title: Sediment and nutrient distribution and resuspension in Lake Winnipeg.
abstract: Severe algal blooms in Lake Winnipeg since the late 1990s have been attributed to increased watershed nutrient loading, much of which is associated with suspended particles. Within-lake transport and fate of this nutrient fraction and the importance of internal loading via resuspension, however, are unknown. We measured radioisotopes (7Be,210Pb,137Cs), metal and nutrient contents of suspended solids in major tributaries and lake-water, in sediment traps and in bottom sediments to estimate sediment resuspension and mass accumulation rates using two models. Sedimentation rates calculated from137Cs and210Pb dated cores and sediment traps indicated that most (95-99%) suspended material is derived from bottom sediment; mixing models using7Be/210Pb and137Cs yielded similarly high estimates (82 and 84%, respectively).137Cs profiles in cores indicated that up to ~7cm remains actively resuspended for times up to 23years before incorporation into deeper sediments. Total and bioavailable phosphorus (TP, BAP) in this top sediment layer were generally lower in the North than the South Basin, likely reflecting inputs from the Assiniboine and Red Rivers at the southern end of Lake Winnipeg, with an average of ~30% TP as BAP. Estimates of average sediment-associated internal TP loading for the South Basin (0.264g/m2/y) were ~2× those for the North Basin (0.146g/m2/y). Together, this internal loading is comparable to the magnitude of the external loading. Our results indicate that surficial sediments in Lake Winnipeg will remain a significant and active source of internal nutrient loading for several decades, a process which may delay the response of the lake to external nutrient management.
authors.affiliation: Dept. Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH 44106-7216, USA. Electronic address: gerald.matisoff@case.edu.
authors.forename: Gerald
authors.initials: G
authors.lastname: Matisoff
authors.affiliation: Watershed Hydrology and Ecology Research Division, Environment and Climate Change Canada, Burlington, ON, L7R 4A6, Canada.
authors.forename: Sue B
authors.initials: SB
authors.lastname: Watson
authors.affiliation: Watershed Hydrology and Ecology Research Division, Environment and Climate Change Canada, Burlington, ON, L7R 4A6, Canada.
authors.forename: Jay
authors.initials: J
authors.lastname: Guo
authors.affiliation: Dept. Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH 44106-7216, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Duewiger
authors.affiliation: Dept. Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH 44106-7216, USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Steely
keywords: Internal loading; Lake Winnipeg; Nutrients; Sediment resuspension; Sedimentation rates