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

Abstract

Trace element concentrations have been measured in soil and sediment samples taken from the Thua Thien Hue (TT-H) Province and the Tam Giang-Cau Hai (TG-CH) Lagoon in 2002 and 2004. Results show 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 lowest internationally accepted sediment quality guidelines. Concentrations in soils are ascribable to natural sources and distributions in the TG-CH Lagoon are mainly influenced by river inputs, with Ag and Cd undergoing estuarine desorption processes. However, concentration-depth profiles of most trace elements in sediments show a recent increasing trend that might be linked to the economic development of the area. The comparison of porosity and 210 Pb depth profiles (confirmed also by Cd and As) from repeated samplings of the same core locations in the TG-CH Lagoon seems to account for a loss of 5-10 cm of surficial sediment that took place during the time interval between the two samplings. It is hypothesized that extreme meteorological events (e.g. a major typhoon that hit the area in November 2003) could be responsible for such sediment displacement.

Extreme events and environmental changes: Tracing sedimentary processes in Central Vietnam coastal lagoons

“…210 Pb profiles ( layers and remained relatively constant downcore. TN differed slightly from this pattern owing to higher values at depth as previously described [27], and values at NM showed large oscillations in the deep levels. The values obtained from 2008 samples span between 0.37 (NN) and 0.78 (CR) and the depth profiles show differences, especially at NM and CR.…”

“…Porosity-depth profiles were used as independent information to check the best correspondences. Giuliani et al [27] found that replicate samples were characterised by similar trends of 210 Pb and porosity, especially in the topmost sections. On this basis, and assuming of constant 210 Pb supply in the topmost levels, a good superimposition was observed when the profiles from 2008 cores were transposed downward (as in Figure 2) to find the best overlap.…”

“…This suggested that also the second sampling is representative of the site, Downloaded by [Kungliga Tekniska Hogskola] at 08:26 05 February 2015 lateral inhomogeneities may be present but unable to disguise the basic information defined by 210 Pb analyses. The combination of temporal records in sediment cores with the stratigraphic comparison of samples taken at the same site in different years [3,4,27] suggests a loss of material between the two samplings. Moreover, since calculated SARs are low but the sediment delivery from land is presumably high, we can assume the existence of mechanisms of sediment accumulation followed by resuspension and displacement during intense meteorological events, such as major typhoons.…”

“…Following the example of Giuliani et al [27], who compared the decay-corrected 210 Pb activities in repeated cores for LC, OL, and TN, the procedure was extended also to NM, NN, CR, and DN. Porosity-depth profiles were used as independent information to check the best correspondences.…”

Recognizing different impacts of human and natural sources on the spatial distribution and temporal trends of PAHs and PCBs (including PCB-11) in sediments of the Nador Lagoon (Morocco)

“…As final repositories of materials coming from land, atmosphere, and overlaying water masses, sediments deposited under low-energy conditions are important in environmental studies as they give a trustworthy picture of both present and past situations (e.g., Frignani et al, 2004;Giuliani et al, 2011a;Bellucci et al, 2012). In addition, they provide information on the chronology of contaminant inputs when conditions of low sediment perturbation are met.…”