APPLICABILITY OF OVERBANK SEDIMENT FOR ENVIRONMENTAL ASSESSMENT ACCORDING TO WIDE-SPACED SAMPLING IN FENNOSCANDIA

IGCP Project 259, International Geochemical Mapping, and its successor IGCP Project 360, Global Geochemical Baselines, aim at a global geoch emical map, which is becoming increasingly an environmental concern. A s a pilot survey for Project 259 overbank sediment, till, humus and ri ver water were sampled from 49 large catchment basins in Fennoscandia. The deeper layers of overbank sediment were deposited hundreds of yea rs ago and reflect natural preindustrial geochemical background. In th is survey the geochemistry of one sample of overbank sediment was foun d to represent catchment basins up to 7000 km(2) in size, and to corre spond to that of composites of 6-20 random till samples taken from the same basin. The surface layers were deposited recently and reflect po llution in the basin. Distinct pollution was detected in some basins w ith mining activities and industries. A large province with high Pb co ntents in the southern parts of Sweden and Norway is caused by atmosph eric deposition. In some basins metal contents from both anthropogenic and natural sources and exceeding values considered (phyto)toxic were measured. According to other surveys 30% of the river plains in Europ e are severely polluted, and many of these plains have toxic contents of heavy metals. Therefore, and because population is concentrated to river valleys, it is of great importance to determine the degree of, a nd future threats from this pollution. Overbank sediment is a most sui table medium for this purpose, because it can be used in basins rangin g from a few up to thousands of km(2) to determine the geochemical bac kground (deep layers), pollution history (profile sample), degree of p ollution (deep vs surface sample), and for monitoring change. Copyrigh t (C) 1996 Elsevier Science Ltd