Oxidation Of Organic Matter In Sedments
Date
1973-09
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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.
Description
Keywords
Oxidation, Organic Matter, Sediments