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Aquatic Geochemistry (v.14, #2)

Determination of Free Nickel Ion Concentrations Using the Ion Exchange Technique: Application to Aqueous Mining and Municipal Effluents by Yamini Gopalapillai; Ismail I. Fasfous; John D. Murimboh; Tahir Yapici; Parthasarathi Chakraborty; Chuni L. Chakrabarti (pp. 99-116).

Free metal ion concentration is generally considered a useful indicator of a metal’s bioavailability and ecotoxicity to aquatic biota. This article reports the speciation of nickel in mining and municipal effluents from Sudbury (Ontario, Canada), and also in model solutions containing a fully characterized laurentian fulvic acid (LFA) at environmentally relevant concentrations. A column ion exchange technique (IET) using a cation exchange resin (Dowex 50W-X8) was applied to determine free nickel ion concentrations. In model solutions, reasonable correlation was found between the predictions of an equilibrium-based computer speciation code, Windermere Humic Aqueous Model (WHAM) VI, and the results obtained by IET at low nickel-to-fulvic acid ratios. However at higher mole ratios, the WHAM VI predicted higher free nickel ion concentrations than IET. Only three out of six effluent samples showed reasonable agreement between the IET and the WHAM VI results, indicating the need for further development of IET for application to effluent waters.

Keywords: Ion exchange technique; Nickel speciation; Free metal ion; WHAM VI; Mine effluent; Dissolved organic carbon; Bioavailability

Coupled Reactive Transport Modeling of Redox Processes in a Nitrate-Polluted Sandy Aquifer by Konrad Miotliński (pp. 117-131).

The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST, a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008. Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying such interactions.

Keywords: Groundwater; Reactive transport modeling; Nitrate; Denitrification; Pyrite; Organic matter; PHREEQC; PHAST

Major Ion Chemistry in a Freshwater Coastal Lagoon from Southern Brazil (Mangueira Lagoon): Influence of Groundwater Inputs by Isaac R. Santos; Maria I. Machado; Luis F. Niencheski; William Burnett; Idel B. Milani; Carlos F. F. Andrade; Richard N. Peterson; Jeffrey Chanton; Paulo Baisch (pp. 133-146).

This paper characterizes major ion distributions and investigates whether groundwater exerts a major control on the chemical functioning of Mangueira Lagoon, a large (90 km long), shallow (∼4–5 m deep), and fresh coastal lagoon in southern Brazil. Water volumes equivalent to ∼80% of the total annual input are used in the summer for irrigating nearby rice plantations, the most important regional economic activity. While Na⁺ and Cl⁻ are the major ions in local groundwater, Na⁺ and HCO ₃ ⁻ are the most enriched ions in lagoon water. The ion concentrations measured in Mangueira Lagoon were homogeneous, except for a few samples affected by rainwater and groundwater inputs. A shore-normal transect starting at the pump house of a rice irrigation canal indicated strong groundwater input at this canal. In spite of the small volume contribution (∼2% of precipitation), groundwater discharge accounts for 50–70% of major ion inputs into the lagoon, with ∼70% of the groundwater inputs being anthropogenically derived (e.g., from the rice irrigation canals). This may have serious implications for the management of the coastal water resources from Mangueira Lagoon and other similar areas as groundwater associated with agricultural systems may be contaminated by fertilizers and pesticides. The results imply that groundwater should not be neglected in dissolved species’ budgets even when its volume contribution is small.

Keywords: Submarine groundwater discharge; Biogeochemistry; Permeable sediments; Coastal lagoons; Hydrogeochemistry

Weathering Processes in the Min Jiang: Major Elements, $$ {}^{87}{ ext{Sr/}}{}^{86}{ ext{Sr}},;delta {}^{34}{ ext{S}}_{{ ext{SO}}_{ ext{4}} } ,;{ ext{and}};delta {}^{18}{ ext{O}}_{{ ext{SO}}_{ ext{4}} } $$ by Junyeon Yoon; Youngsook Huh; Insung Lee; Seulgi Moon; Hyonjeong Noh; Jianhua Qin (pp. 147-170).

We investigated the dissolved major elements, $$ {}^{87}{ ext{Sr/}}{}^{86}{ ext{Sr}},;delta {}^{34}{ ext{S}}_{{ ext{SO}}_{ ext{4}} } ,;{ ext{and}};delta {}^{18}{ ext{O}}_{{ ext{SO}}_{ ext{4}} } $$ composition of the Min Jiang, a headwater tributary of the Chang Jiang (Yangtze River). A forward calculation method was applied to quantify the relative contribution to the dissolved load from rain, evaporite, carbonate, and silicate reservoirs. Input from carbonate weathering dominated the major element composition (58–93%) and that from silicate weathering ranged from 2 to 18% in unperturbed Min Jiang watersheds. Most samples were supersaturated with respect to calcite, and the CO₂ partial pressures were similar to or up to ∼5 times higher than atmospheric levels. The Sr concentrations in our samples were low (1.3–2.5 μM) with isotopic composition ranging from 0.7108 to 0.7127, suggesting some contribution from felsic silicates. The Si/(Na^* + K) ratios ranged from 0.5 to 2.5, which indicate low to moderate silicate weathering intensity. The $$ delta {}^{34}{ ext{S}}_{{ ext{SO}}_{ ext{4}} } ;{ ext{and}};delta {}^{18}{ ext{O}}_{{ ext{SO}}_{ ext{4}} } $$ for five select samples showed that the source of dissolved sulfate was combustion of locally consumed coal. The silicate weathering rates were 23–181 × 10³ mol/km²/year, and the CO₂ consumption rates were 31–246 × 10³ mol/km²/year, which are moderate on a global basis. Upon testing various climatic and geomorphic factors for correlation with the CO₂ consumption rate, the best correlation coefficients found were with water temperature (r ² = 0.284, p = 0.009), water discharge (r ² = 0.253, p = 0.014), and relief (r ² = 0.230, p = 0.019).

Keywords: Min Jiang; CO₂ consumption rate; $$ delta {}^{34}{ ext{S}}_{{ ext{SO}}_{ ext{4}} } $$ ; $$ delta {}^{18}{ ext{O}}_{{ ext{SO}}_{ ext{4}} } $$ ; Silicate weathering

Speciation of Polysulfides and Zerovalent Sulfur in Sulfide-rich Water Wells in Southern and Central Israel by A. Kamyshny Jr.; M. Zilberbrand; I. Ekeltchik; T. Voitsekovski; J. Gun; O. Lev (pp. 171-192).

Zerovalent sulfur and inorganic polysulfides were determined in nine sulfide-rich water wells in central and southern Israel. Although the two locations belong to the same aquifer, they are characterized by different pH and hydrogen sulfide levels. Hydrogen sulfide in the central Israel wells ranged between 19 and 32 μM, and the pH was 7.26 ± 0.07. The southern basin is characterized by lower water circulation, lower pH (around 6.8), and higher hydrogen sulfide levels (>470 μM). Polysulfides were determined by a rapid single-phase methylation using methyl trifluoromethanesulfonate (methyl triflate) reagent. The summary polysulfide concentration for S ₄ ²⁻ –S ₇ ²⁻ species was found to be around 0.14–0.75 μM in the central region of Israel and substantially higher, 2.3–4.6 μM in the southern region. The sum of polysulfide zerovalent sulfur and colloidal sulfur was quantitatively detected by cyanide derivatization and compared to polysulfide sulfur determined by methyl triflate derivatization and to the chloroform extraction of zerovalent sulfur. A method for the determination of sulfur undersaturation level—the ratio between dissolved elemental sulfur and its equilibrium concentration in the presence of solid sulfur—based on the observed levels of the major polysulfide species is described. The observed polysulfide speciation was compared with the predicted speciation under sulfur saturation conditions taking into account the water temperature, its ionic strength, and pH. Criteria for sulfur saturation versus unsaturated conditions were established based on (1) the chain length dependence of the ratio between the observed polysulfide concentrations and their predicted value under sulfur saturated conditions, and (2) the difference between the concentration of zerovalent sulfur, as determined by cyanolysis, and the total polysulfide sulfur. According to this dual criterion five of the water wells were classified as being undersaturated with respect to sulfur, though for all the examined water wells the majority of the zerovalent sulfur was in the form of polysulfide sulfur.

Keywords: Inorganic polysulfides; Sulfide; Speciation; Methyl trifluoromethanesulfonate; Methylation; Derivatization; Reduced sulfur compounds; Dimethylpolysulfanes

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Aquatic Geochemistry (v.14, #2)

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Aquatic Geochemistry (v.14, #2)