Presentation on theme: "Lakes (& Ponds) Lake (& Pond) – body of water in one basin with realtively little flow. Limnology = study of lake ecology. Lentic system = more “still”"— Presentation transcript:
Lakes (& Ponds) Lake (& Pond) – body of water in one basin with realtively little flow. Limnology = study of lake ecology. Lentic system = more “still” (fresh)water system; Lacustrine = of/around lake/pond; limno = lake
Lake Zones Euphotic zone = where light can support photosynthesis. Littoral zone = where attached macrophytes and periphyton can grow (euphotic periphery). Limnetic zone=“Open water” no macrophytes.
Lake Strata (Layers) Epilimnion = warm upper layer in a lake. Much sunlight; affected by wave energy; lower nutrients; high dO 2 Hypolimnion = cool lower layer in a lake. Little sunlight; little affected by waves; higher nnutrients; high or low/no dO 2 Thermocline (Metalimnion) Hypolimnion Epilimnion
Lake Turnover Stratification = thermal layering with a distinct epi- & hypolimnion Temperate lakes may “mix” in the fall & spring (turnover) = destratification. Wind can keep deep lakes from stratifying. surface cools surface warms
Lake Turnover Turnover ensures hypolimnion oxygenation and increases nutrients in epilimnion. Permanently stratified lakes (e.g., deep tropical) may have anoxic hypolimnions; also can build up H 2 S in hypolimnion. Turnover in “permanently” stratified lakes can lead to “fish kills” or eutrophication.
Fetch Fetch = the distance over which winds blow over a lake. Greater fetch = more/larger waves and more mixing; less likely to be stratified wind direction
littoral submerged macrophytes Lake Primary Production Emergent Macrophytes = Littoral; mostly flowering plants (Submerged) Macrophytes = Littoral; mostly flowering plants and green algae Periphyton = Littoral; mostly green algae, diatoms, and cyanobacteria Phytoplankton = Limnetic and Littoral; mostly green algae, diatoms, and cyanobacteria littoral emergent macrophytes limnetic phytoplankton
Allochthonous Inputs In most lakes some nutrients come from surrounding terrestrial environments and tributary streams. Given low flows most particulate organic matter (POM) sinks in lakes/ponds. Many lakes with substantial allochthonous inputs have macroinvertebrate shredders and collectors, like in streams (but usually different species).
Insect Larvae and Decapods Insect Larvae = Many insect larvae are aquatic, esp. common in littoral. dragonflies, damselflies, mayflies, black flies, mosquitoes, horse flies. Crustaceans = crayfishes (in North America).
North Amercan Fishes 979 native freshwater species 82 exotic species 50 taxonomic families Arbitrarily divided into coolwater and warmwater ichthyofauna. Coolwater – water never warmer than 22°C Warmwater – water gets above 22°C
Broad Lake Categories Oligotrophic Lakes = deep, cool, nutrient poor lakes. Usually stratified. Mountain lakes Eutrophic Lakes = shallow, warm, nutrient rich lakes. Often not stratified. Shallow Ponds Oligotrophic-Eutrophic continuum. Cultural Eutrophicaltion – anthropogenic nutrient (P & N) input; can cause anoxia
Broad Lake Categories eutrophic oligotrophic
Macrophyte vs. Algal Systems “Macrophyte systems” – Macrophytes and cladocerans more common. Cladocerans graze algae and macrophytes retain nutrients in tissues. Lower free nutrients in water. Water clear. “Algal systems” – Algae more common. Nutrients rapidly cycled through algae. Higher free nutrients in water. Water turbid. Nutrient increase, removal of macrophytes, or increase in planktiovorous fish can shift from a macrophyte to an algal system.
North American Great Lakes “Gouged” out by glaciers. Experienced many introduced species. S. Great lakes experienced much pollution.
Aral “Sea” Freshwater Lake. Its water input was diverted by the Soviets to irrigate parts of Kazakstan. As an arid environment water levels fell and salinity increased tremendously.
Differences in Tropical Lakes Bacterial and fungal decomposition of allochthonous material is more rapid. Fewer aquatic insects. Fishes ( and in some places decapod crustaceans) serve as the major shredders, collectors, and grazers. If deep, may be permanently stratified.
Lake Victoria Many native cichlid (fish) species (300+). First some cultural eutrophicaltion then intro. of Nile perch (Lates nilotica) around Only <100 cichlid species still extant.