SUBSTANTIAL VARIATION IN ICE PHENOLOGY AND UNDER ICE CONDITIONS ACROSS BACKWATER LAKES OF A LARGE RIVER

Winter can be a bottleneck for riverine organisms, but our understanding of the patterns and controls of winter conditions that support river food webs is limited. Further, large floodplain rivers often have a diversity of off channel areas that provide overwintering habitat and affect how winter conditions are expressed across the river landscape. To evaluate drivers of variability in winter conditions across the Upper Mississippi River (UMR), we combined long-term data analysis with winter field surveys in backwater lakes across three reaches of the UMR spanning a gradient of winter intensity and varying in depth and connectivity to the mainstem river. We quantified the timing and duration of ice and snow cover; continuous oxygen, temperature, and light under ice; and drivers of this variation. Ice duration varied by up to a month between the most northern and southern reaches and one to two weeks among sites within the same reach, indicating local factors mediated regional climate effects on ice dynamics. Oxygen and temperature conditions varied with lake depth and connectivity, and responded dynamically to changes in discharge and snow cover throughout the season. The highest daily fluctuation of oxygen, an indicator of under ice productivity, occurred in shallower, less-connected backwaters and during intermittent ice and snow cover at the edges of winter. These findings show that factors such as depth and connectivity affect ice and under ice conditions in rivers, emphasizing the importance of maintaining habitat diversity in river ecosystems as winters change.

Primary Presenter: Kathi Jo Jankowski, US Geological Survey (kjankowski@usgs.gov)

Authors:

John Kalas, Wisconsin DNR  (john.kalas@wisconsin.gov)

Robert Burdis, Minnesota DNR  (robert.burdis@state.mn.us)

Ashley Johnson, Iowa DNR  (ashley.johnson@dnr.iowa.gov)

Travis Kueter, Iowa DNR  (travis.kueter@dnr.iowa.gov)

Stephanie Szura, Wisconsin DNR  (stephanie.szura@wisconsin.gov)

Kyle Landolt, US Geological Survey Upper Midwest Environmental Sciences Center  (klandolt@usgs.gov)