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Spatial and temporal surveys were conducted to better understand the physicochemical characteristics of the streams in Bukit Timah Nature Reserve (BTNR). A total of 87 survey stations were selected along ten streams for an in-situ water quality study conducted in June 2018. Temporal investigation, including in-situ and ex-situ samplings, was conducted from late November 2017 to July 2018 for Fern Valley and Jungle Fall streams. The in-situ physicochemical parameters included pH, Dissolved Oxygen (DO), Conductivity, Oxidation-Reduction Potential (ORP), Total Dissolved Solids (TDS), Turbidity, Salinity, and Temperature. Water samples were collected for further analysis of Total Suspended Solids (TSS), anions, cations, elements, Total Organic Carbon (TOC), Total Nitrogen (TN) and Total Phosphorus (TP). Water discharge was calculated as stream crosssectional area multiplied by water velocity. Groundwater samples (down to maximum 2 m) were collected at upstream and downstream locations in Fern Valley and Jungle Fall catchments and analysed for water chemistry. Seventy-five soil samples (surface and subsurface) were collected to investigate the hydrogeomorphic conditions of the catchments in an attempt to understand the influence of hillslopes on water quality within the stream channel. Physicochemical baselines of the streams in Bukit Timah Hill were established, the data suggesting that stream temperature, TDS, salinity, the amount of TOC, TP, anions and cations vary within their expected natural ranges. Some parameters including DO and conductivity are slightly lower than expected, which may not be favorable for large aquatic animals. Some issues needing further investigations include low stream pH in Jungle Fall and Seraya streams as well as the significantly high concentration of Cd, Sb and Se in all streams. Follow-up actions are recommended to further investigate the drivers and monitor the effect of stream acidification, the causes and effects of high concentration of Cd, Sb and Se, as well as possible stream rehabilitation measures leading to improvement of water quality.

Physicochemical characteristics of streams in Bukit Timah Nature Reserve, Singapore