This post is a part of a series on Ask a Scientist
Every summer, a low-oxygen area called a dead zone develops off the coast of Texas and Louisiana when nutrient-polluted water from the Mississippi and Atchafalaya rivers flows into the Gulf of Mexico. Over the last five years, the dead zone averaged 5,770 square miles in size, slightly larger than the state of Connecticut.
Mainly caused by nitrogen-rich fertilizer runoff from Midwest farms and livestock operations, nutrient pollution streaming into the Gulf promotes massive algal growth, which depletes oxygen, killing fish and other marine life if they cannot escape. That’s bad news not only for fish, but also the Gulf’s commercial fishing industry, which supplies more than 40 percent of US domestic seafood.
A report released this summer by UCS Food and Environment Program economist Rebecca Boehm, Reviving the Dead Zone, provides the first comprehensive assessment of the Gulf of Mexico dead zone’s economic impact, and warns the root problem—agricultural nutrient pollution—will likely worsen due to climate change. The dead zone causes as much as $2.4 billion in damage to fisheries and marine habitat every year, the report found, but there are proven ways to clean it up that would benefit farmers and the fishing industry alike.
In pre-pandemic days, I would have dropped by Dr. Boehm’s office, which is just across the hall from mine, to ask her a few questions about her report. Now, I’m relegated to exchanging emails with her. An edited transcript is below.
EN: Reviving the Dead Zone sounds like a horror movie. Why do we hear about this dead zone in the Gulf of Mexico year after year? Can you give us some more details about what causes it?
RB: Do you remember your high school chemistry class, when you learned about the element nitrogen?
EN: Vaguely. That was a long time ago! Please remind me.
RB: Well, without nitrogen, plants can’t grow. That’s why farmers use nitrogen fertilizer to ensure better crop yields. Midwest Corn Belt farmers use it extensively. The nitrogen routinely washes off their fields when it rains, or it leaches into the soil and contaminates groundwater. Either way, it finds its way into streams and rivers and eventually into the Mississippi River, which empties into the Gulf of Mexico. Once there, as you mentioned in your intro, it stimulates excess algae growth. This algae overgrowth sets off a chain reaction, ultimately depleting the oxygen marine life need to survive, creating a dead zone.
Our report calculated that since 1980, 31 million tons of fertilizer containing nitrogen has washed off farms in the Missisiippi River basin. On average, that amounts to about 1.7 million tons per year. And, as we show, there has not been any significant reduction in nitrogen pollution in the Mississippi watershed over that time.
Dead zones occur off other US coasts, too, including in the Mid-Atlantic’s Chesapeake Bay. There is also a recurring dead zone in the Baltic Sea. It’s hard to say which one is the world’s biggest, because the size of a dead zone can change from year to year depending upon the amount of nitrogen pollution, ocean dynamics, and in the case of the Gulf of Mexico, hurricanes.
EN: Federal and state agencies have been reporting large dead zones in the Gulf of Mexico for decades, but the Gulf fishery is still one of the most productive in the world. Does the dead zone really matter?
RB: Think of the damage cost we calculated as a lost opportunity. The Gulf could be even more productive, if not for this chronic, preventable problem.
It’s also important to look at the equity implications. Many of the people who fish for a living in the Gulf of Mexico are immigrants, including refugees from Vietnam who fled to Louisiana during the Vietnam War. Others are indigenous to the Gulf Coast, including members of the Houma tribe. It’s a very diverse industry that is struggling economically.
The dead zone compounds other problems that plague the Gulf fishing industry. Shrimp, the Gulf’s top seafood product, are not only harmed by the dead zone, the people who harvest them—the shrimpers—are also having a hard time competing with cheaper, and in some cases unsustainably produced, imports. Meanwhile, climate change is exacerbating the dead zone by triggering heavier rainfall and more frequent flooding. Flooding in the Midwest sends more fresh water into the Gulf, which harms the fishing industry, too. Climate change also warms up Gulf water, turbocharging hurricanes. Hurricane Laura is just a recent example.
There are ripple effects along the Gulf Coast for restaurants, hotels, and recreational fishing and other tourism industry operations. Nationwide, seafood consumers pay higher prices. And this year, Gulf fishers have had a particularly tough time due to yet another major problem—the coronavirus pandemic. Restaurants have shuttered across the region, so there is no market there for their catch.
EN: What impact does nitrogen pollution have on people besides the the folks that work in the commercial fishing industry?
Even before it gets to the Gulf of Mexico, runoff has a negative impact on communities up and down the Mississippi River and its tributaries. Nitrogen pollution from farming contaminates Midwest drinking water sources, which then have to be treated to ensure that the water is safe to drink. That’s expensive. It costs Des Moines, Iowa, a half a million dollars a year to treat nitrate-polluted water. And you can’t see, smell or taste nitrate in water, so people living in rural areas who get their water from private wells may not even know that their water is contaminated with nitrates.
EN: What can farmers in the Midwest do to address this problem?
RB: A combination of current farm policies and market forces, as well as individual challenges, have locked farmers into managing their farms in a particular way. They just can’t rip up a corn field overnight and plant something else. They just can’t sell a machine that is designed to harvest a specific crop and buy something new. It’s more complicated than that. Farmers face pressures from a range of things, including extreme weather, trade instability, high land prices, low crop prices, and increasing consolidation among the brokers that buy corn and soybeans. That’s why it’s so critical to reform state and federal policies to help them transition to better, less-polluting practices.
As it turns out, many farmers are eager to reduce nitrogen runoff, conserve their soil, and protect the environment. The US Department of Agriculture’s Conservation Stewardship Program, which helps farmers adopt holistic conservation practices, even has a waiting list of farmers who want to participate. Unfortunately, that program and other similarly helpful USDA programs are woefully underfunded. They can’t handle the growing demand unless Congress appropriates more money.
Some environmentalists argue that federal policy should require farmers to adopt certain practices to mitigate nutrient runoff and other water pollution problems. Perhaps, but any policy approach must be carefully considered to take into account competing interests and the risk of unintended, negative consequences for farmers and consumers alike.
EN: So, in the absence of truly smart policies, what should farmers and ranchers do? Do the solutions to clean up the dead zone come with enormous costs?
RB: Our Food and Environment Program team would like to see farmers adopt science-based, healthy-soil practices that would help shrink the dead zone. These practices include planting more diverse crops, establishing buffers of native prairie plants in and around crop fields, and “cover cropping”—which is when a farmer plants a crop, such as ryegrass, to cover the soil during the off season so it won’t erode or leach nitrogen, instead of leaving the field bare. Agricultural researchers in the Midwest, who have been assessing the effectiveness of these methods, have seen positive results. They can dramatically reduce environmental damage from typical farming practices.
From an economic perspective, one of the biggest barrier farmers face in adopting these methods is the upfront and yearly costs of maintaining them. That said, over time, farmers may see some significant return on their investment by making these changes. For example, we know that climate change will increase the frequency and severity of rainfall in the Midwest. Some of these practices would help reduce the negative impacts of such extreme weather events. So, in a way, diversifying crops, cover cropping, and other, similar methods could provide some insurance for farmers.
Earlier this year, US Rep. Chellie Pingree, a farmer from Maine, introduced legislation that would help more farmers adopt these practices and advance the science of agroecology. We support that bill. Despite the fact that Congress has a lot of other problems on its plate right now, we will be pushing it to enact Pingree’s bill in the next session.
EN: Finally, just as we were conducting this interview, Hurricane Laura hit the Texas and Louisiana coasts. This year the United States is experiencing above-normal hurricane activity. How do hurricanes affect the dead zone?
RB: Hurricanes can break up the Gulf dead zone. Earlier this summer, Hurricane Hanna blasted through the dead zone just before scientists set sail to measure its size this year, making it appear smaller than it probably was. And of course hurricanes are harmful to Gulf Coast communities in many other ways, as some of our colleagues recently pointed out. So if we want to truly shrink the dead zone in the Gulf—and eventually get rid of it—it will take good policies that help both farmers and fishers. No one should be hoping for more hurricanes!
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