The study of fresh bodies of water
Lentic: standing water (lakes and ponds)
Lotic: flowing water (streams and rivers)
How might they be different?
Glacial erosion and deposition - movement
of glaciers eroded land (Great Lakes)
Deposition of silt, driftwood, and other
debris in slow-flowing streams- cuts off a
meander and forms a crescent shape or
oxbow lake.
Shifts in the Earth’s crust- tectonic
movement; valleys and craters fill with water
Nongeological activity: manmade dams, log
jams, strip mining (all lakes in TX except one,
which one???)
High specific heat of water make aquatic
environment temperatures more stable than
Epilimnion: surface water, small temperature change
Metalimnion: middle mass of water with a rapid
temperature decline (1°C/ meter)
Thermocline: temperature gradient found in
Hypolimnion: deep cold layer cutoff from air; most
Summer- large thermocline. Why?
Winter- Surface water loses heat to
atmosphere therefore thermocline
Overturn: surface water temp. decreases
and causes water to mix and stir up
nutrients and dissolved oxygen because of
density changes (Fall and Spring)
Enters the water by absorption from the
atmosphere and by photosynthesis
The amount of oxygen and other gases
water can hold depends upon pressure and
As temperature increases- solubility of
dissolved oxygen decreases
As pressure increase- solubility of DO
Water loses oxygen through increased
temperature, increased respiration of aquatic
life, and aerobic decomposition
During the summer, oxygen may become
stratified in lakes and ponds
The quantity of oxygen decreases with depth
because of decomposition in the bottom
During Spring and Fall overturn- water
circulation (churning) replenishes oxygen in
the bottom
In winter- DO decreases slightly with depth;
DO is more stable because cold water can
hold more DO than warm water
The depth to which light penetrates is limited by
turbidity of the water and the absorption of light
Trophogenic zone- layer through which light can
penetrate and where photosynthesis occurs (photic
Tropholytic zone- layer through which light cannot
pass through and where decomposition occurs
Compensation level-where photosynthesis ends and
decomposition begins
1. Littoral zone- (horizontal) shallow water
zone where light penetrates the bottom
emergents- plants whose roots are
underwater and stems and leaves are above
water. Live in the littoral zone.
submergents-completely below water
2. Limnetic Zone -Open water zone where
photosynthesis occurs
Plankton- suspended/floating organism
Phytoplankton- photosynthetic plankton;
Zooplankton- animal-like plankton; rotifer
Nekton-free swimming organisms
Is carried out in the limnetic zone by
phytoplankton (ALGAE) and in the littoral
zone by macrophytes- large aquatic plants
(emergents and submergents)
6CO2 + 6H2O + light  C6H12O6 + 6O2
(photosynthetic equation)
1)Title your paper Lentic Ecosystem- mid-summer
2) Draw a cross section of a lake on your paper (this should take up
a considerable amount of room on your paper).
3) Use your Freshwater Ecosystem Notes and laptop to label
following on the cross section of a lake:
Epilimnion, Metalimnion,
Hypolimnion, Thermocline,
Benthic Zone
Littoral Zone, Limnetic Zone,
Trophogenic Zone, Tropholytic
Zone, Compensation Depth
4) Use your freshwater Ecosystem Notes and laptop and draw in
examples in their proper places of the following the cross
section of a lake:
sun, sun rays, emergents,
submergents, algae, and fish.
Label where decomposition and
photosynthesis are occurring.
Rainwater runs off - dissolves and carries
nutrients into lakes.
Water carries with it silt, clay, organic
matter, and nutrients in solution to enrich
the aquatic ecosystem
Human activities including road building,
logging, mining, construction, and
agriculture add to the amount of silt and
organic matter
Eutrophication- nutrient enrichment of an
aquatic ecosystem
Oligotrophication- nutrient poor aquatic
Deeper, steep sides
Poorly developed littoral zone
Blue-green water, clear
High in DO
Poor in phosphorous, nitrogen, and calcium
Few organisms but a high diversity
Very little organic matter
Rich in organic matter and nutrients
DO depletion in hypolimnion during summer
due to decomposition
Eventually will turn into a bog or marsh
Lots of organisms, low diversity
For a healthy ecosystem you want a balance
between eutrophic and oligotrophic.
There needs to be enough nutrients for
organisms to grow and reproduce.
Flowing Water Habitats
Creeks, streams, and rivers
The flow of the water influences the lives of
the organisms inhabiting the waters and the
physical characteristics of the stream.
Headwaters: streams that join together and
form a river
Near headwaters river usually flow fast and
currents are swift
Rocky bottom
Higher levels of D.O. due to flow and
temperature of the water.
Velocity decreases
River gets wider and wider
Meanders become common (curves)
Pools: where water is deeper and slows down,
filled with fine sediments
Riffles: faster, shallower with rocky bottom
Run: fast flowing water, deeper water
The meandering Tigre River, Argentina . PHOTOGRAPH
Read more: http://www.scienceclarified.com/landforms/OceanBasins-to-Volcanoes/Stream-and-River.html#ixzz1147UMeyX
Flat stretches of land on either side of a slow
moving river
During storms, rivers overflow and flood
these areas
When water recedes deposits of rich sediment
are left behind ; fertile land
Less oxygen
Warmer temperature
Communities of catfish, algae, turtles,
dragonflies and other organisms that can live
in lower DO.
Usually empties into an ocean or a lake.
Water slows even more
Sediment is deposited and creates new land
called a delta.
Where a river meets an ocean, freshwater
mixes with salt water, an estuary is formed.
Estuaries are important nurseries for lots of
aquatic organisms.
In temperate regions, leaves and other plant
parts (Coarse particulate organic matter or
CPOM) are the main source of energy
available to the stream ecosystem.
Headwaters: more CPOM
Benthic invertebrates: shredders and collectors
Fish: trout (colder more oxygenated water)
Near headwaters:
high O2, colder
temperatures, CPOM
Further downstream:
lower O2, warmer
temperatures, FPOM
Affects which
species flourish in a
given area
Down stream: Fine particulate organic matter
(FPOM) washed down from headwaters
Algae (both filamentous and planktonic) and
plants are more common because of slower
water and more sunlight.
Few shredders, more collectors and grazers.
Fish: Carp and catfish, tolerate lower D.O.
and warmer temperatures.

File - Bowie Aquatic Science