How Does the Dissolved Oxygen Problem Develop?
In the summer, the water in the Great Lakes separates into two layers. The top layer is warmer than the bottom one, it receives the sunlight, and it mixes with oxygen from the air. The bottom layer is cooler than the top layer, it is usually dark, and it is cut off from the air so it cannot re-supply its oxygen. The Western Basin of Lake Erie is shallower than the typical thickness of the upper layer of water. Winds are able to keep the whole water column stirring, so there is plenty of opportunity for oxygen to dissolve into the water from the air. The bottom of the Central Basin is a broad, shallow plain that is slightly deeper than the typical thickness of the upper layer. Therefore, the bottom layer is relatively thin and contains a relatively small volume of water. In the deeper Eastern Basin, the bottom layer is much thicker and contains more water. If there is much phosphorus in the water, it acts like fertilizer, and more algae will grow in the warm, sunlit top layer. Eventuall
