Students want to determine the impact of soil erosion from the development of new housing. They plan to measure the density of a species of algae growing along the bottom of a river that flows through their town. The town is built in a heavily forested area, but a large area of trees along the river was recently clear-cut to allow for the construction of a new housing development, which has caused exposed soil to wash into the river. The river flows north to south through the town and is still forested both up- and downstream of the town. Which of the following would be the best control sample for the study? A. Water temperature, because a decrease in shading in the area would indicate an increase in soil erosion.
B. Nutrient levels, because a decrease in nitrogen and phosphorus would indicate an increase in soil erosion.
C. The pH level, because an increase in pH would indicate an increase in soil erosion.
D. Turbidity, because a decrease in water clarity would indicate an increase in soil erosion.