Facing up to Phosphorus, continued
Carpenter has been studying eutrophication since the mid-1970s, when the high-profile damage to Lake Erie shamed detergent manufacturers into lowering the phosphate content of their products. By the late 1990s, he observes, researchers were finding most of the ongoing eutrophication in North America was due to phosphorus runoff from farms. Most recently he considered what the ultimate planetary boundary might be for phosphorus discharge into the environment, a matter he explores as co-author of a paper appearing in the February 2011 Environmental Research Letters.
That paper argues that the boundary for the discharge of phosphorus into freshwater has already been exceeded. At the same time, many parts of the world remain in urgent need of phosphorus in order to be able to feed themselves. Carpenter suggests that regions with a surplus of phosphorus could solve two problems at once by packaging that surplus in the form of struvite for markets elsewhere.
“Midwesterners are rich in phosphorus, but they also suffer lots of toxic algae blooms and fish kills,” he says. “Technologies to convert manure to lightweight [high-phosphorus] materials would help cure eutrophication in the Midwest while curing hunger in Africa.”
As straightforward as that objective might appear to be, it conflicts with the ruthless economics of modern agriculture. According to Carpenter’s co-author, Elena Bennett, large-scale livestock operations can leave little financial room for investing in technology to recover phosphorus, as the expenses associated with recovery equipment will not necessarily be recouped by sales of the resulting product.
“We’ve moved from a system a couple of hundred years ago where you had a couple of cows and a couple of chickens and some corn, and so the manure was a useful resource,” explains Bennett, an assistant professor at McGill University’s Department of Natural Resource Sciences. “Now, things are just out of whack at the scale that we operate.”
That doesn’t mean that phosphorus removal is uneconomical, however. Bennett maintains that the cost of reducing phosphorus discharge should be weighed against the value of services provided by the environment under threat. Depending on the site in question, those services could include clean drinking water, recreational opportunities or hydroelectric power generation.
“This isn’t about the natural world versus the developed world,” insists Bennett. “This is about nature providing us with all these things, and some of those things it provides better when it’s in a natural state and other things are better in a built state. If we can understand which states provide which amounts of which services, then we can start making more informed decisions.”
Wetlands to the Rescue
This principle is being put forward to deal with the specific challenge posed by Lake Winnipeg, which has been touted as the world’s largest eutrophic lake. That dubious honor stems from the lake’s role as a catchment basin for four Canadian provinces and four U.S. states, concentrating soil runoff in this primarily agricultural region. According to the International Institute for Sustainable Development, based in the city of Winnipeg, much of that runoff travels unimpeded into the lake because coastal wetlands have been drained for farming.
IISD project manager Vivek Voora says that convincing farmers to leave wetlands in place to capture phosphorus and other nutrients from runoff rather than allow them to fertilize the lake amounts to competing with the value of those wetlands as planted fields. Delta Waterfowl, a longstanding Manitoba organization dedicated to preserving marshes for hunting, tries to match that value dollar for dollar with financial compensation to farmers who set aside wetlands. But as the price of some crops rises, this amount may not remain competitive with other uses for the land.
“We need to find a way to show farmers that managing a wetland is profitable,” Voora explains. “It will provide money in your pocket.”
Over the last few years, Voora has explored how natural wetlands could take part in a novel biological economy. Plants such as cattails could be harvested for conversion into bioplastics, or pelletized to become fuel. Meanwhile, the intact wetland will sop up most of the nutrients that would otherwise reach the lake.
In this sense, Voora points out, wetlands function as important pieces of ecological infrastructure. They may not be as focused and efficient as the kind of infrastructure cities could use to retrieve phosphorus from their wastewater for use elsewhere, but they can provide crucial services on farms where such built infrastructure is unlikely to appear.
“A nutrient that is so fundamental to the economy of this particular region,” he says. “For us to be wasting it, for it to end up in water bodies and causing environmental problems, doesn’t make a bit of sense.”
TIM LOUGHEED has worked as a freelance writer in Ottawa, Canada, since 1991. A past president of the Canadian Science Writers’ Association, his work covers a broad range of topics in science, technology, medicine, and education.
For much of human history, cow manure served as a valuable source of phosphorus for fertilizing crops. Today the concentration of cattle in feedlots creates a localized overabundance of the nutrient, transforming it from treasure to trouble.
Phosphorus leached from soil, vegetation and manure stimulates the growth of algae in surface waters. Nutrient inputs from its mainly agricultural catchment basin have earned Lake Winnipeg the title of the world’s largest eutrophic lake.
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Last modified on January 23, 2012