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Ozone hole living longer than expectedDecember 6, 2005
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Does that make them dangerous to eat?
Diaz: No, not at all. But what it does is it eliminates their habitat. In one year, the lobster fishermen trawled up a record catch. The next year, they didn't get any because they had all died. And right now...Kattegat (a 2,000- to 3,000-square kilometer area) doesn't support the lobster fishery.
So, they had a record catch one year, and then the next year they had none?
Diaz: Yeah. So that's one of the better examples of the direct effect of low oxygen on a fishery species. It stresses them and changes their behavior. They are easy to catch, but then oxygen gets a little lower and they die. And they just don't recuperate, and the area just doesn't support the fishery anymore.
You and your team created a map of the world's dead zones. How do you find them?
Diaz: I have some students and we regularly look through the literature that's published to find accounts of oxygen or fish kills-- anything that would indicate that there is some environmental anomaly. When we find one, we track it down to look at it in more detail to see if it was an oxygen problem. If it is, then we list it. Well, we are investigating over 200 areas. I think we have about 175 confirmed to date that are actually low-oxygen zones that are associated with human activity.
Are you saying that this is being added by fertilizer runoff, or are there other types of things?
Diaz: There are really three major areas that are probably contributing: people through sewage, and people through needing food, and people through burning fossil fuels. So the answer comes down to too many people.
In almost all cases the two most obvious sources are sewage from people and runoff from farm land, agricultural land. The other source, which is less clear (to the public), is atmospheric deposition, which can be very significant. There is a lot of nitrate in fossil-fuel burning. I think something on the order of 25 percent of the nitrogen, that enters the Chesapeake Bay, comes in through atmospheric deposition: power plants, cars, you know, anything that burns fossil fuel.
So, I think it's a little difficult to sort of point out that it's agriculture that's really the problem. Agriculture is just responding to the needs of people, the real problem is just too many people... People are concentrated on the coast, agriculture concentrated in the middle part of the U.S. It's just a bad combination for the environment.
What do you offer as a suggestion?
Diaz: I knew you were going to ask that. I don't know. I honestly don't know what the answer is, other than smarter agriculture practices, better erosion control--if you can keep things from getting into the watersheds, then the problem will be solved--better recycling, better treatment of waste.
Is there anything else you think people need to know about this?
Diaz: Well, my impression is that these low-oxygen zones, these dead zones, really are a major environmental problem that we need to deal with quickly because the consequences to our fisheries resources are really pretty (messed up). If you would look, a lot of these zones have eliminated fishing and from different areas, primarily in Europe.
So far in the U.S., (there are) small areas where fish aren't collected anymore, but in Europe there are some really large areas, and the Baltic Sea for example...
Let me stop you. Is that due to U.S. regulation of runoff and pollution, or is that just due to the location of the North American continent and the situation of surrounding waters?
Diaz: Well, the Clean Water Act that was passed in the '70s was instrumental really in starting the cleaning up and putting attention on water quality...The nature of our coastline and circulations have also helped. We have not had the mass mortalities that have been reported elsewhere in the world.
Of course, now I think that the population is so large that we have to really start thinking hard about doing more to control water quality or improve water quality.
Now, you were going on to explain something about the Baltic Sea?
Diaz: That's probably the largest hypoxic area attributed to humans on Earth. It depends on the year, but it's about 800,000 square kilometers and there you have an area that is permanently--well I shouldn't say permanent--persistently hypoxic, so the oxygen is low all year-round.
It's low all year-round, so you have no bottom fish in it, and the thickness of this layer is increasing.
Basically, what happens is the cod lay their eggs in the water column. They sink down, and they sort of settle in at this stratified level because they are sort of floating on higher salinity water. And the hypoxia reaches up, and eliminates lots of the eggs and kills them.
So, this is a pretty serious consequence for the fishing industry there. You don't need too many years of that happening, year after year, before the stocks are eliminated.