Friday, August 15, 2008

Intro Topic: Dead Zones

I am starting a new series of blog posts for students in my intro to coastal management class. These posts will selectively cut parts of news articles to cover critical coastal management issues.

Photo of the dead zone off Louisiana via Time:

A new study has been published in Science concerning dead zones. From the New York Times:

A study to be published Friday in the journal Science says the number of these marine “dead zones” around the world has doubled about every 10 years since the 1960s. About 400 coastal areas now have periodically or perpetually oxygen-starved bottom waters, many of them growing in size and intensity. Combined, the zones are larger than Oregon.

What are dead zones?
Dead zones are hypoxic (low oxygen) or anoxic (no oxygen) marine or estuarine areas. The absence of oxygen threatens the existence of marine life.

How do dead zones develop? From Oceanus:
The most widespread, chronic environmental problem in the coastal ocean is caused by an excess of chemical nutrients. Over the past century, a wide range of human activities—the intensification of agriculture, waste disposal, coastal development, and fossil fuel use—has substantially increased the discharge of nitrogen, phosphorus, and other nutrients into the environment. These nutrients are moved around by streams, rivers, groundwater, sewage outfalls, and the atmosphere and eventually end up in the ocean.

Once they reach the ocean, nutrients stimulate the growth of tiny marine plants called phytoplankton or algae. When the concentration of nutrients is too high, this growth becomes excessive, leading to a condition called eutrophication.
How do dead zones impact marine life? From the NY Times:

“The overwhelming response of the organisms in our coastal areas is to migrate or to die,” Dr. Diaz said. “To adapt to low oxygen water, it has to be a part of your evolutionary history. It’s not something you can develop in a 40- or 50-year time period.”

Many dead zones are cyclical, recurring each year in the summer months. But over time, they can permanently kill off entire species within the zone. They have also prevented the rebounding of species that are under protection after overfishing, like the Baltic Sea’s cod.

Low oxygen levels also kill off annelid worms and other sources of food for fish and crustaceans.

What are some strategies to address dead zones?

From the NY Times
Robert W. Howarth, a professor of ecology and environmental biology at Cornell, said methods to reduce nitrogen-rich runoff existed, including the planting of winter rye or winter wheat rather than leaving fields fallow after fall harvest. Such planting would cause much fertilizer to be absorbed by the winter crops rather than being leached into waterways by spring rains.
From Oceanus
There are some novel ideas as well. A project is currently underway at Woods Hole Oceanographic Institution to examine the feasibility of using shellfish aquaculture to reduce nutrients in the coastal ocean. The experimental shore-based aquaculture system at the National Center for Mariculture in Eilat, Israel, uses shellfish to absorb excess nutrients excreted by fish. Researchers at WHOI are trying to determine whether the same idea is feasible in the ocean. As the shellfish produced by such an enterprise have economic value, this is an example of a win-win situation.

Examples of Dead Zone Websites
Gulf of Mexico Dead Zone
FAO: Effects of Riverine Inputs on Coastal Ecosystems and Fisheries Resources
NOS: Integrated Assessment of Hypoxia in the Gulf of Mexico
USGS: Gulf of Mexico Hypoxic Zone
USGS: Restoring Life to the Dead Zone


Anonymous said...

Anonymous said...

Paul, you are now famous, referenced in the well-known Running of the Bulls market blog.


Anonymous said...

That last bit about shellfish aquaculture is interesting. Aparently the Chesapeake Bay used to have so many oysters in it that it is estimated that the water was essentially filtered once every 1.5 days. That was before they were fished out, which was before nitrogen based fertlizers were used on a massive scale.