The vegetation and water chemistry of four oligotrophic basin mires in northwestern Ontario

Abstract

Four small oligotrophic basin mires on the Precambrian Shield were quantitatively analyzed for vegetation patterns and surface water and groundwater chemistry. Mean concentrations of ions in the surface waters of all vegetation stands indicate these mires to be characterized by low calcium content (0.6–1.9 mg Ca L−1), low corrected conductivity (12–31 μmho cm−1 (1 mho = 1 S)), and relatively high pH (4.0–5.7). Mire 224 is dominated by Chamaedaphne calyculata, Scheuchzeria palustris, and Carex oligosperma. The surface water mean determinations are Ca, 1.10 ± 0.51 mg L−1; Mg, 0.57 ± 0.2 mg L−1; corrected conductivity, 16.7 ± 4.2 μmho cm−1; and pH 4.37. Abundance patterns of the dominant Carex species can be correlated with pH of the surface water of the mire. Mire 239 is characterized by Smilacina trifolia, Ledum groenlandicum, and Carex trisperma. The mean surface water determinations are Ca, 1.53 ± 0.36 mg L−1; Mg, 0.59 mg L−1; corrected conductivity, 21.2 ± 2.0 μmho cm−1; and pH 4.0. Significant differences in pH, Ca, and Mg occur between the interior and edge portions of this bog. Water chemistry from portions burned in 1974 showed no difference from unburned portions. The vegetation of mire 661 contains a sequence of communities positioned relative to the inflow streams, with a Myrica gale – Alnus rugosa community followed by a zone dominated by Picea mariana then a Larix laricina zone and then by an open Sphagnum papillosum – Menyanthes trifoliata lake edge zone. More ombrotrophic areas are dominated by Sphagnum fuscum. Ca, Mg, and Fe concentrations, pH, and corrected conductivity were reduced through this sequence. Comparison of weekly samples of water entering and leaving this mire in 1981 showed a reduction of Ca, Mg, SO4, NO3 N, alkalinity, and pH.