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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)
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.
surfacecools
surfacewarms
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
littoralsubmerged
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
littoralemergent
macrophyteslimnetic
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 ¯ophytes
grazinginsects &
crustaceans
grazingfishes
bacteria& fungi
fine particulate organic matter (FPOM)
collectinginsects, crust.,nematodes, &
annelids
leaf litter
predatoryinsects &
crustaceans
dissolved organiccompounds (DOC)
runoff orgroundwater entry
coarse particulate organic matter (CPOM)
bacteria& fungi
conditioning(microbial colonization)
shreddinginsects &
crustaceans
“predatory”fishes
Limnetic & Euphotic Food Web
grazing zooplankton
predatory zooplankton
bacteria
phytoplanktonphytobacteria
dissolved organiccompounds (DOC)
“predatory” fishes
phyto-plankti-vorousfishes
microzooplankton
Lake Grazing Zooplankton Cladocerans
Copepods
Cladocerans(Daphnia)
Copepods
Lake Predatory ZooplanktonCladocerans
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 1960.
Only <100 cichlid species still extant.