) were investigated. Usingin situBenthic chambers it was possible to determine Benthic Fluxes of HgTand MeHg at the water–sediment interface throughout the year. Benthic Fluxes were also compared with diffusive Fluxes calculated from porewater profiles. The results indicate that, following hypoxic conditions which occurred in late summer in the sea-bottom layer, highest Benthic efFluxes and porewater concentrations of Hg and MeHg appeared during autumn and winter. This was probably due to the transition from rapid sulphate reduction in late summer to cooler temperatures, higher oxygenation of the bottom water layer, and lower microbial activity which is well suited for Hg transformation, accumulation and Flux. A tentative budget based on Benthic Flux measurements indicates that 75% of HgTis buried in the sediment whereas 25% of HgT, approximately 23% in methylated form, is annually recycled and released at the water–sediment interface.

Andrea Emili - One of the best experts on this subject based on the ideXlab platform.

  • Mobility of heavy metals from polluted sediments of a semi-enclosed basin: in situ Benthic chamber experiments in Taranto’s Mar Piccolo (Ionian Sea, Southern Italy)
    Environmental Science and Pollution Research, 2016
    Co-Authors: Andrea Emili, Stefano Covelli, Alessandro Acquavita, Lucia Spada, Santina Giandomenico, Nicola Cardellicchio
    Abstract:

    In situ Benthic Flux experiments were conducted at two stations in the Mar Piccolo of Taranto (Italy), one of the most industrialised and contaminated coastal areas of the Mediterranean. Sediments of the two stations are notably different in their trace metal content, with a station closer to a Navy harbour showing higher mean concentrations of almost all investigated metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn). Conversely, both stations are characterised by significant Hg contamination, compared to the local baseline. Results of a sequential extraction scheme on surface sediments suggest a relatively scarce mobility of the examined metals (Zn > Ni > Cr > As > Cu > Pb). A Hg-specific extraction procedure showed that most of the element (93.1 %) occurs in a fraction comprising Hg bound to Fe/Mn oxi-hydroxides. Reduction of these oxides may affect Hg remobilisation and redistribution. Porewater profiles of dissolved trace metals were quite similar in the two sites, although significant differences could be observed for Al, Cu, Fe and Hg. The highest diffusive Fluxes were observed for As, Fe and Mn. Mobility rates of several trace elements (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn) were directly measured at the sediment–water interface. Results from Benthic in situ incubation experiments showed increasing dissolved metal concentrations with time, resulting in higher Fluxes for Cu, Fe, Hg, V and Zn in the most contaminated site. Conversely, Fluxes of Mn, Ni and Pb were comparable between the two stations. The estimated Flux of Hg (97 μg m^−2 day^−1) was the highest observed among similar experiments conducted in other highly contaminated Mediterranean coastal environments. Benthic Fluxes could be partially explained by considering rates of organic matter remineralisation, dissolution of Fe/Mn oxy-hydroxides and metal speciation in sediments. Seasonal and spatial variation of biogeochemical parameters can influence metal remobilisation in the Mar Piccolo area. In particular, metals could be promptly remobilised as a consequence of oxygen depletion, posing a serious concern for the widespread fishing and mussel farming activities in the area.

  • Benthic Flux measurements of hg species in a northern adriatic lagoon environment marano and grado lagoon italy
    Estuarine Coastal and Shelf Science, 2012
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Milena Horvat, Alessandro Acquavita, Neža Koron, Suzana žižek, Vesna Fajon
    Abstract:

    As part of the “MIRACLE” project, the biogeochemical cycling of mercury (Hg) at the sediment–water interface was studied in the field in the Marano and Grado Lagoon (Northern Adriatic Sea). Seasonal investigations were conducted at selected experimental sites, where Manila Clams (Tapes philippinarum) were previously seeded. Measurements were performed seasonally during three campaigns, using two Benthic chambers, one transparent and one dark, to evaluate the effect of light on Hg cycling. Total dissolved Hg (THg), methylmercury (MeHg), and dissolved gaseous Hg (DGM) species were considered. Diurnal Benthic Fluxes were found to significantly exceed the diffusive Fluxes at all stations. The assessment of the annual recycling of Hg species from sediments to the water column showed that up to 99% of MeHg is recycled annually to the water column, while Hg recycling ranges from 30 to 60%. MeHg poses the higher risk for potential bioaccumulation in clams, but it is partially mitigated by Hg reduction, which seems to be an important process leading to evasion losses of Hg from these environments. Estimated Benthic Fluxes suggest that Hg recycling at the sediment–water interface is more active in the Grado sector. Hence, based on the estimated release of MeHg from sediments, it is suggested that the western sector seems to be more suitable for clam farming and the extension of rearing activities.

  • does anoxia affect mercury cycling at the sediment water interface in the gulf of trieste northern adriatic sea incubation experiments using Benthic Flux chambers
    Applied Geochemistry, 2011
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Alessandro Acquavita, Neža Koron, S. Predonzani, Cinzia De Vittor
    Abstract:

    Abstract Coastal areas in the northernmost part of the Adriatic Sea (Gulf of Trieste and the adjacent Grado Lagoon) are characterized by high levels of Hg, both in sediments and in the water column, mainly originating from the suspended material inflowing through the Isonzo/Soca River system, draining the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. Hypoxic and anoxic conditions at the sediment–water interface (SWI) are frequently observed in the Gulf of Trieste and in the lagoon, due to strong late summer water stratification and high organic matter input. Mercury mobility at the SWI was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and in the Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature, using a dark Flux chamber simulating an oxic–anoxic transition. Temporal variations of dissolved Hg and methylmercury (MeHg) as well as O2, NH 4 + , NO 3 - + NO 2 - , PO 4 3 - , H2S, dissolved Fe and Mn, dissolved inorganic C (DIC) and dissolved organic C (DOC) were monitored simultaneously. Benthic Hg Fluxes were higher under anoxic conditions than in the oxic phase of the experiment. Methyl Hg release was less noticeable (low or absent) in the oxic phase, probably due to similar methylation and demethylation rates, but high in the anoxic phase of the experiment. The MeHg Flux was linked to SO4 reduction and dissolution of Fe (and Mn) oxyhydroxides, and formation of sulphides. Re-oxygenation was studied at sampling point CZ, where concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) oxyhydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.

Alessandro Acquavita - One of the best experts on this subject based on the ideXlab platform.

  • Mobility of heavy metals from polluted sediments of a semi-enclosed basin: in situ Benthic chamber experiments in Taranto’s Mar Piccolo (Ionian Sea, Southern Italy)
    Environmental Science and Pollution Research, 2016
    Co-Authors: Andrea Emili, Stefano Covelli, Alessandro Acquavita, Lucia Spada, Santina Giandomenico, Nicola Cardellicchio
    Abstract:

    In situ Benthic Flux experiments were conducted at two stations in the Mar Piccolo of Taranto (Italy), one of the most industrialised and contaminated coastal areas of the Mediterranean. Sediments of the two stations are notably different in their trace metal content, with a station closer to a Navy harbour showing higher mean concentrations of almost all investigated metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn). Conversely, both stations are characterised by significant Hg contamination, compared to the local baseline. Results of a sequential extraction scheme on surface sediments suggest a relatively scarce mobility of the examined metals (Zn > Ni > Cr > As > Cu > Pb). A Hg-specific extraction procedure showed that most of the element (93.1 %) occurs in a fraction comprising Hg bound to Fe/Mn oxi-hydroxides. Reduction of these oxides may affect Hg remobilisation and redistribution. Porewater profiles of dissolved trace metals were quite similar in the two sites, although significant differences could be observed for Al, Cu, Fe and Hg. The highest diffusive Fluxes were observed for As, Fe and Mn. Mobility rates of several trace elements (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn) were directly measured at the sediment–water interface. Results from Benthic in situ incubation experiments showed increasing dissolved metal concentrations with time, resulting in higher Fluxes for Cu, Fe, Hg, V and Zn in the most contaminated site. Conversely, Fluxes of Mn, Ni and Pb were comparable between the two stations. The estimated Flux of Hg (97 μg m^−2 day^−1) was the highest observed among similar experiments conducted in other highly contaminated Mediterranean coastal environments. Benthic Fluxes could be partially explained by considering rates of organic matter remineralisation, dissolution of Fe/Mn oxy-hydroxides and metal speciation in sediments. Seasonal and spatial variation of biogeochemical parameters can influence metal remobilisation in the Mar Piccolo area. In particular, metals could be promptly remobilised as a consequence of oxygen depletion, posing a serious concern for the widespread fishing and mussel farming activities in the area.

  • Benthic Flux measurements of hg species in a northern adriatic lagoon environment marano and grado lagoon italy
    Estuarine Coastal and Shelf Science, 2012
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Milena Horvat, Alessandro Acquavita, Neža Koron, Suzana žižek, Vesna Fajon
    Abstract:

    As part of the “MIRACLE” project, the biogeochemical cycling of mercury (Hg) at the sediment–water interface was studied in the field in the Marano and Grado Lagoon (Northern Adriatic Sea). Seasonal investigations were conducted at selected experimental sites, where Manila Clams (Tapes philippinarum) were previously seeded. Measurements were performed seasonally during three campaigns, using two Benthic chambers, one transparent and one dark, to evaluate the effect of light on Hg cycling. Total dissolved Hg (THg), methylmercury (MeHg), and dissolved gaseous Hg (DGM) species were considered. Diurnal Benthic Fluxes were found to significantly exceed the diffusive Fluxes at all stations. The assessment of the annual recycling of Hg species from sediments to the water column showed that up to 99% of MeHg is recycled annually to the water column, while Hg recycling ranges from 30 to 60%. MeHg poses the higher risk for potential bioaccumulation in clams, but it is partially mitigated by Hg reduction, which seems to be an important process leading to evasion losses of Hg from these environments. Estimated Benthic Fluxes suggest that Hg recycling at the sediment–water interface is more active in the Grado sector. Hence, based on the estimated release of MeHg from sediments, it is suggested that the western sector seems to be more suitable for clam farming and the extension of rearing activities.

  • does anoxia affect mercury cycling at the sediment water interface in the gulf of trieste northern adriatic sea incubation experiments using Benthic Flux chambers
    Applied Geochemistry, 2011
    Co-Authors: Andrea Emili, Stefano Covelli, Jadran Faganeli, Alessandro Acquavita, Neža Koron, S. Predonzani, Cinzia De Vittor
    Abstract:

    Abstract Coastal areas in the northernmost part of the Adriatic Sea (Gulf of Trieste and the adjacent Grado Lagoon) are characterized by high levels of Hg, both in sediments and in the water column, mainly originating from the suspended material inflowing through the Isonzo/Soca River system, draining the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. Hypoxic and anoxic conditions at the sediment–water interface (SWI) are frequently observed in the Gulf of Trieste and in the lagoon, due to strong late summer water stratification and high organic matter input. Mercury mobility at the SWI was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and in the Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature, using a dark Flux chamber simulating an oxic–anoxic transition. Temporal variations of dissolved Hg and methylmercury (MeHg) as well as O2, NH 4 + , NO 3 - + NO 2 - , PO 4 3 - , H2S, dissolved Fe and Mn, dissolved inorganic C (DIC) and dissolved organic C (DOC) were monitored simultaneously. Benthic Hg Fluxes were higher under anoxic conditions than in the oxic phase of the experiment. Methyl Hg release was less noticeable (low or absent) in the oxic phase, probably due to similar methylation and demethylation rates, but high in the anoxic phase of the experiment. The MeHg Flux was linked to SO4 reduction and dissolution of Fe (and Mn) oxyhydroxides, and formation of sulphides. Re-oxygenation was studied at sampling point CZ, where concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) oxyhydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.

  • Benthic Fluxes of mercury species in a lagoon environment (Grado Lagoon, Northern Adriatic Sea, Italy)
    Applied Geochemistry, 2008
    Co-Authors: Stefano Covelli, Jadran Faganeli, Alessandro Acquavita, Cinzia De Vittor, S. Predonzani, Milena Horvat
    Abstract:

    Abstract The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal Fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive Fluxes from porewater and overlying water concentrations, (2) measurements of Benthic Fluxes using a deployed light Benthic chamber in situ and (3) measurements of Benthic Fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g−1, showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g−1) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L−1, 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive Fluxes (up to 17 ng m−2 day−1) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and Benthic Flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive Fluxes in the lagoon (up to 110 ng m−2 day−1) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg Benthic Fluxes were highest in summer at both sites (41,000 and 33,000 ng m−2 day−1 at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O2 and inversely with DIC, suggesting an important influence of Benthic photosynthetic activities on lagoon Benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the Benthic Flux of MeHg was up to 15-fold higher in sediments overlain by O2 depleted waters. In the anoxic phase, the MeHg Fluxes proceeded in parallel with Fe Fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column.

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  • Dissolved oxygen and suspended particles regulate the Benthic Flux of iron from continental margins
    Marine Chemistry, 2020
    Co-Authors: William B Homoky, William M Berelson, Silke Severmann, James Mcmanus, Timothy E Riedel, P J Statham, Rachel A Mills
    Abstract:

    We present ex situ sediment incubation results from the California and Oregon shelves and compare the calculated Benthic Flux of dissolved Fe with those from in situ incubations and pore water concentration profiles. We also examine the influence of oxygen depletion and sediment re-suspension on Benthic Fe exchange. Ex situ incubation of the California and Oregon shelf sites yielded average Benthic Fe Fluxes of 3.5 and 8.3μmolm -2day -1, respectively, compared to 17 and 55μmolm -2day -1 from the in situ Lander determinations, and 73 and 103μmolm -2day -1 from modeling of pore water concentration profiles. Differences between Benthic Fe Flux estimates are primarily accounted for by [1] differences in Fe (II) oxidation kinetics, which result from distinct oxygen consumption rates between incubation methods, and the absence of kinetic considerations in the overlying bottom water in pore water Flux calculations, and [2] the effects of biological sediment irrigation that are best represented by in situ incubations due to their sampling area and preservation of bottom water conditions. Bottom water oxygen concentrations were higher at the California shelf site than that at the Oregon shelf site, and probably accounted for the greater discrepancy between methods used to determine Benthic Fe Flux. The comparison of techniques used to determine Benthic Fe Flux indicates that the concentration of bottom water oxygen exerts a principle control over the fate of dissolved Fe entering the overlying bottom water - supporting the view that the expansion of coastal hypoxia has the potential to enhance the Benthic supply of Fe (II) to shelf waters. An episode of surface sediment re-suspension during ex situ incubation led to a rapid removal of 76-89% of dissolved Fe from seawater, followed by a steady return towards initial seawater concentrations during particle settling, indicating that diffusive inputs of dissolved Fe from sediment pore water are rapidly adsorbed and desorbed by particles during periods of Benthic re-suspension. The findings suggest that dissolved Fe concentrations in bottom waters may reflect an equilibrium concentration of non-stabilized aqueous Fe and particle-adsorbed Fe phases - where the addition of suspended particles to bottom waters leads to scavenging of dissolved Fe into labile particulate Fe phases. Thus we suggest that suspended particles are a significant buffer of dissolved Fe released from shelf sediments, an important transport mechanism for Benthic Fe inputs, and a regulator of dissolved Fe concentrations in seawater. © 2012 Elsevier B.V

  • Benthic Flux of oxygen and nutrients across oregon california shelf sediments
    Continental Shelf Research, 2013
    Co-Authors: William M Berelson, Silke Severmann, James Mcmanus, Clare E Reimers
    Abstract:

    Abstract A free vehicle Benthic chamber has been used to define Benthic nutrient Fluxes on the Southern Oregon and Northern California shelf (90–200 m). We measured Fluxes on two occasions, in the spring and fall of 2007, to assess variability in Fluxes and bioirrigation rates. Chambers were also employed to assess the impact of changing oxygen content on Benthic Fluxes. Oxygen uptake rates are similar to within 30% between sites in Oregon, Northern California and Central California, suggesting that a large portion of the Western US continental shelf experiences the same oxygen demand. Oxygen uptake (−2 to −10 mmol m −2  d −1 ) at S. Oregon/N. California sites is likely responsible for org ) oxidized in these sediments as denitrification and other electron transport processes generate much of the observed TCO 2 Flux (4 to 31 mmol C m −2  d −1 ). Much like other coastal regions, these sediments are generally a net sink of water column fixed N as nitrate uptake rates (−0.6 to −2.2 mmol N m −2  d −1 ) typically exceed ammonium efFluxes (0 to 1.9 mmol N m −2  d −1 ). As chamber oxygen concentrations decline during incubation, the concentration vs. time trends in phosphate, nitrate, and silicate remain linear. We interpret this to signify that there is no short-term change in the Flux of these species as a response to changing oxygen concentration. However, there is a non-linear response for ammonium, with some ammonium Fluxes increasing non-linearly by as much as a factor of 14. This occurs after an incubation period of 5–15 h when oxygen levels are 50%–20% of their ambient values. This change in Flux may be related to rather small changes in chamber oxygen concentration, suggesting that under hypoxic conditions, there could be an enhanced efFlux of ammonia to the water column. This would provide a positive feedback leading to enhanced primary productivity and increasing hypoxia.

  • Benthic Flux of oxygen and nutrients across Oregon/California shelf sediments
    Continental Shelf Research, 2013
    Co-Authors: William M Berelson, Silke Severmann, James Mcmanus, Clare E Reimers
    Abstract:

    Abstract A free vehicle Benthic chamber has been used to define Benthic nutrient Fluxes on the Southern Oregon and Northern California shelf (90–200 m). We measured Fluxes on two occasions, in the spring and fall of 2007, to assess variability in Fluxes and bioirrigation rates. Chambers were also employed to assess the impact of changing oxygen content on Benthic Fluxes. Oxygen uptake rates are similar to within 30% between sites in Oregon, Northern California and Central California, suggesting that a large portion of the Western US continental shelf experiences the same oxygen demand. Oxygen uptake (−2 to −10 mmol m −2  d −1 ) at S. Oregon/N. California sites is likely responsible for org ) oxidized in these sediments as denitrification and other electron transport processes generate much of the observed TCO 2 Flux (4 to 31 mmol C m −2  d −1 ). Much like other coastal regions, these sediments are generally a net sink of water column fixed N as nitrate uptake rates (−0.6 to −2.2 mmol N m −2  d −1 ) typically exceed ammonium efFluxes (0 to 1.9 mmol N m −2  d −1 ). As chamber oxygen concentrations decline during incubation, the concentration vs. time trends in phosphate, nitrate, and silicate remain linear. We interpret this to signify that there is no short-term change in the Flux of these species as a response to changing oxygen concentration. However, there is a non-linear response for ammonium, with some ammonium Fluxes increasing non-linearly by as much as a factor of 14. This occurs after an incubation period of 5–15 h when oxygen levels are 50%–20% of their ambient values. This change in Flux may be related to rather small changes in chamber oxygen concentration, suggesting that under hypoxic conditions, there could be an enhanced efFlux of ammonia to the water column. This would provide a positive feedback leading to enhanced primary productivity and increasing hypoxia.

  • dissolved oxygen and suspended particles regulate the Benthic Flux of iron from continental margins
    Marine Chemistry, 2012
    Co-Authors: William B Homoky, William M Berelson, Silke Severmann, James Mcmanus, Timothy E Riedel, P J Statham, Rachel A Mills
    Abstract:

    article We present ex situ sediment incubation results from the California and Oregon shelves and compare the calculated Benthic Flux of dissolved Fe with those from in situ incubations and pore water concentration profiles. We also examine the influence of oxygen depletion and sediment re-suspension on Benthic Fe exchange. Ex situ incubation of the California and Oregon shelf sites yielded average Benthic Fe Fluxes of 3.5 and 8.3 μmol m �2 day �1 , respectively, compared to 17 and 55 μmol m �2 day �1 from the in situ Lander

  • a time series of Benthic Flux measurements from monterey bay ca
    Continental Shelf Research, 2003
    Co-Authors: William M Berelson, James Mcmanus, Kenneth S. Johnson, Kenneth H Coale, David J Burdige, Tammy E Kilgore, Debbie Colodner, Francisco P Chavez, Rafael Kudela, Joceline Boucher
    Abstract:

    Abstract In situ incubation chamber measurements of Benthic nutrient recycling rates were made on the Monterey Bay shelf at 100 m during various years and seasons. Variability in nutrient (Si, PO42+, NH3, NO3−) and trace metal (Mn, Fe (II), Cu) Fluxes correlate with variability in the amount of organic carbon oxidized on the sea floor. Patterns of primary productivity show a mid-year maxima, consistent with the timing of increased rates of Benthic Corg and opal recycling. High rates of Corg rain to the shelf promote nitrate consumption at a rate that equals or exceeds ammonia efFlux. Low rates of Corg rain promote greater efFlux of DIN; thus these margin sediments provide a negative feedback to local productivity cycles. The efFlux of iron (II) from shelf sediments is sufficient to support >100% of new production, yet Fe Flux is positively correlated with Corg recycling which lags the maximum in new production. On account of this time lag, diagenetically recycled Fe is not likely a micro-nutrient trigger of new production, but could serve as a positive feedback. Bio-irrigation rates are seasonally variable by 30% but maximal during the maximum productivity months.