, Volume 16, Issue 2, pp 219-231

Wild-rice and sedimentation processes in a Lake Superior coastal wetland

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Abstract

Sedimentation rate and nutrient concentrations were assessed in 1989 at four sites of differing stream morphometry in the Kakagon Sloughs, a Lake Superior coastal wetland in northern Wisconsin dominated by northern wild-rice (Zizania palustris). Pre-weighed sediment traps were placed at each site along deep-to-shallow water zones. Accrued sediment was collected during five time periods corresponding to differing stages of growth in wild-rice stands. There were higher sedimentation rates at the river sites (straight sections and inside and outside curves) when compared to the backwater site. Differences were also observed among depths and at the different time periods, demonstrating the influence of vegetation on the sedimentation process in this wetland complex. Higher sedimentation rates took place closest to the vegetation-open water interface (deep zones). However, in shallow zones, a significant proportion of the annual sedimentation took place during the submersed and floating leaf stages, showing the importance of these time periods for providing an annual input of sediment to large areas of riverine habitat. Of nutrients tested, both TKN and NO3-N had lower concentrations in the period following wild-rice stem elongation. These data suggest that the early growth habit of wild-rice (submersed and floating stages) promotes pulses of nutrient-rich sediment, which are necessary for the later nutrient-demanding stages of stem elongation and grain formation.