Question

(a) Explain why the concentration of dissolved oxygen in freshwater is an important indicator of the quality of the water. (b) How is the solubility of oxygen in water affected by increasing temperature?

Short answer

(a) The concentration of dissolved oxygen in freshwater is an important indicator of water quality because it is essential for aquatic life. Higher dissolved oxygen concentrations indicate better water quality and a healthier ecosystem, as it enables the survival of fish and other aquatic organisms, decomposition of organic matter, and nutrient cycling. Low dissolved oxygen concentrations can lead to ecological disturbances such as fish kills and algal blooms. (b) The solubility of oxygen in water decreases as temperature increases. This is due to the greater kinetic energy of water molecules at higher temperatures, which makes it harder for oxygen molecules to remain dissolved. Thus, warmer water holds less dissolved oxygen than cooler water, highlighting the importance of maintaining suitable temperatures in freshwater systems for adequate dissolved oxygen levels and a healthy ecosystem.

Step-by-step solution

Part (a): Importance of dissolved oxygen concentration in freshwater

Dissolved oxygen in freshwater is an essential factor for aquatic life. Fish and other aquatic organisms rely on oxygen to survive, and a higher concentration of dissolved oxygen generally indicates better water quality and a healthier ecosystem. Additionally, dissolved oxygen plays a crucial role in the decomposition of organic matter and the cycling of nutrients, which helps maintain a balanced ecosystem. In contrast, low dissolved oxygen concentrations in water can lead to fish kills, algal blooms, and other ecological disturbances.

Part (b): Effect of temperature on oxygen solubility in water

The solubility of oxygen in water is affected by temperature. As the temperature of water increases, the solubility of oxygen decreases. This is because, at higher temperatures, the increased kinetic energy of water molecules causes them to move more rapidly, which makes it more difficult for oxygen molecules to remain dissolved in the water. Therefore, warmer water holds less dissolved oxygen than cooler water. This is why it is essential to maintain an appropriate temperature in freshwater systems to ensure adequate dissolved oxygen levels and maintain a healthy ecosystem.