Global warming and anthropogenic actions have been exerting stress on aquatic systems worldwide, including Canada’s extensive network of lakes. In recent years, escalating nutrient levels have instigated eutrophication in the shallow lakes scattered across Quebec’s Laurentian region, north of Montreal. These alterations have caused a spike in algal proliferation, making the lakes unsuitable for use and potentially disturbing the ecological balance.
Rehabilitating these lakes to a more salubrious state is a convoluted and costly endeavor, but a novel approach under exploration by scholars from Concordia’s Department of Building, Civil and Environmental Engineering could potentially reduce expenses and manpower while being ecologically sustainable.
In an article published in the Water journal, the scholars detail a mechanism comprising buoyant geotextile filters that can effectively eliminate suspended solids, algae, and nutrients from a shallow lake. Although the initiative is still in its nascent stages, the researchers anticipate that it can be upscaled. Consequently, this technology could enhance the well-being of more expansive aquatic systems, including estuaries, rivers, bays, and lagoons.
The research is spearheaded by Antônio Cavalcante Pereira, a Ph.D. student, and professor Catherine Mulligan. Additionally, Dileep Palakkeel Veetil, a research associate, and Sam Bhat from Titan Environmental Containment have also contributed to the study.
During the summer and early autumn of both 2019 and 2020, the scholars installed six geotextile layers in a buoyant filtration system at Lac Caron, a shallow eutrophic lake located in Ste-Anne-des-Lacs, approximately 75 kilometres north of Montreal, with a maximum depth of 2.6 metres. The lake has been under recreational guidance since 2008 due to an abundance of algae growth.
To keep the plexiglas filtration system afloat, an inflatable rubber tube was inserted in the middle of an enclosed space. Geotextile turbidity curtains were utilized to demarcate the area, which hangs down from the surface to the lakebed, or near it, to avoid suspended solid interactions with the remainder of the lake. This approach is intended to prevent interference with the surrounding aquatic ecosystem while enabling the filtration device to function effectively.
The researchers gathered water samples from both the lake and the enclosed zones every two to three days. The samples were subsequently evaluated for various parameters, including turbidity levels, suspended solids (TSS), phosphorus, blue-green-algae-phycocyanin (BGA-PC), chlorophyll-a, and other relevant factors. By analyzing these parameters, the researchers could assess the effectiveness of the filtration system in removing contaminants from the lake water.
The analysis results were encouraging, according to average removal efficiencies in 2019 and 2020. The researchers compared the filtered lake water to the non-filtered lake water and found the following:
Turbidity reduced 53 percent in 2019 and 17 percent in 2020
TSS by 22 percent/36 percent
Phosphorus by 49 percent/18 percent
BGA-PC by 57 percent/34 percent
Chlorophyll-a by 56 percent/32 percent.
Pereira explains that the year-to-year variations are a consequence of the diverse water quality found in lakes because of unique climate and algae growth patterns. In 2019, a prominent, noticeable algae bloom was present, whereas in 2020, the algae was more evenly distributed throughout the entire water body. These differences in algae distribution and concentration can have a substantial impact on the filtration system’s efficacy and, as a result, affect the overall success of the project.
Pereira asserts that expanding the filtration system for large-scale lake remediation is a long-term objective. However, the novelty of this project is that they employed in-situ water filtration as a method of remediating eutrophic water bodies. According to him, no chemicals were added to the lake, yet they were able to achieve positive results, such as algae suppression and decreased turbidity for an entire recreational season. This approach is not only environmentally friendly but also cost-effective, making it an attractive option for lake restoration projects.
An evolving long-term project
Mulligan remarks that this article is part of a series of papers that stem from research that began as early as 2008. The project has undergone multiple iterations and has been implemented in various lakes in the region over the years. This long-term commitment to the project has allowed the researchers to refine and optimize their filtration system, making it a more efficient and effective solution for lake remediation.
Previous studies have focused on shallow lakes that were created by developers through excavation of existing lakes and incomplete tree removal. However, several recent factors are contributing to recurring excessive algae growth in these lakes. These factors include the ongoing degradation of fragmentary tree stumps, potential nutrient release from runoff, and the lack of natural hydrological patterns. These issues highlight the need for innovative and sustainable solutions to restore the health of these lakes and protect their ecosystems.
Mulligan notes that addressing water quality in eutrophic water bodies can be challenging due to the natural variability of water quality from year to year. Warmer temperatures, for example, can exacerbate the effects of excessive algal blooms in eutrophic water bodies. As such, sustainable and effective solutions for restoring the health of these water bodies are needed to address this ongoing challenge.
This research was funded by NSERC, Concordia University and Titan Environmental Containment. Read the cited paper: “An In-Situ Geotextile Filtration Method for Suspended Solids Attenuation and Algae Suppression in a Canadian Eutrophic Lake”