Florida Wastewater Practice Test

What does it indicate if the temperature measurements in a river cross-section are approximately the same?

1. The river is polluted

2. The stream is well mixed

3. The water is stagnant

4. The river is shallow

The correct answer is: The stream is well mixed

When temperature measurements in a river cross-section are approximately the same, it indicates that the stream is well mixed. This uniform temperature distribution suggests that the water is circulating properly and that there is a good degree of turbulence, which allows for mixing of water from different layers and areas. Well-mixed waters typically have similar temperatures because convection currents and other mixing processes distribute heat evenly throughout the water column. This homogeneity is important for aquatic ecosystems, as it affects the distribution of dissolved oxygen and nutrients, making the environment more conducive to the health of various organisms. In contrast, if the river were polluted, you might expect a variation in temperature due to localized discharges creating 'hot spots' or areas with different thermal properties. Stagnant water would show more pronounced temperature stratification, while shallow rivers might also experience temperature variations due to increased solar heating in shallower areas or lack of mixing. Thus, consistent temperature readings indicate effective mixing rather than stagnation or pollution.