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Pore water chemistry of wetlands in Interior and Southcentral Alaska, 2015 and 2016

June 5, 2019

The pore water of eight wetlands in Interior and Southcentral Alaska were collected in 2015 (17 July - 22 July) and 2016 (12 July - 16 July). Wetlands were selected to span a range in trophic status (e.g., from bog to fen). Using ultraclean trace metal clean protocols, pore waters were sampled from shallow (10-15 cm) and deep (20-35 cm) depths below the water table. Field measurements reported for pore waters include temperature, specific conductance, pH, dissolved oxygen (DO) concentration, and oxidation-reduction potential (ORP). Pore waters were filtered on site and measured in-lab for major cations, inorganic anions, simple organic acids, inorganic sulfide, iron oxidation state, dissolved organic carbon (DOC), ultraviolet and visible light (UV-Vis) absorption, dissolved organic matter (DOM) fluorescence, electron release from DOM and iron(II), total mercury (HgT), and methylmercury (MeHg). Unfiltered pore water was collected for quantification of dissolved gaseous mercury (Hg(0)(aq)). Major cation concentrations (calcium, magnesium, manganese, iron, sodium) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Inorganic anion concentrations (chloride, nitrate, sulfate) and simple organic acid concentrations (acetate, formate, butyrate, propanoate, oxalate) were determined by ion chromatography (IC). Inorganic sulfide was measured by ion selective electrode. The distribution of iron oxidation state was determined using a spectrophotometric assay. DOC concentration was quantified by wet-oxidation. Ultraviolet (UV) absorbance at the wavelength of 254 nanometers was measured by UV-Vis spectrophotometry. Iron(III) absorbs UV light at 254 nanometers and, if present at appreciable concentration, can influence UV absorbance values. Therefore, UV absorbance values at 254 nanometers were corrected for the influence of iron(III). Specific UV Absorbance (SUVA) at 254 nanometers is a calculated parameter that correlates with the percent aromatic carbon of the DOM. SUVA at 254 nanometers was calculated using values of UV absorbance at a wavelength of 254 nanometers corrected for iron(III) interference. The DOM fluorescence index was measured and is a proxy for DOM source material. The release of electrons from DOM and iron(II) was measured in the field using a colorimetric assay. HgT, MeHg, and Hg(0)(aq) concentrations were quantified and used to calculate the concentration of inorganic divalent mercury (Hg(II)i).