Final answer:
The statement about the relationship between water temperature and dissolved oxygen is true. As water temperature decreases, its capacity to hold dissolved oxygen increases. When water is warmed, its ability to contain dissolved oxygen decreases, having implications for aquatic ecosystems.
Step-by-step explanation:
The statement that dissolved oxygen levels in water change with temperature is indeed true. As water gets colder, it is capable of holding more dissolved oxygen, and as water gets warmer, its ability to hold dissolved oxygen decreases. This is because the solubility of gases in liquids typically decreases as the temperature increases. When a river, lake, or stream's temperature is raised, thereby warming the water, the solubility of oxygen in the water decreases. Conversely, in cold water, like under the ice in winters, the water can hold more oxygen and support aquatic life just below the ice surface where the water remains liquid. Water is densest at about 4°C, so the deepest parts of a lake during winter will have the densest water that is also potentially oxygen-poor due to the lack of mixing with surface water and oxygen depletion by the decomposition of organic material.