How can the lowering of dissolved oxygen in water be limited?

The correct answer focuses on limiting the amount of vegetation that is killed off in aquatic environments. Vegetation plays a crucial role in maintaining dissolved oxygen levels in water bodies. Aquatic plants and algae produce oxygen through photosynthesis during daylight hours, which contributes to the oxygen content of the water. When there is a significant reduction in plant life, such as through herbicide application or natural die-off, there is less oxygen being produced. Therefore, preserving aquatic vegetation helps to sustain oxygen levels, mitigating the negative effects of lowered dissolved oxygen.

In contrast, increasing water temperature tends to reduce the capacity of water to hold dissolved oxygen, leading to a depletion of oxygen levels. Adding more fish could exacerbate the problem, as more fish would contribute to increased oxygen consumption, further decreasing the oxygen available. Reducing water flow may also negatively impact oxygen levels because stagnant water generally has less oxygen replenishment compared to flowing water, where aeration can occur. Thus, the best strategy to limit the lowering of dissolved oxygen is to protect and maintain existing vegetation.