Transcript What are River Basins

North Carolina Water Systems
Rivers, Wetlands and Tidal
Regions
River Basins
• Three distinct systems
– Flow to the Gulf of Mexico via the Mississippi
• French Broad, Great Kanawha
– Flow to the Atlantic Ocean through South Carolina
• Yadkin, Catawba
– Flow to the Atlantic Ocean through North Carolina
• Chowan, Tar, Roanoke, Neuse, Cape Fear
What are River Basins
• River Basin – portion of land drained by a river
– Eventually empty into an estuary or ocean
• There are 17 river basins in North Carolina
• Drain 52,337 square miles of surface and
underground water
• We ALL live in a river basin
Chowan & lower Roanoke
Pamlico & Neuse
Cape Fear
New River
French Broad
Pee Dee River
Waccamaw
Little Pee Dee (SC)
Lumber
Lynches
Little
Rocky
Coddle Creek
Uwharrie
Little Uwharrie
Yadkin River
Abbotts Creek
South Yadkin
Little Yadkin
Ararat
Elkin
Fisher
Little Fisher
Mitchell
Mulberry
Roaring
Reddies
Santee (SC)
Wateree (SC)
Catawba
Lower Little
Middle Little
Upper Little
Johns
Linville
Congaree (SC)
Broad
Pacolet (SC)
North Pacolet
First Broad
Second Broad
Green
Hungry
Little Hungry
North Carolina Water Systems
Estuaries
What are Estuaries?
• Places near the coast where freshwater and
saltwater mix
• Influenced by both the ocean and freshwater
source
– Tides, waves, major storms
• Time of day and length of the estuary
influence the amount of salt
– More salty at high tide
– More salty closer to the ocean
How Did Estuaries Form?
• North of Cape Lookout
– Thick layers of sand, mud and peat deposited over
1.6 million years as different ice ages caused the
rise and fall of sea levels
• South of Cape Lookout
– Mostly rock covered by a thin layer of sand and
mud
– Formed 90 to 1.6 million years ago
Types of Estuaries
• Three types of estuaries in North Carolina
– Trunk estuaries
• perpendicular to the coast, in-line with the rivers that
feed them
– Tributary estuaries
• Flow into trunk estuaries
– Back barrier sounds
• Parallel to the coast between the barrier islands and
the mainland shore
Why are Estuaries Important?
• Erosion and flooding control
– Sand bars buffer waves
– Plants and shellfish beds anchor the shore against
tides
– Swamps and marshes absorb high winds and
water from heavy rains and storm surge
• Gradually release this water into rivers and ground
water supplies
Why are Estuaries Important?
• Filter out toxins
– Chemically
• Aerobic respiration, sulfate reduction, methanogenesis
• Salt marsh plants trap some chemicals and pathogens
and move them into soil where they are neutralized
– Biologically
• Feeding of estuarine animals and bacteria
• Oysters that filter impurities out of water as they eat
trapping the impurities in their bodies
Why are Estuaries Important?
• Animal and plant habitat
– More than 150 species of fish and invertebrates
live in North Carolina estuaries
• Some species use different habitats within the
estuarine system during different stages of their life
cycles
– Underwater plants cover about 200,000 acres on
the coast of North Carolina
• Submerged plants produce oxygen and nutrients used
by animal species
Why are Estuaries Important?
• Economic
– Three quarters of the fish caught commercially in
the United States live in estuaries
• on average estuaries produce more food per acre than
our most productive farmland
– About thirty commercial fishing species live in
North Carolina estuaries
• Commercial fishing is important to the national
economy and food supply.
– Tourism and recreation
Threats to Estuaries
• Land use changes
– Land is developed for human habitation and use, roads, bridges,
culverts, sewage systems, pipelines, and dams
• change the flow of water through the ecosystem
– wetlands soak up water like a sponge and settle contaminants
in the ground
– asphalt and concrete deflect water so that it runs off with all
its contaminants directly into the rivers, estuaries, and the sea
• Contamination of rivers and oceans
– North Carolina estuaries contain 3,000 square miles of surface water,
but 30,000 square miles of land drains into the Albemarle-Pamlico
• Dredging of channels damages plants and oyster beds and stirs up
sediment that clouds the estuary water
• Since European colonization, nearly half North Carolina’s wetlands have
been lost, and coastal development continues to damage wetlands
Threats to Estuaries
• Global warming
– causes sea levels to rise which threatens the swamp forests, which can
withstand only temporary flooding
– hurricanes also cause high water levels - eroding the shoreline and
flooding organisms adapted to freshwater with ocean water.
– Together sea level rise and storms cause North Carolina wetlands to
erode at a rate of about 800 acres per year
• Excess of nutrients
– sewage treatment plants, septic systems, polluted air, and fertilizers
deposit nutrients such as nitrogen and phosphorus in rivers and
ultimately in estuaries
– high levels of these nutrients can create large growths of algae called
algal blooms blocking sunlight
– As algae dies its decomposition consumes oxygen which eventually
suffocates fish and invertebrates