Paper No. 12
Presentation Time: 11:45 AM
DIATOM INFERRED LAKE LEVEL AND HABITAT TRANSITION IN THREE WILD RICE (ZIZANIA PALUSTRIS) LAKES ON THE FOND DU LAC RESERVATION
MOORE, Cheyenne, Cloquet Schools, Cloquet, MN 55720, BUNCH, Cristina, Northeastern State University, Tahlequah, OK 74664, WOODS, Phillip, LacCore/Limnological Research Center, University of Minnesota, Department of Earth Sciences, Minneapolis, MN 55455, MYRBO, Amy, LacCore/CSDCO, Department of Earth Sciences, University of Minnesota, 500 Pillsbury Dr. SE, Minneapolis, MN 55455, HOWES, Thomas, Fond du Lac Reservation Resource Management Division, 1720 Big Lake Rd, Cloquet, MN 55720, SHINNEMAN, Avery L.C., Biology Department, University of Washington, Seattle, WA 98195 and KOCHEN, Andrew, Large Lakes Observatory, Duluth, MN 55118, munkey_gurl_2006@msn.com
Zizania palustris, otherwise known as wild rice, is a large food source and also an important part of the Ojibwe culture. Man-made ditching in the early part of the 20
th century, intended to drain the wild rice lakes on the Fond du Lac Reservation (Band of Lake Superior Chippewa), provides an interesting case study in how land use change and nutrient loading may affect wild rice production. Sediment cores were taken from Dead Fish, Perch, and Rice Portage lakes using a piston corer, subsampled, and prepared using standard methods. Diatom valves were counted using standard taxonomic references and analyzed using a surface sample training set and comparing relative abundances of planktonic/benthic diatoms. The primary purpose of this research is to better understand how nutrient conditions have changed in these lakes as the lakes have filled in with sediment and become shallow enough to support abundant benthic diatoms and submergent/emergent vegetation.
Preliminary data suggest that lake depth decreased in all three lakes between 2000-1000 cal. yr. BP and as recently as 100 years ago. Decreased lake depth could be the result of increased sediment loading after the surrounding areas were ditched in the 1910s. The diatom communities at all three lakes are currently dominated by benthic diatoms and have been for more than 1000 years. Planktonic diatom communities (mainly Aulacoseira and Stephanodiscus) present throughout the period of transition between 3000 and 1000 cal. yr. BP are now almost completely absent. More recently, benthic diatom community compositions have shifted away from species previously observed in high abundance throughout the sediment cores, suggesting nutrient levels and habitat availability may have increased over the last 100 years.
In the 20th century, these lakes have declined in wild rice production. The reasons for the decline are not well understood; however, land use change in close proximity to these lakes, the sensitivity of wild rice to increased fluctuations in water levels, and diminishing water quality are believed to play a major role. The research described here will help us better understand how lake productivity and wild rice abundance is linked to increasing nutrient and sediment loads
