Aquatic macroinvertebrates of Nee Soon 
73 
towards Lower Seletar Reservoir. The streams are typically shallow (8-70 cm in depth) 
and slow-flowing (mean velocity 1-18 cm/s). Tannins and other chemicals leaching 
from leaf litter stain the water a dark tea-colour, as well as reducing the pH to acidic 
levels (pH 4-6). Only a small amount of dissolved minerals can be found in the water. 
In periods of heavy rainfall, the streams tend to overflow and flood the surrounding 
area, creating small pools and flooded areas which may persist for indeterminate 
periods (Ng & Lim, 1992; Lim et al., 2011). In addition to ground and rainwater input, 
the Nee Soon drainage also receives periodic input from the Upper Seletar Reservoir 
near the northeast edge of the lower catchment. The environment in this area of the 
Nee Soon drainage is quite different from the rest of the swamp forest. Here, pH levels 
tend to be higher (> 5), reflective of the less acidic waters received as well as the more 
open forest canopy. 
Additional information on the hydrology and geomorphology of the Nee Soon 
catchment relevant to the aquatic macroinvertebrates is given by Nguyen et al. (2018) 
and Sun et al. (2018). 
Sample collection 
The diversity of aquatic freshwater macroinvertebrates in the Nee Soon freshwater 
swamp forest was represented by sampling a total of 40 sites throughout the freshwater 
swamp forest each on a single occasion between October 2013 and September 2014 
(Fig. 1). Additionally, sites 18, 33 and 38 (Fig. 1) were surveyed every two weeks 
between December 2013 and January 2015. Macroinvertebrates were sampled 
with a qualitative kick sampling method described in Blakely et al. (2010). The 
sampling procedure involves kicking the stream substrata to disturb and release 
macroinvertebrates into a kick-net (36 x 30 cm, 250 pm mesh size) held downstream. 
Kick samples were collected from a wide range of microhabitats (e.g. leaf packs, 
cobbles, pools, log jams and stream margin) over a 2-minute period within a 10 m 
reach delimiting each site. This procedure facilitated the collection of comparable 
representation of macroinvertebrate communities, while maximising the likelihood 
of collecting all species present including rare and habitat-specific species. All 
macroinvertebrate samples obtained were then immediately preserved in the field with 
molecular grade isopropanol. 
In the laboratory, samples were rinsed with water on a 250 pm mesh Endecott 
sieve, and all aquatic macroinvertebrates were removed and identified under xl00 
magnification. Individuals were identified to family-level, except for class Ostracoda, 
subclass Acari, Collembola and Oligochaeta, order Araneae, and infraorder Brachyura. 
The main references used for taxonomic identification were Merritt & Cummins 
(1996), Yule & Yong (2004), and Blakely et al. (2010). 
In this paper, the distribution of aquatic biodiversity in the Nee Soon drainage 
is represented by a series of maps that show the number of individuals (abundance) 
of each taxonomic group from each site during the spatially extensive survey (one 
sample per site). Taxonomic abundance is represented at the order level for all groups, 
except the Ostracoda that are identified to class-level and the Acari, Collembola and 
Oligochaeta that are identified to subclass-level. Biological notes for each taxonomic 
