Aquatic Ecosystems: Water Depth, Salinity, and Zone Dynamics

9/17

The effect of water depth on sunlight

Less light goes through water the deeper you go

Red wavelengths (needed for peak photosynthetic efficiency) are not available underwater

specific heat

how many energy a gram of a substance can hold

What effect does pressure have on organisms?

Organisms need to be able to withstand the pressure since pressure increases the deeper you go

salinity

‐ freshwater (<0.05% salts)

‐ marine (~3.5% salts)

‐ brackish (0.05‐3% salts)

Stenohaline

organisms that can only live in a narrow range of salinities

Usually live in freshwater or saltwater environments

Euryhaline

organisms that can live in a wide range of salinities

Usually live in brackish environments

Effect of temperature on organisms

Water density increases with temperature increase (until it gets to 4 degrees)

Aphotic zone (lakes)

No light, so organisms get their energy by eating detritus that falls from above

Photic zone (lakes)

Light gets here

composed of the littoral zone and the limnetic zone

littoral zone

light reaches the bottom

limnetic zone

light ends at some point in the water

Vertical stratification in lakes

temperature decreases while density increases in lakes

Lake turnover

Winter: o2 at top, nutrients at bottom

Spring: nutrient mixing

Summer: o2 at top, nutrients at bottom

Fall: nutrient mixing

lake turnover gets messed up by pollution

coastal upwelling

wind blows water off at the surface

cold nutrient water reaches the surface

seamount upwelling

currents move water

since water can't move through the seamount, it goes over it

This brings nutrient rich water to the surface

stream flow

faster water mixes nutrients

main channel (stream)

highest upwards stream zone with fish

benthic zone (stream)

middle zone of stream

features crustaceans

hyporheic zone (stream)

lowest zone of stream

bugs

photic zone (ocean)

has light, has little nutrients

benthic zone ocean

organisms eat detritus

neritic zone (ocean)

high productivity due to increased sunlight

shallow (close to shore)

has lots of nutrients due to tides

How do humans impact the zone?

Introducing pollutants

climate change

irrigation

moving species

oceanic zone

vast open ocean from the edge of the continental shelf outward

scarce nutrients