Exploring the possibility to detect recent temporal changes in highly disturbed sedimentary records through sampling repetitions and core comparisons of porosity and sand content

Dating of sediment cores in dynamic environments (such as tropical coastal lagoons) is often impossible to achieve, due to the difficulty to recover continuous and undisturbed records. Detailed temporal definition of environmental changes cannot be assured, but there is the possibility that information retained in such sediments can still provide useful insights on local or large-scale sedimentary dynamics, when a specific strategy is adopted. This latter consists in repeated core samplings at the same location and in the comparison of core profiles for basic and easily measurable parameters (porosity and sand content). This approach was tested on sediment cores, collected repeatedly during the period 2005-2010, at the same site of the Thi Nai Lagoon (central Vietnam). The proposed procedure was able to evidence the impact on lagoon sediments of activities linked to the construction of industrial settlements in the area, with dredging removing a consistent sediment layer from 2005 to 2008 and waste dumping providing additional sediment input in the following period. Simple statistic confirmed this scenario, together with core profiles of PCBs, As, Cd, Pb, and Zn. The procedure represents a simple tool to study coastal dynamics in places where the level of accuracy of traditional sediment radiodating cannot be reached. Several ameliorations are suggested in order to help developing the monitoring of sedimentary processes in poorly studied areas.