HELP WITH: biology and water pollutants!!?

Question

Why was it important to determine the baseline conditions before assessing the effects of the pollutants on the stream?

Answer 1

Baselines are types of controls.  Without them, you cannot determine if there has been any effect after a treatment is applied.  For example, if there was going to be phosphorous loading into a lake and you wanted to know if the algal abundance increased as a result, you would need to know what the algal abundance was prior to the phosphorous loading.