SAME LAb - Collect a sample of water below some riffles in stream. Stream runs into a lake. 2nd sample from lake. Which smaple would you expect to have the higher DO? Explain
The dissolved oxygen (DO) level in water can vary depending on various factors. In this scenario, we have two samples: one from below some riffles in the stream and the other from the lake where the stream runs into.
Riffles in a stream are areas where the water flows faster and becomes turbulent. This turbulence introduces air into the water, promoting aeration and increasing the oxygen concentration. As a result, it is expected that the sample collected from below the riffles in the stream will have a higher dissolved oxygen level compared to the lake sample.
In the lake, the water is generally calmer as it receives the stream's inflow. The absence of turbulent flow and aeration causes the water in the lake to have lower dissolved oxygen levels compared to the riffle section of the stream.
Therefore, the sample collected from below the riffles in the stream is likely to have a higher dissolved oxygen level compared to the sample collected from the lake.
To determine which sample would likely have a higher Dissolved Oxygen (DO) level, we need to understand the factors that influence DO in water bodies.
Dissolved Oxygen refers to the amount of oxygen dissolved in water, which is essential for the survival of aquatic organisms. The primary source of DO in freshwater systems is from the exchange of gases between the atmosphere and the water surface. Therefore, the factors that affect dissolved oxygen levels include:
1. Temperature: Higher water temperatures decrease the solubility of oxygen, resulting in lower DO levels.
2. Photosynthesis: Aquatic plants and algae release oxygen through photosynthesis during daylight hours, increasing DO levels.
3. Respiration: Aquatic animals consume oxygen and release carbon dioxide through respiration, leading to a decrease in DO levels.
Based on this information, let's analyze the two sampling points:
1. Sample below the riffles in the stream: Riffles are sections of the stream where water flows quickly and tumbles over rocks or obstacles. These turbulent environments increase the chances of oxygen being mixed into the water from the atmosphere. Additionally, the agitation caused by the riffles promotes aeration, aiding in oxygen dissolution. Therefore, the sample below the riffles in the stream is likely to have higher DO levels.
2. Sample from the lake: Lakes, by comparison, are typically more still and undisturbed in nature. Due to less turbulent water movement, the water may have less opportunity to mix with the air, resulting in lower oxygen levels. Moreover, lakes often have a larger biomass of aquatic plants and animals, which consume oxygen through respiration, further reducing DO levels.
In summary, considering the increased oxygen exchange and aeration occurring in the riffles, the sample collected below the riffles in the stream is expected to have higher Dissolved Oxygen levels compared to the sample from the lake.