Reaeration Measurements in a
Eutrophic Stream
WILBERA. BLAIN, Graduate Assistant
ARCHIE J. MCDONNELL, Assistant Professor
Department of Civil Engineering
The Pennsylvania State University
University Park, Pennsylvania
INTRODUCTION
The distribution of dissolved oxygen in streams is determined by spatial and
temporal relationships between oxygen consumption and oxygen supply. Oxygen
supply, in the absence of photosynthetic oxygenation, is provided by the transfer
of oxygen from the atmosphere into the water. This atmospheric reaeration process is conventionally defined by a first order reaction in which the rate of oxygen
transfer is directly proportional to the dissolved oxygen deficit. The proportionality
constant, designated as the reaeration coefficient, K2, characterizes the process
in a stream reach for constant hydraulic, temperature, and water quality conditions. The magnitude of the reaeration coefficient represents an important index
of a stream's natural resistance to deoxygenation and is a fundamental consideration in oxygen balance studies.
Reliable estimates of the reaeration coefficient are often obstructed in stream
reaches where independent evaluation of oxygen metabolism is not feasible. This
commonly occurs in shallow, eutrophic streams. The definition of oxygen metabolism by rooted aquatic plants or benthic algae cannot be established by conventional stream survey water analyses and techniques. A number of equations may
be used to predictK2 from a knowledge of stream hydraulic parameters. However,
estimates of K2 may differ significantly, leaving more or less arbitrary, the proper
rate constant selection.
The purpose of this paper is to present results of reaeration rate studies, conducted on three reaches of a small, shallow, eutrophic stream. Continuous dissolved oxygen and temperature data are analyzed applying modifications of
methods described by Odum (1) to obtain estimates of the reaeration coefficient.
Corrections are applied to estimates for the varying night-time respiration rates of
rooted aquatic plants. Experimental reaeration coefficients are compared with
predicted values calculated from selected rate constant prediction formulae.
STUDY AREA DESCRIPTION
Spring Creek is a small, shallow stream in Central Pennsylvania. The limestone and dolomite formations which comprise much of the 108 square mile drainage basin provide the creek with average low flows of about 0. 35 cfs/sq. mi. and
water which is characteristically hard and alkaline.
Following its junction with Slab Cabin Run (see Figure 1), Spring Creek receives the completely-treated effluent from a sewage treatment plant serving a
population of approximately 40,000. A comparison of typical summer nutrient
concentrations above and below the junction are given in Table I.
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