You have been assigned to conduct a site assessment for a lake in Montana. There is a new biofuels plant operating and discharging into the stream that feeds the lake and agriculture around the lake for cattle and switchgrass. You observed high levels of algae floating on the surface of the lake, and the water was highly turbid. You also measured the DO at 1 meter to be 5 mg/L and at a depth of 20 meters the DO was 1.0 mg/L.

Question

a. How would you describe the productivity level of the lake? Explain your reasoning.
b. Similar lakes have had threatened Yellowstone Cutthroat Trout populations. But this lake does not. What changes would you suggest be made in managing the lake’s water quality prior to the reintroduction of trout to the lake?

What will be an ideal response?

Answer 1

Observations: High levels algae

High turbidity





a. How would you describe the productivity level of the lake? Explain your reasoning.

- Based on above information/description, lake is Eutrophic due to high algae (chlorophyll), limited Secchi disk transparency and low D.O.



b. Similar lakes have had threatened Yellowstone Cutthroat Trout populations. But this lake does not. What changes would you suggest be made in managing the lake’s water quality prior to the reintroduction of trout to the lake?

- Must increase D.O. levels

? increase aeration (mechanically)

? reduce nutrient loading (possibly collect ag. Runoff and threat with constructed wetlands)