Follow the water in and out of a lake with no outlet.
Answer Key
The lake's water budget
Read the passage and study the budget table. Then answer the questions.
The Ring on the Rocks
1Sagebrush Lake lies in a desert basin in Nevada, with snowy mountains rising to its west. The lake and its numbers are made up, but they are based on real desert lakes. Each July, a summer kayak camp paddles along its shore. On the first morning, camper Inés Galarza noticed a white crust on the rocks about half a meter above the water. Ranger Dmitri Volkov explained that it is a ring of salt, left behind where the water once stood higher.
2The Silver River carries water from the mountains down into the lake, but no river flows out. River water holds tiny amounts of dissolved salts that it picks up from soil and rock along the way. The water of Sagebrush Lake is many times saltier than the river water. The lake is about 8 m deep in the middle.
3Rangers keep a water budget for the lake, much like a budget for money. They measure the water flowing in from the river and the rain and snow that fall on the lake itself. They estimate how much water evaporates from the lake's surface using a pan of water on the shore and weather data. Very little lake water soaks into the ground, so the budget leaves it out. For this lake, a change of 2 million cubic meters (m³) of water raises or lowers the lake level by about 1 cm.
4Most of the river's water starts as snow that piles up in the mountains from November through March. Ranger Volkov told the campers that last year was drier than usual in the mountains.
Sagebrush Lake Water Budget, Last Year (million m³)
Season
River in
Rain and snow on lake
Evaporation
Change in lake water
Winter (Dec–Feb)
20
15
10
+25
Spring (Mar–May)
90
10
40
+60
Summer (Jun–Aug)
30
2
110
−78
Fall (Sep–Nov)
15
8
50
−27
1.
Last year, the river and the rain and snow added 190 million m³ of water to the lake in all, and 210 million m³ evaporated.
2.
Use paragraph 3 and the table.
During the summer, the lake level dropped by about 39 cm. By the end of the whole year, the lake was about 10 cm lower than at the start.
3.
Why does the river bring the most water into the lake in spring?
○A.Cool spring air sinks into the river channel and turns straight into liquid water.
○B.Spring rain falls mostly on the lake, which pushes extra water up the river.
○C.Gravity is stronger in spring, so it pulls more water vapor out of the mountain air.
●D.Spring sunlight melts the mountain snow, and gravity pulls the meltwater downhill.
4.
Which explanation best fits the evaporation column of the table?
●A.In summer, more energy from sunlight warms the lake, so more water turns to vapor.
○B.The lake is deepest in summer, so more of its water can rise into the air.
○C.Summer winds blow drops of lake water onto the shore, where they soak in.
○D.The river brings hot water in summer, and that water boils off the lake.
5.
The river water is nearly fresh, but the lake water is very salty. Which explanation fits the passage and the budget best?
○A.Salty water flows up the river from the lake in fall and settles in the mountains.
●B.Water leaves the lake mainly by evaporating, and the salts stay behind in the lake.
○C.Plants and fish in the lake make new salt as they grow each summer.
○D.Salt evaporates along with the water and falls back on the lake as salty rain.
Model the lake's water cycle
Use the passage, the table and your answers above.
6.
Complete this model of one path some of the lake's water can take. Use each word from the word bank once or not at all.
Sunlight warms the lake, and water evaporates into the air as vapor. Winds carry the moist air over the mountains, where it cools and the vapor condenses into tiny cloud droplets. Snow falls on the peaks as precipitation. In spring the snow melts, and gravity pulls the water down the Silver River and back into the lake.
7.
Suppose next winter brings twice as much snow to the mountains, and the summer is as sunny as last year. What is the most likely change in next year's budget?
○A.Summer evaporation drops close to zero, because the extra snow keeps the lake cold.
○B.Spring river flow stays near 90 million m³, because the river bed is already full.
●C.Spring river flow rises, so the lake is likely to end the year higher than it started.
○D.The lake falls faster in spring, because the extra snow covers the lake's surface.
8.
A camper says, "The water that evaporates from Sagebrush Lake is gone for good." Which response fits the model best?
●A.The vapor moves with the air until it condenses and falls, perhaps on the mountains.
○B.The vapor turns into salt on the rocks, which forms the white ring around the lake.
○C.The vapor floats out into space, since water vapor is lighter than the rest of the air.
○D.The vapor sinks straight into the desert soil and becomes groundwater right away.
9.
Sort each event by how the water moves.
Vapor rises from the lake on a hot afternoon.Snow falls on the mountain peaks in January.Meltwater rushes down the Silver River in April.A fall rain shower falls on the lake.Water in the ranger's pan slowly dries up.Melted snow trickles down a slope into the river.
Into the atmosphere
Out of the atmosphere
Across or through the land
Vapor rises from the lake on a hot afternoon.
Water in the ranger's pan slowly dries up.
Snow falls on the mountain peaks in January.
A fall rain shower falls on the lake.
Meltwater rushes down the Silver River in April.
Melted snow trickles down a slope into the river.
10.
Inés says, "The lake drops every summer, so it will dry up in a few years." Do you agree? Write a claim, give evidence from the budget table and the passage, and explain your reasoning. Name the roles of sunlight and gravity in your answer.
Claim: I disagree that the lake will dry up in a few years. Evidence: The lake lost 78 million m³ in summer and 27 million m³ in fall, but it gained 25 million m³ in winter and 60 million m³ in spring. Over the whole year it lost only 20 million m³, which is about 10 cm, and that was in a drier year than usual. The lake is about 8 m deep, so even at 10 cm a year it would take many decades to empty. Reasoning: Sunlight gives the energy that evaporates water from the lake, mostly in summer. But sunlight also melts the mountain snow in spring, and gravity pulls the meltwater down the Silver River into the lake, refilling much of what was lost. A wetter winter with more snow could make the lake rise instead.