Freshwater Ecosystems Notes

Limnology The study of fresh bodies of water Lentic: standing water (lakes and ponds) Lotic: flowing water (streams and rivers)

Lentic vs Lotic How might they be different?

Formation of lakes and ponds: Glacial erosion and deposition - movement of glaciers eroded land (Great Lakes) Deposition of silt, driftwood, and other debris in slow-flowing streams- cuts off a meander and forms a crescent shape or oxbow lake.

Formation of lakes cont. Geologic activity- tectonic movement; valleys and craters fill with water Manmade: dams, log jams, strip mining (all lakes in TX except one, which one???)

Physical Characteristics High specific heat of water make aquatic environment temperatures more stable than terrestrial Epilimnion: surface water, small temperature change Metalimnion: middle mass of water with a rapid temperature decline (1°C/ meter) Thermocline: temperature gradient found in metalimnion Hypolimnion: deep cold layer cutoff from air; most dense

Seasonal Fluctuations Summer- large thermocline. Why? Winter- Surface water loses heat to atmosphere therefore thermocline decreases Overturn: surface water temp. decreases and causes water to mix and stir up nutrients and dissolved oxygen because of density changes (Fall and Spring)

Dissolved Oxygen (D.O.) Enters the water by absorption from the atmosphere and by photosynthesis The amount of oxygen and other gases water can hold depends upon pressure and temperature As temperature increases- solubility of dissolved oxygen decreases As pressure increase- solubility of DO increases

Water loses oxygen through increased temperature, increased respiration of aquatic life, and aerobic decomposition During the summer, oxygen may become stratified in lakes and ponds The quantity of oxygen decreases with depth because of decomposition in the bottom sediments

During Spring and Fall overturn- water circulation (churning) replenishes oxygen in the bottom In winter- DO decreases slightly with depth; DO is more stable because cold water can hold more DO than warm water

Sunlight The depth to which light penetrates is limited by turbidity of the water and the absorption of light rays Trophogenic zone- layer through which light can penetrate and where photosynthesis occurs (photic zone) Tropholytic zone- layer through which light cannot pass through and where decomposition occurs Compensation level-where photosynthesis ends and decomposition begins

Trophogenic Zone: separated into two zones 1. Littoral zone- (horizontal) shallow water zone where light penetrates the bottom emergents- plants whose roots are underwater and stems and leaves are above water. Live in the littoral zone. submergents-completely below water

2. Limnetic Zone -Open water zone where photosynthesis occurs Plankton- suspended/floating organism Phytoplankton- photosynthetic plankton; algae Zooplankton- animal-like plankton; rotifer Nekton-free swimming organisms

Primary Production Is carried out in the limnetic zone by phytoplankton (ALGAE) and in the littoral zone by macrophytes- large aquatic plants (emergents and submergents) 6CO2 + 6H2O + light  C6H12O6 + 6O2 (photosynthetic equation)

Drawing: Lentic Ecosystem in mid-summer 1)Title your paper Lentic Ecosystem- mid-summer 2) Draw a cross section of a lake on your paper (this should take up a considerable amount of room on your paper). 3) Use your Freshwater Ecosystem Notes and laptop to label following on the cross section of a lake: Littoral Zone, Limnetic Zone, Trophogenic Zone, Tropholytic Zone, Compensation Depth, Epilimnion, Metalimnion, Hypolimnion, Thermocline, Benthic Zone, Profundal Zone 4) Use your freshwater Ecosystem Notes and laptop and draw in examples in their proper places of the following the cross section of a lake: sun, sun rays, emergents, submergents, algae, and fish. Label where decomposition and photosynthesis are occurring.