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and snails that tend to be dominant in less “healthy” systems, and indicative of more 
enriched and alkaline conditions, were in abundance at these sites. An abundance 
of introduced fish species was also recorded at these sites, in comparison to the 
predominantly native fauna in the remainder of Nee Soon. 
The downstream “edge habitat” sites were likely influenced by disturbance from 
the spillway discharging water from the reservoir periodically, discharging mixing 
Nee Soon catchment and reservoir water and backing up into the stream system. The 
lack of riparian habitat complexity (sparse tree cover) and dominance of fast-growing 
vegetation, symptomatic of frequent disturbances at these sites, as well as more 
alkaline water chemistry, provided less suitable niches for the more sensitive native 
fish or rare invertebrates (e.g. Megalopterans and Plecopterans). 
The hydrological conditions in Nee Soon freshwater swamp forest reflected 
the wet and dry seasons in Singapore (Chia & Foong, 1991), with high water levels 
recorded during the wet phases of early Northeast monsoon (November to December) 
and Southwest monsoon (June to September); and low levels during the dry phase of 
the late Northeast monsoon season (January to early March). The macroinvertebrate 
composition was reflective of short-term changes in abiotic conditions (Barbour et al., 
1999), where the diversity of community corresponded to dry versus wet seasons (i.e. 
high abundance in wet season, low abundance in dry season). 
Faunal responses to hydrology were examined for the invertebrate fauna since i) 
temporal patterns were evident in invertebrate communities when considered against 
high frequency water-level observations, whereas fish communities were generally 
not correlated with corresponding intra-annual changes in water level; and ii) the 
invertebrates tend to be relatively less mobile than fish and more sensitive to short-term 
changes in the aquatic environment (Barbour et al., 1999). Spatio-temporal patterns in 
fish co mm unities were most strongly evident in the spatial variation of co mm unities 
which points to the importance of factors such as water quality and associated tolerance 
and resilience of the more “typical” (native) swamp forest fish community within the 
heart of the catchment in contrast to the edges of the catchment and in proximity to the 
spillway that discharges water from the reservoir. 
Faunal response models reflected the potential effects of drought and disturbance 
caused by elevated discharge. They revealed that when water levels were at their 
lowest, the richness and abundance of invertebrates were reduced. Conversely, the 
richness and abundance of invertebrate fauna was also reduced when maximum stream 
water levels were greater. 
Model results suggest that effects of minimum water level are more pronounced 
than those of high water levels and that smaller streams are likely to be more susceptible 
to very low faunal counts and even absence of invertebrate fauna altogether at high 
maximum water levels or low minimum water levels. The most pertinent implications 
of these results for the long-term management of the swamp forest streams is the 
potential loss of individuals but perhaps more crucially, loss of taxa is anticipated from 
the smaller streams in particular during periods of extreme, extensive low and high 
flows. This is of particular relevance in the context of predictions of more intense and 
prolonged dry and wet periods in the face of climate change. 
