What killed Frame Lake? A precautionary tale for urban planners

Abstract

Frame Lake, located within the city of Yellowknife, Northwest Territories, Canada, has been identified as requiring significant remediation due to its steadily declining water quality and inability to support fish by the 1970s. Former gold mining operations and urbanization around the lake have been suspected as probable causes for the decline in water quality. While these land-use activities are well documented, little information is available regarding their impact on the lake itself. For this reason, Arcellinida, a group of shelled protozoans known to be reliable bioindicators of land-use change, were used to develop a hydroecological history of the lake. The purpose of this study was to use Arcellinida to: (1) document the contamination history of the lake, particularly related to arsenic (As) associated with aerial deposition from mine roaster stacks; (2) track the progress of water quality deterioration in Frame Lake related to mining, urbanization and other activities; and (3) identify any evidence of natural remediation within the lake. Arcellinida assemblages were assessed at 1-cm intervals through the upper 30 cm of a freeze core obtained from Frame Lake. The assemblages were statistically compared to geochemical and loss-on-ignition results from the core to document the contamination and degradation of conditions in the lake. The chronology of limnological changes recorded in the lake sediments were derived from 210Pb, 14C dating and known stratigraphic events. The progress of urbanization near the lake was tracked using aerial photography. Using Spearman correlations, the five most significant environmental variables impacting Arcellinida distribution were identified as minerogenics, organics, As, iron and mercury (p < 0.05; n = 30). Based on CONISS and ANOSIM analysis, three Arcellinida assemblages are identified. These include the Baseline Limnological Conditions Assemblage (BLCA), ranging from 17–30 cm and deposited in the early Holocene >7,000 years before present; the As Contamination Assemblage (ACA), ranging from 7–16 cm, deposited after ∼1962 when sedimentation began in the lake again following a long hiatus that spanned to the early Holocene; and the Eutrophication Assemblage (EA), ranging from 1–6 cm, comprised of sediments deposited after 1990 following the cessation of As and other metal contaminations. The EA developed in response to nutrient-rich waters entering the lake derived from the urbanization of the lake catchment and a reduction in lake circulation associated with the development at the lake outlet of a major road, later replaced by a causeway with rarely open sluiceways. The eutrophic condition currently charactering the lake—as evidenced by a population explosion of eutrophication indicator taxa Cucurbitella tricuspis—likely led to a massive increase in macrophyte growth and winter fish-kills. This ecological shift ultimately led to a system dominated by Hirudinea (leeches) and cessation of the lake as a recreational area.

The sedimentological and Arsenic contamination history of Frame Lake, Yellowknife, Northwest Territories, Canada

“…Both mean daily temperatures and mean total precipitation have increased in recent years when comparing average mean daily temperatures and annual mean precipitation for the intervals 1961-1990 and 1981-2010 (-5.2°C vs. -4.3°C, 267.3 mm vs. 288.6 mm; and Con mine (CM), Frame Lake (FL) and Yellowknife Bay (YB), City of Yellowknife (Municipal boundary line as dashed line; bottom left); Frame Lake, NWT, Canada (right). Modified after Gavel et al (2018). Environment Canada 1990, 2010.…”

“…Frame Lake existed as an embayment of Ancestral Great Slave Lake until ~7,000 years BP when it slowly became isolated (Lemmen et al 1994;Wolfe et al 2017). Due to the low topographic relief, rocky terrain, and small amounts of precipitation in the area, sedimentation essentially ceased in the Frame Lake basin following early Holocene isolation, until ~1962 when anthropogenic influences within the lake catchment resulted in a renewed, rapid sedimentary infill of the lake basin (Gavel et al 2018). The presentday inflow of water to Frame Lake is mostly derived from sheet wash or from small ephemeral channels during rainfall events and snowmelt (Dirszowsky and Wilson 2016).…”

“…Frame Lake, a highly As-contaminated lake within the Yellowknife city limits, was once an important community recreational area, with the popular McNiven bathing beach established by the 1950s (Healey and Woodall 1973). By the early 1970's, however, Frame Lake had experienced a notable decline in lake health due to the impact of 1) historic gold-mining-induced As contamination; 2) the physical dumping of tailings and/or waste into the lake; 3) runoff of nutrient-rich water from municipal development around the lake; and 4) changes in circulation and water throughput to the lake due to urban development-notably the construction of a causeway equipped with sluiceways at the lake outlet in 1975, though these sluiceways remain closed most of the year, as well as stormwater sewers that diverted a significant amount of inflow from entering the lake , the cumulative impact of these changes led to the collapse and disappearance of fish populations in Frame Lake (Gavel et al 2018). Additionally, in the years following the building of the causeway, there was a concomitant increase in the production of aquatic macrophytes, and the rapid sediment accretion of a dark brown to black organic-rich sedimentary horizon, as the lake became progressively more eutrophic.…”

“…Additionally, in the years following the building of the causeway, there was a concomitant increase in the production of aquatic macrophytes, and the rapid sediment accretion of a dark brown to black organic-rich sedimentary horizon, as the lake became progressively more eutrophic. Deposition of this variable thickness black sedimentary horizon has been associated with high levels of legacy contaminants, primarily As, from the mining operation of Giant Mine and Con Mine (Dirszowsky andWilson 2013, 2016;Gavel et al 2018). By the late 1970s, the steadily deteriorating environmental conditions within the lake resulted in a significant decline in the number of swimmers and beachgoers using McNiven Beach, which in turn led the city to eventually remove recreational facilities there.…”

“…Frame Lake is in the middle of the City of Yellowknife, with City Hall, the Legislative Assembly of the NWT, and the Prince of Wales Northern Heritage Centre on its shore making rehabilitation of the lake also advantageous from a tourism and aesthetic perspective. Several remediation strategies for Frame Lake have been considered, including 1) dredging of contaminated sediments; 2) installation of aerators to permit fish to survive winter anoxia; 3) construction of storm-water management facilities at the inflows; and 4) opening of the sluiceways to increase the amount of outflow to increase lake water throughput (Gavel et al 2018). If the lake is to be dredged, a significant amount of contaminated sediments would have to be removed.…”