38 
Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
Legend 
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Fig. 3. (a) Near-total (mixed acid digestion; ICP-MS; see footnote in Table 1). Chromium 
concentrations (ppm) at 227 surface samples within the Nee Soon Catchment. Shading indicates 
spatial distribution determined by ordinary kriging on the samples, (b) Near-total chromium 
concentrations within the soil profile of pits located in the upper and lower catchment (see Fig. 
2a for pit locations). 
ppm for Cu, Pb, and Zn, respectively) demonstrate the likelihood that human activities 
have elevated concentrations in a manner similar to that reported by Chen et al. (1996) 
for industrial surface soils in Singapore (485, 235, and 3594 ppm, for Cu, Pb, and 
Zn). For Nee Soon, the high Cu and Pb concentrations associated with the military 
lands (Cu = 632 ppm; Pb > 10,000 ppm) indicate potent sources of anthropogenic 
enrichment in isolated areas (e.g. near the berms on firing ranges) that may require 
remediation in the future. 
Some elements that are considered to be pollutants, including As, Cu, Pb, can 
potentially move into the subsoil (Teo, 2016). Measurements of saturated hydraulic 
conductivity (and indicating property for infiltrability) in the soil profiles indicates a 
sharp decrease from about 485 mm h 1 to 23 mm h 1 by a depth of 50 cm (Kho, 2014, 
2016). This decrease, which is typical of a natural tropical forest hillslope with a thin, 
organic-rich and permeable A horizon formed over a clay-rich B horizon (cf. Ziegler 
et al., 2006), may prevent the movement of enriched elements to great depths in the 
soil profile, possibly preventing them from interacting with the groundwater. In 20 
water samples tested for heavy metals (ICP-MS), we found very low concentrations, 
suggesting limited (if any) movement of potentially harmful elements from the soil to 
the stream system (data not shown), or our failure to detect a synoptic signal. From 
