Media Release
Water on the tailing fields of the historical Montague Gold District transports contaminated materials towards Mitchell Brook, which flows into Barry's Run, and then into Lake Charles. Wind is also a mechanism of tailings transport. Credit: Linda Campbell
Study shows long-lasting impacts to lake health from old gold mines
Halifax, NS and Sackville, NB– New findings of a multi-university team of researchers show that severe pollution from historical gold mining in Nova Scotia, Canada, persists at alarming levels and is impacting the health of aquatic ecosystems, despite mine operations closing nearly a century ago.
“Past mining activities that occurred throughout Nova Scotia introduced considerable amounts of arsenic and mercury into the environment,” says lead author Allison Clark, from Mount Allison University. “Although the Montague Gold District closed to mining 80 years ago, lakes nearby still remain severely impacted.”
Over 350 gold mines operated throughout Nova Scotia between the mid-1800s and 1950. Urbanization and land development has taken place nearby some historical mining areas and people sometimes use these areas for recreational activities. Waste tailing materials with toxic levels of arsenic and mercury are found near historical gold mines in Nova Scotia. The tailings can contaminate soil and aquatic sediments through water and wind movement.
This study used dated sediments from the bottom of two urban lakes located near one of the region’s largest historical mining operations. Lake sediments are a well-recognized and information-rich natural archive of past environments which allow the assessment of geochemical and biological conditions of lakes and their watersheds before, during, and after pollution has occurred.
The study was recently published in the peer-reviewed international journal Science of the Total Environment and highlights how pollution from past gold mining combined with contemporary stressors such as climate change and urbanization may contribute to prevent complete lake recovery from century-old mining pollution.
“Mining activities from 100 years ago can still impact freshwater ecosystems today. Our work reveals that lakes may show signs of recovery from those impacts,” notes Saint Mary’s University Professor and co-author Dr. Linda Campbell. “Even so, we must remain vigilant about understanding and monitoring the legacy of those contaminated tailings in our modern ecosystems to support recovery processes.”
Surprisingly, arsenic levels are still very high in the lake sediments—300 times above levels that are known to harm aquatic organisms. Mercury has returned to levels observed before gold mining began. This suggests that arsenic is behaving differently than mercury within the sediments at the bottom of mining-impacted lakes.
“Mining is both a blessing and a curse,” notes Mount Allison University Associate Professor and co-author Dr. Joshua Kurek. “Society benefits but past mining activities practiced throughout Nova Scotia continue to harm ecosystems and citizens are now left with the clean-up costs.”
Additionally, invertebrates that live on and interact with the lake’s sediment have become less diverse, likely due to the mining pollution as well as other recent watershed stressors. Loss of key organisms may affect lake food webs, leading to issues with water quality.
Funding for this research was provided by Natural Sciences and Engineering Research Council of Canada (NSERC) and Genome Atlantic.
NOTE: An early copy of the study can be obtained from the Science of the Total Environment website or by contacting the corresponding author jkurek@mta.ca
View published manuscript:
Click here to access the manuscript.
Researcher sampling lake sediments containing high levels of arsenic and mercury from Nova Scotia, Canada. Credit: Joshua Kurek
Sediment core collection at Lake Charles in May 2019. The core pictured captured over 200 years of lake and watershed conditions, including times before mining began. Credit: Amber LeBlanc
Image of a cladoceran remain found in lake sediments. Cladocera are small aquatic invertebrates, commonly called water fleas, visible to the naked eye, and are important to lake food webs. They are often used as bioindicators and can tell us about the health of an ecosystem. Credit: Allison Clark
Lake Charles in Dartmouth, Nova Scotia, near the Barry’s Run stream from the historical Montague Gold District. Lake Charles sediments contain elevated levels of arsenic and mercury from past mining activities. Credit: Linda Campbell
Research team sampling lake sediments at Loon Lake, a study lake with negligible impacts from historical gold mining that occurred nearby. Credit: Joshua Kurek
Lake sediments are valuable archives of past environmental conditions because they accumulate over time and can be dated. Sediments are composed of materials carried into the lake by water or wind (e.g., pollution from mining), as well as materials produced within the lake (e.g., algae, invertebrates). Credit: Linda Campbell
Contact information for authors
Dr. Linda Campbell, Saint Mary’s University, LM.Campbell@smu.ca Twitter: @LM_Campbell
Dr. Joshua Kurek, Mount Allison University, jkurek@mta.ca Twitter: @drtightline