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Phosphorus: measuring, modelling, and managing – new research on phosphorus dynamics in the Bay of Quinte
By Gord Speksnijder, Quinte Director
How much phosphorus (P) is moving into the Bay of Quinte? What impact is P having on the aquatic ecosystem? On drinking water? What role does agriculture play? The Ecological Modelling Group at the University of Toronto is tackling these big questions and, as you might imagine, the answers are complex.
I recently attended a 3.5-hour webinar during which several researchers in the group summarized their findings thus far. This was my first exposure to all the pieces of the research effort, and I was taken aback by the breadth of work and the many factors being considered from top to bottom of the Quinte watershed. A single article can’t come close to capturing all the details, so here is a quick overview:

Like farmers meeting at a coffee shop, the first topic was the weather. The research group has reams of weather data from the past which they feed into computer models designed to predict the future. These “data-driven” models are tested for their ability to align with existing data before they are used to make predictions. If the models don’t align, analysts find out why, then tweak the models and/or feed them additional data until they do. This testing process gives the researchers confidence that the models are working properly and are based on the right information. Thus far, the models are predicting increases in mean temperatures, more warm days and nights, longer warm spells (30oC+), longer growing seasons, decreasing cold days and nights, shorter cold spells, and fewer frost days. The models don’t predict that total annual precipitation will change much, but they do predict that wet spells will occur more often, be spread over more days, and that fewer of those days will have heavy rainfall. The frequency of precipitation extremes is not expected to increase in the summer but may in fall and winter, which has implications for P movement in the non-growing season.
Next covered was the impact of weather events on the rivers and creeks that feed the bay. Several existing models consider soil type, topography, vegetation etc. to assess the risk of erosion and movement of sediment (with associated nutrients) to waterways. Researchers using these tools to better understand relationships between precipitation and waterway flows noticed unusual results for some rivers and creeks. To understand why, they physically surveyed the waterways and discovered that dams (made by people or beavers), bridge structures, stagnant areas and other obstacles were all impacting flows. In some cases, wetland areas temporarily stored water from large rainfall events and slowly released it back into the system, sometimes trapping P contained in larger soil particles which settled out before they release. Parameters specific to each river and creek are now being fed into the models. This “ground-truthing” process has resulted in models that much more accurately predict the impact of precipitation events and spring thaws on movement of nutrients throughout the watershed.
The total amount of P that ultimately ends up in the bay (“P loading”) is a function of water volume and P concentration. Increasingly accurate measures of each are allowing researchers to better understand where the P is coming from. While “point source” loading (e.g., from water treatment plants) has decreased significantly since the mid 1970’s, the contribution of non-point sources (including agriculture) has not followed the same trend and needs to be better understood. Concentrations of organic P, sediment P, and soluble P are all higher in the southern region of the watershed and it has been known for some time that these concentrations are highly correlated with land use. However, the current research is revealing that the contribution of P from forest and shrubland is higher than previously thought. For example, the Trent River, which contributes the most Total Phosphorus (TP) often exceeds agreed-upon target P concentrations in areas coming from natural sources.
Even though there is little we can do about P coming from natural systems, we can do the best job possible to mitigate the effects of P coming from agricultural soil. Structural measures (tile drainage, erosion control, etc.) and non-structural measures (cover crops, timing of P application, etc.) all have measurable effects, but those from the latter are tough to study, especially when one considers the many forms P can take. Many of these forms can eventually contribute to Dissolved Reactive Phosphorus (DRP) which has a proportionally greater impact on the incidence of algal blooms in the bay. DRP can be released even when soil erosion is controlled. Soil conservation practices can sometimes result in P stratification in the topsoil which can lead to rising DRP/ TP ratios. If those ratios continue to climb, the system eventually reaches a tipping point where it can no longer hold the DRP, and it is lost to surface and tile water. Parallel studies on Lake Erie show that although TP levels are not increasing much, DRP/TP ratios continue to rise. Since P loading is a function of concentration and flow, large precipitation events can still result in too much P getting into the system at once.
When a portion of the bay system is overwhelmed with P, it can have profound effects on aquatic life. Hydrodynamic models are being used to better assess where the P ends up. These are 3D models that take into account weather conditions, inflow and outflows, winds, water temperature, depth, and bottom drag, to mention only a few. These models show how flows (and associated P) from creeks and rivers contribute to bay water throughout the year.
They can even predict when and where conditions conducive to algal blooms can occur after a storm. This information is critical, not only to intakes for drinking water treatment plants, but to the aquatic species throughout the bay and Lake Ontario. In-depth studies of species dynamics throughout the food web in the bay are underway.
The influences of farm-level BMPs on P loading need to be better understood. The research team needs better data from field-scale measurements and information on how agricultural land in the Quinte region is being managed.
They need more farm sites to validate their models and fine-tune them to reflect local conditions. The Quinte Farm Research & Stewardship Collaborative* was formed, in part, to solidify connections between farmers, researchers and conservation authorities so we can all work together to mitigate the impact of P loading in the Bay of Quinte.
From natural vegetation in pristine areas, to soil types, to agricultural activity, to weather patterns, to river flows, to impacts on aquatic environments, the story of P loading in bodies of water like the Bay of Quinte are exceedingly complex. Thorough data analysis, accurate measurements and intelligent modelling by this research group are making sense of this complexity and informing an effective, long-term P management plan. Stay tuned for more details on this research as they come to light.
*The Quinte Farm Research & Stewardship Collaborative (QFRSC) is a network of farmers, university researchers and conservation authorities in Northumberland, Hastings, Prince Edward, and Lennox & Addington counties with a focus on soil health and water quality assessment and planning.

 
“A five-year federal-provincial-territorial initiative to strengthen the agriculture, agri-food, and agri-based products sector and increase its competitiveness, prosperity and sustainability.”
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