Worksheet

The Rock You Cannot See: Dissolved Minerals in the Bramble River

Grade 7 earth science: use calm-day and storm-day water tests from a river cleanup to model how dissolved and solid rock material cycles.

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12 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

Students analyze water test data to explain how rock material moves dissolved and as solid grains.
Students model how dissolved minerals form new rock and name the energy sources that drive the cycle.

How to use

Trace the river from Site 1 to Site 4 on a quick sketch map before students start; compare Tables 1 and 2 together in Section 2.

Curriculum

NGSS standard covered

MS-ESS2-1

Model the cycling of Earth's materials and the energy that drives the rock cycle.

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Name Date

The Rock You Cannot See: Dissolved Minerals in the Bramble River

Use watershed water tests to model how rock material cycles and what energy drives it.

Testing the water on a calm day

Read the passage and study Table 1. Then answer the questions.

Cleanup Day on the Bramble River

1Each June, the Watershed Stewards club at Hollow Oak Middle School joins a cleanup of the Bramble River, which runs from a range of granite hills, through a limestone valley, and into Lake Merrin. While other volunteers pull trash from the banks, seventh grader Ilse Montoya and her club test the water at four sites with Mr. Anders Thorvaldsen, a scientist with the watershed council.

2At each site, the club fills a bottle with river water. They pour part of it through a filter and dry and weigh the mud and sand caught on the filter. They test the filtered water with a meter that shows how much rock material is dissolved in it, which is invisible because it has broken apart into particles far too small to see. Rain picks up a little carbon dioxide from the air and soil, which makes it slightly acidic. Over time, this water slowly dissolves minerals from rock. Granite's minerals dissolve very slowly, but calcite, the main mineral in limestone, dissolves much faster.

3Site 1 is a stream in the granite hills. Site 2 is in the limestone valley, just above Blue Spring. At Blue Spring, water that has soaked into the ground flows out of a cave mouth after spending months moving through cracks and caves in the limestone. Site 3 is just below the spring. Two small streams from the granite hills join the river between Site 3 and Site 4, which is at the river mouth on Lake Merrin. Table 1 shows a calm day with no rain for two weeks. Table 2 shows the morning after a heavy storm.

4Two other things surprised Ilse. At the cave mouth, a cream-colored crust of rock coats the stones and twigs. A twig the club tied there last June now has a crust 2 mm thick. As the spring water meets the air, it loses some carbon dioxide, and some of the dissolved calcite comes back out as solid rock called tufa. In Lake Merrin, the mud near the shore is full of tiny snail and clam shells, which these animals build from minerals dissolved in the water. Mr. Thorvaldsen explained that the valley's limestone itself formed from shells and lime mud on an ancient sea floor, and that forces powered by Earth's hot interior later raised it far above the sea.

Table 1. Calm Day (no rain for 2 weeks)
Site	Rock under the river	Dissolved minerals, mg/L	Mud and sand, mg/L
1: Hill stream	Granite	30	4
2: Above Blue Spring	Limestone	180	8
3: Below Blue Spring	Limestone	260	6
4: River mouth	Limestone and mud	240	10

On the calm day at Site 4, the water held how many times as much dissolved rock material as mud and sand? times as much

From Site 1 to Site 2, dissolved minerals rose from 30 to 180 mg/L. Which explanation fits the passage best?

A. The water at Site 2 was warmer, and warm water makes new minerals out of heat.
B. Rainwater dissolves the calcite in limestone much faster than granite’s minerals.
C. Mud from Site 1 broke apart into dissolved minerals as it rolled downstream.
D. Granite dissolves faster than limestone, so most of it was gone before Site 2.

Which explanation of the rise from Site 2 to Site 3 fits paragraph 3 best?

A. The spring water had dissolved calcite for months on its way through the limestone.
B. The cave at Blue Spring is warmer, so its water melts the limestone it touches.
C. Trash pulled from the banks above the spring left extra minerals in the water.
D. Mud and sand from the cave settled out, which left more dissolved minerals behind.

The morning after a storm

Use Tables 1 and 2 and the passage.

Table 2. The Morning After a Heavy Storm
Site	Dissolved minerals, mg/L	Mud and sand, mg/L
1: Hill stream	20	120
2: Above Blue Spring	110	300
4: River mouth	150	650

The club could not reach Site 3 safely after the storm, so it was not tested.

At Site 4, how many more milligrams of mud and sand did each liter of water carry after the storm than on the calm day? mg/L

Which statement best compares how the river moved rock material at Site 4 on the two days?

A. On the calm day most moved as mud and sand, but after the storm most moved dissolved.
B. On both days, most of the rock material moved dissolved in the water.
C. On the calm day most moved dissolved, but after the storm most moved as mud and sand.
D. On both days, most of the rock material moved as mud and sand.

After the storm, the dissolved minerals at every tested site were lower than on the calm day. Which explanation fits the passage best?

A. Storm water spent months moving through the caves, so it dissolved less.
B. The storm’s fast-moving water turned the dissolved minerals back into mud.
C. Mud in the storm water soaked up the minerals and carried them as grains.
D. Most storm water was fresh rain that ran off quickly and dissolved little rock.

On the calm day, about 2,000 L of water flowed past Site 4 each second.

How many grams of dissolved minerals flowed past Site 4 each second? (1 g = 1,000 mg) g

Modeling the cycle

Use paragraph 4 and the whole sheet.

Sort each example by how the rock material is moving.

Calcite leaving the limestone in water flowing through the caveSand grains rolling along the bed of the hill stream in the stormMud that turned the river brown the morning after the stormMinerals a clam takes from the lake water to build its shellMaterial in the spring water that will form the tufa crustPebbles carried past Site 2 by fast storm water

Moving dissolved in water	Moving as solid bits

The tufa crust on the twig grew 2 mm in one year. Where did the matter in the crust come from?

A. From limestone underground, dissolved and then left as solid calcite
B. From carbon dioxide in the air, which turned into solid rock on the twig
C. From mud and sand that the storm water stuck onto the twig
D. From the twig itself, which slowly hardened into rock in the damp air

10.

Suppose the shells piling up in Lake Merrin are buried under more and more mud for millions of years. Which path through the rock cycle could they follow, based on the passage?

A. Melted by the Sun into magma → cooled into granite → dissolved in the lake
B. Pressed and cemented into limestone → raised by inner forces → dissolved by rain again
C. Turned into tufa by sunlight → melted into lava → cooled as basalt on the lake shore
D. Turned straight into granite → washed downstream → built into new clam shells

11.

Which two energy sources drive the cycle of rock material in the Bramble River watershed?

A. The Sun, which drives the water cycle, and Earth’s hot interior, which raised the limestone
B. Sunlight, which melts rock at the surface, and the river, which makes its own energy as it flows
C. The Sun, which drives the water cycle, and the Moon’s pull, which carries minerals to the lake
D. Earth’s hot interior, which heats the spring water, and the lake, which stores energy in shells

12.

A volunteer at the river mouth says, “On calm days the water here is so clear that the river is not carrying any rock away from the hills.” Do you agree? Make a claim, use evidence from Table 1 and the passage, and explain your reasoning with a model of how this rock material cycles and the energy that drives it.