CLIMATE

Gasping for Air

Climate Change and Failed Agricultural Policies Are Creating an Oceanic Disaster

Every summer, like clockwork, a vast body of nutrient-choked and oxygen-depleted water, roughly the size of New Jersey, forms off the mouth of the Mississippi River in the northern Gulf of Mexico. Fed by millions of tons of nitrogen- and phosphorus-rich agricultural runoff, this hypoxic zone—or, as it’s more commonly known, “dead zone”—has been expanding at an alarming rate over the past few decades as fertilizer and fossil fuel use have surged.

Much of the blame has been laid on anthropogenic activities, such as rising farm production and energy consumption, and the imbalances they have created in the global and phosphorus cycles.

While the Gulf dead zone may be the best-studied (and most infamous) example, many others—over 43, at last count—have sprung up around the country in recent decades, most noticeably in the Chesapeake Bay and off the coasts of Oregon and Washington.^[1] Ranging widely in size from small areas in coastal bays to vast swathes of water in the open ocean, they are typically located in temperate seas. According to a 2004 United Nations report, there are now over 150 documented dead zones around the world. Another report found that the number of dead zones had roughly doubled every decade since the 1960s.^[2]

And here’s the kicker: While most are still seasonal, climate change could prolong these events—and make them much more frequent.

One of the world’s longest river systems, and the country’s largest carrier of river-borne nutrients, the Mississippi River drains 41 percent of the contiguous United States.^[3] At the mouth of this system lies the planet’s second largest zone of oxygen-depleted waters—the Gulf dead zone—that is estimated to cover an area greater than 10,000 square miles this year. Over the past few decades, a number of studies have cast light on the causes and impacts of such hypoxia events.

Much of the blame has been laid on anthropogenic activities, such as rising farm production and energy consumption, and the imbalances they have created in the global nitrogen and phosphorus cycles—increasing these key nutrients’ availability to coastal and ocean ecosystems. The presence of these excess effluents stimulates the rapid growth of phytoplankton, microscopic plant-like organisms, producing massive blooms. When they eventually deteriorate and sink to the seafloor, they are feasted upon by a vast array of microorganisms, which consume all of the available oxygen in the surrounding waters—creating anoxic, or dead, zones. Well-oxygenated waters typically contain up to 10 milligrams of oxygen per liter, or 10 parts per million (ppm). In hypoxic zones, by contrast, the concentration of dissolved oxygen often falls below 2 ppm; in some cases, it can plunge below 0.5 ppm and remain there for several months—leaving behind an area completely devoid of life. This process, which significantly reduces biodiversity and alters entire food webs, is known as eutrophication.

There is great concern among scientists and government officials that booming corn production could seriously harm these already stressed waters. U.S. farms are expected to produce record amounts of heavily fertilized food crops, and the government is signaling that it may free up even more land to plant corn. Combine this with the huge input of farm runoff the floodwaters from the Midwest will bring, and the result is the largest dead zone ever seen in the Gulf. With agricultural production likely to maintain its upward trend—especially in light of the current food crisis—and with more unprecedented weather events in the offing, such problems will become more commonplace.

Indeed, some scientists fear that global warming has already aggravated and prolonged dead zone events off the coasts of Oregon and Washington. Jane Lubchenco, a marine ecologist at Oregon State University, believes that the stronger winds produced as land heats up are prolonging upwelling in coastal waters.^[4] Upwelling is the process by which deep, nutrient-rich waters are driven up to the surface by winds; it provides a vital source of food that stimulates much of the ecosystem’s primary production. In this case, however, too much of a good thing can be harmful. An excess of phytoplankton that isn’t consumed will die and fall to the seafloor, creating large, oxygen-free zones. Worse, Lubchenco and her colleagues found that the low-oxygen areas, which typically reside in deep waters, are spreading to shallow fishing waters—a discovery Francis Chan, a fellow ecologist, described as “unprecedented.”

Efforts begun by the federal and state governments in 2001 to rein in these problems have yielded precious little by way of results. The original proposal, intended as a coordinated federal plan to shrink the dead zones by making cuts to nutrient runoff, never made it past the budget process once the Bush administration took office. A revised plan led by the Environmental Protection Agency would maintain the dual objectives of shrinking the Gulf dead zone to about one-quarter of last summer’s size by 2015 and of slashing nitrogen and phosphorus levels by 45 percent apiece. Yet because the plan mandates that states complete their implementation strategies by 2013, leaving only two years to achieve the necessary reductions, some scientists have already criticized it as being toothless and backward-minded.

At this rate, it is clear that we may be close to reaching a tipping point after which dead zones will be considered the “new normal,” as Lubchenco puts it. The consequences will be devastating: completely altered ecosystems, dwindling biodiversity and exhausted fisheries populations, to name a few. Buffeted by other forces, including acidification and thermal expansion, our oceans may have already passed the point of no return.

Jeremy Jacquot is a graduate student in marine environmental biology at the University of Southern California and is the Los Angeles correspondent for TreeHugger.com.

Notes

[1] Dybas, C.L. 2005. Dead zones spreading in world oceans. BioScience 55(7): 552 – 557.

[2] Dybas, C.L. 2005. Dead zones spreading in world oceans. BioScience 55(7): 552 – 557.

[3] Rabalais, N.N. et al. 2002. Beyond Science into Policy: Gulf of Mexico Hypoxia and the Mississippi River. BioScience 52(2): 129 – 142.

[4] Chan, F. et al. 2008. Emergence of anoxia in the California current large marine ecosystem. Science 319: 920.

Tags: Climate Change, oceans

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