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).

Littoral Zone Food Web periphyton & macrophytes grazing insects & crustaceans grazing fishes bacteria & fungi fine particulate organic matter (FPOM) collecting insects, crust., nematodes, & annelids leaf litter predatory insects & crustaceans dissolved organic compounds (DOC) runoff or groundwater entry coarse particulate organic matter (CPOM) bacteria & fungi conditioning (microbial colonization) shredding insects & crustaceans “predatory” fishes

Limnetic & Euphotic Food Web grazing zooplankton predatory zooplankton bacteria phytoplankton phytobacteria dissolved organic compounds (DOC) “predatory” fishes phyto- plankti- vorous fishes microzooplankton

Lake Grazing Zooplankton  Cladocerans  Copepods Cladocerans (Daphnia) Copepods

Lake Predatory Zooplankton  Cladocerans  Insect Larvae (midge larvae) Cladocerans (Leptodora & Polyphemus) Ghost Midge Larva (Chaoborous)

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  Only <100 cichlid species still extant.