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Publisher: Springer-Verlag   (Total: 2329 journals)

 Aquatic Geochemistry   [SJR: 0.764]   [H-I: 39]   [3 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1573-1421 - ISSN (Online) 1380-6165    Published by Springer-Verlag  [2329 journals]
• The Speciation of Metals in Natural Waters
• Authors: Denis Pierrot; Frank J. Millero
Pages: 1 - 20
Abstract: The equilibria and rates of reactions of trace metals in natural waters are affected by their speciation or the form of the metal in the solution phase. Many workers have shown, for example, that biological uptake (Anderson and Morel in Limnol Oceanogr 27:789–813, 1982), the toxicity (Sunda and Ferguson in Trace metals in seawater, Plenum Press, New York, 1983) as well as the solubility (Millero et al. in Mar Chem 50:21–39, 1995; Liu and Millero in Geochim Cosmochim Acta 63:3487–3497, 1999) are affected by the speciation. For example, Fe(II) and Mn(II) are biologically available for marine organisms, while Fe(III) and Mn(IV) are normally not available. The speciation of metals also affects the rates of oxidation (Millero in Geochim Cosmochim Acta 49:547–553, 1985, Res Trends Curr Top Sol Chem 1:141–169, 1994; Sharma and Millero in Geochim Cosmochim Acta 53:2269–2276, 1989; Vazquez et al. in Geophys Res Lett 16:1363–1366, 1989) and reduction (Res Trends Curr Top Sol Chem 1:141–169, 1994; Millero et al. in Mar Chem 36:71–83, 1991) of metals in natural waters. The ionic interactions of metals are controlled by interactions with inorganic (Cl−, OH−, CO3 2−, etc.) and organic ligands (e.g., Fulvic and Humic acids). The speciation of metals is also affected by the oxidation potential (Eh) and the pH in the solution. In this paper we have developed a Pitzer Model (Pitzer in J Phys Chem 77:268–277, 1973, Activity coefficients in electrolyte solutions, 2nd edn, CRC Press, Boca Raton, 1991) that can be used to determine the speciation of trace metals in seawater and other natural waters. It is based upon the Miami Pitzer Model (Millero and Pierrot in Aquatic Geochem 4:153–199, 1998) that has been shown to predict reliable activity coefficients for the major components of seawater. The computer code (Pierrot in Ph.D. Thesis, University of Miami, Miami, Florida, 2002) for these calculations is described in detail, in this paper. It has been used in an earlier paper (Millero and Pierrot in Chemistry of marine water and sediments, Springer, Berlin, 2002) and more recently used to examine the effect of pH on the speciation of metals in seawater (Millero et al. in Oceanography 22(4):72–85, 2009).
PubDate: 2017-02-01
DOI: 10.1007/s10498-016-9292-4
Issue No: Vol. 23, No. 1 (2017)

• Assessment of the Hydrogeochemical Processes Affecting Groundwater Quality
in the Eocene Limestone Aquifer at the Desert Fringes of El Minia
Governorate, Egypt
• Authors: Reda G. M. Ibrahim; W. Berry Lyons
Pages: 33 - 52
Abstract: El Minia Governorate is within the Nile Valley and is surrounded by the Eocene limestone plateaus from the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer in both the eastern and western desert fringes of El Minia. Thirty groundwater samples from the Eocene aquifer (east and west of the Nile) and seven samples from post-Eocene aquifers in this area were analyzed to assess the groundwater geochemistry, isotopic compositions and the subsurface hydrology. Samples obtained from depths of 24–120 m were measured for major components, nutrients, oxygen-18, deuterium and carbon-13. The groundwater TDS (total dissolved solids) concentrations ranged from 530 to 2788 and 453 to 1903 mg/l at the western and eastern desert fringes, respectively. Values of Eocene aquifer water δ18O ranged from −8.31 to −0.44 and −2.07 to 0.55 ‰, and those of water δD ranged from −63.6 to −2.32 and −9.03 to 5.03 ‰ for the Eocene aquifer at the western and eastern side, respectively. Chemical analysis shows that the main chemical facies of the Eocene water are Ca–Mg–HCO3 and Ca–SO4. The chemical and isotopic data show that water–rock interaction (calcite dissolution and silicate weathering) and mixing between different water types control the major ion chemistry of Eocene aquifer water. The chemical composition of Eocene water has also evolved by evaporation and ion exchange. The present study indicates the need for regional chemical and isotopic study for the Eocene aquifer along the Nile Valley region to delineate the sources of recharge to this important aquifer.
PubDate: 2017-02-01
DOI: 10.1007/s10498-016-9298-y
Issue No: Vol. 23, No. 1 (2017)

• 2α-Methylhopane: Indicator for Oil–Source Correlation in the Pearl
River Mouth Basin, China
• Authors: Wanfeng Zhang; Xiangtao Jiang; Liling Pang; Xuanbo Gao; Shukui Zhu
Abstract: Oil samples collected from the Pearl River Mouth Basin (PRMB) were analyzed using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS). High abundances of compounds in the 2α-methylhopane series were observed and accurately quantified. Although the 2α-methylhopane series can be a prominent biomarker in the oil and source rock samples, it has generally been used less than non-methylated hopanes. In this study, the 2α-MHI [C312α-methylhopane × 100/(C312α-methylhopane + C30-αβ-hopane) (%)] ranges from 0.81 to 5.77% and 9.06 to 23.93% in Enping Formation- and Wenchang Formation-derived oils, respectively. The high abundance of the 2α-methylhopane series in Wenchang Formation-derived oils is attributed to anoxygenic phototrophs. The relevant 2α-methylhopane parameters showed correlations with C30-4-methyl steranes/∑C29 steranes, Pr/Ph and bicadinane-T/C30-αβ-hopane. Furthermore, the 2α-methylhopane series are rich in middle-deep lacustrine environments as well as marine sedimentary environment. The results indicated that the 2α-methylhopane series could be used as effective biomarkers to distinguish oils derived from different source rocks, as well as to enlarge the PRMB biomarker assemblages, which is beneficial to the evaluation of petroleum resources.
PubDate: 2017-05-16
DOI: 10.1007/s10498-017-9317-7

• Dissolution Rates of Actinolite in Water and Its Modified Mineral Surface
Across the Critical State
• Authors: Ronghua Zhang; Xuetong Zhang; Shumin Hu
Abstract: Dissolution kinetic experiments of actinolite in water were performed using a flow-through reactor at temperatures from 20 to 400 °C and 23.5±0.5 MPa. The results indicate that the steady-state release rates of the different elements of actinolite vary with temperature. Generally, Ca, Mg, Fe, and Al dissolve more quickly than Si at temperatures from 20 °C to near 300 °C, but slower from 300 to 400 °C. The Si release rate increases with temperatures from 20 to 300 °C and then decreases from 300 to 400 °C. Si release rate reaches the maximum at 300 °C. Amorphous Si-rich surface layers occur at temperature <300 °C. Hydrations of actinolite are relatively faster, and proton–metal exchange reactions are weakening across the critical point. Mi-rich (Fe, Ca, Mg) and Si-deficient surface layers form at temperatures ≥300 °C. XPS, TEM, and SEM observations indicate that the hydrated silicate occurred at surface as temperature >300 °C. Water property variations within the critical region strongly affect the dissolution rates and the modification of surface.
PubDate: 2017-04-28
DOI: 10.1007/s10498-017-9316-8

• Sediment Biogeochemistry of Mesophotic Meadows of Calcifying Macroalgae
• Authors: Francis J. Sansone; Heather L. Spalding; Celia M. Smith
Abstract: Mesophotic (low light) sands were studied in Hawaiian coastal waters (39–204 m water depth) from O‘ahu to Kaho‘olawe by sampling inside and outside of extensive macroalgal meadows of chlorophytes Halimeda kanaloana and Udotea sp. during September 2004, December 2004, and November 2006. Porewater nutrient concentrations in these permeable sediments were comparable to those in nearshore sands and were highly elevated at sediment depths available to holdfasts of some algae (5–10 cm); maximum levels were 3.0 µM reactive phosphorus, 33 µM nitrate, 0.70 µM nitrite, 38 µM ammonium, and 130 µM silicic acid. Benthic material is calculated to be the major source of organic matter driving diagenesis in these sediments. Vegetated sediments appeared more oxidizing than unvegetated sediments, and the presence of macroalgae, particularly Halimeda, was generally associated with higher sediment dissolved inorganic carbon levels. Halimeda-vegetated sediments generally had low dissolved inorganic nitrogen (DIN) levels compared to the Udotea-vegetated and non-vegetated sediments, consistent with the net N loss indicated by sediment stoichiometric relationships. In contrast, Udotea-vegetated sediments showed minimal apparent algal DIN uptake.
PubDate: 2017-03-30
DOI: 10.1007/s10498-017-9315-9

• Chemical Analysis of Gaet’ale, a Hypersaline Pond in Danakil Depression
(Ethiopia): New Record for the Most Saline Water Body on Earth
• Authors: Eduardo Pérez; Yonas Chebude
Abstract: The chemical analysis of the water of Gaet’ale Pond, a small water body located in Danakil Depression, Ethiopia, resulted to be the most saline water body on earth with total dissolved solids (TDS) of 433 g kg−1. The composition of the water indicates the predominance of two main salts: CaCl2 and MgCl2 at a proportion of Ca:Mg = 3.1 (w/w). Traces of K+, Na+ and NO3 − are also detected, as well as Fe(III) complexes that give the water a characteristic yellow color. Density measurements, elemental analysis, thermogravimetrical analysis (TGA) and powder X-ray diffraction data are consistent with the composition and salinity determined. The water of this pond has a similar composition to Don Juan Pond, Antarctica, but a higher salinity, which can be explained in terms of temperature and solubility of the main components.
PubDate: 2017-03-23
DOI: 10.1007/s10498-017-9312-z

• Evolution of Mg/Ca Ratios During Limestone Dissolution Under Epikarstic
Conditions
• Authors: Pavel Pracný; Jiří Faimon; Dalibor Všianský; Ludvík Kabelka
Abstract: The Mg/Ca ratios in karst water are generally believed to comprise information on climate, and, being encoded in speleothems, they are utilized as paleoenvironmental proxy. However, the mechanism and dynamic of Mg release from limestone during dissolution is not well understood. A theoretical evolution of the Mg/Ca ratios during limestone dissolution under epikarstic conditions (T = 10 °C, $$\log P_{{{\text{CO}}_{2} }}$$  = −1.5) was studied via a dynamic model. The results were compared with (1) the dripwater data set collected in Punkva Caves (Moravian Karst, Czech Republic) during one-year period and (2) the published data from various locations worldwide. The modeling showed that the Mg/Ca ratios are governed by composition of Mg-calcite present in limestone. Two distinct stages in the dissolution dynamics were recognized: (1) an initial congruent dissolution with stoichiometric release of Ca and Mg and, subsequently, (2) an incongruent dissolution demonstrated by the gradual release of Mg with simultaneous Ca decrease via calcite precipitation. Additional identified factors influencing the reaction path and Mg/Ca ratio evolution were the dolomitic component of limestone and the ratio of limestone/solution boundary area to water volume. Finally, the water–rock interaction time controls the resulting Mg/Ca ratio in dripwater determining how far the dissolution proceeds along the reaction path. Thus, the study results indicate that Mg/Ca ratio depends on many factors in addition to climatic variables.
PubDate: 2017-03-04
DOI: 10.1007/s10498-017-9313-y

• Lipid Biomarker Analysis of Suspended Particulate Matter from the Great
Kwa River, SE Nigeria: Origins and Environmental Implications of Biogenic
and Anthropogenic Organic Compounds
• Authors: Bernd R. T. Simoneit; Oliva Pisani; Bassey O. Ekpo; Ebirien P. Fubara; Prince J. Nna; Okon D. Ekpa
Abstract: Biomarkers found in natural waters, sediments, soils, fossils, crude oil, and coal can be unambiguously linked to specific precursors biosynthesized by biota. Petroleum and its refinery products carry their biomarker information into the environment when they are released by pollution. Lipid biomarkers can be used to assess the environmental status of an ecosystem and the degree to which it has been influenced by biogenic and anthropogenic inputs. The marine ecosystem of the southeastern Niger Delta of Nigeria is receiving new attention due to increased human and industrial development and the consequent potential health effects. Suspended particulate matter (SPM) from the Great Kwa River was characterized using biomarkers to assess such pollution. The total organic carbon contents of SPM from the river at low and high tide was 12–50% (avg 34.75%) and 16–28% (avg 24.25%), respectively. The lipid biomarkers identified using gas chromatography–mass spectrometry were mainly n-alkanes, n-alkan-2-ones, triterpenoids and minor amounts of aromatic compounds. The n-alkanes ranged from C 17 to C 35, with an odd/even predominance and C max > 27, indicating a mixed origin from higher plant wax, biodegraded detritus, and petroleum. The n-alkan-2-ones in most samples ranged from C 16 to C 33, with C max = 31, also supporting an input from vascular plants dominating the riparian zone along the river. The triterpenoids, mainly taraxerone, taraxerol, α- and β-amyrins, and friedelin, also derived from higher plants (angiosperms). Minor amounts of aromatic hydrocarbon derivatives from α- and β-amyrins were present and are likely the result of different diagenetic processes. The presence of trace fossil fuel-derived hopanes with an unresolved complex mixture of branched and cyclic hydrocarbons supported a minor petroleum product input to the SPM of the Great Kwa River.
PubDate: 2017-02-04
DOI: 10.1007/s10498-017-9311-0

• Spatiotemporal Assessment of CO 2 –Carbonic Acid System Dynamics in a
Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern
Hawaiian Islands
• Authors: Andrea K. Kealoha; Fred T. Mackenzie; Samuel E. Kahng; Randall K. Kosaki; Simone R. Alin; Christopher D. Winn
Abstract: Observations of surface seawater fugacity of carbon dioxide (fCO2) and pH were collected over a period of several days at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands (NWHI) in order to gain an understanding of the natural spatiotemporal variability of the marine inorganic carbon system in a pristine coral reef ecosystem. These data show clear island-to-open ocean gradients in fCO2 and total alkalinity that can be measured 10–20 km offshore, indicating that metabolic processes influence the CO2–carbonic acid system over large areas of ocean surrounding FFS and by implication the islands and atolls of the NWHI. The magnitude and extent of this spatial gradient may be driven by a combination of physical and biogeochemical processes including reef water residence time, hydrodynamic forcing of currents and tidal flow, and metabolic processes that occur both on the reef and within the lagoon.
PubDate: 2017-01-27
DOI: 10.1007/s10498-017-9310-1

• Decadal Change in Sediment Community Oxygen Consumption in the Abyssal
Northeast Pacific
• Authors: K. L. Smith; C. L. Huffard; A. D. Sherman; H. A. Ruhl
Pages: 401 - 417
Abstract: Long time-series studies are critical to assessing impacts of climate change on the marine carbon cycle. A 27-year time-series study in the abyssal northeast Pacific (Sta. M, 4000 m depth) has provided the first concurrent measurements of sinking particulate organic carbon supply (POC flux) and remineralization by the benthic community. Sediment community oxygen consumption (SCOC), an estimate of organic carbon remineralization, was measured in situ over daily to interannual periods with four different instruments. Daily averages of SCOC ranged from a low of 5.0 mg C m−2 day−1 in February 1991 to a high of 31.0 mg C m−2 day−1 in June 2012. POC flux estimated from sediment trap collections at 600 and 50 m above bottom ranged from 0.3 mg C m−2 day−1 in October 2013 to 32.0 mg C m−2 day−1 in June 2011. Monthly averages of SCOC and POC flux correlated significantly with no time lag. Over the long time series, yearly average POC flux accounted for 63 % of the estimated carbon demand of the benthic community. Long time-series studies of sediment community processes, particularly SCOC, have shown similar fluctuations with the flux of POC reaching the abyssal seafloor. SCOC quickly responds to changes in food supply and tracks POC flux. Yet, SCOC consistently exceeds POC flux as measured by sediment traps alone. The shortfall of ~37 % could be explained by sediment trap sampling artifacts over decadal scales including undersampling of large sinking particles. High-resolution measurements of SCOC are critical to developing a realistic carbon cycle model for the open ocean. Such input is essential to evaluate the impact of climate change on the oceanic carbon cycle, and the long-term influences on the sedimentation record.
PubDate: 2016-12-01
DOI: 10.1007/s10498-016-9293-3
Issue No: Vol. 22, No. 5-6 (2016)

• Using a Thermal Proxy to Examine Sediment–Water Exchange in
Mid-Continental Shelf Sandy Sediments
• Authors: William B. Savidge; Alicia Wilson; Gwendolyn Woodward
Pages: 419 - 441
Abstract: Fluid exchange across the sediment–water interface in a sandy open continental shelf setting was studied using heat as a tracer. Summertime tidal oscillation of cross-shelf thermal fronts on the South Atlantic Bight provided a sufficient signal at the sediment–water interface to trace the advective and conductive transport of heat into and out of the seabed, indicating rapid flushing of ocean water through the upper 10–40 cm of the sandy seafloor. A newly developed transport model was applied to the in situ temperature data set to estimate the extent to which heat was transported by advection rather than conduction. Heat transported by shallow 3-D porewater flow processes was accounted for in the model by using a dispersion term, the depth and intensity of which reflected the depth and intensity of shallow flushing. Similar to the results of past studies in shallower and more energetic nearshore settings, transport of heat was greater when higher near-bed velocities and shear stresses occurred over a rippled bed. However, boundary layer processes by themselves were insufficient to promote non-conductive heat transport. Advective heat transport only occurred when both larger boundary layer stresses and thermal instabilities within the porespace were present. The latter process is dependent on shelf-scale heating and cooling of bottom water associated with upwelling events that are not coupled to local-scale boundary layer processes.
PubDate: 2016-12-01
DOI: 10.1007/s10498-016-9295-1
Issue No: Vol. 22, No. 5-6 (2016)

• A Tribute to Rick and Debbie Jahnke: From Deep Sea Pore Water to Coastal
Permeable Sediments-Contributions that Cover the Oceans
• Authors: Timothy J. Shaw; Steve Emerson; Herbert L. Windom
PubDate: 2016-12-09
DOI: 10.1007/s10498-016-9309-z

• CO 2 Outgassing from Spring Waters
• Authors: Benjamin J. Maas; Carol M. Wicks
Abstract: CO2 released from lakes, rivers, and estuaries has been included in estimates of the global CO2 budget; however, CO2 released from carbonate springs has not been routinely included in the estimate of the global CO2 budget. The omission of carbonate spring water as a source of CO2 might result in an underestimation of the overall flux of CO2 from surface waters to the atmosphere. In this study, the flux of CO2 from carbonate springs was calculated and compared to the rate of outgassing of CO2 reported in the literature for other surface water bodies. The calculated fluxes of CO2 from carbonate springs ranged 280–380,000 mmol m−2 d−1. A range that is larger than the range of CO2 fluxes reported for estuaries (100–1900 mmol m−2 d−1), headwater streams and rivers (100–1600 mmol m−2 d−1), freshwater lakes (−300 to 3200 mmol m−2 d−1), and saline lakes (−300 to 9900 mmol m−2 d−1). This work demonstrates that the outgassing of CO2 from springs should be included in the global CO2 budget.
PubDate: 2016-11-30
DOI: 10.1007/s10498-016-9302-6

• Recycling of Organic Matter in the Sediments of Santa Monica Basin,
California Borderland
• Authors: Tomoko Komada; David J. Burdige; Cédric Magen; Huan-Lei Li; Jeffrey Chanton
Abstract: Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH4) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH4 that is fueled by CH4 supplied from a relict reservoir that is decoupled from local organic carbon (Corg) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of Corg have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched Corg within the sedimentary matrix. While the exact nature of this Corg is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within Corg-poor turbidite sections.
PubDate: 2016-11-29
DOI: 10.1007/s10498-016-9308-0

• Enhanced Dissolved Organic Matter Recovery from Saltwater Samples with
Electrodialysis
• Authors: Luke R. Chambers; Ellery D. Ingall; Emily M. Saad; Amelia F. Longo; Masayuki Takeuchi; Yuanzhi Tang; Claudia Benitez-Nelson; Sheean T. Haley; Sonya T. Dyhrman; Jay Brandes; Aron Stubbins
Abstract: Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. DOM isolation efficiency by electrodialysis (ED) from salt-containing waters was optimized and evaluated on samples including coastal ocean seawater, open ocean seawater, artificial seawater from axenic cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2–10 L sample volumes. Additionally, the combination of ED and solid-phase extraction, using Bond Elut PPL exchange resin, was evaluated. Using only ED, the following DOC recoveries were achieved: coastal seawater, 71.3 ± 6.5 %; open ocean, 50.5 ± 3.1 %; phytoplankton cultures, 70.3 ± 12.5 %; glucose, 90.2 ± 2.1 %; EDTA, 67.5 ± 9.9 %; and vitamin B12, 98.3 ± 1.6 %. With the combination of PPL and ED techniques, an average DOC recovery of 76.7 ± 2.6 % was obtained for coastal seawater, but this recovery was not statistically different from seawater recoveries using only ED. Comparison of C/N ratios and fluorescence excitation emission matrices taken at the beginning and end of the recovery process for coastal samples processed using only ED indicated that the final recovered material was representative of the DOM present in the original samples. Typical recoveries using combined PPL and ED exceed those of previous isolation methods.
PubDate: 2016-10-24
DOI: 10.1007/s10498-016-9306-2

• Benthic Oxygen Fluxes Measured by Eddy Covariance in Permeable Gulf of
Mexico Shallow-Water Sands
• Authors: Lindsay Chipman; Peter Berg; Markus Huettel
Abstract: Oxygen fluxes across the sediment–water interface reflect primary production and organic matter degradation in coastal sediments and thus provide data that can be used for assessing ecosystem function, carbon cycling and the response to coastal eutrophication. In this study, the aquatic eddy covariance technique was used to measure seafloor–water column oxygen fluxes at shallow coastal sites with highly permeable sandy sediment in the northeastern Gulf of Mexico for which oxygen flux data currently are lacking. Oxygen fluxes at wave-exposed Gulf sites were compared to those at protected Bay sites over a period of 4 years and covering the four seasons. A total of 17 daytime and 14 nighttime deployments, producing 408 flux measurements (14.5 min each), were conducted. Average annual oxygen release and uptake (mean ± standard error) were 191 ± 66 and −191 ± 45 mmol m−2 day−1 for the Gulf sites and 130 ± 57 and −152 ± 64 mmol m−2 day−1 for the Bay sites. Seasonal variation in oxygen flux was observed, with high rates typically occurring during spring and lower rates during summer. The ratio of average oxygen release to uptake at both sites was close to 1 (Bay: 0.9, Gulf: 1.0). Close responses of the flux to changes in light, temperature, bottom current velocity, and wave action (significant wave height) documented tight physical–biological, benthic–pelagic coupling. The increase of the sedimentary oxygen uptake with increasing temperature corresponded to a Q10 temperature coefficient of 1.4 ± 0.3. An increase in flow velocity resulted in increased oxygen uptake (by a factor of 1–6 for a doubling in flow), which is explained by the enhanced transport of organic matter and electron acceptors into the permeable sediment. Benthic photosynthetic production and oxygen release from the sediment was modulated by light intensity at the temporal scale (minutes) of the flux measurements. The fluxes measured in this study contribute to baseline data in a region with rapid coastal development and can be used in large-scale assessments and estimates of carbon transformations.
PubDate: 2016-10-21
DOI: 10.1007/s10498-016-9305-3

• Dissolution of Al-Substituted Goethite in the Presence of Ferrichrome and
Enterobactin at pH 6.5
• Authors: William E. Dubbin; Florence Bullough
Abstract: Naturally occurring goethites often show Al for Fe substitution approaching 33 mol% Al. This substitution has potential to influence the rate of goethite dissolution and therefore the supply of bioavailable Fe. Siderophores such as ferrichrome and enterobactin have considerable potential to dissolve Fe from Fe3+ rich minerals, including Al-substituted goethites. Here, we show that Al substitution in synthetic goethites (0.021 ≥ x ≥ 0.098) gives rise to a significant increase in both ferrichrome- and enterobactin-mediated dissolution rates. In the presence of ferrichrome, Al-goethite (x = 0.033) yields a dissolution rate of 19.0 × 10−3 µmol m−2 h−1, nearly twice that of pure goethite, whereas dissolution of the most highly substituted Al-goethite (x = 0.098) is 36.9 × 10−3 µmol m−2 h−1, more than threefold greater than the pure mineral. Similarly, in the presence of enterobactin, the dissolution rate of Al-goethite increases with increasing Al substitution. Ferrichrome is a less effective ligand than enterobactin in its dissolution of both pure goethite and the range of Al-goethites, an observation we ascribe to the lower affinity of the hydroxamate functional groups of ferrichrome for both Fe3+ and Al3+. Despite greater affinity of both ferrichrome and enterobactin for Fe3+ over Al3+, we observe a broadly congruent dissolution of all our Al-goethites.
PubDate: 2016-10-12
DOI: 10.1007/s10498-016-9304-4

• The Dynamics of Benthic Respiration at a Mid-Shelf Station Off Oregon
• Abstract: Mid-shelf sediments off the Oregon coast are characterized as fine sands that trap and remineralize phytodetritus leading to the consumption of significant quantities of dissolved oxygen. Sediment oxygen consumption (SOC) can be delayed from seasonal organic matter inputs because of a transient buildup of reduced constituents during periods of quiescent physical processes. Between 2009 and 2013, benthic oxygen exchange rates were measured using the noninvasive eddy covariance (EC) method five separate times at a single 80-m station. Ancillary measurements included in situ microprofiles of oxygen at the sediment–water interface, and concentration profiles of pore water nutrients and trace metals, and solid-phase organic C and sulfide minerals from cores. Sediment cores were also incubated to derive anaerobic respiration rates. The EC measurements were made during spring, summer, and fall conditions, and they produced average benthic oxygen flux estimates that varied between −2 and −15 mmol m−2 d−1. The EC oxygen fluxes were most highly correlated with bottom-sensed, significant wave heights (H s). The relationship with H s was used with an annual record of deepwater swell heights to predict an integrated oxygen consumption rate for the mid-shelf of 1.5 mol m−2 for the upwelling season (May–September) and 6.8 mol m−2 y−1. The annual prediction requires that SOC rates are enhanced in the winter because of sand filtering and pore water advection under large waves, and it counters budgets that assume a dominance of organic matter export from the shelf. Refined budgets will require winter flux measurements and observations from cross-shelf transects over multiple years.
PubDate: 2016-09-27
DOI: 10.1007/s10498-016-9303-5

• Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea
Loch: An Integrative In Situ Study
• Authors: Ronnie N. Glud; Peter Berg; Henrik Stahl; Andrew Hume; Morten Larsen; Bradley D. Eyre; Perran L. M. Cook
Abstract: Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated by the brittle star A. filiformis. The numerous burrows were intensively irrigated enhancing the benthic in situ O2 uptake by ~50 %, and inducing highly variable redox conditions and O2 distribution in the surface sediment as also documented by complementary laboratory-based planar optode measurements. The average benthic O2 exchange as derived by chamber incubations and the eddy covariance approach were similar (14.9 ± 2.5 and 13.1 ± 9.0 mmol m−2 day−1) providing confidence in the two measuring approaches. Moreover, the non-invasive eddy approach revealed a flow-dependent benthic O2 flux that was partly ascribed to enhanced ventilation of infauna burrows during periods of elevated flow rates. The ratio in exchange rates of ΣCO2 and O2 was close to unity, confirming that the O2 uptake was a good proxy for the benthic carbon mineralization in this setting. The infauna activity resulted in highly dynamic redox conditions that presumably facilitated an efficient degradation of both terrestrial and marine-derived organic material. The complex O2 dynamics of the burrow environment also concurrently stimulated nitrification and coupled denitrification rates making the sediment an efficient sink for bioavailable nitrogen. Furthermore, bioturbation mediated a high efflux of dissolved phosphorus and silicate. The study documents a high spatial and temporal variation in benthic solute exchange with important implications for benthic turnover of organic carbon and nutrients. However, more long-term in situ investigations with like approaches are required to fully understand how environmental events and spatio-temporal variations interrelate to the overall biogeochemical functioning of coastal sediments.
PubDate: 2016-09-08
DOI: 10.1007/s10498-016-9300-8

• The Application of Raman Spectroscopy to Probe the Association of H 4 SiO
4 with Iron Oxides
• Authors: Yohan Ferras; John Robertson; Peter J. Swedlund
Abstract: The aquatic geochemistry of many trace elements is influenced by two important products from the weathering of minerals: iron oxide solid phases and silicic acid (H4SiO4) in the aqueous phase. The chemistry of H4SiO4 on iron oxide surfaces is an interesting mix of sorption and polymerization, and this has been shown to affect the sorption, coprecipitation and transport of many trace elements. Infrared spectroscopy is a valuable probe of H4SiO4 chemistry on iron oxide surfaces, and in this study, we assess the utility of Raman spectroscopy for studying H4SiO4 chemistry on the poorly ordered iron oxide ferrihydrite. This was undertaken because Raman spectroscopy provides complimentary information to IR, in addition to often having narrower bands than IR spectra and less interference from water during in situ measurements. The IR spectra of H4SiO4 adsorbed on ferrihydrite showed the expected strong Si–O stretching feature, termed ν(Si–O), which had a central band and shoulders on either side. As the surface concentration of H4SiO4 increased, there was a clear shift in the position of the central band of the ν(Si–O) feature from ~950 to 1060 cm−1 reflecting the degree of silicate polymerization. The Raman spectra of the same samples had a very broad and weak ν(Si–O) feature which had a poor signal-to-noise ratio even after accumulating spectra over 1 h. The ν(Si–O) in the Raman spectra did not have discernable shoulders, as observed in the IR spectra, and there was only a fairly subtle shift in the position of this feature from 950 to 970 cm−1 as the degree of silicate polymerization increased. Overall, the results indicate that Raman spectroscopy can be used to study H4SiO4 adsorption and polymerization on iron oxides, but its utility is constrained by a weak signal combined with a subtle shift in peak position with H4SiO4 polymerization.
PubDate: 2016-08-17
DOI: 10.1007/s10498-016-9294-2

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