Water for Schools
Menu

Reading passage Grade 7 English Language Arts

Too Much of a Good Thing: Nutrients at Widgeon Lake

A grade 7 informational passage on how nitrogen and phosphorus can be both fertilizer and pollutant, with comprehension questions mixing literal and inferential thinking.

Objectives

  1. Students will explain how the same nutrient can act as both a resource and a pollutant.
  2. Students will cite textual evidence to support an inference about the lake's fish kill.

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, runoff

Teacher overview

This informational passage explains how the same nitrogen and phosphorus that make crops grow can also ruin a lake. Set at the fictional Widgeon Lake, the passage traces how fertilizer washing off nearby fields feeds an algae bloom, and how that bloom ends up starving fish of oxygen. It works well before a science unit on water quality or as a stand-alone reading that rewards careful evidence-gathering.

Too Much of a Good Thing: Nutrients at Widgeon Lake — Grade 7 English Language Arts
Name: ____________________________ Date: ______________

Passage

Nitrogen and phosphorus are nutrients. Plants need them to grow, which is why farmers and gardeners add them to soil as fertilizer. In the right place, these nutrients are useful. The problem at the fictional Widgeon Lake shows what happens when they end up in the wrong place.

Widgeon Lake sits at the bottom of a wide, gently sloping valley. Farms cover much of the land around it. Every spring, farmers spread fertilizer on their fields so their crops will grow. Most of that fertilizer stays in the soil and does its job. But when heavy rain falls, some of it washes off the fields and runs downhill into the creeks that feed the lake. Water that carries soil, fertilizer, or other material off the land is called runoff.

For most of the year, the extra nutrients in Widgeon Lake are hard to notice. Then summer arrives. The days grow long and warm, and the lake fills with sunlight. Algae, the tiny green living things that float near the surface, use that sunlight and those nutrients to grow. With so much food and light, the algae grow far faster than usual. Soon a thick green layer spreads across the water. Scientists call this fast growth a bloom.

At first, the bloom does not look dangerous. It is just green, and a little smelly. But algae do not live long. As the older algae die, they sink toward the bottom of the lake. There, bacteria break them down. Those bacteria use oxygen to do their work, and there are now enormous numbers of dead algae for them to break down. As the bacteria feed, they pull oxygen out of the water faster than the lake can replace it.

This is the hidden danger of a bloom. Fish do not breathe air; they take in oxygen that is dissolved in the water through their gills. Most fish need dissolved oxygen above 5 milligrams per liter to stay healthy. When the bacteria near the bottom use up the oxygen, the amount left drops well below that level. Fish crowd toward the surface, where a little more oxygen remains. If the oxygen falls far enough, many fish die. A sudden death of many fish is called a fish kill, and Widgeon Lake had one last August.

The strange part is that nothing poisonous was ever dumped into the lake. The nutrients that caused the trouble are the very same ones that help crops grow. They were not a poison. They were simply too much of a good thing, in a place that could not handle them.

People who live near Widgeon Lake have started to change how they treat the land. Some farmers now leave strips of grass and shrubs between their fields and the creeks. These strips slow the runoff and soak up nutrients before the water reaches the lake. Others test their soil and add only as much fertilizer as their crops truly need. None of these steps fixes the lake overnight. But each one keeps some nutrients out of the water, and over several years, fewer nutrients should mean smaller blooms and healthier fish.

Questions

  1. According to the passage, why do farmers add nitrogen and phosphorus to their soil?
  2. What is runoff, as the passage defines it?
  3. What conditions in summer let the algae in Widgeon Lake grow so quickly?
  4. Explain how a bloom of algae can lead to a fish kill. Cite at least two details from the passage in your answer.
  5. The passage says the nutrients were "too much of a good thing." What does this phrase mean in the context of the lake?
  6. Why does the passage say nothing "poisonous" was dumped in the lake, even though fish died?
  7. Based on the passage, why might the grass strips between fields and creeks help the lake over time? Support your answer with evidence.
  8. What can you infer about why the changes near Widgeon Lake will not fix the lake quickly?

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: So their crops will grow. The passage says plants need these nutrients, "which is why farmers and gardeners add them to soil as fertilizer."
  2. Answer: Water that carries soil, fertilizer, or other material off the land. The passage defines runoff in exactly those words.
  3. Answer: Long, warm, sunny summer days combined with the extra nutrients already in the lake. The passage says the algae use "that sunlight and those nutrients" to grow fast.
  4. Answer: Answers should cite that dead algae sink and bacteria break them down, and that the bacteria "use oxygen" faster than the lake can replace it, dropping dissolved oxygen below what fish need. Two such details support the chain from bloom to fish kill.
  5. Answer: It means the nutrients were helpful in small amounts but harmful in large amounts in the lake. The passage stresses they were useful on fields but caused trouble once too many reached the water.
  6. Answer: Because the nutrients themselves are not a poison; they are the same ones that help crops grow. The fish died from a loss of oxygen caused by the bloom, not from a toxic substance.
  7. Answer: Because the strips "slow the runoff and soak up nutrients before the water reaches the lake," so fewer nutrients enter, which should lead to smaller blooms over time. Students should cite the runoff-slowing detail.
  8. Answer: Answers will vary but should infer that nutrients already in the lake and land take years to decline, and the passage says the steps do not fix the lake "overnight," so improvement is gradual.

Differentiation

Support

Provide a simple cause-and-effect chain graphic (fertilizer to runoff to bloom to low oxygen to fish kill) for students to reference while answering, and let question 4 be answered orally before writing. Allow the literal questions (1 through 3) to be answered with short phrases.

Extension

Ask students to write a short paragraph explaining what a "resource" and a "pollutant" have in common in this passage, and to propose one more action, based only on the passage, that could keep nutrients out of Widgeon Lake.

ELL supports

Pre-teach "nutrient," "algae," "bloom," "dissolved oxygen," and "runoff" with pictures and simple definitions before reading. Provide a sentence frame for the inference questions: "The passage says ___, so I can infer ___."