Lakes (& Ponds)

1. 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

2. 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.

3. 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

4. surface warms surface cools 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.

5. 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.

6. 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

7. 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 littoral submerged macrophytes limnetic phytoplankton

8. 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).

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

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

11. Lake Grazing Zooplankton • Cladocerans • Copepods Cladocerans (Daphnia) Copepods

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

13. 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).

14. “Lake Fishes”

15. 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

16. 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

17. Broad Lake Categories eutrophic oligotrophic

18. Cultural Eutrophication

19. 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.

20. North American Great Lakes • “Gouged” out by glaciers. • Experienced many introduced species. • S. Great lakes experienced much pollution.

21. 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.

22. Aral “Sea”

23. 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.

24. 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.