THE EFFECT OF RIVER-ICE BREAK-UP ON SUSPENDED SEDIMENT AND SELECT TRACE-ELEMENT FLUXES

Ice break-up on northern rivers presents a unique research challenge b ecause of its dynamic nature and complexity of physical, chemical and biological processes. Rapidly moving ice, ice jamming, flood levels, a nd enhanced flow velocities can produce significant sediment transport and trace-element fluxes. Systematic sampling for these parameters, h owever, is rarely conducted because of logistical difficulties. This p aper discusses the magnitude and relative significance of sediment and trace-element fluxes during break-up of the Liard River in northern C anada. Historical data for the open-water and stable ice-covered perio ds are compared to that measured during the 1987 and 1993 break-up eve nts. Analysis reveals that a break-up pulse occurs during this period that if not accounted, can lead to significant underestimation of susp ended sediment and trace-element fluxes. More generally, any estimates of annual sediment or trace-elements for northern rivers that do not include data for the critical break-up period must be regarded as bein g conservative.