But the nascent plan to rebuild Louisiana’s coastal wetlands, estimated to cost $14 billion, will be only the first step to solving that problem, said William Mitsch, a professor of natural resources and environment sciences at Ohio State University and co-author of “Wetlands,” an authoritative reference and textbook.
Mitsch told the Society of Wetlands Scientists, meeting at the Hyatt Regency New Orleans this week, that as much as $80 billion would have to be spent rebuilding and restoring wetlands throughout the Mississippi River basin to curb the nitrogen levels that cause the dead zone. In all, he said, 24 million acres of wetlands would have to be rebuilt – an area just a bit smaller than Kentucky – throughout the basin, which includes all or parts of 31 states and two Canadian provinces.
Nitrogen, the main ingredient in fertilizer used on agricultural lands in the Midwest, is moved by rainwater through vast drainage networks in agricultural lands to myriad streams and rivers that carry it to the Mississippi, which channels it through Louisiana to the Gulf of Mexico.
There, it fuels huge algae blooms in the layer of freshwater that spreads over heavier saltwater of the Gulf. When the algae die, it sinks to the bottom and decomposes, using up oxygen. The laying of fresh – and salt water inhibits the mixing of oxygen from the air into the deeper water, and the amount of oxygen near the bottom falls to below tow parts per million, enough to kill tiny organisms that form the base of the Gulfs food chain.
Fish and shrimp avoid the low oxygen area or they die. Last summer, the dead zone expanded to a record 8 thousand square miles.
Mitsch said that by diverting river water into new areas to the east and west of the existing channeled course of the Mississippi in Louisiana, the nutrients would be absorbed by emerging wetland plants, reducing the amount that reaches the Gulf.
In the upper reaches of the river, marginal cropland could be restored to wetlands to help strain part of the nutrients out of rainwater runoff. Along the Mississippi and its tributaries, bottomland hardwood forests and swamps also could be restored to act as nutrient sinks.
Better use of fertilizers must be part of the solution, Mitsch said, “but it’s not going to solve this problem unless there’s a really draconian policy put in place” to force farmers to use less. And that’s not going to be politically acceptable, he said.
Instead a variety of voluntary programs would have to be retooled to target specific areas to reduce nitrogen loads, he said.
The role of wetlands scientists, he said, will be to help officials build the new wetlands properly.
The last thing we want to do is spend a lot of money and build them incorrectly,” he said. “Those involved in building them will have to understand wetland ecology."