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 directly affects the health and survival of aquatic organisms. High concentrations signify a healthy ecosystem, while low concentrations can indicate pollution, excessive algae growth, or other environmental issues negatively affecting water quality and aquatic life. (b) The solubility of oxygen in water decreases as temperature increases due to faster-moving water molecules, allowing gases, including oxygen, to escape from the water more easily. Higher temperatures thus result in lower dissolved oxygen concentrations, making it harder for aquatic organisms to obtain the oxygen they need to survive.

Step-by-step solution

Part a: Importance of dissolved oxygen concentration in water quality

The concentration of dissolved oxygen in freshwater is a crucial parameter when determining water quality because it directly impacts the health and survival of aquatic organisms. Oxygen dissolves in water and is consumed by fish and other aquatic lifeforms through respiration. A higher concentration of dissolved oxygen means there is more oxygen available for aquatic life to take in, which generally results in a healthier ecosystem. A lower concentration of dissolved oxygen can be indicative of pollution, excessive algae growth, or other environmental issues that negatively affect the overall water quality. This can lead to stress or even death for the aquatic organisms living in the water. Therefore, monitoring the concentration of dissolved oxygen is essential for assessing the health of a freshwater ecosystem and determining if any interventions are necessary.

Part b: Effect of temperature on oxygen solubility in water

The solubility of oxygen in water is affected by temperature, among other factors such as pressure and salinity. As temperature increases, the solubility of oxygen generally decreases. This means that warm water can hold less dissolved oxygen compared to cold water. The relationship between temperature and oxygen solubility in water is due to the fact that water molecules move faster at higher temperatures. This increased movement allows gases, including oxygen, to escape from the water more easily. As a result, higher temperatures cause a decrease in the amount of dissolved oxygen in the water. Therefore, when the temperature of a body of freshwater increases, the solubility of oxygen in the water decreases, making it harder for aquatic organisms to obtain the oxygen they need to survive. This relationship further highlights the significance of monitoring dissolved oxygen concentrations in water quality assessments.