Soil genesis on a chronosequence, Pinery Provincial Park, Ontario

Abstract

Soils on a late Holocene dune chronosequence were studied along Lake Huron at Pinery Provincial Park, in southwestern Ontario. Progressive exposure of new materials, associated with declining lake levels, has allowed the development of soils in a sequential manner from the shoreline (approximately time zero) to about 2.3 km inland. Six soil pits were excavated and sampled in narrow depth increments along a transect ranging in estimated age from 100 to 4700 yr B.P. Chronofunctions were formulated based on pedogenic properties in order to evaluate the rates and pathways of soil genesis in southern Ontario. The soils graded from an Orthic Regosol near the shore to an Eluviated Dystric Brunisol to 2.3 km inland. The increasing thickness of the solum and darker chroma in the B horizons were the most obvious morphological indications of a progression in soil weathering. Linear chronofunctions of increasing total silt and clay contents with soil age suggest that physical breakdown of sand particles to silt and clay may be occurring. Total organic matter in the profiles increases logarithmically with soil age with a rapid increase in the first 2000 yr or so. The depth of CaCO3 leaching increased linearly with increasing soil age. Data indicate that mean annual precipitation may be the most important influence on the rates of carbonate weathering. Soil pH decreases linearly with soil age in the first 2900 yr. However, vegetative variations appear to influence the pH beyond 2900 yr of soil development. Depth to, and thickness of, the B horizons also increased linearly with soil age. Key words: CaCO3 weathering, solum thickness, clay accumulation, dune chronosequence