Charting a New Path: Overcoming a Legacy of Pollution
Nandita Basu wants to know what’s hiding in our soils. What she’s learning is helping redefine the way we manage nutrient pollution and protect freshwater health.
When professor Nandita Basu explains the kind of research she does, she’s often asked about what’s causing those stinky algal blooms that cover lakes in the summer months. The answer is that these blooms form when there is too much nitrogen and phosphorus in the lake. When the fertilizers being applied to crops and lawns are washed away by the rain, these nutrients can trickle into freshwater bodies and cause trouble across the ecosystem.
The cause of algal blooms may be simple to identify, but solving the nutrient problem has been an incredible challenge. Even when we take steps to reduce fertilizer runoff, water quality does not always improve.
Part of the reason lies in the past – the fertilizers we applied to cultivate crops decades ago are coming back to haunt us. Research has shown that the nutrients from fertilizer applied years ago can accumulate over time in soils, reservoirs, and lake sediments, and continue to pollute and degrade water quality, threatening animal, human, and ecosystem health.
Photo: Nandita Basu, Professor & Tier I Canada Research Chair in Global Water Sustainability and Ecohydrology, Departments of Civil and Environmental Engineering Earth and Environmental Sciences.
According to the U.S. Environmental Protection Agency, nutrient pollution is one of America’s most widespread, costly, and challenging environmental problems. Governments across the world have been trying to solve this problem for decades with not much measurable improvement.
It’s a similar situation in Canada, especially in the Great Lakes Region.
“In Ontario, our provincial and federal governments are trying to manage the amount of nutrients making their way into freshwater bodies,” says Basu, who is Canada Research Chair in Global Water Sustainability and Ecohydrology at University of Waterloo. “It’s a tricky problem.”
Basu is interested in how humans are changing the landscape. She wants to find solutions that that reduce the excess nutrients that enter our lakes, groundwater and streams, while maintaining agricultural production and economic viability of our landscapes.
Due to nutrient legacies, we need to pay attention to what we are doing now and, at the same time, try to understand and manage the impacts of past decisions. If you determine that manure or fertilizer is an issue, you can stop applying it. You can come up with ways to use less of it, or you use it more efficiently. But if there is already phosphorus in our soils, we’ll be dealing with it for a long time to come.
Determining the current scenario
Legacy phosphorus is difficult to quantify, Basu explains. Part of the challenge has been finding ways to collect and analyze historical data in a way that accurately describes the legacy that has accumulated, and how that impacts the current situation.
As part of Lake Futures, a project funded by the Global Water Futures (GWF) program, Basu and her colleagues developed the first-ever model that estimates the amount of legacy phosphorus that has accumulated in the Grand River basin. When staff at Environment and Climate Change Canada (ECCC) saw the results, they funded an expansion of the model to cover additional watersheds.
By making use of 70 years of agricultural census data to understand the history of fertilizer and manure application in the region, the model can predict how long it will take see water quality improvements, depending on the rate of fertilizer application reductions.
“We stitched the data together, made some assumptions, and began to see the story emerge,” Basu says. “We found that only a small percentage of the net phosphorus (4%) that is applied on the land runs off into streams and lakes. This made it clear that we needed to find out where the rest of the phosphorus ended up.”
The team collected sediment core samples and used water quality data collected by the Ontario government to validate their models. “We found over 500 kilotons of legacy phosphorus in reservoirs and soils of the Grand River Watershed in the Lake Erie Basin,” she says. Gaining a better understanding of the current situation is extremely relevant for achieving targets for phosphorus reduction within the required timeframe, as per commitments established through the Canada-U.S. Great Lakes Water Quality Agreement, she adds.
Collaborating to find solutions
Models are necessary, but we really need to identify what actions can be taken based on results and insights. This is not just a question for science to solve, she adds. “Making our systems more efficient is also a societal issue. And a political one.”
For example, this model revealed the enormity of the livestock manure issue – which also contributes to nutrient loading. “It told us that focusing on appropriate management of livestock waste might be one of the keys to addressing water pollution issues,” Basu says. The team is now collaborating with the Ontario Ministry of Agriculture and Rural Affairs, and Canadian Biogas Association, as well as academics from the energy sector, to consider how the strategic placement of biodigesters on the landscape could help turn manure into energy.
“Together, we are developing models to show how many biodigesters you might need in a given region, and how funding their development could improve water quality,” she says. “This is part of making the transition to a circular economy. We don’t want to eliminate manure entirely. Instead, we want to help find ways to manage it – to treat it like a resource instead of a waste product. Our models provide the data that shines a light on new decision paths.”
The model also revealed that legacy phosphorus in our soils and sediments will continue to leak into water supplies for decades, making downstream nature-based solutions like wetlands another key solution for trapping pollutants before they’re released into the lake.
“Wetlands are great for managing nutrient runoff – they are one of nature’s great filters. But with increasing pressure to build more housing, we’re losing a lot of them, especially in the Greater Toronto Area. Without research that demonstrates the inherent value of wetlands, it’s difficult to argue for keeping them,” Basu says.
In partnership with Ducks Unlimited, and with new funding from ECCC, Basu’s team is using satellite data to show how smaller wetlands are more effective than larger wetlands in removing nutrients like nitrogen and phosphorus.
“In the future, this work will help us create blueprints for where to get the most benefit from wetland restoration,” she says. “In a nutshell: If you have money for wetland restoration, where is the best place to spend it? Where can you get the best value? What kind of impact will it create?”
Building a new legacy
Basu says she prefers to conduct science that has an eye towards societal impact, and that stakeholder-driven projects are a key part of GWF’s success. “The program and access to funding gave researchers a space to think deeply with our partners about their questions and connect with a new network of colleagues to discover some answers.”
The results of Basu’s research on the nutrient legacies, both in the Lake Erie Basin, as well as globally, are charting a new path forward as governments in Canada and other countries grapple with how to improve water quality in the presence of legacy pollutants.
The last seven years of work on the Lake Futures project has also taught Basu the tremendous value of making data and model results easily accessible by decision makers, researchers, and partners. “From conservation authorities to government to citizen groups, there is significant interest in our work,” she says. “It is important to me that our partners and community can easily access our findings, outside of the peer-reviewed literature.”
On this note, Basu’s newest project will develop an open data portal called POSEIDON. Working with partners such as Datastream, ECCC, and a few conservation authorities, the goal is to use machine learning models to convert sparse stream nutrient data into real-time daily nutrient loading estimates for monitoring stations, as well as provide gridded nutrient input (fertilizer, manure) datasets across Ontario.
“The idea of the open data portal stems from questions and conversations from the community about how we can collaborate to solve challenges,” Basu says. “Water and climate data should not become obsolete when a project ends. It needs to stay consistent, alive, and useful, especially as we try to sustainably manage water resources and work toward a healthy climate. This is our ‘why.’ It’s about changing how science works.”