The Dead Zone
JB: This is Earth and Sky. Every summer – from spring until about November – the Gulf of Mexico experiences a growing “hypoxic zone” – an area of seafloor pretty much devoid of life.
DB: This season, scientists reported that the dead zone is the size of Massachusetts. They say that this hypoxic zone happens not because of too few nutrients, but too many. Nitrates and phosphates from agricultural fertilizers run off into rivers and are washed out to sea. These rich nutrients spur the growth of enormous algae blooms at the surface. The algae dies, then settles to the bottom to decompose. This process uses up the dissolved oxygen in the lower depths – and that leaves too little oxygen for most aquatic species to survive.
JB: One solution, some researchers say, is wetlands – bogs, marshes, swamps and streamside forests. Wetlands filter out the chemicals that wash into waterways. Most of the nitrates turn into harmless nitrogen gas that floats away into the atmosphere. But to save the Gulf, we’d need millions more acres of wetlands in the Midwest and the lower Mississippi River basin. Two centuries ago, much of this area was swampy. Eighty percent of those natural wetlands are now gone.
DB: Today’s program was made possible by the National Fish and Wildlife Foundation, in cooperation with the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individual(s) were interviewed for today’s show. Our thanks to:
Dr. William J. Mitsch
Director, Olentangy River Wetland Research Park
School of Natural Resources
The Ohio State University
Columbus, OH
Author’s Notes:
Restoring wetlands could be easy – you just break the drainage tiles that are under most of the farms of the Midwest. Instant wetlands!
In the Gulf’s hypoxic zone, dissolved oxygen levels dip below two parts per million, and most aquatic species can’t live in waters containing less than that. Dissolved oxygen levels in the Gulf are normally about 5 to 10 part per million.
The “dead zone” typically begins in the spring, when planting and fertilizing fields peaks. The accumulation of nitrogen and other chemicals usually reaches a maximum in midsummer and disappears in the fall.
It’s estimated that the American Midwest has lost about 80 percent of its wetlands in the last two centuries, compared to a 50 percent loss in the contiguous United States. Under current conservation programs, about 577,000 acres of wetlands have already been created or restored. So about 10 to 25 times more wetlands are needed to cause a significant reduction of nitrogen levels in the Gulf, says Dr. William Mitsch of Ohio State
University.
Ohio has lost ninety percent of its wetlands.
Additional Teacher Resources
U.S. Environmental Protection Agency, Mississippi River Basin Challenges: Hypoxia
This page offers a brief explanation of hypoxia, as well as its effects in the Gulf of Mexico and the efforts being made by the EPA to address the problem.
U.S. Geological Survey: The Gulf of Mexico Hypoxic Zone
This brief overview provides an easily understandable scientific explanation of the Hypoxic zone in the Gulf of Mexico complete with maps and links to other research.
U.S. Environmental Protection Agency: Wetlands
A great resource for introducing wetlands. This page provides sections covering: What are Wetlands?; Why protect Wetlands?; How are Wetlands Protected?; What You Can Do to Protect our Vital Resource!
The University of Illinois: Keeping the Stygian Waters at Bay
This article focuses on the 2001 implementation of an ambitious plan that sought to banish a recurring nightmare form the Gulf of Mexico: a seasonal dead zone that turns the sea floor into a graveyard. The primary subjects are the mid-western agricultural practices that cause the dead zone and the efforts being made by stake-holders to remedy the problem.
