THE RESPONSE OF OSTRACOD ASSEMBLAGES TO RECENT POLLUTION AND SEDIMENTARY PROCESSES IN THE HUELVA ESTUARY, SW SPAIN

By studying the ostracod assemblages in the Huelva Estuary, the impact of natural and human factors on the populations of these organisms ca n be determined. Three periods were defined in 12 cores collected alon g the estuary: (1) pre-industrial period (before 1966), with moderate pollution in some estuarine sectors because of prehistoric mining; (2) industrial period (1966-1985), with pollution increasing by wastes de rived from industrial processes; and (3) post-industrial period (1991) . No ostracods and live macrofauna were found in environments with ext reme subaerial exposure (fluvial bars, meanders and salt marshes), eve n in pre-industrial sediments. During this period, the ostracod distri bution was controlled by the salinity tolerance in the main channel of the Odiel River, the euryhaline species being replaced by marine form s toward the estuary mouth. Acidic industrial wastes causes the disapp earance of ostracod assemblages (mainly Loxoconcha elliptica) in this environment and the channel border. Fillings of some distributary chan nels have greatly affected the ostracod and macrofaunal assemblages in these zones, with a dramatic drop in the diversity and number of indi viduals. In April 1991, live ostracods were exclusively found in the P unta Umbria subsystem, a relatively protected environment because dist ance and salt-marsh barriers protect it from industrial effluents. (C) 1997 Elsevier Science B.V.