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Garrow Lake NAM-50

Riparian Nation(s) Canada
Lat. 75°24' N Lng. 96°48' W Alt. 7 m
Surface Area 4 km2 Mean Depth 24.5 m Volume 0.1 km3
Shoreline 10 km Catchment Area 10.5 km2 Residence Time  
Frozen Period Sep-Aug   Mixing Type Meromictic   Morphogenesis/Dam  
Related Info/Site  

Description

First surveyed in 1974, Garrow Lake lies on Cornwallis Island, NWT,95 km NNW of Resolute and 3 km from the coast. The lake is ice-covered for 11 months of the year. It is one of only two arctic lakes discovered to date which are both permanently stratified (meromictic) and containing layers of high salinity water (hypersaline). Near the lake surface the salinity approaches that of freshwater, while it is nearly three times that of sea water near the bottom. The water is anoxic below 20 m.

The watershed is gently rolling desert tundra overlying Ordovician shale and limestone. A thick glacial drift covers the area and soils are fluvial with smooth slopes and thick regolith, abundant polygons, frost cracks and solifluction structures. There are several small stream valley systems with runoff generally restricted to June-August. Wide-spread fossil shells indicate post-glacial uplift from marine or brackish water during Wisconsin post-glacial period. It is estimated that the lake was established approximately 3,000 years B. P. Lead and zinc deposits are located near the lake.

In November 1981, COMINCO Ltd's Polaris Mine Project began discharging lead and zinc mine tailings into Garrow Lake at a depth of 20 m at the rate over 2,500 metric tons per day, which might irreversibly alter the lake by the impact to its anaerobic bacterial population. This is unfortunate because the anaerobic production of sulfide causes the precipitation of lead and zinc ions from the mine tailings, which, in the absence of sulfide producers, will remain in solution and may eventually find their way into the sea. The sulfide producers also form an essential link in the web of life in Garrow Lake, since the photosynthetic bacteria, the major primary producer in the lake, are dependent on the supply of H2S from anaerobic sulfide producers. To date this major primary producer has all but been eliminated from the lake's chemocline.

The only fish living in the lake is the fourhorn sculpin (Myoxocephalus quadricornis). It is likely that the marine form of this species was trapped in Garrow Lake 3,000 years ago, and has slowly been changing within the lake to adapt to a virtually predator-free system of variable salinity. Chironomids and copepods, the most frequent invertebrates in the lake, are assumed to represent this fish's basic diet. In one sense, Garrow Lake can be viewed as a sort of time capsule offering an ideal area for the study of natural selection and speciation. However, the extirpation of the sculpin is likely to occur over the next decade unless COMINCO changes its mode of discharging toxic mine tailings into this unique body of water (Q, 1-8, 20- 23).

Photo of Garrow Lake
Photo: M. Dickman