Temporal and spatial distributions of moisture and organic contents across a macro-tidal mudflat

The purpose of this study was to make comprehensive surface measurements of the changes in moisture and organic contents across the Skeffling mudflats (Humber Estuary, UK) and to examine the effects of exposure and location on the sediment properties. Sediment cores were collected using modified 50 ml syringes, and the data compared with measurements of chlorophyll a and colloidal carbohydrate concentrations. The temporal and spatial relationships between these surface sediment properties were quantified and related to the measured critical erosion shear stress. Moisture and organic contents correlate significantly with respect to morphology, both across the mudflat and with depth below the sediment surface. These variations affected the distributions of bulk density and sediment erodibility, although these two variables were not directly related. The relatively coarse vertical resolution of the cores prevented clear relationships being identified between critical erosion shear stress, moisture and organic contents, and the chlorophyll a and colloidal carbohydrate concentrations. Analysis of mean values removed some of the spatial variability and a reasonable exponential relationship was obtained between erosion shear stress and colloidal carbohydrate. This paper highlights the influence of the physical, morphological and biological characteristics of the surface sediment upon its erosion resistance. The implications for the development of the surface morphology and mudflat are considered.