What is the role of oxygen in lakes and how does it affect the lake's trophic state?

One of the major parameters that affect lake trophic state is oxygen:

What is the role of oxygen in lakes? 

Oxygen in lakes:

Oxygen is of major importance for aquatic life in lakes, fish need oxygen for respiration, and also the degradation of organic materials is dependence on the presence of dissolved oxygen in water. It is well known that the percentage of oxygen in water is high comparing to nitrogen percentage due to the ability of oxygen to dissolve in water, unlike nitrogen. It is important to understand the oxygen regime in lakes because oxygen drives the biological and chemical processes. Temperature and pressure are two of many factors that can affect the amount of dissolved oxygen. The level of dissolved oxygen differs in different locations due to the difference in temperature, latitude, and stratification (change in the temperature at different depth). Winter is an important factor in oxygen depletion, at latitude below 4^oC the surface of water freezes, the freezing of surface water cause thin layer of ice to form which prevents the dissolving of the atmospheric oxygen in water. The depletion of oxygen during ice cover increases the mortality of fish in what is known as "winterkill" phenomenon (Fox, 1990). Michigan lakes between years 1944-1945 suffered from the formation of a thick layer of heavy winter that cause DO level to decrease to 0.3 and 0.2 leading to high fish mortality during that winter (Barica, 1979). The winter oxygen depletion rates are believed to be non-linear, Prairie Pthole lakes showed fast oxygen depletion rates that start to equilibrate in water column. Oxygen concentrations become stabilized once reached levels between 0.5-2.0mg.L^{-1 (Baird, 1987)}. High anoxic conditions occur at the sediment –water boundaries due to the organic sediments decomposition that consume oxygen, while near the surface oxygen concentration decreases rapidly at the beginning of ice formation then stabilize, but never reaches zero (Golosov, 2007). Studying Lake St. George showed a significant decrease in the oxygen concentration during winter, the oxygen depletion reached 71%. The increase in the nitrification process was accounted for oxygen consumption during winter (Knowles, 1987). 

The other two factors that affect oxygen consumption during winter are the depth and trophic state of lakes. In a study of four sets of Canadian lakes, the lakes morphometries and trophic states showed an inverse relationship to the oxygen depletion. Ice-covered eutrophic Prairie lakes recorded oxygen consumption three times higher than Ontario oligotrophic lakes. As for depth factor, shallow lakes showed less concentration of dissolved oxygen comparing to deeper lakes (Mathias, 1980). It is worth mention that, no complete kill of all fish species is recorded during winter (Barica, 1979), studies show a decrease of oxygen consumption and an increase in the affinity of fish to extract oxygen from water during winter (Irving, 1941). This provides evidence that, although winterkill phenomenon decreases the fish population during winter yet the recovery of the fish population can occur during summer.

The global warming played a key role in oxygen concentration in lakes, the temperature of the surface of water during summer increases and this increase in temperature extent to the lower parts of water body. Increasing temperature has inverse effect on the amount of dissolved oxygen (DO) in lakes, as temperature increases during summer the DO concentration decreases and anoxic conditions are accelerated.

By,

Dr. Rania S. Seoudi

References

Baird, D. G. T. a. D. R., 1987. Oxygen conditions in two prairie pothole lakes during winter ice cover. Canadian Journal of Fisheries and Aquatic Sciences, 44(5), pp. 1092-1095.

Barica, J. a. M. J., 1979. Oxygen depletion and winterkill risk in small prairie lakes under extended ice cover. Journal of the Fisheries Board of Canada, 36(8), pp. 980-986.

Fox, M. a. K. A., 1990. Effects of winterkill on population structure, body size, and prey consumption patterns of pumpkinseed in isolated beaver ponds. Canadian journal of zoology, 68(12), pp. 2489-2498.

Golosov, S. M. O. S. E. T. A. Z. G. a. K. G., 2007. Physical background of the development of oxygen depletion in ice-covered lakes. Oecologia, 151(2), pp. 331-340.

Irving, L. B. E. a. S. V., 1941. The influence of temperature upon the combination of oxygen with the blood of trout. The Biological Bulletin, 80(1), pp. 1-17.

Knowles, R. a. D. R. L., 1987. Nitrification: a significant cause of oxygen depletion under winter ice. Canadian Journal of Fisheries and Aquatic Sciences , 44(4), pp. 743-749.

Mathias, J. A. &. B. J., 1980. Factors controlling oxygen depletion in ice-covered lakes. Canadian Journal of Fisheries and Aquatic Sciences, 37(2), pp. 185-194.