Recent anthropogenic impacts on the bilbao estuary, Northern Spain: Geochemical and microfaunal evidence

The distributions of a range of elements (including Cs-137 and Pb-210) have been studied in surface sediments and 0.5 m cores from the Bilbao Estuary (Cantabrian coast, northern Spain) to determine recent and historical sedim ent contamination. Benthic foraminifera have also been examined to infer re cent ecosystem changes. High concentrations of a range of metals are observ ed in three cores and in surface-scrapes. Observed concentrations depend on the proximity to sources of pollutants. Living foraminifera are absent fro m surface sediments in the upper estuary, and are scarce in the middle and lower estuary, due to persistent anoxia in the estuarine channel, and possi bly, high pollutant concentrations. High metal concentrations in sediment c ore profiles, combined with the sporadic presence of foraminifera, indicate that environmental degradation has persisted in this estuary for at least the last 40 years. This degradation has been caused by the discharge of unt reated industrial and domestic effluents. Surface sediments show a few tran sported living foraminifera of species char have been identified as dominan t in nearby, less-polluted estuarine environments.. Successful recolonizati on by these species may occur if the sediment conditions improve sufficient ly. Foraminiferal assemblages could therefore be used as environmental qual ity indicators to assess the effectiveness of current regeneration schemes implemented under strategic local authority plans. (C) 2000 Academic Press.