RA-226 CONTENTS AND RA-228 RA-226 ACTIVITY RATIOS OF THE FENLAND RIVERS AND THE WASH, EASTERN ENGLAND - SPATIAL AND SEASONAL TRENDS/

Measurements of Ra-226 and Ra-228 in the Fenland rivers and The Wash s how that physical and hydrological factors play an important role in c ontrolling the transport and fate of radium isotopes. In the surficial environment, higher Ra-226 contents and lower Ra-228/Ra-226 activity ratios are found in waters from catchments with a greater proportion o f carbonate-rich source materials. This relationship is more obvious d uring periods of high runoff and river discharge when enhanced surfici al weathering and regolith saturation takes place. In the nearshore zo ne, Ra-226 content is relatively uniform whilst Ra-228/Ra-226 activity ratio is controlled by ionic concentrations (Cl, SO4 and CO3) and the acquisition of ''marine'' characteristics. The observed Ra-228/Ra-226 activity ratio trend can be attributed to a combination of conservati ve mixing and radium desorption from suspended sediments, whilst more uniform Ra-226 contents may reflect bottom sediment diffusion of exces s Ra-226 over a greater area. The relative importance of these two pro cesses is controlled by differential input from the freshwater and sal ine end-members of the estuary.