Lakes are getting greener on a global basis – and in this case, “going green” is not a good thing, said Rebecca North, assistant professor in the School of Natural Resources.
The greening of lakes around the world is due to algal blooms, which form in a body of water when sunlight and nutrients like phosphorus and nitrogen combine to promote aquatic plant growth. The blooms form on the top of the water, and then fall to the bottom. As they fall, they consume oxygen, forming a “dead zone,” and can also produce toxins such as microcystin.
“The nutrients that make crops grow on land makes algae grow in water,” North said of the process.
Lately, these algal blooms have been found more frequently and are more widespread than ever before. Scientists have been curious as to why this is happening, especially since regulations and improved sewage treatment options have been around since the 1970s to restrict the ability of these nutrients to reach water sources.
The toxic blooms are a health concern, especially in areas where groundwater cannot be used for drinking water, North said. In some places, bodies of water like lakes and reservoirs provide drinking water. In the summer of 2014, dangerous levels of the toxin caused Toledo, Ohio, to shut down its drinking water supply for three days, for example. Toledo draws its drinking water from Lake Erie, which is again experiencing a significant algal bloom, although toxin levels are currently low in the areas from which drinking water is drawn.
North’s research looks to why blooms are forming more often and what can be done to stop formations. She is part of a research team that has found that “legacy phosphorus” – phosphorus stored at the bottom of these bodies of water – might be a key part of the ongoing issue of greening lakes.
“Lakes are a giant collector basin,” she said. “Everything is stored in the sediment.” It’s a cyclical issue – the lack of oxygen caused by the blooms helps release the phosphorus from the sediments.
Her team found that geology has a large role to play in the problem – prairie soils release more legacy phosphorus, for example. The goal of this research is to improve how blooms are managed and develop realistic goals for lake restoration, North said.
Another piece to the blooming puzzle is to keep nutrients out of the bodies of water in the first place, North said. Nutrient management includes fertilizing crops – and lawns – at ideal times such as not right before rain storms when it will wash off the land or on frozen soils, and keeping septic systems in good repair.
“It’s all about awareness – when are you applying fertilizer to your lawn, and where your waste goes,” North said.
Storm water run-off in both agricultural and urban settings are big contributors to the issue, she said. Producers can plant winter crops and cover crops to use up the nutrients rather than having them potentially wash away.
North’s research most recently looked at blooms under ice in Canada, where she was a research associate at the Global Institute for Water Security at the University of Saskatchewan. She joined the University of Missouri last fall. Here she directs two programs, the Lakes of Missouri Volunteer Program and the Statewide Lake Assessment Project (SLAP). SLAP has monitored water bodies in the state with consistent methods since 1979. That data is now helping the state to set parameters for calling a body of water “impaired,” North said. The only issue with this monitoring, is that it relies on student labor, so most of the water monitoring is done in the summer months. This makes it hard to tell if the data is reliable enough to make year-round assumptions about algal blooms, since abundant sunlight is a primary factor in their creation and they can occur year-round.
The Lakes of Missouri Volunteer Program uses trained members of the public to monitor bodies of water six times per year.
North has also started a new program with local youth – ROSS (Reservoir Observer Student Scientists) where Rock Bridge High School students sample water weekly, year-round, from Bethel Lake, which has suffered from algal blooms.
“Our data tends to have a summer-centric view,” North said. “We don’t have data on winter.”
North was co-author on a paper published in September 2017 in the Canadian Journal of Fisheries and Aquatic Sciences, “Internal phosphorus loading in Canadian freshwaters: a critical review and data analysis.” The article was also selected by the journal as an “Editors’ Choice” paper for 2017, which highlights articles of particularly high caliber and topical importance.