limnology

1. limnology The study of inland waters (like lakes and rivers)

2. Essential question • How do physical factors of a lake determine the ecological characteristics?

3. How lakes are formed • Tectonic plates- formed by movement of Earth’s crust, slow uplift, earthquakes • Ex. Abert Lake, Summer Lake (eastern Oregon) • Volcanic activity- formed by craters of extinct volcanoes, depressions of lava flows, or lava damming • Ex. Crater Lake, Davis Lake (near Bend) • Landslides- formed by landslide dams (not common in Oregon) • Ex. Fish Lake, Triangle Lake (outside Eugene) • Glacial Activity- formed by ice scour of rock basins, or damming valleys by glacial deposits • Ex. Lakes in High Cascades (alpine lakes) • Shoreline Activity- formed behind migrating coastal sand dunes • Ex. Mercer Lake, Tenmile Lake (near coast) • River Activity- Basins excavated by waterfalls and lateral erosion • Ex. Oxbow Lakes of the Willamette River (outside Portlant) • Artificial Lakes- Reservoirs formed by damming rivers to fill a valley • Ex. Emigrant Lake, Lost Creek Reservoir

4. Two types of lakes (productivity-wise) • Oligotrophic- usually deeper, steep-sided lakes with very clear, often cold water, (ex. Crater Lake, Lake Tahoe) • Unproductive (very little life) • More dissolved oxygen • Cold-water fish species • No taste or odor problems • High diversity • Eutrophic lakes- usually shallower, warmer, more productive and less clear water (ex. Diamond Lake, Emigrant Lake) • Very productive (lots of life) • Less dissolved oxygen • Simple food chains • Taste and odor problems • Toxic algae present

5. Lake tahoeoligotrophic Klamath lake eutrophic

6. Physical characteristics of LakesLake size and shape Bathymetric map= shape and depth of lake • Size= surface area of lake (lake= 50 acres or larger) • Shape determines ecological characteristics • Shallow: Light penetrates to bottom => growth of plants; nutrients stirred up • Deep: Materials settle to bottom; temperature gradient more defined Crater Lake!

7. Physical characteristics of LakesDrainage basin aka “Watershed” • Indirectly influenced by activities in watershed • Lake with small watershed= typically have low productivity • Lake with large drainage basin relative to its size= high concentrations of plant nutrients • Most Oregon lakes with large drainage basins are reservoirs • Nature of soils, vegetation, and land-use activities influence amount of material washed into lake

8. Physical characteristics of LakesLight • Single most important source of energy • Basis of aquatic food chain • Depth of sunlight depends on transparency of water • Use Secchi disk to test • Factors affecting transparency • Suspended particulate material (silt, clay, plants, animal plankton) • Dissolved organic material (soil humus) • Turbidity in reservoirs (suspended inorganic matter like dirt)

9. Physical characteristics of LakesThermal stratification • Annual temp. cycle in Oregon lakes: warm in summer, cool in winter • No Oregon lake freezes solid to the bottom • Deeper lakes tend to be less productive, because they have more stratification (nutrient cycling limited) https://www.youtube.com/watch?v=X26ocQkhNH4

11. Physical characteristics of Lakeswater chemistry • Inorganic ions • 99% of dissolved ions in Oregon lakes (ex. Na, K, Ca, Mg, Cl) • Variations in climate and rock/soil type • Dissolved organic matter • Decaying plant material (containing Carbon) • Nutrients • Needed by plants to grow (ex. Phosphorus and Nitrogen) • pH • Acidity of water (no significant impact of acid rain in Oregon) • Dissolved oxygen • Essential to fish and other aquatic animals • Oxygen consumption directly related to how much organic matter in water

12. Random fact: Why are lakes blue?? • Explanation: Pure water absorbs red and green light, while blue light is reflected back from deep in the lake and scattered through the water • The cleaner the water, the bluer it will appear