Baseline concentrations of ten metals in the freshwater sediments of a watershed in Taiwan

Freshwater sediments and water samples were quarterly collected at different sampling stations from August 1996 to April 1998 in the Fei-Tsui reservoir watershed (FTRW) of northern Taiwan. The sediment and soil samples were digested using mixture of inorganic acids to analyze the total concentration of ten metals. The baseline concentrations of ten metals in the sediments of FTRW were calculated from the geometric mean (GM) values and the geometric standard deviation (GSD). The baseline concentrations of 10 metals in the 239 sediments of this watershed are listed as followings (mg/kg, only % for Fe): As 1.80-51.5, Cd 0.04-7.54, Cr 5.25-273, Cu 2.65-91.7, Hg 0.03-0.26, Mn 18.6-2310, Ni 3.95-167, Pb 1.10-75.4, Zn 6.46-327, and Fe 0.47-9.63%. However, the GMs of 10 metal concentrations in the sediments were lower than the regulated threshold concentrations in Taiwan rural soils. Highly correlations among different metals in the sediments of FTRW indicate that very similar sediments of formation process control the metal content associated with the parent materials. Inadequate land use results in As, Cr, Mn, and Ni accumulated in the sediment to show potentially contamination risk in the study area associated with accelerated erosion and runoff.