A new research study published by the Canadian Journal of Fisheries and Aquatic Sciences investigated the phosphorus loading in Canadian fresh waters. It aimed to understand the geographic patterns and environmental drivers of this vital process in aquatic ecosystems.
The journal’s article “Internal Phosphorus Loading in Canadian Fresh Waters: A Critical Review and Data Analysis” was written and researched by Diane Orihel (Queen’s University), Helen Baulch (University of Saskatchewan), Nora Casson (University of Winnipeg), Rebecca North (University of Missouri), Chris Parsons (University of Waterloo), Dalila Seckar (Queen’s University), and Jason Venkiteswaran (Wilfrid Laurier University).
The nutrient phosphorus (P) is a major contributor to the growth of toxic algal blooms. The study combined 43 publications and consolidated 618 estimates of internal phosphorus loading from ponds, lakes, reservoirs and coastal wetlands.
Around the world, the occurrence of eutrophication poses a serious threat that results in poor water quality. It occurs when a water body is enriched too much with nutrients and the excess induces the over growth of plants and algae. Consequences include oxygen depletion resulting in fish killings and biodiversity loss. One common cause of eutrophication is phosphorus run-off from agricultural lands that have been treated with chemical fertilizers or enriched with biosolids.
In the new study, scientists investigated a significant, but poorly understood, process in Canada’s aquatic ecosystems: the recycling of phosphorus between mud at the bottom of lakes and the overlying water. Nutrient enrichment also worsens infection rates and diseases in animals as many cyanobacteria present in eutrophication produce brain and liver toxins.
Experts in the field and government agencies have sought to find solutions to improve water quality in nutrient-polluted bodies of water. Initiatives to minimize eutrophication by diverting sewage effluent or developing advanced wastewater treatment have had a significant impact. However, such measures still did not result in ideal outcomes as improvements are often delayed for several years or even decades.
According to previous studies by Dennis Cooke and Eugene Welch (1995), and Martin Søndergaard (2013), the delayed recovery of bodies of water combined with the long history of nutrient pollution results in sediments containing a large amount of legacy phosphorus, which under certain circumstances can be recycled to surface waters and stimulate algal blooms. The release of nutrients from sediments, known as “internal loading”, is a complicated process that can trigger a number of physical and biogeochemical mechanisms.
The new research aims to understand how phosphorus speciation in sediment changes over time and with depth. Internal phosphorus loading differs widely among water bodies, ranging from an almost negligible contribution in some systems to dire consequences in others. This complexity makes regulating eutrophication in fresh waters a difficult problem for resource managers. The study details the molecular-level mechanisms by which phosphorus may be released from the solid to the aqueous phase. It also examines how mobilization mechanisms are affected by changing conditions that either enhance or inhibit internal phosphorus loading.
The authors of this study also identified the key factors controlling this process, such as oxygen, pH, geology, and lake nutrient status, which often acts against the best efforts of lake managers. They also acknowledged areas where there are large gaps in data. Helen Baulch, assistant professor at the University of Saskatchewan said, “There’s a lot more we need to know about internal phosphorus loading, such as if this process is important in the thousands of reservoirs of our country, and we have huge data gaps for this process in our northern lakes that are undergoing rapid change.”
“Our main goal was to better understand where, when, and why this process occurs in Canadian fresh waters so that we can make improvements to how algal blooms are managed and develop realistic goals for lake restoration,” said lead author Diane Orihel, an assistant professor at Queen’s University. “We need to stop dumping phosphorus into our lakes, because it’s not only causing problems right now, but in many lakes, it continues to deteriorate water quality for our children and grandchildren.”
Jason Venkiteswaran, an assistant professor at Wilfrid Laurier University said, “We rely on phosphorus to fertilize our soils and produce the food that the world needs. However, we don’t know how long that phosphorus sticks around in our lakes after we allow it to wash off the land and down our drains. Our work here cautions that we should have different expectations for the recovery of different types of lakes across the country.”
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