Soils and sediments of the Thua Thien-Hue Province (central Vietnam): recognizing trace element sources and the likely influence of natural events

Trace element concentrations have been measured in soil and sediment samples taken from the ThuaThien Hue (TT-H) Province and the Tam Giang-Cau Hai (TG-CH) Lagoon in 2002 and 2004. Resultsshow that the lagoon is only slightly contaminated by elements such as Ag, Cd, Cr, Cu, Ni, Pb and Zn,whereas As, probably naturally enriched in this Asian region, reaches values above the lowestinternationally accepted sediment quality guidelines. Concentrations in soils are ascribable to naturalsources and distributions in the TG-CH Lagoon are mainly influenced by river inputs, with Ag and Cdundergoing estuarine desorption processes. However, concentration-depth profiles of most traceelements in sediments show a recent increasing trend that might be linked to the economic developmentof the area. The comparison of porosity and 210 Pb depth profiles (confirmed also by Cd and As) fromrepeated samplings of the same core locations in the TG-CH Lagoon seems to account for a loss of5-10 cm of surficial sediment that took place during the time interval between the two samplings. It ishypothesized that extreme meteorological events (e.g. a major typhoon that hit the area in November2003) could be responsible for such sediment displacement.