Water is a fascinating substance – and not just because we need it to live! Water is colorless and has no taste or smell, which may make it seem uninteresting to study. However, it has many unique physical properties. For example, it is the only natural substance that is found in all three states — liquid, solid (ice) and gas (steam) — at temperatures naturally found on earth. Also, the density of water is related to its temperature, which can drive aquatic life and influence climate and weather. This lesson explores how water temperature and density are related and what effect that can have on the environment.
- National Science Education Standards, 5th-8th grade
- Michigan Grade Level Content Expectations, 5th-7th grade
- MS-ESS2.4 Earth’s Systems. Develop a model to describe the cycling of water through Earth’s systems driven by energy from the sun and the force of gravity.
- 3-ESS2.1 Earth’s Systems. Represent data in tables and graphical displays to describe typical weather conditions expected during a particular season.
For alignment, see: NGSS Summary
- List physical properties of water.
- Explain how water temperature and density are related.
- Communicate and defend conclusions (from demonstrations) using evidence.
Many lakes within the Great Lakes region undergo seasonal cycles that are affected by the physical properties of water. During the summer, sun warms the surface of the lake. The lake begins to disperse into layers with warmer, less dense water near the surface and colder, denser water near the bottom. Sandwiched between the warmer layer above (epilimnion) and colder layer below (hypolimnion) is a layer of water called the metalimnion. The metlimnion is a region in which the temperature rapidly changes. As water cools in the fall, its density increases and it sinks. This separation of the lake into layers is called thermal stratification and is a factor in how much life a lake can support (called productivity).
- Epilimnion: Warm water at the surface
- Hypolimnion: Cold water at depth
- Metalimnion: Layer of water between the epilimnion and hypolimnion. Water temperature changes rapidly within the metalimnion.
More Detail on Seasonal Stratification
A typical year in the Great Lakes region can lead to the following type of stratification and mixing:
Summer: The sun warms the lake from the surface down. Warm water is less dense (lighter), creating a layer of warm water floating over the more dense (heavier) cold water. During the summer, the differences in water temperatures prevent complete mixing. Surface water becomes too warm and too buoyant to mix with denser, deeper water. Water only mixes in the epilimnion. Warm water, sunlight and nutrients in the epilimnion are ideal for algae growth.
Fall: The fall air drops the surface water temperature of the lakes — making the upper layers and the lower layers similar in temperature and density. Wind contributes to the seasonal change and helps mix up the layers. Throughout the fall, winds mix the lake water to greater depths. When surface and bottom water approach the same temperature and density, wind can mix or turnover the entire lake. This mixing process replenishes oxygen and nutrients throughout the lake.
Winter: The Great Lakes are rarely completely ice covered in the winter and may continue to mix continuously during the season, which is different from most other lakes in the region that remain stratified in the winter.
When ice does form — as surface temperature approaches 0 degrees Centigrade — it floats on top of the lake (because ice is almost 10 times less dense than liquid water). Most of the water column is 4 degrees C. However, there is a layer of colder, lighter water just below the ice. Stratification is weak because the temperature difference between the layers is small. Ice prevents wind from mixing the layers.
Spring: As weather warms, surface temperatures rise and water decreases in density. When the temperature and density of surface water equals the bottom water, very little wind energy is needed to mix the lake completely.
- Discovering Water Density
Summary: Students complete data sheets and discover the densities of hot and cold water through an in-class experiment.
Time: One 50-minute class period
- Investigating Seasonal Cycles
Summary: Students investigate how the unique properties of water contribute to seasonal cycles.
Time: One 50-minute period
Investigating Seasonal Cycles A Standards and Assessment
- Interpreting Lake Erie Temperatures
Summary: Students use data and graphs to examine the changes in Lake Erie water temperatures.
Time: Up to two 50-minute class periods
Investigating Seasonal Cycles B Standards and Assessments
Ford, B.A. and P.S. Smith. 1994. Over and under: Why water’s weird. Project Earth science: Physical oceanography. National science teachers’ association press. 37-39
The Life of the Lakes, A Guide to the Great Lakes Fishery, Schroeder, B., Michigan Sea Grant, 2012, MICHU-12-501
Water on the Web – Teaching about temperature variation
Great Lakes Climate and Water Movement. Earth Systems – Education Activities for Great Lakes Schools (ES-EAGLS). 1996. Series EP-085. Ohio Sea Grant. Ohio State University, Columbus, OH 43212. Authors: Fortner, RW, Miller, H, Sheaffer, AL
Louisiana Marine Education Resources – Gateways to Aquatic Science. On Again, Off Again – The Dead Zone. Louisiana Sea Grant. Louisiana State University, Baton Rouge, LA 70803. Authors: Lindstedt, D. Website, accessed December 1, 2009.
Water on the Web – Monitoring Minnesota Lakes on the Internet and Training Water Science Technicians for the Future – A National Online Curriculum using Advanced Technologies and Real-time Data. University of Minnesota-Duluth, Duluth, MN 55812. Authors: Munson, BH, Axler, R, Hagley C, Host G, Merrick G, Richards C. Website, accessed December 1, 2009.
How Do the Great Lakes Change Through the Seasons? Fortner, R.W., A.L. Sheaffer, and H. Miller. 1996.
Earth Systems: Education Activities for Great Lakes Schools (ES-EAGLS). Series: ES-EAGLS – Great Lakes climate and water movement (EP-083). Ohio Sea Grant Publications. Ohio State University. 71-77. Modified from OEAGLS EP – 28 ‘Lake Layers: Stratification’ by Chris Brothers, David A. Culver and Rosanne W. Fortner.
Great Lakes Coastal Forecasting System. NOAA-Great Lakes Environmental Research Laboratory (GLERL) Ann Arbor, MI 48108. Authors: Schwab, DJ, Beletsky, D, Bedford, KW, Lang, GA.
Great Lakes Water Data Sets for Teachers. Eastern Michigan University, Ypsilanti, MI 48197. Project supported by the Office of Education and Outreach at NOAA’s Great Lakes Environmental Research Laboratory, Ann Arbor, 48108. Authors: Rutherford, S, Coffman, M, Marshall, A, Sturtevant, R, Klang, G, Schwab, D, LaPorte, E.