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 &macrophytes

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.