scholarly journals A model of mercury cycling and isotopic fractionation in the ocean

2018 ◽  
Author(s):  
David E. Archer ◽  
Joel D. Blum
Keyword(s):  
Particle Transport ◽  
Human Exposure ◽  
Human Impacts ◽  
Isotopic Fractionation ◽  
Sea Surface ◽  
Spatial Distributions ◽  
Mercury Cycling ◽  
Isotopic Signatures ◽  
Subsurface Maximum ◽  
Model Ocean

Abstract. Mercury speciation and isotopic fractionation processes have been incorporated into the HAMOCC offline ocean tracer advection code. The model is fast enough to allow a wide exploration of the sensitivity of the Hg cycle in the oceans, and of human exposure to Hg via monomethyl-Hg incorporation into fish. Vertical particle transport of Hg appears to play a discernable role in setting present-day Hg distributions, which we surmise by the fact that in simulations without particle transport, the high present-day Hg deposition rate leads to an Hg maximum at the sea surface, rather than a subsurface maximum as observed. Hg particle transport has only a relatively small impact on anthropogenic Hg uptake, but it sequesters Hg deeper in the water column, so that excess Hg is retained in the model ocean for longer after anthropogenic Hg deposition is stopped. The concentration of monomethyl Hg is sensitive to its production rate, with model experiments suggesting that human impacts on ocean oxygen concentrations could have as significant an impact on oceanic MMHg concentration as the anthropogenic Hg emission itself. Eight different isotopic fractionation mechanisms are simulated, independently and combined together, to predict their expression in the spatial distributions of isotopic signatures of Hg species in the ocean.

scholarly journals A model of mercury cycling and isotopic fractionation in the ocean

2018 ◽  
Vol 15 (20) ◽  
pp. 6297-6313 ◽  
Author(s):  
David E. Archer ◽  
Joel D. Blum
Keyword(s):  
Particle Transport ◽  
Isotopic Fractionation ◽  
Mercury Cycling ◽  
Isotopic Signatures ◽  
Surface Ocean ◽  
Mass Independent Fractionation ◽  
Sink Term ◽  
Dissolved Species ◽  
The Impact ◽  
Model Subject

Abstract. Mercury speciation and isotopic fractionation processes have been incorporated into the HAMOCC offline ocean tracer advection code. The model is fast enough to allow a wide exploration of the sensitivity of the Hg cycle in the oceans, and of factors controlling human exposure to monomethyl-Hg through the consumption of fish. Vertical particle transport of Hg appears to play a discernable role in setting present-day Hg distributions, which we surmise by the fact that in simulations without particle transport, the high present-day Hg deposition rate leads to an Hg maximum at the sea surface, rather than a subsurface maximum as observed. Hg particle transport has a relatively small impact on anthropogenic Hg uptake, but it sequesters Hg deeper in the water column, so that excess Hg is retained in the model ocean for a longer period of time after anthropogenic Hg deposition is stopped. Among 10 rate constants in the model, steady-state Hg concentrations are most sensitive to reactions that are sources or sinks of Hg(0), the evasion of which to the atmosphere is the dominant sink term in the surface ocean. Isotopic fractionations in the interconversion reactions are most strongly expressed, in the isotopic signatures of dissolved Hg, in reactions that involve the dominant dissolved species, Hg(II), including mass independent fractionation during Hg photoreduction. The Δ199Hg of MMHg in the model, subject to photoreduction fractionation, reproduces the Δ199Hg of fish in the upper 1000 m of the ocean, while the impact of anthropogenic Hg deposition on Hg isotope ratios is essentially negligible.

scholarly journals Geostatistical study of spatial correlations of lead and zinc concentration in urban reservoir. Study case Czerniakowskie Lake, Warsaw, Poland

2016 ◽  
Vol 8 (1) ◽  
Author(s):  
Piotr Fabijańczyk ◽  
Jarosław Zawadzki ◽  
Małgorzata Wojtkowska
Keyword(s):  
Bottom Sediments ◽  
Cross Sections ◽  
Zinc Concentration ◽  
Human Impacts ◽  
Large City ◽  
Field Measurements ◽  
Anthropogenic Pressure ◽  
Spatial Distributions ◽  
Water Suspension ◽  
Lead And Zinc

AbstractThe article presents detailed geostatistical analysis of spatial distribution of lead and zinc concentration in water, suspension and bottom sediments of large, urban lake exposed to intensive anthropogenic pressure within a large city. Systematic chemical measurements were performed at eleven cross-sections located along Czerniakowskie Lake, the largest lake in Warsaw, the capital of Poland. During the summer, the lake is used as a public bathing area, therefore, to better evaluate human impacts, field measurements were carried out in high-use seasons. It was found that the spatial distributions of aqueous lead and zinc differ during the summer and autumn. In summer several Pb and Zn hot-spots were observed, while during autumn spatial distributions of Pb and Zn were rather homogenous throughout the entire lake. Large seasonal differences in spatial distributions of Pb and Zn were found in bottom sediments. Autumn concentrations of both heavy metals were ten times higher in comparison with summer values.Clear cross-correlations of Pb and Zn concentrations in water, suspension and bottom sediments suggest that both Pb and Zn came to Czerniakowskie Lake from the same source.

scholarly journals Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

2012 ◽  
Vol 9 (5) ◽  
pp. 1671-1690 ◽  
Author(s):  
J. B. Heffernan ◽  
A. R. Albertin ◽  
M. L. Fork ◽  
B. G. Katz ◽  
M. J. Cohen
Keyword(s):  
Noble Gas ◽  
Regional Scale ◽  
Isotopic Fractionation ◽  
Nitrogen Sources ◽  
Spatial And Temporal Variability ◽  
Limited Information ◽  
Nitrogen Budgets ◽  
Isotopic Signatures ◽  
Floridan Aquifer ◽  
Upper Floridan Aquifer

Abstract. Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationships between O2 and δ15NNO3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N:18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32 % of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source δ15NNO3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3–) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs.

scholarly journals Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

2011 ◽  
Vol 8 (5) ◽  
pp. 10247-10294
Author(s):  
J. B. Heffernan ◽  
A. R. Albertin ◽  
M. L. Fork ◽  
B. G. Katz ◽  
M. J. Cohen
Keyword(s):  
Regional Scale ◽  
Negative Relationship ◽  
Isotopic Fractionation ◽  
Nitrogen Sources ◽  
Spatial And Temporal Variability ◽  
Limited Information ◽  
Nitrogen Budgets ◽  
Isotopic Signatures ◽  
Floridan Aquifer ◽  
Upper Floridan Aquifer

Abstract. Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationship between O2 and δ15NNO3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N : 18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32% of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source δ15NNO3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3−) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs.

scholarly journals Diel variation in mercury stable isotope ratios records photoreduction of PM<sub>2.5</sub>-bound mercury

2019 ◽  
Vol 19 (1) ◽  
pp. 315-325 ◽  
Author(s):  
Qiang Huang ◽  
Jiubin Chen ◽  
Weilin Huang ◽  
John R. Reinfelder ◽  
Pingqing Fu ◽  
...  
Keyword(s):  
Isotopic Fractionation ◽  
Emission Sources ◽  
Diel Variation ◽  
Strong Correlations ◽  
Important Process ◽  
Positive Slope ◽  
Photochemical Reduction ◽  
Isotopic Signatures ◽  
Paired Samples ◽  
Beijing China

Abstract. Mercury (Hg) bound to fine aerosols (PM2.5-Hg) may undergo photochemical reaction that causes isotopic fractionation and obscures the initial isotopic signatures. In this study, we quantified Hg isotopic compositions for 56 PM2.5 samples collected between 15 September and 16 October 2015 from Beijing, China, among which 26 were collected during daytime (between 08:00 and 18:30 LT) and 30 during night (between 19:00 and 07:30 LT). The results show that diel variation was statistically significant (p < 0.05) for Hg content, Δ199Hg and Δ200Hg, with Hg content during daytime (0.32±0.14 µg g−1) lower than at night (0.48±0.24 µg g−1) and Δ199Hg and Δ200Hg values during daytime (mean of 0.26 ‰±0.40 ‰ and 0.09 ‰±0.06 ‰, respectively) higher than during nighttime (0.04 ‰±0.22 ‰ and 0.06 ‰±0.05 ‰, respectively), whereas PM2.5 concentrations and δ202Hg values showed insignificant (p > 0.05) diel variation. Geochemical characteristics of the samples and the air mass backward trajectories (PM2.5 source related) suggest that diel variation in Δ199Hg values resulted primarily from the photochemical reduction of divalent PM2.5-Hg, rather than variations in emission sources. The importance of photoreduction is supported by the strong correlations between Δ199Hg and (i) Δ201Hg (positive, slope = 1.1), (ii) δ202Hg (positive, slope = 1.15), (iii) content of Hg in PM2.5 (negative), (iv) sunshine durations (positive) and (v) ozone concentration (positive) observed for consecutive day–night paired samples. Our results provide isotopic evidence that local, daily photochemical reduction of divalent Hg is of critical importance to the fate of PM2.5-Hg in urban atmospheres and that, in addition to variation in sources, photochemical reduction appears to be an important process that affects both the particle mass-specific abundance and isotopic composition of PM2.5-Hg.

scholarly journals Past climate and continentality inferred from ice wedges at Batagay megaslump in the Northern Hemisphere's most continental region, Yana Highlands, interior Yakutia

2019 ◽  
Vol 15 (4) ◽  
pp. 1443-1461 ◽  
Author(s):  
Thomas Opel ◽  
Julian B. Murton ◽  
Sebastian Wetterich ◽  
Hanno Meyer ◽  
Kseniia Ashastina ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Middle Pleistocene ◽  
Winter Climate ◽  
Isotopic Signatures ◽  
Mis 3 ◽  
Winter Temperatures ◽  
Ice Wedge ◽  
Study Sites ◽  
Ice Complex

Abstract. Ice wedges in the Yana Highlands of interior Yakutia – the most continental region of the Northern Hemisphere – were investigated to elucidate changes in winter climate and continentality that have taken place since the Middle Pleistocene. The Batagay megaslump exposes ice wedges and composite wedges that were sampled from three cryostratigraphic units: the lower ice complex of likely pre-Marine Isotope Stage (MIS) 6 age, the upper ice complex (Yedoma) and the upper sand unit (both MIS 3 to 2). A terrace of the nearby Adycha River provides a Late Holocene (MIS 1) ice wedge that serves as a modern reference for interpretation. The stable-isotope composition of ice wedges in the MIS 3 upper ice complex at Batagay is more depleted (mean δ18O about −35 ‰) than those from 17 other ice-wedge study sites across coastal and central Yakutia. This observation points to lower winter temperatures and therefore higher continentality in the Yana Highlands during MIS 3. Likewise, more depleted isotope values are found in Holocene wedge ice (mean δ18O about −29 ‰) compared to other sites in Yakutia. Ice-wedge isotopic signatures of the lower ice complex (mean δ18O about −33 ‰) and of the MIS 3–2 upper sand unit (mean δ18O from about −33 ‰ to −30 ‰) are less distinctive regionally. The latter unit preserves traces of fast formation in rapidly accumulating sand sheets and of post-depositional isotopic fractionation.

scholarly journals Natural bounds on herbivorous coral reef fishes

2016 ◽  
Vol 283 (1843) ◽  
pp. 20161716 ◽  
Author(s):  
Adel Heenan ◽  
Andrew S. Hoey ◽  
Gareth J. Williams ◽  
Ivor D. Williams
Keyword(s):  
Coral Reefs ◽  
Human Impacts ◽  
Structural Complexity ◽  
Reef Fishes ◽  
Sea Surface ◽  
Relative Importance ◽  
Western Pacific Ocean ◽  
Biological Communities ◽  
Opposing Effects ◽  
Ecosystem State

Humans are an increasingly dominant driver of Earth's biological communities, but differentiating human impacts from natural drivers of ecosystem state is crucial. Herbivorous fish play a key role in maintaining coral dominance on coral reefs, and are widely affected by human activities, principally fishing. We assess the relative importance of human and biophysical (habitat and oceanographic) drivers on the biomass of five herbivorous functional groups among 33 islands in the central and western Pacific Ocean. Human impacts were clear for some, but not all, herbivore groups. Biomass of browsers, large excavators, and of all herbivores combined declined rapidly with increasing human population density, whereas grazers, scrapers, and detritivores displayed no relationship. Sea-surface temperature had significant but opposing effects on the biomass of detritivores (positive) and browsers (negative). Similarly, the biomass of scrapers, grazers, and detritivores correlated with habitat structural complexity; however, relationships were group specific. Finally, the biomass of browsers and large excavators was related to island geomorphology, both peaking on low-lying islands and atolls. The substantial variability in herbivore populations explained by natural biophysical drivers highlights the need for locally appropriate management targets on coral reefs.

scholarly journals Isotopic signatures of production and uptake of H<sub>2</sub> by soil

2015 ◽  
Vol 15 (22) ◽  
pp. 13003-13021 ◽  
Author(s):  
Q. Chen ◽  
M. E. Popa ◽  
A. M. Batenburg ◽  
T. Röckmann
Keyword(s):  
Isotope Effects ◽  
Deposition Velocity ◽  
Isotopic Fractionation ◽  
Isotopic Signature ◽  
Deuterium Content ◽  
Forest Site ◽  
Fractionation Factor ◽  
Isotopic Signatures ◽  
The Difference ◽  
Isotope Equilibrium

Abstract. Molecular hydrogen (H2) is the second most abundant reduced trace gas (after methane) in the atmosphere, but its biogeochemical cycle is not well understood. Our study focuses on the soil production and uptake of H2 and the associated isotope effects. Air samples from a grass field and a forest site in the Netherlands were collected using soil chambers. The results show that uptake and emission of H2 occurred simultaneously at all sampling sites, with strongest emission at the grassland sites where clover (N2 fixing legume) was present. The H2 mole fraction and deuterium content were measured in the laboratory to determine the isotopic fractionation factor during H2 soil uptake (αsoil) and the isotopic signature of H2 that is simultaneously emitted from the soil (δDsoil). By considering all net-uptake experiments, an overall fractionation factor for deposition of αsoil = kHD / kHH = 0.945 ± 0.004 (95 % CI) was obtained. The difference in mean αsoil between the forest soil 0.937 ± 0.008 and the grassland 0.951 ± 0.026 is not statistically significant. For two experiments, the removal of soil cover increased the deposition velocity (vd) and αsoil simultaneously, but a general positive correlation between vd and αsoil was not found in this study. When the data are evaluated with a model of simultaneous production and uptake, the isotopic composition of H2 that is emitted at the grassland site is calculated as δDsoil = (−530 ± 40) ‰. This is less deuterium depleted than what is expected from isotope equilibrium between H2O and H2.

Influence of Suspended Sediment and Sea Surface Temperature on Alga in Changjiang Estuary

2013 ◽  
Vol 295-298 ◽  
pp. 1957-1962
Author(s):  
Xin Feng Zhang ◽  
Feng Pan Zhang ◽  
Xin Jun Chen
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Suspended Sediment ◽  
Spatial Correlation ◽  
Correlation Effect ◽  
Changjiang Estuary ◽  
Sea Surface ◽  
Dominant Factor ◽  
Spatial Distributions ◽  
Spatial Autoregressive

The main theories of spatial autoregressive model and model selection were used to study the spatial correlation between suspended sediment, sea surface temperature and alga during summer 2011 in Changjiang estuary. The results indicated that: there were significant high spatial autocorrelations in the spatial distributions of suspended sediment, sea surface temperature and alga, respectively; Suspended sediment always had significant and positive spatial correlation effect on the distribution of alga, Sea surface temperature had significant and positive spatial correlation effect on the spatial distribution of alga in June and August, but this effect decreased in July; The spatial distributions of suspended sediment and alga were closely correlated. Suspended sediment was the key dominant factor of the growth and bloom of alga, also the source of nutriment of alga.

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