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The problem with phosphorus

Lake Winnipeg is suffering from phosphorus overload, but agriculture is just one contributor

Lake Winnipeg has a phosphorus problem. That’s not a controversial statement. But what can spark plenty of arguments is just what’s causing the problem.

One of the handiest targets has long been local agriculture in general, and the province’s hog sector in particular.

The hog sector and provincial government both claim the sector faces some of the most stringent regulatory requirements in the country, including a ban on winter spreading.

“In addition, the province continues to monitor nutrients, algae and their associated toxins in Lake Winnipeg and also in rivers and streams flowing into the lake,” a spokesperson from Manitoba Sustainable Development said. “This information is critical to track progress and assess change over time.”

An illustration showing the changing nature of algal blooms on Lake Winnipeg from year-to-year.
photo: Source: Shawn Stankewich/Greg McCullough

But anti-hog activist group Hog Watch says that’s not going far enough. They want the province to halt new barn development until a new study can be done.

“We’re not talking about the smaller family-run farms that might have a few hundred or up to a thousand pigs,” Vicki Burns of Hog Watch said. “We’re talking about the large, corporate-owned barns where there are thousands of animals.”

What the group is proposing is a “edge of field” story to measure phosphorous runoff from fields treated with hog manure. They’re using issues with agal blooms to bolster their pitch, but others say that would be too simplistic, and would examine just one potential source of the problem.

Why it matters: Field edge monitoring might be worth doing, experts say, but any such study will have to take in the full scope of the phosphorus problem in Lake Winnipeg, and that gets complicated fast.

The study would take samples from April to October at “several sites around the province,” to gauge both snowmelt and rain events, Burns said. Samples would be taken upstream of a field treated with hog manure and compared to a downstream sample.

“What we’re hoping to determine is much more concrete data on what phosphorus is running off of hog fields,” Burns said.

The hog industry, meanwhile, says they are tired of being painted as the villains when the issue is actually far more complicated than just hog manure.

“We’re replacing nutrients to crops from crops that we actually fed to pigs, so in other words, this is a recycling process and it’s a sustainable practice,” Manitoba Pork Council general manager Andrew Dickson. “This is good for agriculture and it also displaces the importation of rock phosphate.”

Much of Manitoba’s soil is actually low in phosphorus. A Manitoba Agriculture soil survey in 2015 found that 64 per cent of soils were critically low on the nutrient, up from 57 per cent in 2010.

At the same time, he argued, spreading is audited by Manitoba Sustainable Development and farms must have a provincially approved manure plan.

“Is there an issue with phosphorus leaking off the landscape to Lake Winnipeg? Of course there is and numerous studies have shown that,” Dickson said, but argued those nutrients come from, “a series of sources.”

Lake Winnipeg receives drainage from a total of four Canadian provinces and the same number of U.S. states.
photo: Source: Province of Manitoba

Many of those sources, he pointed out, are totally outside of the province’s jurisdiction.

According to the Lake Winnipeg Basin Initiative (LWBI), more than 50 per cent of nutrient loading in the lake comes from outside Manitoba. The lake’s basin is massive, crossing four provinces and four states. More land drains into the lake for every kilometre of water surface than “any of the great lakes of the world,” an LWBI report noted.

That 50 per cent, however is more than enough to merit stronger controls, as far as HogWatch is concerned.

“Our feeling on that is let’s put a lot of energy into doing what we can within our own borders to demonstrate leadership,” Burns said. “I don’t think it’s really practical to put a lot of pressure on [others] when we haven’t done our own work here.”

Adding it up

Don Flaten, a soil scientist at the University of Manitoba, applauds any effort to kick start more field studies, although he worries that a study only focused on hog manure will miss the bigger picture.

“The majority of manure that is produced in the province is actually produced by cattle, not pigs,” he said. “If we take a look at the total quantity of phosphorus produced in manure by all of our livestock, it’s still maybe only one-quarter of the amount of phosphorus that we apply synthetic fertilizers or that we remove in our crops when they’re harvested.”

Other sources include treated human waste that may be safe from a human health standpoint, but can still contain significant nutrients.

Those sources are “at least as important in terms of potential contributions to phosphorus loss,” he noted.

Different management practices would also impact those results and should be included in any study, he added.

The phrase “4R” has permeated the agriculture industry. The management philosophy seeks to reduce nutrient loss by putting the right type fertilizer down at the right rate, place and time.

Natural landscapes can both contribute phosphorous and filter it out before it reaches the lake.
photo: Lake Winnipeg Foundation

“We can manage our nutrients better,” Dickson acknowledged. “So we apply it at the rate that crops can pick up on. We can minimize the amount of phosphorus we need to add to the landscape in terms of growing crops. We can do a lot more in terms of municipal waste disposal, in terms of sewage and so on, and there are some issues that we’re never going to be able to solve. Like, we can’t stop dust landing on the lake.”

Research done in places like Indiana have shown the benefit of injecting liquid manure, Flaten said, adding that a study should be used to validate some of those results locally.

Past fertilizer

Even that, however, is not the end of the complexity.

The 2018 report from the Lake Winnipeg Basin Initiative noted that forages and residue from conservation tillage increased dissolved phosphorus in melt water. Frozen forage stands, in particular, lost more phosphorus than cereal stubble when conditions were simulated in a laboratory.

At the same time, those practices are also being tapped to reduce erosion and nutrient loss.

Risk of phosphorus loss plummets below the first few centimetres of soil, Flaten said, and management practices that increase infiltration can arguably pull down those nutrients rather than eroding the field and sending those nutrients downstream.

Practices like no-till, cover crops, and perennial cover have gotten a healthy push from Manitoba Agriculture’s livestock and soil extension staff for those reasons. Increased organic matter from perennial cover and cover crops have also been tied to better soil structure and reduced compaction, both tipping the scales towards infiltration rather than run-off.

“We need to be considering the loss of water as well as the loss of nutrients in order to figure out the total load, and this is where it gets complicated and the studies need to be conducted very carefully,” Flaten said. “You can’t just take a run-off sample from ‘this’ field, compare it to a run-off sample from ‘that’ field, see the phosphorus concentration and then start jumping to conclusions.”

Let the research flow

Flaten agreed, however, that there is little current data from the field edge itself, regardless of whether that field has been treated with chemical phosphorus or manure.

“That’s partly because the methods are very difficult to employ,” he said.

It’s hard to predict where snowmelt will flow in Manitoba’s flat topography, he said, making sampling difficult. The still freezing overnight temperatures add another problem, since it risks equipment damage.

There is some work happening, he said, citing research from David Lobb, his colleague at the University of Manitoba, as well as soil scientists around Brandon.

Environment and Climate Change Canada says they are also looking at field edge run-off results as part of the Lake Winnipeg Basin Initiative, although results will take time. The initiative launched field edge monitoring between 2012 and 2017, but were unable to complete the project before the second phase’s final report at the end of the period. The initiative’s third round inherited that research and is set to end in 2022, according to the agency.

“The transport of nutrients from agricultural fields is highly dependent on weather conditions and in the case of hog manure applications, the timing of the application with respect to weather is critical,” a spokesperson said. “Manure applications on agricultural fields are not made every year and therefore research of this nature requires several years to complete.”

The Lake Winnipeg Foundation is also looking for more data.

There are “multiple sources of phosphorus and multiple factors that impact phosphorus loss from fields,” the foundation’s executive director, Alexis Kanu, said.

The foundation supports the idea of the study proposed by Hog Watch, although Kanu did note the need for research to, “tease apart the different sources of phosphorus in our rural landscape.”

“I think we’re at the point of saying we need to firstly identify where the phosphorus is coming from in terms of geography,” she said.

Burns also acknowledged the role of other phosphorus sources, although the group’s August press release singled out hog manure. Their group has requested a meeting with the University of Manitoba’s dean of agriculture to discuss the form and scope of the study, she said.

About the author

Reporter

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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