Resurrecting the Dead Zone
Reducing U.S. agribusiness' nitrogen runoff could reverse past damage to the Gulf of Mexico
- By Erica Pincus
- Sep 01, 2006
The Dead Zone -- sounds creepy doesn't it? But what is it? It's
a crisis that's attacking oceans and bays throughout the world, and a reality
more frightening than current governmental policies and actions have led the public
to believe. Over the past 13 years, oxygen levels in the Gulf of Mexico have dropped
to levels that endanger the health of aquatic animal and plant species and will
soon no doubt impede the production of the coast's fisheries. Aside from
these environmental and economic impacts, nearly 50 percent of the American population
lives on coastal lands that are trapped in a cycle of pollution and health imperilment.
The menace behind this situation is oxygen depletion down to levels of 2 milligrams
per liter (mg/l) or less, a condition known as hypoxia. Under these conditions,
aerobic species cannot survive, so they are forced to migrate further offshore
The Louisiana Universities Marine Consortium discovered the hypoxic zone of the
Gulf of Mexico in 1974, and an original member of this team, Nancy N. Rabalais,
PhD, has annually monitored the location's size since 1985. Although scientists
were aware of the situation, it went seemingly unnoticed until flooding of the
Midwest in 1993 caused the Dead Zone to double in size. The Zone is seasonal and
ceases in the winter months, but every April through September it returns to roughly
the same size and has been slowly increasing since 1993. In 1993, Rabalais saw
a hypoxic zone of 6,800 square miles, and by 1995, it had increased to 7,032 square
miles. In 2001 the Dead Zone covered 7,722 square miles. In contrast, during the
summer of 2005 the area was determined to cover 4,564 square miles, or roughly
the size of Connecticut. Since monitoring began in 1985, the hypoxic zone has
averaged 4,800 square miles, making it the second largest hypoxic zone in the
world, right behind the Black Sea.
Causes of the Dead Zone
Nonpoint sources are the most pervasive contributors to the Gulf Coastal hypoxic
zone. The increase of nitrogen loads, freshwater discharge, and sediment discharge
throughout the area has resulted in unsustainable oxygen levels. The Mississippi
River Basin encompasses 41 percent of the lower 48 states and all rivers in
this region exit into the Gulf of Mexico through the Mississippi River or the
Atchafalaya River. These two rivers are responsible for 80 percent of the total
water discharge and 91 percent of the nitrogen load into the Gulf.
The most direct cause of hypoxia is nitrogen (more specifically nitrate) loads
from fertilizer runoff, decomposed crop residue, human and animal waste, and
atmospheric deposition. The breakdown of nitrogen in the Gulf of Mexico is as
follows: 70 percent fertilizers, 11 percent municipal sewage, 12 percent animal
waste, and 6 percent atmospheric deposition. When nitrogen enters the water
system, it causes massive algal blooms, resulting in an influx of organic material.
This substantial intake of oxygen depletes the water source and results in hypoxia.
Loads from the Mississippi River have grown two- to seven-fold over the last
century, and unmanageable, large-scale agricultural practices are to blame.
The Midwest loads the 3 million acres of wetlands with an estimated 7.8 billion
pounds of fertilizer each spring. Since nitrogen is stored in soils and groundwater,
nitrates will continue to be loaded in the water supply even after fertilizer
The Environmental Working Group (EWG), a nonprofit environmental research organization
based in Washington, D.C., issued a report in August 2005 explaining the effects
of farming practices and government subsidies on the hypoxic zone. The report
stated that, for every tax dollar spent on conservation, there are $500 tax
dollars devoted to farm subsidies. One hundred and twenty four counties deemed
as top polluting counties, in Illinois, western Iowa, western Indiana, northeastern
Arkansas, and southeastern Missouri received $11.4 billion in subsidies from
1995 through 2002; during this same period, government spending on water quality
payments was only $22.5 million.
Although they cover only 5 percent of the Mississippi River Basin, these government-funded
farms account for 40 percent of nitrate fertilizer pollution in the Gulf. An
Action Plan proposed by the National Oceanic and Atmospheric Administration
(NOAA) in 1999 is mostly a call for voluntary efforts on the part of farmers
and agribusinesses to use best management practices to prevent fertilizer runoff
from farmed lands. Although the government is encouraging sustainable farming
techniques, the practicality of that request is minimal. Farmers, in general,
are more concerned with the rising price of energy than a remote body of water.
The EWG report suggested that the Dead Zone could be reduced by shifting a portion
of the government subsidies, which often go to the largest and most profitable
agricultural operations, into programs that encourage more careful fertilizer
use, wetland restoration, and the planting of streamside buffers of grass and
trees to absorb runoff.
Freshwater discharge is also cause of concern for the Gulf Coast. High freshwater
dischargers into the Gulf are not as salty as the existing water, and they float
to the top. This prevents oxygen recharge to lower waters and depletes benthic
oxygen at the lowest strata of the ocean. The Mississippi and Atchafalaya Rivers
account for 80 percent of the total freshwater input to the Gulf. The U.S. Army
Corps of Engineers began maintaining water delivery of the coast in 1977 at
30 percent, but the discharge from the Atchafalaya continues to increase. The
increase in freshwater discharge has been associated with increased precipitation
from global warming.
The greater amounts of total suspended solids (TSS) in a body of water, the
murkier, or more turbid it is. Phytoplankton is the most typical source of turbidity.
The direct correlation between nitrogen levels and phytoplankton populations
prove that this is a treacherous cycle. Watershed development and poor land-use
practices increase erosion, organic matter, and nutrients, which all cause an
increase in suspended particulates and algae growth. High concentrations of
particulate matter can modify light penetration and smother benthic communities.
As matter settles to the ocean floor it can suffocate newly hatched larvae and
displace space that could have been used for habitat. After days of exposure
to TSSs measuring over 100 nephelometric turbidity units (NTU), fish will abandon
cover, show avoidance behavior, increase respiration, reduce feeding rates,
and increase coughing rates. Weeks of high turbidity result in reduced growth
rates, delayed hatching rates, and long-term reduction in feeding successes;
and months of exposure will lead to death. Aside from the immediate effects
of TSS, organic nitrogen desorbs from sediment particles in the freshwater/seawater
mixing zone and contributes to the total nitrogen load of the Gulf of Mexico.
Effects on Aquatic Organisms
When waters reach the dangerously low oxygen levels of less than 2 mg/l, aerobic
species are forced to migrate farther offshore or die. Species exposed to hypoxic
conditions experience decreased size of reproductive organs, low egg counts,
and a lack of spawning. It has been found that female fish living in hypoxic
areas have one-seventh the number of eggs as fish living in normal conditions.
The most common problems associated with hypoxia are avoidance of an area and
migratory disturbances, which interferes with regular life processes.
Benthic species -- organisms that live in the bottom of water bodies -- are
accustomed to cool temperatures, low oxygen levels, and little to no sunlight,
yet these species are the first to feel the effects of hypoxia. Slow-moving
clams, lobsters and oysters are unable to escape the hypoxic areas and die.
Brown shrimp is a commercially important benthic species whose migratory patterns
have been dramatically changed by depleted oxygen. Brown shrimp are affected
more than similar species because they require offshore shelf habitat; thus,
they inhabit a guaranteed hypoxic area. Limited migration has left fisheries
with new problems. The brown shrimp catch in the Gulf declined from a record
high in 1990 to below the historical average during 1992 to 1997, coinciding
with years of high hypoxia.
Algal blooms associated with hypoxia pose an immediate threat to fish living
in the Dead Zone. When excess nitrates enter the body of water, organic material
responds with massive growth. Algal blooms are directly linked to fish kills,
and, at the very least, fish habitats are restricted and the risk of predation
Impact on the Gulf Region's Economy
The Gulf of Mexico supports many local residents through the commercial fishing
of red snapper, amberjack, tilefish, swordfish, shrimp, and crabs. As well,
the region supports many industries, including shipping, petrochemical processing,
paper manufacturing, and tourism. Residents of the region have strong economic
ties to the Gulf of Mexico that are being threatened by the far-ranging impacts
The Louisiana Department of Wildlife and Fisheries conducted a project from
1998 to 2002 titled "Effects of Hypoxia on Commercial Shrimp and Charter
Boat Fisheries in Louisiana." This project was conducted along the Louisiana
coast from Quatre Bayou to Belle Pass to determine the impacts of adverse environmental
and climatological conditions on fishing patterns and subsequent income of commercial
fishermen. Through a voluntary logbook by coastal fishermen and biweekly oxygen
concentration measurements, the project concluded that environmental events
are rarely isolated to a time frame suitable for analysis, and no correlation
between hypoxia and lowered productivity could be established. It did note that
fishermen showed a drastic drop in activity during the month of July when hypoxia
is at its peak, so growth in productivity may be stifled by the condition.
Although commercial fishing in the Gulf Region has not yet suffered a steep
decline as a result of hypoxia, this does not mean the economy will not be affected
in the future. Based on other historical hypoxic events, the possible adverse
impacts on the fisheries could progressively worsen as the level of hypoxia
in the area increases. Additionally, some experts worry about the possible negative
health effects on people who consume the fish, shellfish, and other animal species
that are harvested from the Dead Zone area of the Gulf of Mexico.
Government in Action
In 1997, the White House Office of Science and Technology Policy commissioned
the U.S. Department of Commerce, as well as the National Oceanic and Atmospheric
Administration (NOAA), the National Ocean Service, the National Centers for
Coastal Ocean Science, and the Center for Sponsored Coastal Ocean Research to
put together a series of reports to explain the hypoxic situation of the coast
and propose a plan of rehabilitation. Topics included a general explanation
of hypoxia, the ecological and economic consequences of hypoxia, the flux and
sources of nutrients in the river basin, the effects of reducing nutrient loads,
and an evaluation of the costs and benefits of reducing nutrient loads in the
The reports forecasted that a 30 percent reduction in nitrogen loads will solve
hypoxia in the Gulf of Mexico and improve water quality and habitat within the
Mississippi River Basin. Furthermore, the report stated this goal was to be
obtained by the Action Plan. This plan spelled out a voluntary, incentive-based
strategy to implement best management practices on agricultural lands, wetland
restoration and creation, river hydrology remediation, and stormwater and wastewater
Solving the Dead Zone Problem
If the government's advice is properly executed and U.S. agribusinesses
internalize the cost of managing their pollutants, a 20 percent decrease in
nitrate loads is economically feasible. One way to do this is to cut down on
fertilizer use and apply fertilizers at rates and times at which they can be
absorbed and used most efficiently. According to NOAA reports, the demand for
fertilizer is inelastic so a 500-percent tax would be necessary for a 45-percent
nitrate decrease, resulting in an aggregate loss of $14.9 billion. This approach
is unrealistic from an economic perspective; consequently, it appears that it
would be far more effective to place some type of restriction on the amounts
of fertilizer used by agricultural operations.
Another possible way to deal with the Dead Zone is to restore wetlands to intercept
nitrogen and cause dentrification. By restoring 13 to 18 million acres of wetlands
at $495 million to $32.4 billion, the total nitrate loads would decrease by
50 to 70 percent. Additionally, this initiative would preserve critically endangered
areas. The least economically desirable approach is using riparian buffers to
intercept nitrogen runoff and promote dentrification before water reaches streams
and rivers. According to research, approximately 46 million to 68 million acres
of buffers, which would cost at an estimated $46.3 billion, would be needed
to accrue a 50- to 80-percent decrease in nitrate loads. The high opportunity
cost of retiring fertile land compared to the relatively small environmental
payoff makes this option unattractive.
The most feasible way to reach the goal of a 20-percent decrease in nitrate
loads is to use both pre-emptive methods, like fertilizer restrictions and riparian
buffers, and rehabilitative methods, including restoring wetlands. Achieving
this goal would decrease the contamination of surface water, which, in turn,
would reduce the cost of treating raw water in order to convert it into potable
drinking water. This approach would also expand the area of recreational waters,
reduce soil erosion, restore wetlands, and reduce nutrient contamination of
This article originally appeared in the 09/01/2006 issue of Environmental Protection.
Erica Pincus is an editorial assistant at Environmental Protection and Water Products magazines. She is currently enrolled as a student at the University of Texas in Austin, Texas, where she studies politics, philosophy,and economics.