A study of processes affecting the uptake of contaminants by intertidal sediments, using the radioactive tracers: 7Be, 137Cs and unsupported 210Pb

The vertical distribution of the radio-nuclides 7Be, 137Cs and unsupported 210Pb were used to describe the processes of accretion, mixing, mixing depth and focusing, that influence the responses of intertidal bed sediments to contaminant inputs. These processes were studied in the mid and lower Tamar Estuary at six different sites sampled on eight occasions, over a period of 2 years. The maximum depth to which sediment deposits were mixed ranged from 10 cm to greater than 40 cm. Mixing coefficients derived from the 7Be and unsupported 210Pb profiles ranged from 0•56 × 10−7 to 34•2 × 10−7 cm2 s−1. The sediment inventories of 7Be, 137Cs and unsupported 210Pb, the maximum depths of mixing and the mixing coefficients were significantly higher in the bed sediments of the creek site and at two sites situated 12–14 km up the estuary than those observed at sites situated nearer to the seaward end of the estuary. With the exception of the site closest to the mouth of the estuary, the 7Be inventory at all sites was consistently higher during the period October–November than during the period March–September. Using data derived from the 7Be and unsupported 210Pb sediment profiles, the profiles of 137Cs were simulated and compared with the observed data recorded at each site.