The influence of subaerial exposure on the bulk properties of fine-grained intertidal sediment from Minas Basin, Bay of Fundy

Measurements of the bulk properties of fine-grained, surface sediment were made bi-weekly across an intertidal mudflat in Minas Basin between June and September 1984. Spatial and temporal variations were substantial. The vane shear strength increased shoreward at a rate of 0·4 kPa km^-1 and, at any point, showed a dramatic mid-summer increase from less than 4 to 5-42 kPa. Relationships between vane shear strength, sediment properties (grain size, bulk density, water content, organic content) and biological activity or abundance were often weak because of both spatial and temporal changes in exposure time, exposure index, evaporation index and precipitation. Shear strength at any site was most sensitive to changes in exposure index and evaporation, and least sensitive to organic content and biological activity. The bed level co-varied positively with shear strength, i.e. shear strength increased despite deposition. It is proposed that summertime, mudflat deposition is controlled by surface-sediment shear strength which is, in turn, controlled directly by atmospheric effects.