CORRELATING PHYTOLITH AND POLLEN DATA FROM WILD RICE LAKES AND DESIGNATION OF FIRST OCCURRENCE – A CAUTIONARY NOTE

Wild rice (Zizania palustris) is central to Ojibwe culture. For example, the Fond du Lac Band of Lake Superior Chippewa chose the location of their reservation in the 1854 treaty based on the presence of several wild rice lakes in this area. The manoomin project, a shared effort between the Fond du Lac band and the University of Minnesota, is studying the history of the wild rice lakes on the reservation using sediment core samples. The lakes share a basic history, having been formed in depressions left by melting of ice blocks calving off the retreating glacier. Variations in hydrology impact this history differently for each lake. Nevertheless, a basic pattern of lakes filling in gradually through the Holocene is shared by the three lakes cored in the first year of this study: Dead Fish Lake, Perch Lake and Rice Portage Lake. Each of these lakes was infilled first with organic-poor silt in the early Holocene, then later with organic rich, fine-grained sediment (diatomaceous silty sapropel) with interspersed plant macrofossils. Both phytoliths and pollen were recovered from cores taken from each of these lakes, and their respective abundance in subsample splits from the uppermost levels of the lake cores were compared. In each of the lakes, pollen, and in particular grass pollen, is abundant in the surface sediments of the lakes. While wild rice does not produce unique pollen, the abundance of grass pollen is thought to reflect the presence of wild rice. Wild rice phytoliths (in fact any phytoliths) are sparse in the surface levels, beginning to concentrate 15-20 cm below the surface. Phytoliths have a specific gravity of 2.3- 2.35, which allows them to sink further than pollen. The disjunct between grass (presumed wild rice) pollen and wild rice phytoliths demonstrates the need for caution in interpreting the correlation between phytoliths and pollen recovered from the same core horizons. In addition, the first appearance of wild rice phytoliths in the sedimentary record may predate the first appearance of wild rice plants in the lake.