An example of dissolved oxygen is the oxygen present in a freshwater stream that supports aquatic life like fish and insects.
Here's a more detailed explanation:
Dissolved oxygen (DO) refers to the amount of oxygen gas (O2) that is present in water. This oxygen is crucial for the survival of aquatic organisms, much like oxygen in the air is vital for terrestrial animals. Several processes contribute to dissolved oxygen levels in aquatic environments:
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Re-aeration: This is the process where oxygen from the atmosphere dissolves into the water. Turbulence, such as that created by:
- Water tumbling over rocks in rapids: The churning water exposes more surface area to the air, facilitating oxygen dissolution.
- Waterfalls: Similar to rapids, waterfalls create significant turbulence, increasing oxygen levels.
- Wave action: Waves mix air into the water, boosting DO.
- Riffles: Shallow, turbulent areas in streams and rivers enhance re-aeration.
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Photosynthesis: Aquatic plants and algae produce oxygen as a byproduct of photosynthesis during daylight hours. This process significantly contributes to the DO levels in many aquatic ecosystems.
Examples in different environments:
- Rivers and Streams: High DO levels are often found in fast-flowing rivers and streams with numerous rapids and riffles. This supports a diverse community of oxygen-dependent organisms.
- Lakes and Ponds: DO levels can vary significantly with depth and time of day in lakes and ponds. Photosynthesis near the surface can lead to high DO during the day, while decomposition at the bottom can deplete oxygen.
- Oceans: Wave action and mixing contribute to DO in ocean surface waters.
Low dissolved oxygen levels can lead to stress, suffocation, and death for aquatic organisms. Pollution, excessive nutrients (leading to algal blooms and subsequent decomposition), and warm water temperatures can all reduce DO levels.
