What factor is considered the most important in determining dissolved oxygen concentration in water?

The most important factor in determining dissolved oxygen concentration in water is the amount of aquatic plants present. Aquatic plants, including algae and submerged vegetation, play a critical role in the oxygen cycle of a water body. Through the process of photosynthesis, they produce oxygen during daylight hours, which contributes significantly to the dissolved oxygen levels in the water.

Increased plant biomass typically leads to higher oxygen production, particularly in sunny conditions. During the day, these plants can increase oxygen levels significantly, which is essential for the survival of fish and other aquatic organisms that rely on sufficient oxygen concentrations. However, at night, plants respire just like animals, consuming oxygen, but this is usually outweighed by daytime production.

Other factors, while important, tend to influence the overall dynamics of dissolved oxygen in a supporting manner. For instance, temperature affects solubility—warmer water holds less oxygen. The type of biota present can influence oxygen levels due to their metabolic processes, and water movement helps to distribute oxygen and bring in fresh oxygenated water from the atmosphere. Each of these factors has its relevance, but the presence of aquatic plants is a direct source of oxygen production, establishing it as the most pivotal factor in determining dissolved oxygen concentration.