Rethinking Agricultural Drainage Methods with ‘Wet Lands’

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Kevin Bunch
October 09, 2018
mockup canal

Wetlands help provide habitat, mitigate flooding and filter excess nutrients and contaminants from lakes and other water bodies. But vast stretches of wetlands around Lake Erie were drained in the past 200 years for agricultural use. Researchers with the University of Toronto are using Essex County, Ontario, as a testbed for maintaining farming while restoring wetland functions.

Since the 1800s, Essex County has lost about 97 percent of its wetlands, primarily to agriculture, leaving it with the highest wetland losses in Ontario. That agricultural land is dominated by monoculture (identical) crops, limiting its usefulness as habitat for birds and other wildlife. The habitat left is largely fragmented, with the exception of Point Pelee National Park, said Sandra Cook, independent landscape designer and researcher, during a presentation at the 2018 International Association of Great Lakes Research conference in Toronto. Overall, only 7 percent of the land in Essex County is still natural forests, wetlands or prairie, according to the Essex Region Conservation Authority.

mockup canal
A mockup of a widened agricultural drainage canal. Credit: Credit: Sandra Cook and Justine Holzman

The re-engineering of Essex County land using intensive drainage has left it susceptible to flooding and drought, Cook said, which is likely to be exacerbated by climate change. The land also is prone to producing nutrient runoff, which makes its way into Lake Erie and contributes to harmful algal blooms. It’s not feasible to turn all the farmland back into wetlands, Cook said, so she and University of Toronto Assistant Professor of Landscape Architecture Justine Holzman are looking at ways to restore some functionality and habitat within the existing environment through a speculative design research project called “Wet Land.

Holzman said Essex County made for an interesting region because of existing mapping data from the Essex Region Conservation Authority and due to its history and geography. The dramatic shift from wetland to farmland, its location on the north end of Lake Erie and the severity of algal blooms in the lake all were factors in choosing it for this project.

The researchers are using advanced mapping technology to build a flexible model of Essex County that considers the physical, political and social dynamics of the county. Since the Essex Region Conservation Authority already has detailed map data to call on, Holzman added, this allows them to investigate the impacts of different potential solutions to the issues of water pollution and flooding.

essex county map
Essex County is located in the southern end of Ontario along Lake Erie and the Detroit River. Credit: County of Essex

“You want to be as specific as possible for an individual site, while still addressing a regional scale problem,” Holzman said. “How to do that in a complex landscape is quite difficult, especially when the region under consideration is largely privately owned.”

In its strategic planning document, the conservation authority notes that due to the vast amount of private agricultural land in the county, overlaying restoration opportunities atop the agricultural system while focusing restoration efforts on areas ripe for the most gain is their recommended approach; notably, these also can include “soft” recreational benefits like trails or boardwalks. Part of these efforts include mitigation techniques to move runoff away from sensitive, natural areas – something Cook and Holzman are focused on.

Flooding Fields

The first concept the researchers are looking at is the flooding of agricultural fields with water diverted from municipal surface drains, either earlier in the season during the spring melt or for the entire year. This would allow them to potentially be used as habitat while retaining water and runoff, said Holzman. Berms would hold the spring runoff, allowing excess phosphorus to be absorbed into soil particles; the field can then be used for late-season planting of frost-sensitive crops or left fallow for a year as a temporary wetland to recharge the soil. Cook said these temporary wetlands could provide habitat and resting points for migrating birds. The details of such a project are still being developed as a set of best management practices that farmers could tailor to their specific land.

“You could say flooding in agricultural fields would be similar to creating a rain garden on a homeowner’s property in a city, with different policies and incentives,” Holzman said. She added that is still in the conceptual design stage, which involves mapping and strategizing; this would be followed by working with scientists to develop an experimental test to see how the environment and people react. On the whole, whenever this experiment is started, it is expected to run for eight years, with a focus on monitoring nutrient runoff.

Collecting Runoff

Another idea involves collecting field runoff for irrigating crops later in the season, which would be a beneficial buffer during a drought. Cook said using their mapping data, the researchers can look at the potential for “recycling reservoirs” that could be set up throughout the county to store excess water in the spring for usage later in the season. The edges of the reservoirs also could make for suitable habitat for plants that can sequester excess nutrients in the water and reduce erosion. Similar projects have been tested in Essex County using demonstration farms with positive results.

“The (controlled drainage system) combined with a wetland-reservoir can be highly effective for improving crop yield and reducing nonpoint source pollution from agricultural fields,” wrote Chin Sheng Tan of Agricultura & Agri-Food Canada in a 2007 paper about water quality and crop production using these wetland reservoirs.

Other items include developing maps and tools that individual landowners could use to size out and place buffer strips and other habitat sites. Cook said buffer zones are voluntary in the county, so research is focused on ways to make them mandated but still fair to farmers. The Essex Region Conservation Authority issued a strategy document in 2013 providing guidance as to where buffer strips should go in and how large they should be for each type of habitat opportunity – as well as the general locations of those opportunities – but this project would build on that to provide advice and information for each specific parcel of land.

“Rather than mandate that everyone must have a 20 meter or 5 meter (65 foot or 16 foot) buffer, we can use spatial modelling to showcase the value of flexible policies that cater to individual farmers,” Cook said. “What does a buffer at 1- or 5-percent of a property look like and what potential effect does it have for the watershed?”

Finally, the researchers are considering ways to encourage farmers in Essex County to move from growing low-value crops on large amounts of land to high-value crops on less land. Holzman said this “intensive farming” is already happening, but their research notes that a large number of farmers in Essex County need to take a second job to make ends meet. The now-unused land could be set aside for conservation efforts.

If these efforts pay off and are implemented in the county, the amount of natural cover and water storage and filtration would dramatically increase over the 8.5 percent of overall land they’re both at now, according to Cook. At even a 10 percent adoption rate countywide, habitat could increase by 68 percent in the off-season months and 19 percent year-round while providing 46 percent more water storage; those numbers continue to dramatically climb as more people get involved. Funding these changes would require farmers moving to higher value crops, which Cook said could in turn be funded through government loans and grants; she added this could end up being an economically valuable approach as Ontario could import fewer of these high-value crops (such as fruits and vegetables) and potentially reduce the impact of harmful algal blooms.

Picture of Kevin Bunch
Kevin Bunch

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.