Metals in Sediment Cores from Nine Coastal Lagoons in Central Vietnam

Abstract

Problem statement: After being dramatically hit by war events, Vietnam is presently experiencing a huge economical and social development. However, very few data, relative to pollution levels and trends, are available for the correct management of critical areas such as coastal lagoons, where many economical activities are linked to high value environmental features. Approach: A set of sediment cores from nine coastal lagoons of central Vietnam (Lang Co, Truong Giang, An Khe, Nuoc Man, Nuoc Ngot, Thi Nai, O Loan, Thuy Trieu and Dam Nai) were sampled in 2008 and analyzed to assess metal and (Al, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb, V, U and Zn) and As levels and historical trends. Results: Concentrations are generally low, with the exception of As, which often exceeds ERL guidelines and Ni that does the same at O Loan. In some cases, concentrations-depth profiles account for recent increasing trends but surficial values are still low when compared to both international guidelines and polluted sediments all around the world. Sediment grain size seems to affect the depth distribution of a number of metals and when normalized to the content of silt and clay, values are particularly high at Dam Nai and Thi Nai, due to the very coarse composition of surficial sediments. Conclusion: Metal concentrations in lagoon sediments derive from the composition of rocks and soils in the watersheds. However, recent increasing trends need for further monitoring.

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

“…Metal and As levels in cores sampled in 2008 from the seven lagoons have comparable ranges and were discussed by Romano et al [28]. In some cases, concentrations-depth profiles account for recent increasing trends but surficial values are still low when compared to both international guidelines and polluted sediments all around the world [28].…”

“…However, concentration-depth profiles of Al and Ni from LC ( Figure 3) appear similar downcore, but not completely superimposable. In addition, one of the most important difference is the decreasing trend at the surface in 2008, more evident for As and Zn, probably linked to the grain size pattern [28]. No clear conclusion about erosion can be drawn from these profiles.…”

“…Fine sediments characterise also the cores sampled in 2008, with the exception of DN (with sand always >50%), TN (that shows an upward constant increase of the coarse component up to ∼60% at surface), and CR, where sand reaches a peak value (65%) between 35 and 20 cm depth and remains 48% at the top. [28] The sediment from DN is characterised by a high content of shell tests (ranging from 3 to 18%) that may weaken any interpretation. Downloaded by [Kungliga Tekniska Hogskola] at 08:26 05 February 2015…”

“…In some cases, concentrations-depth profiles account for recent increasing trends but surficial values are still low when compared to both international guidelines and polluted sediments all around the world [28].…”

“…Romano et al [28] discussed the contents and patterns of major and trace elements in cores taken in 2008. They concluded that the main factor influencing element distributions is the terrigenous clay mineral input.…”