Significance of natural and anthropogenic sediment inputs to the saguenay Fjord, Quebec

Abstract

One-centimeter interval Pb-210 dating and 4-cm interval size analysis was carried out on a sediment core collected in a prodelta depositional environment near the head of the Saguenay Fjord. Results show a direct relationship between modal diameter of the sand fraction and annual maximum mean monthly river discharge events that are usually associated with the spring freshet. Indirect evidence of sediment flux to the head of the fjord includes a series of sand waves that are developed on a prograding submarine delta at the mouth of the Saguenay River. Clay-pellet zones observed in a gravity core are related to catastrophic events such as the 1971 St. Jean Vianney landslide, or to anthropogenic activities associated with the construction of dams and powerhouses at upriver locations. A subtle change in the slope of a graph relating cumulative annual mean river discharge and sediment accumulation for the 1950–1970 interval is in agreement with the timing of dam construction on the lower reaches of the Saguenay River system.