Quantification of soil redistribution and sediment budget in a Canadian watershed from fallout caesium-137 ( super(137)Cs) data

The intensification and specialization of agriculture that took place in the past decades have resulted in soil and water degradation in several areas of eastern Canada. Most studies on soil erosion in Quebec have been conducted at the experimental plot scale. Although this approach generates precise data, extrapolation at the field or watershed scale is difficult. In this study, caesium-137 ( super(137)Cs) was used to investigate the spatial extent and severity of soil erosion for an 80-ha watershed in Southeastern Quebec (cultivated area = 75 ha). Soil samples were collected based on a 25 X 30 m grid and revealed soil redistribution rates ranging from -20 to +12 Mg ha super(-1) yr super(-1). From radiocaesium measurements, it was estimated that the experimental watershed experienced an average loss of 3.0 Mg ha super(-1) yr super(-1) with net sediment export of 2.8 Mg ha super(-1) yr super(-1) and a sediment delivery ratio of 93%. Snowmelt erosion is believed to have played an important role in the soil redistribution in this small watershed. Changing sampling strategy was tested (50 X 60 m and 100 X 120 m grid rather than 25 X 30 m) and only minor changes were noticed on soil erosion and sediment production estimates, when samples corresponding to the 50 X 60 m grid were used.