A STUDY OF PROCESSES AFFECTING THE UPTAKE OF CONTAMINANTS BY INTERTIDAL SEDIMENTS, USING THE RADIOACTIVE-TRACERS - BE-7, CS-137 AND UNSUPPORTED PB-210

The vertical distribution of the radio-nuclides Be-7, Cs-137 and unsupported Pb-210 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 Be-7 and unsupported Pb-210 profiles ranged from 0.56 x 10(-7) to 34.2 x 10(-7) cm(2) s(-1). The sediment inventories of Be-7, Cs-137 and unsupported Pb-210, 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 Be-7 inventory at all sites was consistently higher during the period October-November than during the period March-September. Using data derived from the Be-7 and unsupported Pb-210 Sediment profiles, the profiles of Cs-137 were simulated and compared with the observed data recorded at each site. (C) 1995 Academic Press Limited