What does a decrease in dissolved oxygen in water typically signify?

A decrease in dissolved oxygen in water is typically indicative of excess organic matter decomposition. When there is an accumulation of organic material, microorganisms break it down through the process of decomposition. This microbial activity consumes dissolved oxygen as they metabolize the organic matter. As a result, the concentration of dissolved oxygen decreases, which can have serious implications for aquatic life, as many fish and invertebrates rely on sufficient levels of oxygen in the water to survive.

While high levels of nutrients can lead to the growth of excessive algae (a phenomenon known as eutrophication), it is the decomposition of this organic matter that primarily results in the reduction of oxygen levels. High temperatures can also influence dissolved oxygen levels but typically lead to more oxygen depletion through increased metabolic rates of organisms. Therefore, recognizing the link between organic matter decomposition and reduced oxygen levels is crucial for understanding water quality dynamics and ecosystem health.