"It's just another impact, one of the continually growing cumulative impacts, to these fairly sensitive freshwater ecosystems we have," co-author Joshua Thienpont of Brock University said Friday.
Thienpont and his colleagues wanted to test the ongoing effectiveness of sumps still being used in the Northwest Territories to dispose of oil drilling wastes.
Sumps are large pits dug near a wellsite and intended to permanently get rid of wastes such as drilling mud, rock cuttings and drilling fluids, which commonly contain detergents and highly concentrated salt solutions. The sumps — which can contain tens of thousands of cubic metres of waste — are capped with clean material and frozen into place by permafrost.
The Mackenzie Delta has at least 150 sumps that date back as far as the mid-1960s.
But permafrost in the southern Arctic has been gradually degrading as a result of climate change. In the delta, permafrost has warmed by an average of two degrees over historic levels.
Thienpont looked at 101 lakes in the area. Some were near a sump, some were far away but affected by permafrost slumping and some were unaffected by either.
Of the 20 lakes near a sump, many lakes showed high salt levels, Thienpont discovered.
"At least four and as many as 15, depending on how you look at it."
Those levels are high enough to change the micro-organisms that live in the lakes and anchor the food chain.
The team also looked at bottom sediments in one of the affected lakes to try to pinpoint when the contamination occurred.
"In that lake, we found that at the time, or very near the time the sump was built, there was really striking and rapid shift of species known to be tolerant of higher salinity," Thienpont said.
He said some sumps were probably leaching because they were badly built in the first place.
But Thienpont said the degrading permafrost in the area is likely to have been the culprit for most of the seeping.
"If our goal is the complete containment of all the wastes associated with drilling in the Arctic region, then in areas of warm permafrost, drilling sumps may not be the preferable mechanism for containing those wastes."
Drilling in the Northwest Territories is growing after a major discovery of shale oil near Norman Wells, which is underlain by the same kind of warm permafrost seen in the delta.
N.W.T. government officials estimate that energy companies have committed spending $637 million to explore the area.
Sumps remain a recommended method of waste disposal under federal guidelines for drilling in the Arctic. Figures from the N.W.T. government show that between January 2009 and June 2011, seven sumps were constructed for drilling wastes.
Wastes from another seven wells were trucked outside the territory for disposal.