Every year, an oxygen-deprived hypoxia zone builds at the mouth of the Mississippi River and spreads into the Gulf of Mexico. Also referred to as the “dead zone” because of its inability to sustain marine life, the area has been studied by scientists for several decades and appears to be growing.
Hypoxia occurs when huge algae blooms, largely fed by nutrients brought to the gulf through run-off, die. The algal decomposition process then starves the water of oxygen making it uninhabitable.
Although agricultural run-off has often been pointed to as a chief cause, only recently has the zone become a potential factor in the 2007 farm bill debate (see http://deltafarmpress.com/news/060505-Bill-EWG/index.htm and http://deltafarmpress.com/news/042106fertilizer/index.html). Agriculture policy could be influenced by the zone. How much is truly known about it? How much damage is it doing to the fishing industry? How easy would it be to fix or reduce in size?
Mapping the zone
Mapping the zone is among Nancy Rabelais' duties. So every year, usually in late July, the Louisiana Universities Marine Consortium professor, along with research colleagues from LSU, climbs aboard a boat and strikes out to find where the fish aren't. The search doesn't take long.
“We work our way from the Mississippi River delta west and travel as far as the hypoxia goes,” says Rabelais. “As long as we have enough time on the ship, we'll keep mapping. That allows us to outline the zone and see what the water characteristics, nutrients and chlorophyll levels are.”
Gathering such data since 1985 has been “very productive” for the science of hypoxia. Without the mapping “we'd never know if a difference was being made (with nutrient reduction programs). For me, the work is most important in terms of science: how the system works, how the nutrients lead to phytoplankton growth, how that gets to the bottom, how it is used by bacteria.”
Scientists know the linkages between the systems. Unfortunately, they don't know all the details. For example, there remain questions about the bottom's water and sediment.
“We don't know how the surface water ecosystem has been responding to changes in nutrients and ratios of nutrients over the years. There's also a lot not known about organic nutrients coming out and the recycling of those materials. We also don't know all the effects on the fishery resources — that's a big gap. There's plenty of work left to do.”
Meanwhile, over the last five years, the average size of the dead zone has been 6,000 square miles. The average size since 1985 is about 5,000 square miles. The zone's largest recorded size was in 2002 at 8,500 square miles.
There is quite a bit of variation in the area of the zone from year to year. The size depends on a number of things, including seasonal, weather and the river's level. Mixing events are another.
“Last year, as everyone knows, we had three hurricanes and a number of tropical storms. That meant the Gulf water column stayed pretty mixed. That can help mitigate the zone.”
To remove nutrients prior to reaching the Gulf, some have suggested re-routing some Mississippi River water into Louisiana wetlands. The thinking is the degraded wetlands vegetation would benefit from the extra nutrients and sediment would help rebuild eroded land.
“The way it would work is as you spread this water over more surface area — the ‘sheet flow’ — you get much more assimilation and nutrient reduction,” says Rex Caffey, an LSU economist who has covered coastal wetlands restoration and fisheries economics since 1998. “As we're doing now — sending the water straight to the Gulf — it has no ability to spread.”
Studies have looked at the percentage reduction in nitrogen flux and phosphorus loading that can be achieved by rerouting water. Unfortunately, the percentages aren't as high as many had hoped. Caffey says such a project would only help marginally compared to farmer and municipality conservation practices further upriver.
“It's feasible to divert river water but it's not feasible to expect it to take out a large amount of nutrients,” says Rabelais. “The acreage needed to do that is simply too great.”
While well-managed diversions — if specifically targeted for nutrient removal — could help, “most diversions are planned for other reasons: to move large amounts of water, to move the salinity line lower in the wetlands, to move sediment to build up land. The way to engineer such diversions is very different depending on what the ultimate goal is. Nutrient removal is only one of many reasons cited for proposed diversions.”
Using coastal restoration as a mechanism to solve hypoxia “isn't appropriate,” says Rabelais. “I believe only about 5 percent of the total nutrient load of the river could be reduced through coastal wetlands. And that's using the maximum amount of wetlands. That's not likely to happen.”
The effect of hypoxia on the fishing industry is hard to quantify.
“It's hard to measure the impact because when (the zone) forms, the mobile critters move out of it,” says Doug Daigle, who works with the Mississippi River Basin Alliance (MRBA). “They congregate on top of it or off to the side. Shrimpers or fishermen can make good hauls if they find a congregation. When they bring that catch to the dock, it doesn't indicate anything is wrong. So, thus far, it's hard to measure the impact exactly.”
Caffey says science has yet to weigh in and he is frustrated with those blaming hypoxia for “devastating fisheries.” There simply isn't enough data to back up such claims.
“Yeah, I think it does have an impact on fisheries,” says the economist. “But there aren't enough studies linking declines in commercial fisheries and hypoxia. As far as I know, those don't exist yet. It's kind of convoluted. Anyone who isn't looking for balance could easily take away the wrong message. Yes, let me repeat: there are impacts. However, it's dishonest to claim impacts that haven't been documented.”
It's only been since 1999 that Louisiana began tracking where fish are caught through the Trips Ticket Program. “That program is exactly what it sounds like — you make a fishing trip and you fill out a ticket saying where you fished, what you caught, how much you caught and who you sold it to.”
Using that data, researchers have begun to check where people are fishing compared to the hypoxic zone and if they're attempting to avoid it. Caffey says it appears they might be.
“That's the kind of data we need. But we need to follow this for a longer time to come up with solid conclusions.”
Caffey also wants to know how much hypoxia and stratification was in place prior to the advent of industrial agriculture. Because of the natural course of nutrients and turbidity at the mouth of the river, there likely has been a dead zone for thousands of years.
“That's being aggravated mostly by agriculture run-off. But we don't know what the baseline was 70, 80, 100 years ago. Hypoxia as a major issue is only a decade or two old.”
A national plan
To help reduce the hypoxia problem, Daigle and MRBA colleagues have been coordinating with the lower river states — Mississippi, Louisiana, Arkansas, Tennessee and Missouri.
“The Lower Mississippi Sub-basin Committee on Hypoxia (which Daigle heads) was formed in 2003 but I've been working on this issue since 1999. There's a national action plan to deal with hypoxia. We're trying to implement that. That involves agricultural management practices, wetlands restoration, river management, and industry and municipal point-source issues.”
Since they're linked, it's important that coastal restoration and hypoxia zone issues be coordinated, says Daigle. Before last year's hurricanes, planners said a coastal restoration plan would take 20 years to implement. Now, “we're not sure if there's 20 years to get it done. Obviously, the coast is very vulnerable to hurricanes.”
As for agriculture's role in the dead zone, Daigle says the national action plan should be funded and producers shouldn't feel threatened.
“There are areas in the Corn Belt that are major sources of nitrates in the Mississippi River. Many there see any regulations coming in as a threat. What should be happening is to see this as an opportunity — to take the federal money available and restore the wetlands and build farm systems that will improve water quality. Instead, some are fixated on ‘We don't want to deal with this because it will hurt us.’ But this is a national problem and since it is, national money should be available to help fix this.
Daigle also has words for environmental groups lobbying for changes in farm policy based, at least in part, on the hypoxia zone.
“I think they're missing a couple of important issues. For example, in the Midwest, it isn't just the fertilizer use that's a problem. That area also has a massive system of underground drainage. Traditionally, there's a snow pack and when it melts in the spring, the faster it drains off the faster they can work the fields. So there are thousands of miles of underground pipes. And when draining, it just flushes whatever's in the soil directly into creeks and rivers.”
There are efforts under way to revamp those systems. Many of the older ones are breaking down and must be replaced anyway. Daigle says it would be better to fix them in a way to allow water to be held. That would be useful in droughts and, “if held for long enough, the nitrate inputs into rivers could be reduced.”
Daigle admits that many believe the hypoxia problem is so large it can't be fixed.
“But I believe the problem can be reversed. It's probably easier to deal with than the coastal restoration problems. This should be an opportunity for states to get federal money for projects they probably want to do anyway. That would include conservation programs, nutrient management programs and other things.”
And what happens if current trends continue? “It's hard to say for sure. This involves a collection of very dynamic systems. But our efforts aren't punitive, at all. We're trying to care for farmers upstream and shrimpers downstream.”