Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 dO2 • Hypolimnion = cool lower layer in a lake. Little sunlight; little affected by waves; higher nnutrients; high or low/no dO2 • Thermocline (Metalimnion) Epilimnion Hypolimnion 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 warms surface cools 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 H2S 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 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 limnetic phytoplankton littoral emergent macrophytes littoral submerged macrophytes 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). Littoral Zone Food Web runoff or groundwater entry leaf litter periphyton & macrophytes conditioning (microbial colonization) bacteria coarse particulate & fungi organic matter (CPOM) grazing grazing fishes insects & crustaceans shredding dissolved organic compounds (DOC) fine particulate organic matter (FPOM) insects & crustaceans collecting predatory “predatory” fishes insects & crustaceans insects, crust., nematodes, & annelids bacteria & fungi Limnetic & Euphotic Food Web phytoplankton dissolved organic compounds (DOC) phytobacteria microzooplankton phytoplanktivorous grazing zooplankton fishes bacteria predatory zooplankton “predatory” fishes Lake Grazing Zooplankton • Cladocerans • Copepods Cladocerans (Daphnia) Copepods Lake Predatory Zooplankton • Cladocerans • Insect Larvae (midge larvae) Ghost Midge Larva (Chaoborous) Cladocerans (Leptodora & Polyphemus) 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). “Lake Fishes” 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 Cultural Eutrophication 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. Aral “Sea” 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 1960. • Only <100 cichlid species still extant.