Where should the DO test be performed?

• A. The field
• B. The laboratory
• C. The office
• D. The shore

Answer: (A)

Dissolved oxygen readings reflect the water’s actual conditions at the moment of measurement, and DO can change rapidly with temperature, mixing, and microbial activity. Testing in the field allows you to measure on-site with a portable DO meter or perform an immediate field titration, capturing the true in-situ value and minimizing changes that can occur during storage or transport. If the sample waits to be tested in a lab or office, oxygen can diffuse out or be consumed, leading to readings that don’t represent the water at the time of sampling. Field testing also accounts for the water’s location and conditions where it was collected, which helps address any vertical or horizontal variability. For these reasons, the field is the best place to perform the DO test.