Nutrient pollution and water quality is a common challenge in many for freshwater ecosystems in Manitoba and globally, causing persistent and damaging eutrophication.

Although many prairie lakes are monitored, the information available on the specific nutrient sources and in-lake processes that change the lake’s chemistry are not well understood. This poses challenges for identifying the best management options.

The International Institute of Sustainable Development (IISD) has released a new study where researchers developed a nutrient mass balance model that can be used to identify the variance and relative importance of different nutrient sources and internal lake processes. The study’s stated objective was, “to conduct a water and nutrient mass balance, identifying the variance and relative importance of different nutrient sources and internal lake processes for a lake that could be used as a general model for other prairie lakes.”

Figure 1. Map and location of the study site, Pelican Lake, within Manitoba. Source: IISD.
Broader relevance

Pelican Lake is a turbid, eutrophic lake, with a surface area of 27.7 square kilometres that has experienced regular algal blooms. The lake’s mean depth is 3.88 metres and its average volume is 108,084,000 square metres. The authors used Pelican Lake as a study site, but the methodology and findings are more widely applicable to shallow prairie lakes in general.

Among the findings, the authors found that “high external phosphorus loads and low N:P ratios of inputs appear to drive high rates of biological nitrogen fixation within lakes, leading to significant losses of nitrogen from the lake to groundwater; that prairie lakes are net sinks of phosphorus; and that internal recycling of phosphorus within the lakes is likely of high importance to managing eutrophication.”

The report, Manitoba Prairie Lakes: Mass balance budget for nutrient management at Pelican Lake, was written by Kimberly Lewtas, Hisham Osman, Geoffrey Gunn, and Dimple Roy, and is available for download online.

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