Use of gel probes for the determination of high resolution solute distributions in marine and estuarine pore waters

• Published in: Marine chemistry Vol. 63; no. 1; pp. 119 - 129
• Main Authors: Mortimer, R.J.G, Krom, M.D, Hall, P.O.J, Hulth, S, Ståhl, H
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.1998; Elsevier Science
• Subjects: Earth sciences; Earth, ocean, space; estuarine; Exact sciences and technology; External geophysics; gel probe; Geochemistry; high resolution; marine; Mineralogy; Physical and chemical properties of sea water; Physics of the oceans; pore water; Silicates; Water geochemistry; United Kingdom; Scotland; Great Britain; Western Europe; gel probe; estuarine; marine; pore water; high resolution; sulfates; nitrates; spatial distribution; ammonium ion; hydrochemistry; anions; marine sediments; chlorides; sea water; carbon dioxide; salinity; estuarine environment; solutes; calcium; Europe; sampling; halides; alkalinity; Ammonia; Rotaliacea; foraminifera; marine environment; Invertebrata; Protista; Rotaliina
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(98)00055-3

Pore water profiles were obtained at high resolution (millimeter scale) in marine sediments using a DET (diffusive equilibration in thin films) gel probe. A plastic probe which holds a 1–2 mm thick polyacrylamide gel covered by a 0.45 μm Millipore filter is inserted into the sediment. The gel was prehydrated in water of similar salinity to the in situ sampling conditions. Chloride and sulphate needed 24 and 48 h for complete front and back equilibration, respectively, while 6–8 h (front) and 4–6 h (back) were used for calcium and alkalinity. Ammonia-N and total CO 2 were back-equilibrated for 2 h. Probes were sectioned immediately after sampling, stored for up to 1–2 days (NH 4 +, ∑CO 2) or for up to 1–2 weeks (Ca, alkalinity, Cl, SO 4, NO 3), before they were back-equilibrated into Milli-Q water or 0.7 M NaCl (calcium and alkalinity). The gel retains between 3–7% of the total sulphate. A simple procedure has been developed to correct for this incomplete recovery. Recovery tests using seawater and 50% seawater spiked to concentrations found in nearshore pore waters, showed recoveries of 101.4±0.5% (chloride), 101.4±0.7% (bromide), 100.3±0.2% (nitrate), 96.6±0.7% (sulphate), 99.7±0.8% (ammonia-N), 99.1±1.2% (∑CO 2), 96.9±0.8% (calcium) and 96.8±1.4% (alkalinity) (mean±standard error). Pore water profiles obtained simultaneously using gel probes and conventional techniques (box core-anoxic slicing followed by centrifugation) showed excellent comparability at cm resolution though features which required higher resolution which could only be seen in the gel profiles.