Effect of Environmental
Factors on Benthal Oxygen Uptake
ARCHIE J. MCDONNELL, Assistant Professor
Civil Engineering Department
The Pennsylvania state University
University Park, Pennsylvania
S. DOUGLAS HALL, Engineer
Dow Chemical Company
Midland, Michigan
INTRODUCTION
In recent years a renewed interest has been generated in the role played by
benthal deposits on the oxygen economy of receiving streams. In large river
systems, a definition of the oxygen source and sink interaction has been achieved
primarily, through the use of many simplifying assumptions. In shallow rivers,
however, the rules of definition are more rigorous, since with decreasing depth
the effect of the benthos with its associated plants and animals becomes increasingly important.
The mechanisms involved in oxygen uptake due to benthal decomposition
have been delineated (1,2). These include: 1) BOD addition due to benthal scour,
2) diffusion of benthal organics into the overlying water, and 3) diffusion of oxygen into the aerobic zone of the benthal layer.
Attempts to determine the effects of various environmental factors on the rate
of oxygen utilization by benthal deposits have resulted in a variety of conclusions.
Baity (3), and Fair (1), working with settled sewage sludges, found the oxygen uptake of benthal deposits to be independent of the oxygen concentration ofthe supernatant water above 1.5 mg/l, and dependent on depth of deposit. Their conclusions indicate that oxygen uptake was controlled by the rate of transport oJ
oxidable substances from the interior of the deposits to the overlying water, and
not by the rate of diffusion of oxygen into the deposit. Hanes (4), in studies on a
paper waste sludge, demonstrated the existence of the processes of substrate transport and oxygen diffusion. His data indicated an independence of oxygen uptake
with dissolved oxygen concentration.
Edwards and Rolley (5), using samples of benthal material collected from
several English rivers, reached the conclusion that oxygen consumption was dependent on oxygen concentration up to levels of about eight mg/l, and independent of depth of deposit. Their samples were characterized as having measureable
populations of macro-invertebrates.
The present study represents an attempt to define the relative effects such
factors as oxygen concentration, temperature, and the character of the biologic
community, have on the oxygen demand of benthal deposits sampled from a
mildly polluted, eutrophic stream.
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