Abstract
This study investigates iron (Fe) and sulfur (S) cycling in sediments from the eutrophic Peel-Harvey Estuary in Western Australia, which is subject to localized accumulation of strongly reducing, organic-and sulfide-rich sediments. Sedimentary iron was mostly present in highly reactive form (on average 73% of total Fe) and showed extensive sulfidization even in surface sediments, despite being overlain by a well-mixed oxygenated water column. This indicates that, under eutrophic marine conditions, Fe sulfidization may be driven by reductive processes in the sediment without requiring oxygen depletion in the overlying waters. Strong enrichments in iron monosulfide (FeS > 300 mu mol g(-1)) were observed in fine-grained sediment intervals up to 45 cm depth. This metastable Fe sulfide is commonly restricted to thin subsurface sediment intervals, below which pyrite (FeS2) dominates. Our findings suggest inhibition of the dissolution-precipitation processes that replace FeS with FeS2 in sediments. Rates of pyrite formation based on the FeS2 profiles were much lower than those predicted by applying commonly used kinetic equations for pyrite formation. Dissolved H2S was present at millimolar levels throughout the investigated sediment profiles. This may indicate that (i) pyrite formation via reaction between dissolved Fe (including Fe clusters) and H2S was limited by low availability of dissolved Fe or (ii) reaction kinetics of pyrite formation via the H2S pathway may be relatively slow in natural reducing sediments. We propose that rapid burial of the FeS under anoxic conditions in these organic-rich reducing sediments minimizes the potential for pyrite formation, possibly by preventing dissolution of FeS or by limiting the availability of oxidized sulfur species that are required for pyrite formation via the polysulfide pathway. (C) 2013 Elsevier Ltd. All rights reserved.
| Original language | English |
|---|---|
| Pages (from-to) | 75-88 |
| Number of pages | 14 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 122 |
| Early online date | 28 Aug 2013 |
| DOIs | |
| Publication status | Published - 1 Dec 2013 |
Funding
This research is part of a Linkage Project (LP0991658) cofunded by the Australian Research Council. We are grateful to Michael D. Cheetham and Andrew L. Rose from Southern Cross GeoScience for their help with all aspects of the field work. We also thank the Department of Water in Western Australia, in particular Zitty Wesolowski and John Pszczola, for their help with sample collection. Our partners at the Western Australian Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, in particular Kliti Grice and Robert Lockhart, are gratefully acknowledged for their assistance during core processing. The <SUP>210</SUP>Pb analyses were funded by the Australian Institute of Nuclear Science and Engineering (AINGRA11P070) and performed with the help of Atun Zawadzki, Henk Heijnis, and Daniela Fierro. We thank L.-Y. Jang of the NSRRC in Taiwan for providing assistance and advice during collection of the S XANES data. Maxine Dawes of the Southern Cross School of Environment, Science and Engineering is thanked for her help with the SEM-EDS analyses. We are very grateful to associate editor Silke Severmann, David Rickard and two anonymous reviewers for their insightful comments and advice that greatly enhanced the quality of this article.
Keywords
- ACID VOLATILE SULFIDE
- BLACK-SEA SEDIMENTS
- GREEN-ALGAL BLOOMS
- 125 DEGREES-C
- MARINE-SEDIMENTS
- NATURAL-WATERS
- AUSTRALIAN ESTUARY
- AQUEOUS-SOLUTIONS
- ORGANIC-MATTER
- H2S OXIDATION
