Factors Controlling Oxygen Depletion in the Hypolimnion

Abstract

<p>The purpose of this research was to determine the factors controlling oxygen depletion in the water column (more specifically, the hypolimnion).</p> <p>Five factors were hypothesized to be important:</p> <p>1. Soluble organic carbon concentration</p> <p>2. Temperature</p> <p>3. Nutrient concentration</p> <p>4. Initial oxygen concentration</p> <p>5. Algal respiration</p> <p>These factors were related by a two-level Factorial Experimental Design. Two separate but related Designs were used to "block" and "average" the effects, allowing for differentiation between main effects (for example, temperature) and two-factor interactions (for example, the combined effect of soluble organic carbon concentration and temperature).</p> <p>Four bodies of water (Hamilton Harbour, Guelph reservoir, Red Chalk Lake, and Chub Lake) were tested. The results show that in all cases, except Chub Lake, temperature is the most important factor controlling oxygen depletion. Soluble organic carbon concentration is the most important variable in Chub Lake. The second most important variables are: soluble organic carbon concentration in Hamilton Harbour and Red Chalk Lake, temperature in Chub Lake and the initial oxygen concentration in the Guelph Reservoir. The remaining factors have varying degrees of importance depending on the water body. This suggests that biodegradation is not limited by nutrients and that algal respiration is a small component of oxygen consumption.</p> <p>In addition to these main studies, Temperature and Oxygen Kinetics were also investigated. The Temperature Kinetic experiments showed that higher temperatures produce higher oxygen uptake rates. The Oxygen Kinetic experiments showed no trends except when Hamilton Harbour water was tested. In Hamilton Harbour, higher initial oxygen concentrations produced higher oxygen uptake rates.</p> <p>It is proposed that the Experimental Design represents a bioassay on oxygen consumption. It represents quantification of biodegradation under standard conditions. The relative magnitudes of oxygen consumption under these standard conditions correlate with empirical ideas of degradability of organics in the different water bodies. More work is required to refine the scaling of factors selected, seasonal variability, etc.</p>