Evolution of the pollution in the Piedras River Natural Site (Gulf of Cadiz, southern Spain) during the Holocene

The Piedras River marshland and El Rompido spit bar is a Natural Site in close proximity to two of the most polluted rivers in the world: the Tinto and Odiel Rivers. The aim of this study is to determine the degree of contamination of this Natural Site using a variety of pollution indices. At this site the Holocene infilling sequence is recorded and applied to a study of the pollution history and the possible impacts of human activity. The depositional history of the Piedras River estuary during the Holocene recorded open marine conditions at ca. 6500 calBP when sea-level was at its Holocene maximum. To study the pollution of the estuary during the Holocene, catchment background geochemistry was established using samples that pre-date human activity (agriculture and mining). Additionally, the sedimentary environment was reconstructed throughout the Holocene; comparison of pollution levels is interpreted to be more reliable if the sedimentary environment has remained similar throughout the depositional record. Results show that, despite being located nearby very polluted estuaries, the Piedras River marshland contains unpolluted sediments mainly because of the small catchment area relative to that of neighbouring more polluted rivers, and thus has not been affected by human activity such as mining.