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Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
seasons, which had relatively well oxygenated and low turbid waters. The differences 
in seasonal hydrology impacted fish diversity, abundance and biomass, which were 
significantly higher in falling and low water seasons than during the high water 
season (da Silva et al., 2010). In tropical wetland forests similar changes have been 
documented in macroinvertebrate communities with stream physico-chemistry as well 
as insect assemblages, density and biomass reflecting fluctuations in seasonal rainfall 
(Ramirez et al., 2006). How rainfall impacts tropical wetlands, however, is varied and 
can depend on both regional and local biotic and abiotic factors. 
The effect of flood pulses on tropical wetlands can vary because catchment 
hydrology is influenced by the amount of rainfall and speed of the run-off (Page et 
al., 2009; Yule, 2010). In tropical peat swamp forests the topography, biodiversity of 
the forest and its microtopography can buffer the speed of run-off and thus mitigate 
potential impacts further downstream (Page et al., 2009). On a microtopographical 
or local scale buffering is partly caused by the presence of hollows, roots, buttresses 
and pneumatophores (Page et al., 1999). However, what primarily influences rainfall 
run-off and hydrology in a tropical peat swamp forest is how water flows laterally 
through the peat and the hydraulic connectivity of the peat near to its surface (Page 
et al., 1999). If the water table is consistently high, the amount of peat able to be 
sequestered increases as well as the system’s water holding capacity (Page et al., 
1999). Alternatively, if the water table is low or if the swamp forest is being drained, 
the speed of the run-off can become faster because of peat oxidation and subsidence 
processes (Page et al., 1999, 2009). The impact that faster run-off can have on the 
catchment varies from flooding downstream to scouring of the soil, which can have an 
impact on water chemistry. 
Water quality in freshwater swamp forests 
Gasim et al. (2007) conducted a detailed physico-chemistry study in the Bebar river in 
the Pahang peat swamp forests in Peninsular Malaysia where the authors documented 
low dissolved oxygen (DO) and pH, whilst the average stream flow was estimated at 
5 x 10 5 m 3 daily. Indeed, the pH recorded ranged from 3.53 to 4.55 whilst DO ranged 
from 0.54 to 1.76 mg L b The high organic content and high biological decomposition 
resulted in a high deoxygenation rate when compared with the reoxygenation rate (Das 
6 Acharya, 2003; Gasim et al., 2007). Similarly, low levels of DO have been observed 
at the Beriah swamp forest in Perak (1.21-2.14 mg L 1 ; Mashhor et al., 2004). Arecent 
study by Gandaseca et al. (2015), determined the water quality of four rivers in peat 
swamp forests in Sarawak, Malaysia. The authors also documented low levels of DO 
(4.98-5.02 mg L' 1 ) and attributed this to the high levels of organic matter in the rivers. 
Reported ranges of total dissolved solids (TDS) varied from 0.75 to 15.75 
mg L 1 , whilst turbidity ranged from 1.5 to 17.15 NTU. Temporal investigations by 
Ramirez et al. (2006) on a tropical wet forest documented a decrease in streamwater 
pH throughout the year, from near neutral (pH >6.0) to near acidic (pH <4.5), while 
N0 3 -N concentrations were high throughout the year and were independent of 
