Unit 1 Louisiana’s Changing Wetlands

Introductory Facts: –So. Louisiana contains 40% of total coastal marshland in the contiguous United States –Wetlands provide critical wildlife habitat, food, recreation, and fuel to whole country –A football-field-size piece of Louisiana wetland is lost to the sea every 30 minutes—25-35 sq mi per year in last 100 years

What is a river system? –All the waters feeding into the main river, or stem, & all waters branching from it –Tributaries flow into it –Distributaries flow from it –Source of Mississippi is in Lake Itasca, MN (450 m, or 1,475 ft above sea level) –Mouth of Mississippi is 4,107 km (2,552 mi) later in Gulf of Mexico at Louisiana –Land area drained by river is a drainage basin, or watershed

How did the Mississippi River create Louisiana’s coastal wetlands? –River collects everything that runs off surrounding land, including pollutants –Force of the river carries these materials away & sweeps sediments (mostly of clay, silt & fine sand) along the river’s path –Most sediment is deposited at river’s mouth –Sediments compact & subside---process repeated over & over –Plants root & form a marsh & finally, a delta

This is a photograph taken north of the Marine Center in Cocodrie on April 9, (from website

–If new sediment is deposited at faster rate than the old sediment subsides, new land forms at the river delta. –The river eventually changes direction & forms new delta—hence the 7 deltas up to the current Birdsfoot. –If new sediment isn’t deposited fast enough before the old subsides, wetlands are lost to open water, and salinity replaces freshwater.

Why are Louisiana wetlands disappearing? –Always in a state of gaining & losing land due to subsidence, wave action & severe storms –Rise in sea level & subsidence allows salt water to flow into freshwater areas –Freshwater plants die & the marsh dies so land is easily washed away –People have built levees & dams to reduce flooding so that not enough sediment gets to the mouth –Oil & natural gas pumping increases subsidence

Changes to Birdsfoot Delta

Is there hope for Louisiana’s wetlands? –Scientists are working on short & long-range solutions. –Rachael Sweeney manages variety of projects that support natural land-building forces –Projects depend on work of researchers such as Denise Reed—data is used to design the projects –Fences & rock walls slow wave erosion & trap sediment. Ocean sediment used to rebuild beaches

–Grasses are planted to hold soil in place. –Agencies across state trying to restore original hydrology (patterns of water flow) by filling in canals & opening levees, so river water can build land again –Goal is to allow sediment deposition to occur through a controlled process of natural flooding

Experiments/ Activities Let’s Settle This! p28 (discussion) 1.l A Bird’s-Eye View of Land Change p Monitoring the Marsh: A “Core” Issue (discussion) p37 Fieldwork in Your Neighborhood: Testing for Density & Salinity p41 (discussion)