Determination of Total Free Sulphides in Sediment Porewater and Artefacts Related to the Mobility of Mineral Sulphides |
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| Authors: | Kristina A Brown Eric R McGreer Bernie Taekema Jay T Cullen |
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| Institution: | (1) University of Victoria, School of Earth and Ocean Sciences, Bob Wright Centre, Victoria, BC, Canada;(2) Environmental Protection Division, British Columbia Ministry of Environment, Nanaimo, BC, V9T 6J9, Canada |
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| Abstract: | A field and laboratory study of the accuracy of a method commonly used to determine free sulphide concentrations in the porewater
of marine sediments is presented. The method uses an ion-selective electrode (ISE), sensitive to the sulphide ion (S2−), in sediments buffered to high pH (>12) and is commonly used in regulatory monitoring programs to assess the impacts of
open net-pen finfish aquaculture on local marine habitats. Here we report that on the timescale of field measurements, the
accepted protocol can lead to significant bias of free sulphide measurements, with orders of magnitude higher concentration
detected in the buffered sediment–porewater slurry than in porewater samples isolated and analysed separately. Laboratory
experiments with model marine sediments and analysis of sediment composition indicate that this bias is likely introduced
by the dissolution of particulate sulphides and/or sulphur present in the sediments under the intense alkaline conditions
of the protocol. Recommendations for the modification and continued use of this commonly applied field methodology are discussed. |
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