Geomorphology and hydrology of Nee Soon 
45 
dates on pollen indicate three distinct periods of accumulation: (1) present to 1273 CE 
(0-58 cm; 0.08 cmy 1 ); (2) 1273-1241 CE (58-62 cm; 0.125 cmy 1 ); and (3) 1241 CE 
to 657 CE (62-115cm; 0.09 cm y' 1 ). However, given the uncertainty in each estimate, 
as well as the similarity in accumulation rates, one rate of 0.1 cm y 1 can be assumed 
for the entire core, representing about 1360 years of deposition. The sedimentation 
rates suggest that the upper catchment swamp was not disturbed substantially by forest 
conversion to agriculture in the mid-19th century, whereas disturbance/change in the 
lower catchment has been dynamic with respect to climate and human activity. Again, 
direct comparison with the lower swamp is impossible, because sediments associated 
with the period between 1950 CE and 5500 BCE are missing in the lower core. 
Lastly, anthropogenic inputs of Pb, and perhaps Ba and Cu, are detectable in 
the upper few centimetres of the cores (Kho, 2014, 2016; Nguyen, 2017). According 
to Chen et al. (2016) there are several possible sources contributing Pb to the nearby 
MacRitchie Reservoir in Singapore, including power generation-based coal combustion 
from nearby Indonesia (Lucarelli, 2010). Our isotope data are less variable than those 
of Chen et al. (2016), but also appear to be enriched by external sources, although it is 
not possible to calculate a source budget at this time. 
Conclusions 
The hillslopes and stream network of the Nee Soon catchment have been degraded by 
many decades of human impact, but their resilience is being demonstrated by clear 
evidence of recovery of the vegetation, soils, swamps and streams. Resilience of the 
hydrologic system helps to explain the apparent resilience of the aquatic fauna (e.g. 
Ng & Lim, 1992; Ho et al., 2018), including the survival of hyperendemics, despite 
disturbance of the associated vegetation. The upper catchment forested hillslopes 
were disturbed by anthropogenic activities beginning about 1850 when agriculture 
was first established. Some of the greatest disturbances occurred about 70-100 years 
later when the firing ranges were established, the lower stream and swamp network 
were disturbed by channel straightening, and erosion was accelerated from building 
and maintaining a water pipeline. Further, much of the lower catchment vegetation has 
been converted to urban land uses, including a golf course and roads, and the existence 
and operation of nearby reservoirs alters the catchment hydrology. 
With respect to management, the following represent some of the most obvious 
current challenges to address: (a) disruption of the natural stream flow by water 
release from adjacent reservoirs; (b) high concentrations of some heavy metals in the 
soils within the military firing range; (c) inputs of heavy metal contaminants to the 
catchment through atmospheric deposition; and (d) disturbance of the forest slopes and 
the stream network by hikers, mountain bikers, and military personnel during training. 
Given that Nee Soon is the last remaining freshwater swamp forest in Singapore and 
an important site of biodiversity, we recommend addressing these management issues 
in tandem with conducting additional baseline research and a campaign of educational 
awareness. 
Beyond identifying negative impacts, the goal of this study was to develop 
