Distribution of plant macroremains in surface sediments of Marion Lake, southwestern British Columbia

Abstract

Thirty surface sediment samples were collected from Marion Lake to establish the present-day distribution patterns of potential plant macrofossils, with emphasis on remains derived from upland species. Sample sites could be separated into three distinct groups on the basis of their macrofossil representation: offshore sites, west shore sites, and east shore sites. Significantly fewer macrofossils were found in offshore sites than in nearshore sites. East shore sites had fewer forest macrofossils because of the presumed filtering effect of a bordering sedge marsh. Conifer needles were always more abundant that their seeds, whereas for most other taxa, reproductive structures were more common than vegetative ones. Thuja plicata and Tsuga heterophylla were well represented by vegetative remains reflecting their shared dominance (ca. 90%) within 100 m of the lakeshore. The highest frequencies and concentrations of macroremains were scale leaves and branchlets of Thuja, indicating that western red cedar should be readily detectable in older fossil deposits. A proportional relationship exists between macrofossil concentrations and site frequency, indicating mixing and dispersal before deposition in the lake. A major inlet stream (Jacob's Creek) brings in many macroremains and appears to be the major source of Alnus rubra seeds and foliage of Abies amabilis and Pinus monticola. Seeds of the aquatic macrophyte Najas flexilis and oospores of the alga Nitella were frequently encountered in surface samples, although neither taxon was reported as growing in Marion Lake. This surface sediment study provided insights valuable to the interpretation of a postglacial macrofossil record in a companion study (N. W. Wainman and R. W. Mathewes 1987. Can. J. Bot. 65: 2179–2187).