Contaminants from Mount Polley tailings spill continue to affect Quesnel
lake

Date:
August 13, 2020
Source:
University of Alberta
Summary:
Natural mixing of lake waters may re-suspend contaminants deposited
in a catastrophic mine spill six years ago, according to a new
article.



FULL STORY ========================================================================== Natural mixing of lake waters may resuspend contaminants deposited in a catastrophic mine spill six years ago, according to a new paper led by
a University of Alberta scientist.


==========================================================================
The results show that the turbidity, or cloudiness, in portions of British Columbia's Quesnel Lake increases each spring and fall when the lake mixes
from top to bottom in a natural process called turnover. The source of
the turbidity appears to be the resuspension of spill-related material
from the bottom of the lake, raising concerns about contaminants being reintroduced to the water column.

On August 4, 2014, a tailings dam containing mine waste from the Mount
Polley copper and gold mine failed. "The catastrophic tailings spill
dumped 18 million cubic metres of waste water and sediments into the
West Basin of Quesnel Lake," explained Andrew Hamilton, postdoctoral
fellow in the Department of Earth and Atmospheric Sciences and lead
author on the paper. "At the time, it was the largest mine-related spill
ever documented." Since 2014, Hamilton and an interdisciplinary group of scientists from the University of British Columbia (UBC), the University
of Northern British Columbia (UNBC), and Fisheries and Oceans Canada
(DFO) have monitored the effects of the spill. This study presents
results from 2014 through 2017.

"During the first turnover after the spill, mixing brought suspended
sediment to the surface, turning the previous clear-blue lake to bright
green -- a change that was readily apparent in satellite imagery,"
explained Hamilton.

"Remarkably, 12 months after the spill the suspended sediment loads
had substantially reduced, and the lake waters had appeared to return
to their pre- spill state, but it turns out this was only temporary."
"Over the subsequent three years, we saw an increase in turbidity
above the spill deposits at the bottom of the West Basin every spring
and fall when winds drove large basin-scale wave motions, like the
sloshing of water in your bathtub. As turnover occurred, this sediment
was then mixed from depths below 100 metres over the whole water column." Understanding effects The biggest concern is the unknown effects of this phenomenon on the ecology of the lake. The tailings contained elevated concentrations of some metals, such as copper, and if these metals are
being seasonally remobilized from the lake bed they could make their way
into the food web. Chronic exposure to elevated copper concentrations
can reduce the growth, reproduction, and survival of fish populations,
and small changes to colour and clarity of a lake can alter algal
communities at the base of the food web.

"In other related research, we have seen a seasonal increase in some
metal concentrations in the Quesnel River that corresponds to the
timing of the turbidity increase observed in the lake," explained Ellen Petticrew, professor at UNBC and co-author on the study. "This paper
will help us explain some of these other processes we are observing,
and helps build a more complete understanding of the long-term impact of
the spill on the lake." "While the immediate environmental devastation
of other catastrophic mine waste spills around the world may have been
more apparent, our research shows that the environmental impacts of the
spill in Quesnel Lake are long-term," said Bernard Laval, professor of
civil engineering at UBC. "Investigating these subtle impacts over time
will help inform if and how Quesnel Lake recovers, and the potential for lasting impacts of other tailings spills which are increasingly frequent globally." "Understanding all factors affecting the long-term water
quality of Quesnel Lake is critical as its watershed supports substantial recreation, world- renowned resident trout fisheries, and multiple Fraser
River Pacific salmon stocks that are vital to Indigenous, recreational,
and commercial fisheries," added Hamilton. "Inevitably these spills end
up flowing downstream into lakes or the ocean where they can disappear
from view, yet that doesn't mean the impact is over."

========================================================================== Story Source: Materials provided by University_of_Alberta. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Andrew K. Hamilton, Bernard E. Laval, Ellen L. Petticrew, Sam
J. Albers,
Michael Allchin, Susan A. Baldwin, Eddy C. Carmack, Stephen
J. De'ry, Todd D. French, Brody Granger, Kelly E. Graves, Philip
N. Owens, Daniel T. Selbie, Svein Vagle. Seasonal Turbidity Linked
to Physical Dynamics in a Deep Lake Following the Catastrophic
2014 Mount Polley Mine Tailings Spill. Water Resources Research,
2020; 56 (8) DOI: 10.1029/2019WR025790 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813134555.htm

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