RELIABILITY OF SALT MARSHES AS GEOCHEMICAL RECORDERS OF POLLUTION INPUT - A CASE-STUDY FROM CONTRASTING ESTUARIES IN SOUTHERN ENGLAND

Temperate, mesotidal salt marshes are usually good ''geochemical recor ders'' of pollutant input. Dated salt marsh cores from the Hamble, Itc hen (Southampton Water), and Beaulieu estuaries (southern U.K.) are as sessed. Sediments show clear labeling from effluents, which varies dep ending on their proximity to major urban or industrial areas. For elem ents where input is dominantly from a single source and periods of pea k discharge are known (i.e., Cu, Cs-137, and (CO)-C-60), historical re cords of pollutant input can be reconstructed, provided redistribution through sediment mixing or early diagenetic processes is minimal. Whe re the pollutant has a range of sources (i.e., Pb) or where physical m ixing in-estuary produces a time-integrated signal, it can prove extre mely difficult to relate concentration depth profiles to discharge his tories. Using concentration and stable Pb isotope data, the observed t emporal input of Pb to these marshes is shown to reflects complex, mix ed marine/atmospheric input from regional (automobile emission) and lo cal (urban/industrial) sources. While general trends in pollutant load ing may still be observed, it is extremely difficult to reconstruct ac curately temporal trends in Pb input and sources of Ph in these estuar ies using salt marsh records due to the importance of local, poorly-de fined Pb sources and in-estuary mixing processes.