Rigler 1975

Rigler FH. 1975. The Char Lake project, an introduction to limnology in the Canadian arctic. In: Energy Flow – Its Biological Dimensions (Eds. Cameron TWMC and Billingsley LW). Royal Society of Canada, Ottawa.

This book was published to provide educated laypeople with information about the International Biological Programme (IBP) as it was conducted in Canada. Chapter 10, by this author, provides an overview of the work conducted at Char Lake and adjacent areas, and some of the results obtained.

Arctic lakes are much simpler ecosystems than are temperate lakes, with fewer species and a less structured physical environment. Unlike often-stratified and occasionally anoxic temperate lakes, most Arctic lakes including Char Lake are remarkably homogeneous, with well mixed waters varying in temperature between 0°C and 4°C. Most are never anoxic, due to no summer thermal stratification, high levels of winter mixing driven by temperature differences through the lake, and oxygen supply to the water by freeze-out from the usually large mass of winter ice.

Char Lake sits in a catchment basin about 8 times larger in area than the lake itself. The lake and its basin are very unproductive, with biomass accumulation rates a small fraction of temperate or even tundra ecosystems. The plankton is apparently nearly homogeneous across the lake at all depths, driven by well mixed water and the very low species richness. Only one species of zooplankter was reported, a copepod. This author divides the benthos into four regions. The first, comprising the shallow fringe of the lake to about 4m depth, freezes solid in winter and is composed of rocks grading into silt, with diatoms lying on the surface of the sediment. The second zone is silty and extends down to about 15m. This zone is dominated by abundant terrestrial mosses and an epiphytic community of algae and small grazers. The third zone is comprised of bare patches of silt among the mosses, centered on depressions likely generated by down-pushing winter ice. This author hypothesizes that these depressions become anoxic in winter due to barriers to water flow, but are gradually recolonized by mosses from the shallow edge. In summer these depressions attract relatively high densities of animals. The last zone is the deepest part of the lake, too deep for sufficient sunlight to penetrate for the mosses. This is a flat, silty plain of oxygenated sediments a few centimetres deep overlying older strata that reflect the lake’s history as a raised feature of the bottom of the Arctic Ocean.

Char Lake appears to be stuck in a post-glacial stage that most temperate lakes passed through rapidly. About 5300 years ago, Char Lake was a bay on the coast of Cornwallis Island that was isolated from the sea by isostatic rebound. This lead to a period of perhaps a few thousand years in which the lake had a deep benthos occupied by seawater and no organisms, which was gradually flushed out by freshwater flows through the system.