CHARACTERISTICS AND EXTENT OF ACIDIFICATION OF THE WATERS IN NEE SOON SWAMP FOREST

Abstract

An ecologically important habitat, Nee Soon Swamp Forest (NSSF) contains acidified waters that can detriment organisms across multiple trophic levels. However, neither acidification nor the characteristics of waters at NSSF are well studied. This thesis thus aimed to bridge this research gap by studying surface and soil waters collected along the upper catchment (UPPER), mid-catchment (MID) and the confluence of MID (CON) at NSSF. The parameters studied were pH, electrical conductivity (EC), salinity, total dissolved solids (TDS), dissolved oxygen (DO), dissolved organic carbon (DOC), trace metals and ions. Ions were also used to determine Acid Neutralising Capacity (ANC), which measures the ability to buffer acids. Methods were modified from United States Geological Survey protocol according to the conditions at NSSF and limitations of the study, namely manpower. Overall, samples were acidic, dilute and well-oxygenated freshwaters with low DOC and trace metal content. Most samples were Ca2+-HCO3 - types that were chronically (i.e. ANC below 0 ?eq/L) or extremely sensitive (i.e. ANC between 0 to ?eq/L) to acidification. Spatially, parameters generally followed the trend of CON > MID > UPPER. Cations followed the order of Ca2+ > Na+ > Mg2+ > NH4 + > K+ for CON and Ca2+ > Na+ > Mg2+ > K+ > NH4 + for MID and UPPER, while anions followed the order of HCO3 - > Cl- > SO4 2- > NO3 - > F- > Br- ? CO3 2- ? NO2 -. Similarly, stream samples were generally more acidic, dilute and oxygenated, but less able to buffer acids than well samples. Cations typically followed the order of Ca2+ > Na+ > Mg2+ > K+ > NH4 + in well samples and Na+ > Ca2+ > Mg2+ > K+ > NH4 + in stream samples, while anions for all samples followed the same order seen in the catchments. Based on the observed trends, organic ii acidity, geology and, to a lesser extent, mineral acidity were hypothesised to be the drivers of acidification at NSSF.