Earth & Environmental Sciences
September 16, 2013
Dissolved Oxygen (DO) is simply oxygen gas (O2) dissolved in water, but it’s one of the best indicators of a healthy aquatic ecosystem. For most freshwater environments, a DO concentration of 5–10 mg/L (or ppm) is needed to sustain fish species. Many factors can affect DO concentrations and the solubility of oxygen in water. The activity below examines some of these factors and presents a great opportunity for inquiry experiments that integrate other disciplines (biology, chemistry, and even physics!).
*If using a Dissolved Oxygen Sensor instead of a Water Quality Sensor, use the Fast Response Temperature Probe to prevent electrical interference. Do not use a Dissolved Oxygen Sensor with a Stainless Steel Temperature Probe. The Water Quality Sensor can be used with either temperature probe.
To introduce the sensor and lab activity, conduct the following as a demo. Before beginning, discuss the concept of dissolved oxygen.
Now that students have seen how to use the sensor and discussed factors that can affect DO concentrations, they can design and conduct their own experiments. Many relevant variables are easily manipulated in the lab environment. Using other PASPORT sensors, students can easily quantify the dependent variable as well. Here are some suggested variables for students to consider:
This nomogram can be used to calculate the % saturation from water samples if the temperature and oxygen concentration are known. Use a ruler or other straight edge to line up the water temperature and oxygen concentration. The straight edge will intersect the % saturation scale at the estimated value.