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Reading passage Grade 9 Social Studies & Civics

Nutrients as Pollutant and Resource in the Wend River Estuary

A grade 9 passage on how nitrogen and phosphorus both feed crops and choke a fictional estuary, and how a town's nutrient program produced mixed outcomes.

Objectives

  1. Students will explain how excess nutrients lower a waterway's dissolved oxygen.
  2. Students will describe how the same nutrient can be both a resource and a pollutant.
  3. Students will evaluate the outcomes of a local nutrient-reduction program.

Vocabulary

Dissolved oxygen
Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.

Also: nutrient, algae bloom, point source, nonpoint source

Teacher overview

Nitrogen and phosphorus help grow the crops people eat, yet the same nutrients can strip the oxygen from a river when too much of them washes in. This passage follows the fictional Wend River estuary, where summer algae blooms once killed fish, and traces how a town's nutrient-reduction program brought the water back while creating new costs and questions. It supports a unit on environmental policy, and it asks students to hold two ideas at once: nutrients are valuable, and nutrients can pollute. The water-quality figures come from federal treatment standards and standard benchmarks.

Nutrients as Pollutant and Resource in the Wend River Estuary — Grade 9 Social Studies & Civics
Name: ____________________________ Date: ______________

Passage

Nitrogen and phosphorus are nutrients that living things need in order to grow. Farmers add them to fields as fertilizer because crops depend on them. In the right place these nutrients are valuable, because they help grow the food a community eats.

In the wrong place, the same nutrients become a pollutant. When heavy rain washes extra fertilizer off a field and into a river, it feeds more than crops. It feeds algae. The algae grow fast and cover the water in a thick layer. Scientists call this an algae bloom.

An algae bloom looks harmless, but it starts a harmful chain. Algae do not live long. When they die, bacteria break them down. Those bacteria use oxygen from the water as they work. As more algae die, the bacteria multiply and pull more and more oxygen out of the water.

Fish depend on that oxygen. Most fish need dissolved oxygen above 5 milligrams per liter to survive. When a bloom dies off, oxygen can fall well below that level. Fish cannot breathe, and many die. A patch of water with too little oxygen is called a dead zone.

The fictional Wend River estuary suffered these dead zones each summer. Two sources sent nutrients into the water. The first was runoff from farms across the valley. This kind of pollution comes from a wide area and is called a nonpoint source. The second was the town's old sewage plant, which released partly treated wastewater from a single pipe. Pollution from one clear spot like that is called a point source.

The old plant was the easier problem to fix, because it had one owner and one pipe. Raw sewage carries a heavy load of organic matter. Its BOD, a measure of how much oxygen bacteria will use to break it down, usually runs about 200 to 300 milligrams per liter. Federal rules require secondary treatment to cut BOD and solids to 30 milligrams per liter or less. That is roughly 85 percent removal. The town rebuilt its plant to meet that standard and added a step to remove extra nitrogen before the water reached the estuary.

The story did not stop at cleanup. The rebuilt plant now captures some of the phosphorus it removes and turns it into a fertilizer product. A pollutant became a resource again. Meanwhile, many farms changed their practices. They planted cover crops and left strips of grass along streams. These steps keep nutrients on the fields, where they are useful, instead of letting them run into the river.

The program worked in important ways. Within a few years, oxygen levels in the estuary rose, and fish returned to areas that had been dead zones each summer. That was the outcome the town wanted.

Other outcomes were harder. The plant upgrade was expensive, and water bills rose to pay for it. Farmers spent money and effort on new practices. The fertilizer product the plant makes must find buyers, or it becomes a cost instead of a benefit. And the rules are not the same for everyone. The town's plant must meet firm limits, while farm runoff is reduced mostly through voluntary steps. Some residents argue that this is unfair, because the point source carries the legal weight while the larger nonpoint source does not.

The Wend River shows that a nutrient is not simply good or bad. It is a resource in one place and a pollutant in another, and a policy that moves it from the second place back to the first can succeed and still leave hard questions behind.

Questions

  1. Name the two nutrients the passage says can act as both a resource and a pollutant.
  2. According to the passage, what level of dissolved oxygen do most fish need to survive?
  3. What does secondary treatment have to reduce BOD and solids to, and about what percent removal is that?
  4. Explain, step by step, how extra nutrients in the river lead to fish dying.
  5. The passage calls nutrients both a resource and a pollutant. Explain how the same nitrogen can be each.
  6. Identify one intended outcome and one unintended outcome of the Wend River nutrient program.
  7. The town's plant faces firm legal limits, while farm runoff is reduced through voluntary steps. Why might some people see that difference as a weakness in the program?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: Nitrogen and phosphorus. The passage names both as nutrients that crops need but that can also pollute a river.
  2. Answer: Above 5 milligrams per liter. The passage states most fish need dissolved oxygen above this level to survive.
  3. Answer: To 30 milligrams per liter or less, which is roughly 85 percent removal. The passage gives both the limit and the removal figure when describing the plant upgrade.
  4. Answer: Extra nutrients feed algae, causing a bloom; the algae die; bacteria break them down and use up oxygen; dissolved oxygen falls below what fish need; and the fish die. The passage lays out this chain in order.
  5. Answer: On a farm field, nitrogen is a resource because crops need it to grow, but washed into a river it becomes a pollutant that feeds algae and lowers oxygen. The same nutrient's effect depends on where it ends up, as the passage explains.
  6. Answer: Intended outcome: oxygen levels rose and fish returned to the estuary. Unintended outcome: water bills rose, farmers bore new costs, or the fertilizer product must find buyers. The passage names each of these.
  7. Answer: Because the smaller, single point source carries firm legal limits while the larger, spread-out nonpoint source relies on voluntary action. Some people see this as unfair or incomplete, since the source contributing more may face weaker rules, a tension the passage raises.

Differentiation

Support

Provide a simple flow chart of the algae-to-dead-zone chain (extra nutrients, bloom, algae die, bacteria use oxygen, fish die) for students to reference while answering question 4, and allow the literal questions to be answered with short phrases.

Extension

Ask students to write a short proposal for how the town could make the rules more even between the point source and the nonpoint farm runoff, using only ideas and facts from the passage and explaining one likely objection to their proposal.

ELL supports

Pre-teach "nutrient," "algae bloom," "dissolved oxygen," "point source," and "nonpoint source" with a labeled picture of a river receiving runoff from a field and from a pipe. Allow students to answer question 4 by numbering the steps of the chain rather than writing full sentences.