Oxidation Of Organic Matter In Sedments

Date
1973-09
Authors
Pamatmat, Mario M.
Jones, R. Stephen
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Abstract
A suitable sampler for taking undisturbed sediment samples was developed. Techniques were worked out for measuring (a) oxygen uptake by intact sediment cores, (b) dehydrogenase activity of sediment bacteria, and (c) their actual metabolic heat release. Dehydrogenase activity as a relative measure of anaerobic metabolism was calibrated by direct calorimetry for use in determining natural rates of sediment metabolism. The concentration of reduced end products of anaerobic metabolism was determined by an iodometric and dichromate method. Laboratory experiments were conducted to determine the equivalents between rates of oxygen consumption on the one hand and loss of organic carbon of sediments and liberation of nutrient salts, e.g. nitrates, phosphates, silicates, and ammonia, on the other. Seasonal measurements of oxygen consumption at 33 stations in Puget Sound provided benchmark information for an area that may be subject to worsening conditions due to the impact of increasing human population. In situ oxygen uptake by the sediment can be estimated by shipboard measurements with sufficient accuracy. The original working hypothesis, however, that total oxygen uptake represents a measure of total metabolism, aerobic plus anaerobic, in the sediment column appears erroneous, at least in organically rich sediment. The rate of total oxygen uptake by intact cores represents aerobic plus part of the anaerobic metabolism in a surface layer of indeterminate thickness. At present the only practical way to estimate total aerobic and total anaerobic metabolism in sediments is to combine the rates of respiratory oxygen uptake by undisturbed sediment cores with estimates of anaerobic metabolism derived from dehydrogenase assay of subsurface sediment layers. The rate of oxygen uptake by the sediment, however remains a useful index of equilibrium conditions among the various factors that affect this rate: oxygen tension, temperature salinity turbulence, available metabolizable energy, size and composition of the community, compactness and porosity of sediments and perhaps more. As sedimentation rate of oxidizable organic matter increases, e.g. in cases of organic population and eutrophication, anaerobic metabolism becomes a relatively more important process in the mineralization of organic matter in sediments. In this situation, the estimation of anaerobic metabolism by the dehydrogenase assay technique is particularly desirable. This report was submitted in fulfillment of project 16070 EKZ under the partial sponsorship of the Environmental Protection Agency.
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Keywords
Oxidation , Organic Matter , Sediments
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