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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)
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
submerged
macrophytes
littoral
emergent
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”
fishes
predatory
insects &
crustaceans
insects, crust.,
nematodes, &
annelids
bacteria
& fungi
Limnetic & Euphotic Food Web
phytoplankton
phytobacteria
microzooplankton
phytoplanktivorous grazing zooplankton
fishes
predatory zooplankton
“predatory” fishes
dissolved organic
compounds (DOC)
bacteria
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.