BIOL 2306 – Living Planet (hybrid)
CONCEPTS FOR EPISODE 8 – Sweet Fresh Water
I.
Characteristics of freshwater habitats
A. Temperature determined by
1. climate of geographic region
2. amount of sunlight
3. volume of water – water resists temperature changes; the larger
the volume, the slower the change
B. Oxygen content determined by
1. diffusion of oxygen from air into water – increased flow rate and
turbulence increase oxygenation
2. photosynthesis by aquatic plants and algae releases oxygen into
water (oxygen increases during day and decreases at night)
3. water temperature – warmer water holds less oxygen
C. Nutrient levels (nitrogen and phosphorus)
1. decomposition of aquatic organisms releases nutrients
2. runoff from adjacent land areas adds nutrients from soil erosion,
decomposition, feces, fertilizer, sewage
3. classification
a. eutrophic
- high levels of nutrients and organic matter
- surface clogged with algae (dies when reaches max
density)
- turbid (cloudy) water
- decomposers thrive and deplete oxygen
- fish and other animals die from insufficient oxygen
b. oligotrophic
- low levels of nutrients and organic matter
- low algal density
- clear water
- high oxygen levels
- diverse community of fish and other animals
II. Aquatic Lifestyles
A. plankton – organisms that float in water; basis of open water food webs
1. phytoplankton – producers
2. zooplankton – consumers
B. nekton – strong swimmers
- fishes
- consumers
C. benthos – bottom-dwellers
- mud, gravel, rocks, sand
- decomposers dominant; grazers, predators, scavengers also
- worms, insect young, crustaceans, bacteria, algae, protozoans
III. Current
A. running water – streams and rivers
1. headwaters
- cold
- clear
- low nutrients
- high oxygen
- steep, so fast flow
- high erosion
2. downstream
- warm
- turbid
- high nutrients
- low oxygen
- slow
- meandering flow as fast water cuts away outside
bank and slow water drops sediment along inside
bank
3. mouth
- flat and wide
- silty
- drops sediment where it meets ocean, creating area
of land known as delta
B. still water – lakes and ponds
1. formation
a. lakes formed by geological faults – depressions hold water
b. lakes formed by damming rivers – volcanic activity,
landslides, natural log jams, humans
c. lakes formed by glaciers – large bodies of ice move slowly
down slopes, grinding away underlying rock and forming
depressions that hold water
d. lakes formed by meandering rivers – bends in river may be
cut off during floods when river cuts across land. (oxbow
lake)
2. zonation
a. littoral zone – shallow, near-shore, light hits bottom,
emergent plants (rooted in mud), habitat for animals
b. limnetic zone – open water away from shore, top layer lit by
sun, floating algae and cyanobacteria, zooplankton, fishes, and
other large animals
c. profundal zone – deep water away from shore, dark, dead
organisms settle out from limnetic zone, decomposers,
scavengers, most trophic activity is in benthic region (bottom)
3. succession – changes in the life of a pond over time
a. birth – when stream is dammed,, water pools behind it
- little organic matter, nutrient poor
- very little life
b. youth – stream adds organic matter and nutrients to pond
- phytoplantkton become established
- rooted aquatic plants move in
c. middle age – increased organic matter on bottom as
organisms die and are decomposed
- littoral zone moves farther into center of pond
d. old age – soil and rock particles accumulate
- pond slowly fills in
- bottom becomes exposed to life
- aquatic plants cover bottom of entire pond, forming
a marsh
e. Death - organic matter and sediment continue to build up
until lake fills in entirely, and grassland meadow is formed
IV. Breeding strategies of fishes - evolutionary strategy is to leave maximum number
of fertile offspring
A. r strategy (example: Pacific salmon)
- many offspring
- invest little energy in care
- most offspring die
B. K strategy (example: Stickleback)
- few offspring
- invest lots of energy in care
- each offspring has good chance of survival