Freshwater Ecosystems

Stream and River Ecosystems• Water in brooks, streams, and

rivers may flow from meltingmelting ice or snow or come from a spring

• Each stream of water that joins a larger stream is called a tributarytributary

• As more tributaries join, the stream gets strongerstronger and becomes a river

stream

tributary

river

Pond and Lake EcosystemsLife Near Shore

Littoral zone: area of water closest to the edge of a lake or pond

Sunlight reaches bottom of littoral zone, making it possible for algae and plants to growBeneath surface of water: algaeNear shore: cattails and rushesFloating plants: water liliesSmall animals: snails, insects, clams, worms, frogs, salamanders, turtles, fishes, and snakes

Littoral zone

Life Away from ShoreOpen-water zone: area of lake or pond that extends from littoral zone across top of waterGoes as deep as sunlight can reachHome to bass, trout, and other fishesMany photosynthetic plankton live in this area

Deep-water zone: beneath open-water zone where no sunlight can reachCatfish, carp, worms, crustaceans, fungi, and bacteria live hereThese organisms often feed on dead organisms that sink from above

Three Zones of a Pond or Lake

Open water zone

Deep water zone

Wetland Ecosystems

Wetland: area that is sometimes underwater or whose soil contains a great deal of moisturePlay important role in flood control—soaks up large amounts of water during heavy rainsWater in wetlands moves deeper into ground, so helps replenish underground water supplies

MarshesTreeless wetland ecosystem where plants, such as grasses, growCommon marsh plants: grasses, reeds, bulrushes, and wild riceCommon animals: muskrats, turtles, frogs, and birds

SwampsSwamp: wetland ecosystem in which trees and vines growFound in low-lying areas and beside slow-moving riversMost swamps are flooded part of the year, depending on rainfallSwamp plants: poison ivy, orchids, water liliesSwamp animals: fishes, snakes, and birds

From a Lake to a Forest

Did you know that a lake or pond can disappear?Water entering a standing body of water usually carries nutrients and sediment—these settle at the bottom of the lakeDead leaves and decaying matter also settle at bottom of pond or lakeBacteria decomposes this material

This process uses oxygen in the waterLoss of oxygen affects the kinds of animals that survive in a pond or lake

Over time, pond or lake fills with sediment and plants start to grow in new soilEventually, the wetland can become a forest

Marine Ecosystems• Shaped by abiotic factors: water,

temperature, water depth, amount of sunlight

• Very diverse: ocean contains whales, the largest animals on Earth

• Tiny plankton form the base of the ocean’s food chains

• Temperature– Temperature of ocean water

decreases as depth of water increases

– Surface zone is warm, top layer; surface currents mix the water

– Thermocline in this zone, temperature decreases with increased depth

– Deep zone bottom layer of water; averages a chilling 2 degrees C

Get in the Zone!• Major ocean

zones: intertidal, neritic, oceanic, benthic

• Intertidal Zone place where ocean meets land and is exposed to air for part of the day

• Neritic Zone ocean floor slopes downward, water is warm and receives lots of sunlight– Corals, sea

turtles, fish, dolphins

• Oceanic Zone sea floor drops sharply, deep water– Animals often get food

from material that sinks down from ocean surface

• Benthic Zone ocean floor; does not get much sunlight; very deep– Bacteria get

energy from chemicals that escape from thermal vents on ocean floor

A Closer Look

• Through evaporation, the ocean provides most of the water that makes up Earth’s precipitation

Intertidal Areas• Coral Reefs most found in neritic zone• Estuaries area where fresh water from

streams and rivers spills into ocean– Fresh water and salt water are always mixing, so

amount of salt in water is always changing

• The Sargasso Sea found in middle of Atlantic Ocean– Contains floating

rafts of algae called sargassum

• Polar Ice the Artic Oceans and the ocean around Antarctica – Ice water rich in

nutrients, which support large numbers of plankton