NATURALLY ACIDIC OR ANTHROPOGENICALLY ACIDIFIED? UNCOVERING THE DRIVERS OF STREAM ACIDITY DURING STORMFLOW IN THE NEE SOON CATCHMENT, SINGAPORE

Episodic acidification occurs as periods of high flow temporarily reduce the streams’ acid neutralizing capacity (ANC). In Singapore, the acidification of streams in the Nee Soon Swamp Forest (NSSF) is thought to have deleterious impacts on aquatic ecosystems. This research aims to understand potential mechanisms responsible for episodic acidification in the Nee Soon Catchment (NSC). Five streams were selected in the NSC. The pH and major ions in precipitation, throughfall and shallow groundwater and streamwater samples were analysed. Soil cores were collected for analysis of pH, particle size distribution, organic matter content, effective cation exchange capacity (ECEC) and base saturation (BS). During storm flow, all streams experienced a decrease in ANC as the concentration of nitrate and sulfate increased. BS of the soils was low, indicating that soil exchangeable acidity may increase and contribute to further stream acidification. The results suggest that stream acidification in the NSC is primarily driven by the flushing of previously deposited acid anions through the soil and into the streams during storm events.

Author dc:creator

• KOH YAN TING RACHEL

• Acid deposition, Episodic stream acidification, Acid-neutralizing capacity, Base cation surplus, Base cation depletion, Nee Soon Catchment