PALEOFLORA OF WILD RICE COMMUNITIES

Wild rice (manoomin; Zizania palustris) plays a significant role culturally for the Ojibwe, so lake sediment cores were taken to better understand its past environment. As part of a five-year research and education project, we are studying manoomin lakes on the Fond du Lac Chippewa Reservation in northern Minnesota, USA. Plant macrofossil analysis of sediment cores from wild rice lakes provides information on past floral communities, and shows how the lakes have changed over the Holocene. Results show that the lakes, which are now 1-3m deep, were originally 7-10m deep glacial kettles with low biological productivity. As the lakes have filled in with sediment over the past ~9000 years, the community has shifted from primarily aquatic plants such as Najas flexilis and Potamogeton natans to include more sedges such as Carex and Scirpus along with Zizania. The Scirpus is recent, only appearing in the upper 30cm (~50 yr) of the core; however, Potamogeton spirillus appeared in the lake about 2000 yr. BP. This species of Potamogeton survives best in water ~1m deep, showing the lake was transitioning to suitable Zizania habitat. The iron phosphate mineral vivianite was found throughout a core from Dead Fish Lake, suggesting a historically P-rich watershed. This abundance of nutrients may have allowed a more diverse plant community to develop in this than in the other lakes studied. With a more diverse surrounding, and high-P sediments, Zizania in the lake has thrived and it is currently one of the best-producing rice lakes on the Reservation.