The significance of temporal variability in sediment quality for contamination assessment in a coastal wetland

This paper is an extension of a previous study by Lau and Chu (1999a) (Lau, S. S. S. and Chu, L. M. (1999a) The significance of sediment contamination in a coastal wetland, Hong Kong, China. Water Research (in press)) which focused upon patterns of sediment contamination at the internationally important wetlands Mai Po Marshes (Hong Kong), which receive continual pollution inputs from Mainland China and Hong Kong. The core aims of the present study were to investigate the potential effects of temporal variability in the assessment of sediment contamination in subtropical inter-tidal wetlands and in the evaluation of the sink-source nature of contaminated sediment. Sediment quality was examined for four seasons (spring, summer, autumn and winter) across six inter-tidal sites at the Marshes. Sediment contamination by total concentrations of Cd, Cu, Ni and Zn exceeded fifteen times the background level. Results of one-way ANOVA tests showed that the total and soluble concentrations of nutrients (N and P) and metals (Cd, Cu, Ni and Zn) in sediments were highly temporally dependent, with variations from contaminant to contaminant. Significant temporal variability may effect the interpretation of contamination assessment and implementation of management regimes for subtropical inter-tidal wetland ecosystems. Overall, the results ran counter to conventional wisdom that effects of temporal variability are negligible in the assessment of sediment quality.