Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Research article Soil elemental analysis in a high conservation tropical forest in Singapore Canh Tien Trinh Nguyen a,b,* , Robert James Wasson c , Elvagris Segovia Estrada a , Sebastian I. Cantarero d , Charlene Teo e , Alan D. Ziegler a a Department of Geography, National University of Singapore, AS2, #03-01, 1 Arts Link, Kent Ridge, Singapore, 117570, Singapore b Tropical Marine Science Institute, National University of Singapore, S2S Building, 18 Kent Ridge Road, Singapore, 119227, Singapore c Institute of Water Policy, Lee Kuan Yew School of Public Policy, National University of Singapore, 469C Bukit Timah Road Level 2, Wing A, Singapore, 259772, Singapore d Department of Geological Sciences, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, UCB 399, Boulder, CO, 80309-0399, USA e Ministry of Education, Singapore, 1 North Buona Vista Drive, Singapore, 138675, Singapore ARTICLE INFO Keywords: Trace metal Forest catchment Elemental distribution Land uses/land covers Tropics ABSTRACT To understand the distribution of soil elemental concentrations and their potential sources of trace metal con- tamination in the high-conservation Nee Soon freshwater swamp forest in Singapore, we analyzed samples from 227 surface and 35 subsurface (auger profiles) locations. Our assessment involved distribution maps, principle component analysis, cluster analysis, and correlation analysis of element concentrations determined from a mixed acid digestion and measurement on an ICP-MS. We found a distinct zonation in the distribution of several elements (Ba, Cr, Cu, Fe, Mn, Pb, Sr, Ti, V, and Zn) between the upper and lower catchment that gives an erroneous notion of widespread contamination in the lower catchment. We believe this zonation is natural, likely related to differences in the underlying geology. However, Cu, Pb, and Sb concentrations were greatly enriched by anthropogenic activities on military training lands in the lower catchment, firing ranges in particular. Barium, Sr, and Zn also appear to be enriched in the lower part of the catchment, possibly from anthropogenic activities including military activity and roads. Although soils in the catchment are not highly contaminated, isolated areas with high concentrations of Cu, Pb and Sb may warrant management attention given the sensitive nature of the urban forest, which includes the last remaining fresh water swamp forest in Singapore. 1. Introduction Forested urban catchments are potential “hotspots” for ecosystem provisioning—e.g., biodiversity preservation (Roy et al., 2006), high carbon storage (Friess et al., 2016; Phang et al., 2015), sources of clean water, flood protection, and pollution mitigation (Welsch, 1991)—juxtaposed among highly disturbed, converted urbanized lands. The Central Catchment Nature Reserve in Singapore is one example of an isolated tropical forest reserve in a densely populated island city in SE Asia that is expected to become even more urbanized in the future (Wong et al., 2008). The catchment contains large reservoirs and is a principle capture area for rainwater runoff within the country's stra- tegic water supply scheme (PUB, 2018). The catchment contains about 200-ha of primary dryland forest, supporting key tree species such as Keruing (Dipterocarpus spp.), Meranti (Shorea spp.), and Jelutong (Dyera costulata)(NParks, 2018; Museum, 2018). Further, the catchment contains Nee Soon freshwater swamp forest, which as the last re- maining intact freshwater swamp forest in Singapore is of critical conservation value (Corlett, 1997; Ng and Lim, 1992; Wee and Ng, 1994; Cai et al., 2018; Clews et al., 2018). Recent studies have found several endemic species in Nee Soon including Parathelphusa reticulata (Yeo et al., 2010; Cai et al., 2016), Irmengardia johnsoni (Ng and Yang, 1985; Ho et al., 2016; Cai et al., 2016), Syzygium pseudocrenulatum (rediscoveries) (Chong et al., 2018), Amphidromus atricallosus temasek (Tan et al., 2011; Lim et al., 2018). Difficulties facing urban forest reserves in general are encroachment of human activities that disturb sensitive ecosystems through tram- pling, hunting, land-cover conversion (e.g. logging, road-building, agriculture activities) (Corlett, 1992; Murphy, 1997; Nguyen et al., 2018), stream alteration (Murphy, 1997), accelerated erosion (Nguyen, 2017; Nguyen et al., 2018), and contamination (Puckett, 1995; Nguyen et al., 2018). With respect to trace metal contamination, the focus of this paper, elemental enrichment is often associated with particular activities such as vehicle wear or waste products from building/main- tenance/burning. Contaminants enter a system through atmospheric deposition or transport from up-slope areas by hydrogeomorphological https://doi.org/10.1016/j.jenvman.2018.11.106 Received 16 July 2018; Received in revised form 21 October 2018; Accepted 23 November 2018 * Corresponding author. Tropical Marine Science Institute, National University of Singapore, S2S Building, 18 Kent Ridge Road, Singapore, 119227, Singapore. E-mail address: tmsnguy@nus.edu.sg (C.T.T. Nguyen). Journal of Environmental Management 232 (2019) 999–1011 0301-4797/ © 2018 Elsevier Ltd. All rights reserved. T