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Micro-scale biogeochemical heterogeneity in sediments : a review of available technology and observed evidence.

Stockdale, Anthony and Davison, William and Zhang, Hao (2009) Micro-scale biogeochemical heterogeneity in sediments : a review of available technology and observed evidence. Earth-Science Reviews, 92 (1-2). pp. 81-97. ISSN 0012-8252

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    Abstract

    The hypothesis that reducing conditions exist in localized zones of high organic matter, termed microniches, was first suggested over a century ago, but only relatively recently have high-resolution techniques been available to investigate them. In any sediment containing benthic fauna, bioturbation affects the distribution of a number of redox-sensitive components. Direct faecal deposition and the death of fauna may be expected to cause particles of labile organic matter (microniches) to be distributed heterogeneously within the sediment. This review discusses the significance and future direction of microniche studies by considering, exclusively, data obtained on a sub-mm scale that provide significant evidence for the existence and properties of microniches. Microelectrodes and planar optodes have shown the significant effect of burrowing organisms on localized O2 distributions and revealed distinct depletions in O2 due to microniches. Localized increases in pCO2 and decreases in pH measured by optodes were attributed to elevated activity at microniches. Diffusive gradients in thin-films have shown isolated supersaturation of metals and sulphide, providing evidence for possible simultaneous oxidation of organic matter by sulphate and iron oxides. The stochastic nature of these data and the lack of information for the same precise location hinders interpretation in terms of sediment diagenesis. If microniches are known to account for a significant proportion of organic matter degradation, re-examination of the current understanding of sedimentary diagenesis may be needed. Further investigation on the distribution and frequency of microniches is required, including a wider range of analytes, in order to estimate their cumulative effect on element diagenesis, immobilisation/remobilisation processes and ultimately pollutant fate.

    Item Type: Article
    Journal or Publication Title: Earth-Science Reviews
    Additional Information: This article is cited in some sources as: Experimental evidence for micro-scale biogeochemical heterogeneity in sediments: a review
    Uncontrolled Keywords: microniche ; planar optodes ; faecal pellet ; burrow ; DGT ; bioturbation ; early diagenesis
    Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 22957
    Deposited By: Dr Tony Stockdale
    Deposited On: 12 Jan 2009 14:30
    Refereed?: Yes
    Published?: Published
    Last Modified: 06 Sep 2013 18:54
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/22957

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