Gardens’ Bulletin Singapore 70 (Suppl. 1): 33-48. 2018 
doi: 10.26492/gbs70(suppl.l). 2018-03 
33 
The hydro-geomorphic status of Nee Soon freshwater 
swamp forest catchment of Singapore 
C.T.T. Nguyen 1 , R.J. Wasson 2 & A.D. Ziegler 3 
‘Tropical Marine Science Institute, National University of Singapore, 
18 Kent Ridge Road, 119227 Singapore 
2 Lee Kuan Yew School of Public Policy, National University of Singapore, 
469C Bukit Timah Road, 259772 Singapore 
department of Geography, National University of Singapore, 
1 Arts Link, 117570 Singapore 
geoadz @ nus.edu. sg 
ABSTRACT. This paper presents initial findings from research on the hydro-geomorphic status 
of Nee Soon freshwater swamp forest catchment in Singapore. The hydrological system of 
Nee Soon contains a swamp that is best described as an organic-rich wetland, with organic 
matter content as high as 40% near the surface (too low to be classified as peat). Total long¬ 
term denudation rate in the catchment is an estimated 23.4 ± 2.08 Mg knr 2 yr 1 , with physical 
erosion (5.6 + 0.5 Mg knr 2 yr 1 ) and chemical weathering (17.8 + 1.58 Mg knr 2 yr 1 ) accounting 
for 24% and 76% of the totals, respectively. Age dating of a 1.95-m sediment core from the 
lower swamp indicates several distinct periods of variable sediment deposition (0.04 to 0.009 
cm y 1 ) since 15,000 BCE, across a variety of climate regimes. A missing layer, representing 
more than a 7000 year period, verifies substantial channel erosion in the swamp occurring 
since 1950. Accelerated erosion associated with forest conversion to agriculture in the upper 
catchment could not be verified through examination of sediment cores. High concentrations 
of several heavy metals (e.g. As, Cr, Mn, Ni, Sr, V) in the lower catchment, compared with the 
upper catchment, appear to be natural (e.g. related to differences in the underlying bedrock), 
rather than contamination. The very high concentrations of lead, copper, and zinc associated 
with firing activities in the military range in the lower catchment are spatially isolated (e.g. 
shooting berms), and currently not posing a threat to the swamp environment. Other hydro- 
geomorphic degradation processes/activities now include disruption to hillslope soils and 
streams by trampling and mountain biking, back-flow of reservoir release water into the lower 
swamp area, and atmospheric deposition of contaminants. 
Keywords. Conservation, erosion, heavy metals, hydrology, Pleistocene, vegetation history 
Introduction 
The transformation of Singapore from a forested island to a modern first-world city 
over the last two centuries has been rapid and has been termed environmentally 
“catastrophic” (Sodhi et al., 2004), leaving the island nation with less than 1% of 
its original forest cover. Historically, the 582 km 2 island was covered by three types 
of forest ecosystems (Corlett, 1991; O’Dempsey, 2014): lowland dipterocarp forest 
(80-82%), mangroves (13%), and freshwater swamp forests (5%). Between the arrival 
