The hydro-geomorphic status of Nee Soon freshwater swamp forest catchment of Singapore

Abstract

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 longterm denudation rate in the catchment is an estimated 23.4 ± 2.08 Mg km -2 yr -1 , with physical erosion (5.6 ± 0.5 Mg km -2 yr -1 ) and chemical weathering (17.8 ± 1.58 Mg km -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 hydrogeomorphic 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.

Diversity of terrestrial snails and slugs in Nee Soon freshwater swamp forest, Singapore

“…However, Singapore's tropical soils are generally acidic and poor in calcium (Chia & Foong, 1991), especially in freshwater swamp forest. Thus a shortage of calcium in Nee Soon soils (Nguyen et al, 2018) may be a limiting factor to the growth and reproduction of these land snails. The sampling method also plays a part in the observed low abundance.…”

Conservation outputs and recommendations for Nee Soon freshwater swamp forest, Singapore

“…The construction of the firing range, golf course, and expressway within or close to the Nee Soon freshwater swamp forest may be affecting the water and soil quality of the stream channels (Nguyen et al, 2018;Sun et al, 2018). Analysis of soils for heavy metals throughout the reserve found that soils in the lower catchment are significantly more enriched than those in the upper catchment.…”

“…The excavation of a soil pit in the upper catchment uncovered ancient charcoal remains, indicating clear evidence of past fires (Nguyen et al, 2018). Fires along the hillslopes and dryland forests are not only capable of removing large swathes of primary and old secondary forest, but may expose the slopes to significant erosion during subsequent precipitation and inundation.…”

“…Analysis of soils for heavy metals throughout the reserve found that soils in the lower catchment are significantly more enriched than those in the upper catchment. Due to the compositional homogeneity of soils in the enriched and normal zones, it has been concluded that some components of the heavy metal enrichments may be a result of such nearby developments (Nguyen et al, 2018).…”

“…Another eight papers have been accepted for publication Chong et al, 2018;Clews et al, 2018;Ho et al, 2018;Kutty et al, 2018;Lim et al, 2018;Nguyen et al, 2018;Sun et al, 2018). used for editing and data management.…”