estuary

upwelling

salt marsh

wetland

benthos

B a r r i e r I s l a n d

plankton

swamps

nekton

lake benthic zone

saltwater

littoral zone

eutrophication

freshwater

algal bloom

coral reef

ocean

salinity

river

AQUATIC ECOSYSTEMS

CHAPTER 7

Freshwater Ecosystems

...determine where Org livesin the water.

• Temp

• Sunlight

• O2

• Nutrients

TYPES of ORGS

• Plankton (phyto - & zoo -)– Float near surface– Principal food source in aquatic ecosystems

• Nekton– Free-swimming orgs: fish, turtles, whales...

• Benthos– Bottom-dwellers: mussels, worms, barnacles...

TYPES of FW Ecosystems

• Lakes

• Ponds

• Wetlands

• Rivers

• Streams

LIFE in a LAKE...

• LITTORAL ZONE– Near shore– Nutrient-rich– Abundant/diverse life

due to sunlight (photosynthesis)

• BENTHIC ZONE– Lake bottom – no light

for photosynthesis– Dead & decaying orgs– Decomposers, insect

larvae, clams...carp.

...depends on the amount of sunlight available!

Eutrophication• “Increase in amount of nutrients in

aquatic ecosystem.”

• Nutrients cause plants & algae to increase...

• Bacteria increase as dead plant matter grows...bacteria use up dissolved O2...

• O2 - loving organisms die off.

• Lakes naturally become eutrophic over time....

...but the process can be accelerated by sewer system or agricultural runoff that places fertilizer (and I use the term loosely!) into lakes & ponds.

FW WETLANDS

• “Areas of land periodically covered with water.”

• MARSHES: contain non-woody plants (cattails, reeds, rushes)

• SWAMPS: woody plants (trees, shrubs)

Marshes• Characterized by low, flat land...little

water movement...some “brackish,” some saltier.

• Flat-billed fowl (ducks, grebes) adapted for skimming insects off surface; those with spear-like beaks (herons) suited to grasping small fish & digging for buried frogs.

• Florida Everglades: largest freshwater wetland in U.S.

Swamps

• Flat, poorly drained land; woody shrubs or water-loving trees.

• Snakes...bullfrogs...alligators!

Freshwater WETLANDS provide important environmental functions:

• Act as filters or sponges to absorb & remove pollutants from groundwater; improve water quality of lakes/reservoirs downstream.

• Control flooding by absorbing extra water from rivers & hurricane storm surges...saving urban/residential areas from damage.

• Habitat for migratory waterfowl...spawning grounds for game fish...cranberries!

• Buffer zones to protect against shoreline erosion.

...they used to be wastelands...

• For decades, it was believed they were just breeding grounds for mosquitoes...

• Millions of acres were “recovered” via drainage, filling in, clearing...

• Now (thanks to envi sci!) they are protected by government...their destruction is prohibited.

Rivers• Rivers have been long used as free water

sources for industry (and dumping grounds...)

• Toxins have killed off much river life and made river fish inedible...city & farm runoff put pesticides & other poisons in rivers.

• Dams alter ecosystems in and around rivers.

Marine Ecosystems

Estuaries• “Freshwater source (river) mixes with

saltwater source (ocean).”

• Currents cause nutrient trap to form @ bottom. Sunlight penetrates shallow waters.

• Rich nutrients/photosynthesis make estuaries some of the most biologically productive ecosystems on the planet.

• Protected from waves by peninsula/barrier islands.

Estuary Life

• Plants & plankton fish dolphins, manatees, seals et al...abundant food web.

• Oysters, barnacles, clams (filter feeders)

• Orgs are able to tolerate varying salinity

• Humans love estuaries too...

Threats to Estuaries

• Of the 10 largest urban areas on the planet, 6 are built on estuaries: – Tokyo– New York City– Shanghai– Buenos Aires– Rio de Janeiro– Bombay

Threats to Estuaries

• California: estuaries filled in with waste & used as building sites.

• Rivers carry pollutants downstream to estuary (sewage, ag waste, pesticides, toxic chemicals)

Chesapeake Bay

Barrier Islands

• Formed by rising sea levels (over the past 15,000 years)

• Long, narrow sand ridges parallel to coastline, 3 to 30 km out.

• Protect mainland & coastal wetlands from storms & waves.

• ...don’t spend a lot of $ buying a home on ‘em...

Sanibel Island

Southern Rhode Island

Coral Reefs

• Limestone ridges built by photosynthetic algae & skeletons of coral polyps.

• Found only in clear, warm, shallow saltwater.

• Among the most diverse ecosystems on planet (thousands of species).

• Convoluted shape provides habitats for fish, snails, clams, sponges...

Coral Reefs

• 27% of world’s coral reefs in danger...

• Oil spills...sewage...pesticides...silt runoff...overfishing...– If water gets too warm/too cold...– If fresh water drains onto reef...– If water gets too muddy/polluted...

• Reefs are fragile, they grow too slowly to repair themselves in time...

Great Barrier Reef

Oceans

• “Usable” sunlight penetrates to only 100 m depth...

• ...most ocean life thus located in shallow coastal areas, not in open oceans.– Seaweed, algae, plankton...inverts & fish that

feed on them are concentrated near-shore.

• Many different “minisystems” exist...

• Open oceans are possibly the least productive of all ecosystems.

UPWELLING

• @ coastlines: surface currents carry water away from shore...

• Deeper, nutrient rich bottom water “wells up”to fill in...

• Phytoplankton love it...fish come for phytoplankton...humans come for fish...it’s all good?

Threats to Oceans

• Fertilizer runoff from shore causes algal bloom...some are poisonous!

• Industrial waste & sewage = coastal pollution.

• Overfishing is destroying some fish populations...

• Stupid fishing methods are murdering innocent creatures...