ROLE OF TRIBUTARY NUTRIENT TRANSPORT AND SEDIMENT PHOSPHORUS PROCESSES ON NUTRIENT DYNAMICS IN NEARSHORE LAKE SUPERIOR

Over the past decade, cyanobacterial blooms have occurred along the southwestern shore of oligotrophic Lake Superior. Previous studies indicate that watershed fluxes of sediment and nutrients, in particular phosphorus (P), may play an important role in driving these blooms.  To understand how tributary loads of nutrients and sediment contribute to nearshore blooms, two key tributaries, Bois Brule and Siskiwit Rivers, were sampled in the vicinity of recurring cyanobacterial blooms in the nearshore. We monitored discharge and water quality to compute nutrient and sediment loads and collected suspended and streambed sediment to assess the capacity for the sediment to store and transport bioavailable P in the rivers. Strong positive relations between discharge and concentrations of suspended sediment, total P, and total nitrogen indicated storm flows drove export. A strong positive relation between total P and suspended sediment indicated that sediment may serve as a vector for P.  Additionally, evaluation of equilibrium P concentrations revealed that suspended sediment sorbed P as it is moved through the stream network across sites and seasons and was a potential source of P to the nearshore. However, the streambed sediment in both watersheds were P sinks during the summer, which potentially delayed transport of dissolved P to the lake.

Primary Presenter: Rebecca Kreiling, UMESC - Laboratory/Office - #1 (rkreiling@usgs.gov)

Authors:

Rebecca Kreiling, United States Geological Survey  (rkreiling@usgs.gov)

Anna Baker, United States Geological Survey  (abaker@usgs.gov)

Carrie Givens, United States Geological Survey  (cgivens@usgs.gov)

Richard Kiesling, United States Geological Survey  (kiesling@usgs.gov)

Eric Dantoin, United States Geological Survey  (edantoin@usgs.gov)

Patrick Perner, United States Geological Survey  (pperner@usgs.gov)

Shelby Sterner, United States Geological Survey  (ssterner@usgs.gov)

Krimson Anderson, United States Geological Survey  (kanderson@usgs.gov)

Gerald Storey, United States Geological Survey  (gstorey@usgs.gov)

Kenna Gierke, United States Geological Survey  (kgierke@usgs.gov)