1. The Great Salt Lake: Case Study
Learning Target: I can analyze a case study and begin to explain how changes can affect an entire ecosystem.

2. Warm Up Why is the Great Salt Lake salty?
What factors affect the salinity of the Great Salt Lake?
How would and increase in salinity affect the biodiversity of organisms living in the aquatic portion of the Great Salt Lake?

3. Great Salt Lake - Case Study Details
What is a causeway? Let’s look at the next slide to find out.
Setting: A large body of water
Time: 1952
Event: A causeway is built across the body of water separating the north end from the south end. No water is exchanged between the two sides.
The general question: What effect does this have on the ecosystem?

4. The Specifics
In 1902, a railroad built a train trestle that went directly across the body of water. In the 1950’s, a causeway replaced the trestle allowing for safer and faster travel of the trains.
The causeway is a solid, raised roadway made of 50 million cubic yards of rock, sand and gravel. However, unlike the trestle, the causeway does not allow circulation of water between the two sides. This basically split the lake into two halves, the North arm and the South arm.
Use the information from this slide to answer questions 1 & 2.

5. Turn & Talk: What do you see in this picture?
South Arm of Lake
North Arm of Lake
White stuff

6. The causeway separating the North and South arms
What do you notice about the colors of water on both sides of the causeway?
Question #3
South Arm of Lake
North Arm of Lake

7. This body of water is a dynamic ecosystem and is affected by the amount of rainfall received
How does the size compare in 1984 and 2004?
Question #4
1984
2004
What inference could you make about the amount of rainfall received in 2004?
Question #5

8. Brainstorming
What differences do you notice, if any, between the north and the south arms?
Why could building a causeway cause the water to be two different colors?
What might be some causes of the change seen?
As a class, create a list of possibilities. Write down your classmates’ ideas. Question #6

9. New Information Both arms of the lake contain salt.
Only one arm of this body of water receives freshwater on a continuous basis.
2 rivers flow into that arm.
Does this help you explain why the body of water is two different colors?
Answer questions 7 and 8
Turn & Talk: What is freshwater?

10. These are red onion cells
These are red onion cells. The purple stuff is the cytoplasm inside the cell.

11. After adding salt, look what happens
After adding salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell?

12. What do you think is causing that to happen?
After adding EVEN MORE salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell?
In osmosis: water follows salt!
- Wherever there is more salt, water will go because it loves salt!
What do you think is causing that to happen?

13. #9: What inference can you make about which plant received salt water
#9: What inference can you make about which plant received salt water? Why?

14. The causeway separating the North and South arms
South Arm of Lake
North Arm of Lake

15. A Lake Divided: Salinity Before and After the Causeway
300
270
240
210
180
150
120 90 60 30 ?
SALINITY, IN PPT

16. Water Level History of the South Arm of the Great Salt Lake

17. Historic low GSL level
Historic high GSL level

18. Lake Level and Water Density Inversely Correlate
Which arm of the Great Salt Lake is saltier? Evidence?
How does lake level influence density?

19. Digging in to the GSL Salinity Data
Salt concentration can be measured in:
Percent Salinity
Parts Per Thousand (= % x 10)
Salt concentration can be inferred as:
Density of Water
Density of water = 1 gram / cm3 = 1 g / mL
If density is greater than 1 g/mL, there is something dissolved in the water (i.e. salt)

20. Digging in to the GSL Salinity Data
The Great Salt Lake was once a vast body of salt water
Over time, the GSL evaporated to its present size, leaving behind salt deposits
The size of the GSL continues to change, while the amount of salt stays the same
Salinity and density inversely co rrelate with water level
When water level ↑, salinity (% or ppt) and density ↓
When water level ↓, salinity (% or ppt) and density ↑

21. North Arm
(after the causeway)
Halobacteria
Answer questions #10-11 from looking at the Great Salt Lake Ecosystem Picture.
Brine fly
Northern Harrier
Diatoms
South Arm
(before the causeway)
Brine shrimp
Eared Grebe
Avocet
Cyanobacteria

22. The Great Salt Lake Ecosystem
Answer question #12 (Hint: what are the arrows pointing to?)

23. The causeway separating the North and South arms
South Arm of Lake
North Arm of Lake
Answer question #13

24. Want More? (Of course you do!)
Check out the Science Friday podcast from April 26, 2013: The Great Lake Is No ‘Dead Sea’

25. Work Time
Hypothesize what would happen to the Great Salt Lake ecosystem if the railroad causeway were removed. Record your thoughts – at least 4 sentences – on the back of the case study worksheet.