Quiz & test questions Grade 9 Science

Sturgeon Lake Nutrients: A Grade 9 Eutrophication Unit Test

A grade 9 test on nutrients as pollutant and resource, mixing multiple-choice, short-answer, and pounds-formula computation around a fictional lake's nutrient loading.

Grade: Grade 9
Subject: Science
Material: Quiz & test questions
Time: 40 min
Prep: No prep
Materials: None

Standards

HS-LS2-7 NGSS

Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.

How this material aligns: Items 7 and 9 ask students to trace the nutrient-to-fish-kill pathway and propose a solution that reduces the impact of nutrient runoff on Sturgeon Lake's fish, the design-and-evaluate reasoning this standard requires.

All materials for HS-LS2-7 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Items 4, 5, and 6 carry milligrams per liter and million gallons per day through the pounds formula and a percent-reduction calculation while keeping units consistent to report nutrient loading in pounds per day.

All materials for HSN-Q.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will calculate nutrient loading and percent reduction from effluent concentration and flow.
Students will explain eutrophication and propose a solution to reduce nutrients reaching a lake.

Vocabulary

Eutrophication: Eutrophication is what happens when a lake or bay gets overfed with nutrients: algae grows out of control, and when it dies and rots, the water loses the oxygen that fish need.
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 loading, nitrogen, phosphorus

Teacher overview

This 30-point unit test checks whether students understand nutrients as both a resource and a pollutant and can calculate nutrient loading. It uses Sturgeon Lake, a fictional lake near the town of Fen Harbor, as the shared setting. The test mixes three multiple-choice items, three short-answer items, and three computation items that apply the pounds formula and percent reasoning.

Sturgeon Lake Nutrients: A Grade 9 Eutrophication Unit Test — Grade 9 Science

Name: ____________________________ Date: ______________

Assessment

Use these facts about Sturgeon Lake, a fictional lake, where noted. The pounds formula is loading (lbs/day) = concentration (mg/L) x flow (MGD) x 8.34.

(2 points) Which two nutrients most often drive algae blooms in fresh water?
- A) Chlorine and fluoride
- B) Nitrogen and phosphorus
- C) Sodium and calcium
- D) Oxygen and carbon
(2 points) The process in which excess nutrients feed algae that later die and are decomposed, lowering the water's dissolved oxygen, is called:
- A) Filtration
- B) Chlorination
- C) Eutrophication
- D) Desalination
(3 points) Explain why nitrogen and phosphorus are both a resource and a pollutant. Give one example of each role.
(4 points) A wastewater plant discharges effluent containing 8 mg/L of nitrogen at a flow of 2 MGD into Sturgeon Lake. Using the pounds formula, how many pounds of nitrogen enter the lake each day?
(4 points) The lake's dissolved oxygen falls from 8 mg/L above the discharge to 3 mg/L below it. Most fish need at least 5 mg/L. By how many mg/L is the downstream reading below that benchmark, and is it enough for those fish?
(4 points) A nutrient-reduction upgrade cuts the effluent nitrogen from 8 mg/L to 2 mg/L at the same 2 MGD flow. What is the percent reduction in nitrogen concentration?
(4 points) Propose one solution the town of Fen Harbor could use to reduce the nutrients reaching Sturgeon Lake, and explain how it would help the fish.
(3 points) Which statement is best supported by the data in this test?
- A) Adding nutrients always raises dissolved oxygen.
- B) Reducing the effluent nitrogen lowers the nutrient load reaching the lake.
- C) Fish are unaffected by dissolved oxygen levels.
- D) Phosphorus is the only possible cause of algae blooms.
(4 points) Put the following steps in the correct order to connect fertilizer runoff to a fish kill, and briefly explain the sequence: algae die, nutrients enter the lake, oxygen drops, algae grow quickly, bacteria decompose the dead algae.

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

Answer Key

Answer: B. Nitrogen and phosphorus are the main nutrients that drive algae blooms in fresh water; the other pairs are not the limiting nutrients for algae growth.
Answer: C. Eutrophication is the process in which extra nutrients feed algae, which die and are decomposed, using up dissolved oxygen.
Answer: Accept any answer that names both roles. As a resource, nitrogen and phosphorus are nutrients that plants and crops need to grow. As a pollutant, too much of them washes into lakes and feeds algae blooms that lower oxygen and harm fish.
Answer: 133 lb/day. 8 mg/L x 2 MGD x 8.34 = 16 x 8.34 = 133.44, which rounds to 133 pounds of nitrogen per day.
Answer: 2 mg/L short, and no. The downstream reading of 3 mg/L is 5 - 3 = 2 mg/L below the 5 mg/L benchmark, so it is not enough for fish that need at least 5 mg/L.
Answer: 75 %. (8 - 2) / 8 x 100 = 6 / 8 x 100 = 75 percent. The new loading also falls to 2 x 2 x 8.34 = 33 pounds per day.
Answer: Accept any workable solution with reasoning, such as upgrading the plant to remove more nitrogen, adding vegetated buffer strips along farm fields, or reducing fertilizer use. A valid answer explains that less nutrient reaching the lake means smaller algae blooms, so decomposition uses less oxygen and more oxygen stays available for fish.
Answer: B. The test's numbers show that lowering effluent nitrogen from 8 to 2 mg/L cuts the daily nitrogen load, so reducing effluent nitrogen lowers the load reaching the lake.
Answer: Correct order: nutrients enter the lake, algae grow quickly, algae die, bacteria decompose the dead algae, oxygen drops. The decomposition of the large amount of dead algae consumes dissolved oxygen, and the resulting low oxygen can cause a fish kill.

Differentiation

Support

Provide a word bank for items 2 and 9 (eutrophication, decompose, dissolved oxygen) and give the pounds formula already set up for item 4, so students complete only the arithmetic. Allow a calculator on all computation items.

Extension

Ask students to calculate how many total pounds of nitrogen per year the upgrade in item 6 keeps out of Sturgeon Lake, assuming the plant runs every day, and to argue whether that reduction is worth a stated upgrade cost.

ELL supports

Provide a labeled diagram of the eutrophication sequence for reference, and allow short-answer items 3 and 7 to be answered with a labeled sketch plus a sentence frame such as "Nitrogen is a resource because ___ and a pollutant because ___."

Extensions

Have students find a real lake or bay with a published nutrient or algae-bloom problem, identify whether its main nutrient source is a wastewater plant or farm runoff, and summarize in a paragraph one solution the responsible agency has proposed.