Page 409 - Environment: The Science Behind the Stories

Mississippi River watershed

Helena
Y e l l o w s t o n e R i v e r M i s s o u r i R i v e r
Sioux Falls M i s s i s s i p p i Pittsburgh
Des Moines I l l i n o i s R . Chicago
1839 P l a t t e R i v e r St. Louis Columbus O h i o R
Louisville

Memphis Te n n e s s e e R
M i s s i s s i p p i R i v e r
Oklahoma
City A r k a n s a s R i v e r
R e d R i v e r
New Orleans
Gulf of
1993 Mexico

(b) Mississippi River watershed

2020

(a) Coastal wetland area in 1839, 1993,
and 2020

Figure 15.1 Human modifications all along the Mississippi
River affect coastal wetlands at the river’s mouth. The size of
Louisiana’s coastal wetlands shrank substantially (a) from 1839 to
1993. It is predicted to shrink even more by 2020 because people
have modified sediment deposition patterns in the river’s delta by
constructing extensive levees along the river and blocking sedi-
ments upriver behind dams. The Mississippi River system (b) is the
largest in the United States, draining over 40% of the land area of
the lower 48 states. A satellite image of south Louisiana (c) shows
the brown plumes of sediments being released into the deep
waters of the Gulf of Mexico from the Mississippi River (plume on (c) Sediment plumes from Mississippi River entering Gulf
the right) and the Atchafalaya River (plume on the left). (a) Adapted
from Environmental Defense Fund.

and saline groundwater associated with oil deposits causes volume. The Atchafalaya delta, fed by this water and sediment,
the land to compact, lowering soil levels. Additionally, engi- is actually gaining coastal land area. Gulf restoration efforts
neers have cut nearly 13,000 km (8000 mi) of canals through are being bolstered by the 2012 Resources and Ecosystems
coastal wetlands to facilitate shipping and oil and gas explo- Sustainability, Tourist Opportunities and Revived Economies of
ration. These canals fragment the wetlands and increase ero- the Gulf Coast States Act (RESTORE Act), legislation passed
sion rates. They also enable salty ocean water to penetrate in the aftermath of the Deepwater Horizon spill. The Act cre-
inland and damage vegetation and wildlife in freshwater ates a comprehensive ecosystem restoration plan for the Gulf
marshes. The 2010 Deepwater Horizon oil spill in the Gulf of Coast, and uses 80% of the fines paid for Clean Water Act
Mexico (pp. 556–559) also affected Louisiana’s marshes by (p. 431) violations associated with the spill to support Gulf Coast
coating marsh grasses with oil and impairing their ability to restoration.
secure oxygen. Given the conflicting demands we put on freshwater
Proposed solutions for coastal erosion center on restor- waterways for water withdrawal, shipping, and flood con-
ing the system to its natural state by diverting large quanti- trol, there are no easy solutions to the problems faced in the
ties of water from the Mississippi River into coastal wetlands Mississippi River and southern Louisiana. But how we tackle
instead of shotgunning it out into the Gulf in the river’s main problems like those in Louisiana’s coastal wetlands will help
channel. Proponents of this approach point to the Atchafalaya determine the long-term sustainability of our most precious
River, which currently drains one-third of the Mississippi River’s natural resource—water.
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