Exercises: Eutrophication and Thermal Pollution

Define eutrophication. Name two nutrients that commonly cause it in lakes and coastal waters.

State what dissolved oxygen (DO) measures and whether a healthy trout stream would have high or low DO. Give one reason.

A power plant releases heated water into a river. Name this type of pollution and state one immediate effect on the water's dissolved oxygen.

Fertilizer runoff from farms in the Mississippi River basin flows into the Gulf of Mexico. Explain the sequence of events, from the arrival of nitrates to the formation of a hypoxic "dead zone." Include the roles of algal blooms and decomposers.

Students at a high school in Ohio test a pond at three sites.

(a) Identify the site most affected by nutrient pollution.

(b) Explain the relationship between nitrate and dissolved oxygen shown in the data.

(c) Suggest one way to reduce nitrate input near the farm.

Explain why warm water holds less dissolved oxygen than cold water. Then describe two effects that thermal pollution from a factory can have on fish populations in a stream.

A lake near Chicago is monitored over a summer.

(a) Explain why surface DO rises in July even though bottom DO falls.

(b) Explain why bottom DO is lowest in September, after the algae peak.

(c) Predict the effect on fish that live near the bottom, and propose two actions to reduce the problem, one for farms and one for cities.

A river receives treated water at 30 °C from a power plant. Upstream the river is 14 °C. Fish downstream show stress and fewer cold-water species are found.

(a) Explain, using solubility and metabolism, why the higher temperature harms fish.

(b) Describe a cooling system design that could reduce thermal pollution.

(c) Compare thermal pollution with eutrophication: how are their effects on DO similar, and how are their causes different?