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 oxygen is essential for the survival and growth of aquatic organisms. Higher dissolved oxygen levels represent better water quality, allowing diverse aquatic life to thrive. In contrast, low oxygen levels can lead to the death of fish and other aquatic life and promote the growth of undesirable organisms, such as certain bacteria. High oxygen levels also help in decomposing organic matter and breaking down pollutants more efficiently. (b) The solubility of oxygen in water is negatively affected by increasing temperature. As the temperature of water increases, the solubility of oxygen decreases, meaning that warmer water holds less dissolved oxygen than colder water. This temperature-solubility relationship is significant because it has direct implications for aquatic life and water quality. Warmer water can hold less dissolved oxygen, potentially resulting in reduced oxygen availability for aquatic organisms, which can lead to their death and degradation of water quality.

Step-by-step solution

Part (a) Importance of dissolved oxygen concentration in freshwater

Dissolved oxygen (DO) is the amount of oxygen that is present in water. It is an important factor in determining the quality of water, as oxygen is essential for the survival and growth of aquatic organisms, such as fish, invertebrates, and bacteria. A healthy water ecosystem requires adequate levels of dissolved oxygen to support its living organisms. Higher concentrations of dissolved oxygen typically represent better water quality, as adequate oxygen levels allow for a diverse range of aquatic life to thrive. In contrast, low oxygen levels can lead to the death of fish and other aquatic life, as they cannot survive in an oxygen-deprived environment. Additionally, low oxygen levels can promote the growth of undesirable organisms, such as some types of bacteria, which can further degrade water quality and contribute to other environmental problems. Water with a high level of oxygen helps in decomposing organic matter and breaking down pollutants more efficiently. Therefore, the concentration of dissolved oxygen in freshwater is an important indicator of the quality of water and the overall health of the aquatic ecosystem.

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

The solubility of oxygen in water is affected by temperature, among other factors. As the temperature of water increases, the solubility of oxygen decreases, meaning that warmer water holds less dissolved oxygen than colder water. The relationship between temperature and oxygen solubility can be explained by the kinetic energy associated with water molecules. At higher temperatures, water molecules have increased kinetic energy and move more rapidly, which makes it harder for oxygen molecules to interact with water molecules and dissolve. As a result, less oxygen can be dissolved in warmer water than in colder water. Conversely, as the temperature decreases, water molecules move more slowly, and their decreased kinetic energy allows oxygen molecules to interact more easily with water molecules, leading to a higher solubility of oxygen in colder water. This temperature-solubility relationship is significant because it has direct implications for aquatic life and water quality. Warmer water can hold less dissolved oxygen, potentially resulting in reduced oxygen availability for aquatic organisms. In extreme cases, this oxygen depletion can lead to the death of fish and other aquatic life, contributing to the overall degradation of water quality.

Key concepts

Water Quality

Water quality is a measure of the condition of water based on chemical, physical, and biological characteristics. One essential component in assessing water quality is the concentration of dissolved oxygen (DO). DO is vital because it supports aquatic life. Without sufficient oxygen, fish and other organisms can't survive, which significantly impacts water quality.

In addition to sustaining life, adequate DO levels indicate that the water can naturally decompose organic material and pollutants. This means cleaner water. When water possesses high levels of dissolved oxygen, it often signifies a healthy and clean ecosystem. However, low DO levels can encourage harmful bacteria growth, which deteriorates water quality and leads to environmental issues.

Oxygen Solubility

Oxygen solubility refers to the ability of oxygen to dissolve in water. Several factors influence this solubility, including temperature, pressure, and salinity. The important aspect to note here is that solubility is vital for aquatic organisms that rely on dissolved oxygen for survival.

Higher solubility of oxygen in water means more oxygen is available for these organisms, promoting a balanced ecosystem. Any changes in factors affecting solubility can have significant consequences for water quality and the organisms living within it. Therefore, understanding oxygen solubility is crucial for maintaining healthy aquatic environments.

Aquatic Life

Aquatic life thrives based on the availability of dissolved oxygen in water. Fish, invertebrates, and even some plant species rely heavily on oxygen to live and reproduce. When oxygen levels are adequate, these organisms can sustain themselves and maintain their populations.

However, when dissolved oxygen levels drop, aquatic life faces significant threats. Insufficient oxygen can lead to stress, altered behavior, and even massive die-offs. Thus, monitoring dissolved oxygen is essential to ensure the survival and health of aquatic life. It reflects the resilience and biodiversity of the water ecosystem.

Temperature Effects on Solubility

The temperature of water plays a significant role in oxygen solubility. As water temperature increases, the oxygen solubility decreases, meaning warmer water holds less oxygen. This occurs because higher temperatures increase the kinetic energy of water molecules, making it harder for oxygen molecules to dissolve.

Conversely, colder water temperatures result in higher oxygen solubility. Lower kinetic energy allows water molecules to interact more easily with oxygen, enhancing solubility. This relationship can impact aquatic ecosystems. In warm water, reduced oxygen levels may stress or kill aquatic life. Conversely, colder water may support more oxygen, benefiting aquatic organisms.

It's important to consider and manage temperature fluctuations to maintain optimal oxygen levels, which are crucial for healthy aquatic ecosystems.