Physical, Chemical, and Biological Characteristics of the Turkey Lakes Watershed, Central Ontario, Canada

Abstract

The Turkey Lakes Watershed (TLW) in central Ontario was selected for intensive research into the effects of the long-range transport of air pollutants (primarily acidic deposition) at a site on the Canadian Shield having both vulnerable terrain and an undisturbed Great Lakes forest type. The terrestrial and aquatic resources within the basin are representative of the surrounding region of Algoma, although for Ontario, it does have high relief (290 m) and high annual precipitation (>1200 mm). The TLW contains a chain of four lakes (five distinct lake basins) that range from 5.8 to 52.0 ha in area and 2.2 to 12.2 m in mean depth. The lakes are dimictic and, except for the deepest lake, experience dissolved oxygen depletion in undisturbed bottom waters. There is a gradient in the major ion composition of lakes within the TLW, the most dilute waters occurring at high elevations. Calcium levels increase from 55 to 138 μmol∙L⁻¹ down the chain. Sulphate is the dominant lake water anion in the headwater lake, while alkalinity dominates in the lowest lake. Phosphorus is the limiting nutrient in these lakes; NO₃-N levels are relatively high (7.9–16.4 μmol∙L⁻¹) because the terrestrial basin exhibits low utilization of this nitrogen species. Seasonal and episodic variations in surface water composition can be large. The headwater lake contains no fish; however, fish communities in the lower three lakes (composed of 8-11 species) are typical of the Algoma region. The distribution of benthic organisms is primarily a function of lake depth and presence/absence of fish rather than variations in water chemistry. Zooplankton species composition is similar across all lakes, and cyanophytes are the dominant algae throughout. The forest is an uneven-aged, mature-to-overmature, old-growth tolerant hardwood stand. The principal tree species is sugar maple (90%) with lesser amounts of other hardwoods (9%, usually yellow birch) and various conifers (1%). Production is typical of forest at this northerly latitude (47°N). Foliar bioelement concentrations are generally similar to those observed at Hubbard Brook, New Hampshire.