INTERFACIAL VELOCITY EFFECTS ON SEDIMENT
OXYGEN DEMAND MEASUREMENT
Raymond C. Whittemore, Research Engineer
National Council of the Paper Industry for Air and Stream Improvement
Tufts University
Medford, Massachusetts 02155
The importance of organic bottom deposits on the oxygen balance of a river or estuary
was recognized in 1925 [1]. Since that time research efforts attempting to define the
mechanism of oxygen consumption, effects of pertinent environmental variables, and
methods of measurement of sediment oxygen demand (SOD) have appeared in numerous
journals. SOD remains of interest in receiving waters where bottom deposits are seasonal
or historical (i.e., built up during years preceding treatment). Present and future water
quality management decisions require an accurate assessment of the impact of these deposits on the oxygen balance.
Bowman and Delfino [2) concluded that an acceptable SOD measurement technique
should be consistent, reproducible, and efficient. They further state that laboratory experiments with undisturbed cores accommodate these three criteria and, therefore, represent
a realistic approach to standardizing SOD measurements.
There is, however, little evidence to suggest that laboratory experiments produce the
same results as in-situ methods. The hydrodynamics and biology of the instream sediment
interface cannot be consistently simulated with laboratory core methods.
A standardized SOD measurement technique cannot be developed until this question
of accuracy is resolved. The research to be described in this paper will focus on defining
the hydrodynamic factors affecting SOD, particularly velocity at the sediment-water interface. Two different in-situ SOD devices were constructed and used in several rivers in the
Northeast and Mid-Atlantic states during the period 1977-1980.
EXPERIMENTAL PROCEDURES
In-Situ Respirometer
An in-situ respirometer was built for field work and is pictured in Figure 1. It consisted
of an 18" diameter plexiglass cylinder 12" in height. A steel flange (30" outside diameter
with an 18" diameter hole) was placed around the bottom. A 3" diameter steel cutting
KCL SYRINGE
0,   PROBE \ .
DC   STIRHifl
mill,
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SEDIMENT
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Figure 1. Schematic of an in-situ respirometer.
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