Newsmaker: Troubled waters for ocean 'dead zones'

(continued from previous page)

The World Meteorological Organization/UNEP "Scientific Assessment of Ozone Depletion: 2006" (click for PDF) said that despite the Montreal Protocol, which curbed world use of ozone pollutants, the ozone hole is still not going to repair itself completely until 2065, and it will probably get worse before it gets better. Is this the situation with the world's dead zones? If the U.N. can get countries to agree to curb ocean pollution, will we see an immediate improvement, or is this another situation where Earth will need time to recover?
Diaz: It may be a little bit of both if you look at areas where, basically, nutrient management--either from runoff, sewage treatment improvements or erosion control in systems--has been implemented. For example, in the Mersey Estuary that runs by Liverpool or the Mondego Estuary in Portugal, these low oxygen zones have been drastically reduced and eliminated, and over a very short period of time.

How long was that?
Diaz: It was called severely hypoxic by researchers in 1997 and here we are in 2006. And I think changes in hydrology and runoff control have eliminated the hypoxia--I think eliminated it by 2003, 2004. So within a few years, you can get the system to respond.

Then there are other places like the Chesapeake Bay where there has been pretty intense nutrient management in terms of what runs into the bay and there have been some measurable reductions, but the level of hypoxia hasn't really gone down. The Chesapeake is a system that may be prone to hypoxia, so it has a longer memory and will probably take several more decades before we see significant improvements.

But I think we would have other areas, some of the low-oxygen zones in Europe, that I think would improve very quickly with nutrient management.

Which zones?
Diaz: The central part of the Dead Sea is actually the largest anoxic, no-oxygen, zone on Earth and it's natural in origin. But to the north, along the Ukrainian area, the Volga River comes in there and that carries a lot of nutrients and other things into the shallow sea on the continental shelf, and creates an annual dead zone that is even larger than the one we have here in the U.S.

It's interesting because when agricultural industrial subsidies were eliminated for a period of time--when the Soviet empire was breaking up--there was a period following right after where nutrients and pollution going into the Volga were drastically reduced, and this produced an almost instantaneous decline in the area of hypoxia. So, even large systems can respond very quickly. Now that nutrients are coming back in, the hypoxia has increased again.

So how are dead zones affected by wind, wave movements and ocean current? And what about more drastic things, especially in the case of the Gulf of Mexico, like hurricanes?
Diaz: Yes, winds and storms are positive in terms of mixing water and breaking up hypoxia. So in a sense, the rough weather is one way of getting rid of the low-oxygen areas.

If you look at the Gulf of Mexico, dead zones...If the storms come earlier, then the hypoxia breaks up earlier; if they come later, it breaks up later.

What about NASA scientists saying that Earth is the warmest it has been in a million years, especially in parts of the Pacific Ocean? How is that affecting dead zones?
Diaz: Well now, that's a damn good question, as far as the sea surface temperatures are really what control our weather and climate from year to year. If we get shifts in our weather patterns, which will mean shifts in rain patterns, then I think what you would find is areas that tend to get wetter with more rainfall will probably tend to get more hypoxia. Areas that get drier will probably tend to have less hypoxia.

Why is that?
Diaz: Well because, in the Gulf of Mexico that's a very good example there, where the size of the dead zone is really highly correlated with the runoff from the Mississippi River, high (runoff) flow years produce more hypoxia than low-flow years.

The same thing happens in the Chesapeake Bay where the size of the low-oxygen area is highly correlated with spring runoff. So as the globe warms up, and climate...and weather patterns change, weather systems will probably increase in hypoxia because in a dry year you don't get as much as stratification; you know, that isolation factor.

I am working with a group of people from University of Delaware in a small tributary up in Delaware (Pepper Creek) looking at the effects of low oxygen...Right now, we are in the middle of trying to determine if (the fish) are actually taking advantage of stressed invertebrates.

When you are referring to stressed invertebrates, what type of marine life is that?
Diaz: Oh, small worms, small clams, little small amphipods. The fish are eating off of the small invertebrates because the invertebrates for the most part cannot move. They have to sit tight and try and survive. And one of the common survival strategies is to basically come out of the sediment and lay on the surface of the sediment, and hope enough oxygen washes by you to keep you alive until oxygen returns. And then you can burrow back down into the sediment.

This is what happened to the Norway lobster, which were in a big fishery on the west coast of Sweden and Denmark. The fishermen were catching lots of these lobsters, and unusually high catches, but what they didn't understand was that they were all oxygen-stressed.

More Newsmakers