Recognizing that the topic of managing water quality is complex and that any solution needs to be tailored to the specific environment, the Friends of Swan Lake Park engaged Dr. Barbara Siembida-Losch, a senior scientist at the Centre for Advancement of Water and Wastewater Technologies at Fleming College to assess what, in addition to Phoslock, should be considered to address the issues in Swan Lake.
Following is the Executive Summary from her report followed by a link to the full report.
Literature Review of Potential Engineering Solutions for the Restoration of Swan Lake
By Dr. Barbara Siembida-Lösch
Executive Summary
Swan Lake, a man-made lake located in Markham, Ontario, has long suffered the effects of eutrophication, an over enrichment of minerals and nutrients. A surplus of external nutrient inputs has resulted in the continued accumulation of nutrients stored within the lake from year to year (referred to as legacy nutrients). The overall nutrient load, accompanied with warm weather conditions, allowed for prolonged cyanobacteria blooms throughout Swan Lake and perpetuating the eutrophication issue even further.
The Friends of Swan Lake Park (FSLP) are citizens of Markham and stewards committed to the health and restoration of Swan Lake and Swan Lake Park. In partnership with Fleming College’s Centre for Advancement of Water and Wastewater Technologies (CAWT), the FSLP are interested in improving the water quality of Swan Lake and identifying solutions to do so. Water quality concerns include improving oxygen levels, decreasing phosphorous and nitrogen levels, and reducing chloride concentrations. FSLP’s primary objective is to identify a sustainable treatment program that will provide a long term stable aquatic environment in Swan Lake. FSLP’s ultimate goal is to establish Swan Lake as mesotrophic: a lake classified as having moderate productivity and nutrient concentrations.
In 2020, the City of Markham initiated a phosphorus management effort that includes an enhanced Canada Geese management program, a shoreline redesign effort, and a periodic Phoslock treatment program to begin in the Spring of 2021.
The results of this comprehensive literature review are meant to help FSLP better understand some of the environmentally sound options available, and to guide them on next steps for the future restoration and improvement of water quality in Swan Lake. These options may serve as complementary approaches to the current phosphorus management plan, contributing to an enhanced and sustainable aquatic environment. Ideally, these additional strategies will also result in savings by reducing the frequency, or eliminating completely, the need for future Phoslock treatments.
This document presents solutions that address the water quality issues faced by Swan Lake and the pros and cons to each approach. While vendors are named and provided, the CAWT does not endorse any one product and is simply providing these systems as a reference.
The solutions presented in this report include: 1) water recirculation through a bioswale and use of floating treatment wetlands for increasing oxygen levels while lowering phosphorus, nitrogen and chloride levels; 2) oxygenation and circulation systems for increasing dissolved oxygen concentration and decreasing phosphorus and nitrogen drawn from the sediments, and 3) sorptive media, biological processes, and solar stills for lowering chloride levels.
Conclusions and Recommendations
Overall, and based in conjunction with existing water quality reports previously done, it is apparent that besides phosphorus, other water quality issues (nitrogen and chloride pollution, and oxygen depletion) need to be addressed for the successful restoration of Swan Lake.
There are several approaches that can be taken to achieve this goal, options range from a large and all-encompassing approach to taking several small steps gradually and making meaningful impacts over time. However, due to a significant initial capital expenditure, the former approach should be investigated and assessed with some preliminary pilot studies to ensure water clarity will not deteriorate due to water movement.
Therefore, we recommend proceeding with a series of incremental targeted efforts in order to validate the impact of each new process introduced. To mitigate the existing water quality issues in Swan Lake, any technique employed should be quick to implement and be sustainable. Additionally, any technique used will also need to be ecologically safe and cost effective.
To complement the current phosphorus management program we recommend consideration be given to three additional initiatives. Following the introduction of each initiative, we recommend an assessment of the impact before introducing an additional technique.
The three programs that may complement the planned periodic Phoslock treatment are:
- A periodic treatment of granulated calcium peroxide to increase oxygen levels;
- Adding chloride-tolerant plants to further decrease nutrients and chlorides in conjunction with the shoreline restoration plan and through the installation of floating treatment wetlands in areas near the former dump sites;
- In parallel, laboratory and/or field tests should be performed to determine if diffused aeration systems (such as “bubblers”) are a feasible long-term solution for maintaining oxygen in the proper range without worsening water clarity.
The CAWT at Fleming College has the required expertise and resources to support and assess this type of investigation.
Although an important and potentially long-term goal, restoring Swan Lake water quality from the current hypereutrophic state to mesotrophic nutrients level may require significant resources. It will be necessary to evaluate what kind of lake management tools are possible, affordable, and preferable for reliable management and restoration of Swan Lake. Before a decision is made or implemented the objectives, patterns, and expectations shaping future water management should be further explored and defined.