LAKE FUTURES: Enhancing Adaptive Capacity and Resilience of Lakes and their Watersheds

Canada’s numerous lakes are an unparalleled treasure - providing drinking water, energy, food, and recreational opportunities. In a world increasingly facing water shortages, Canada’s relative abundance of water gives it a robust competitive advantage. Yet, water quality is vulnerable to changes in the climate and land use. The way we use the land surrounding lakes, including how we farm and build on the land, has an impact on the health of our lakes. In Lake Erie for instance, the annual occurrence of harmful algal blooms is a clear indication of declining lake health. Finding enduring solutions that will improve and protect  water quality requires tools and strategies that help us understand and manage the interaction between a lake and its watershed.

TheLake Futures research team aimed to identify water quality solutions for the lower Great Lakes to improve water quality, while supporting economic growth. They combined data synthesis and process modelling to explore the connections between land use, lake processes, ecosystem health, and economic values. 

Key Findings

Changing Climate and Agricultural Intensification drives Nutrient Pollution

By analyzing stream concentration and land use data from hundreds of streams across the Great Lakes Basin, researchers were able to identify two important landscape drivers of higher nitrate and soluble phosphorus concentrations which lead to more severe algal blooms in the Great Lakes. They found that increasing livestock density and tile drain density contributed to increasing concentrations of soluble, bioavailable phosphorus and nitrogen runoff, which is more potent than other forms of the nutrient for bloom formation.

Further, they also found that climate change was aggravating the problem and increasing concentrations of bioavailable phosphorus. Concentration increases were greater at higher latitudes, and occurred even in pristine forested streams. This is potentially due to warmer winters and increased activation of the subsurface flow pathways that mobilized phosphorus from soils.

The Role of Legacy Nutrients

In addition to present day nutrient inputs, researchers found that fertilizers applied on farms decades ago are contributing to ongoing phosphorus pollution -- a concept known as “legacy phosphorus”. The reservoir of phosphorus remains in the field, sediments and water bodies for extended periods, meaning that it will take time to draw down the phosphorus. This can mask the success of current management strategies aimed at reducing nutrient runoff and its mobilization. As a result, it is unlikely that phosphorus loads in Lake Erie will be reduced by 40 per cent by 2025, a target set by the Government of Ontario through the Great Lakes Protection Act.

Researchers found over 500 kilotons of legacy phosphorus and 600 kilotons of legacy nitrogen in the Grand River Watershed, which drains into Lake Erie. Over 90% of the legacy remains in farm fields. Legacy nutrients accumulated in farm fields creates management opportunities as these legacies can be accessed by reducing fertilizer applications so crops can tap into these legacy stores.

Legacy sediments can also accumulate in small reservoirs within the watershed, and although the magnitude of legacy accumulations in reservoirs is small, they are more easily accessible and can continue to supply phosphorus to the water column and contribute to blooms.

Researchers uncovered an interesting phenomenon where nutrient legacies from agricultural land use can interact with elevated chloride concentrations from road salt applications to aggravate bloom formations. Specifically, increased chloride can decrease lake mixing, and this can lead to low oxygen levels, which in turn promotes release of legacy phosphorus from sediments and increases blooms.

Legacy nutrients were also found in the sediments of Lake Erie, and they were moved around and recycled between the sediment and the water column. Researchers found that recycling is being exacerbated because of climate change, as increasingly intense precipitation events are causing shoreline erosion, and releasing sediment-bound legacy nutrients.

The Economic Connection

Researchers also undertook several economic analyses to evaluate taxpayer willingness to pay for water quality improvements, costs associated with nutrient reduction, and the importance of water to the Canadian economy. Beginning with some good news, the Great Lakes are incredibly valuable to society [can we add include stat that demonstrates this, perhaps about willingness to pay. However, reducing nutrient pollution comes with significant costs, which can have ripple effects on the economy. At the same time, the benefits associated with landscape intervention programs depend largely on their location, suggesting a need for cost-share programs to be spatially targeted. Finally, findings from hydro-economic modelling suggest that if water becomes more scarce in the Great Lakes region, there will be significant impacts on the economy as a whole, which will have implications beyond the watershed. If water scarcity starts to impact energy and food security, the impacts will be even greater.

Management Implications

Researchers undertook a study where they identified six key watershed management strategies to improve water quality, given the reality of legacy nutrients. The study suggests that we need to directly acknowledge and address legacies in the design of management strategies, such as those guiding fertilizer application rates. They also showed from modelling that reducing manure losses can be one of the key farm practices for fast improvements in water quality. On-farm practices alone are not adequate. Therefore, targeted restoration of wetlands located strategically in the watershed can help filter the nutrients that have already made their way into waterways.

Decision Support

Over the duration of the project, Lake Futures developed and/or enhanced several predictive tools and datasets.

• ELEMeNT is the world’s first water quality model  that can capture nutrient legacies and time lags. It was developed to (1) predict river nitrogen and phosphorus concentrations, (2) quantify accumulated legacies in soils and reservoir sediment, and (3) predict how long it will take for water quality to improve following implementation of various best management practices. The model was applied across 40+ watersheds in the Lake Erie Basin, and results were analyzed to identify the most effective management practices for addressing legacy nutrients.
• An open access dataset with seasonal nitrogen (N) and phosphorus (P) loads for 202 monitored watersheds in the Great Lakes Basin (GLB).
• A machine learning model can predict seasonal nitrogen and phosphorus concentrations for any watershed in the Great lakes Basin, as a function of land use and climate.
• Another machine model predicts chlorophyll-a concentrations (an indication of algal blooms)and lake ice in large northern lakes.
• An integrated cross sectoral modelling framework can determine the cost effectiveness of water quality improvement interventions in agriculture and urban wastewater treatment.
• A hydro-economic model assesses potential climate change impacts on the Great Lakes economy
• An open-access database of water quality trading programs in North America supports an assessment of the instrument’s effectiveness in pollution control.