TY - JOUR
T1 - Flowpath influence on stream acid events in tropical urban streams in Singapore
AU - Ramchunder, Sorain J.
AU - Voutchkova, Denitza D.
AU - Estrada, Elvagris Segovia
AU - Chuah, C. Joon
AU - Evaristo, Jaivime
AU - Ng, Daniel
AU - Cai, Yixiong
AU - Koh, Rachel Y.T.
AU - Ziegler, Alan D.
N1 - Funding Information:
This research was conducted as part of “Drivers and Consequences of Water Acidification in Singapore's Nature Streams” supported by Singapore's National Parks Board. Field work was conducted under research permit NP/RP17‐040. We thank the hard work of the core team of research assistants: Khairun Nisha Binte Mohamed Ramzdan, Valerie Lee, Dawn Ho, Jocelyn Lim Shi Hui. We also acknowledge the research of several students: Pak Hui Ying; Thio Eng Loon; Chia Jia Min, Sandra; Bian, Ruoyi; Tan Rou Ming and Chua Yan Yi Alvina. We are grateful for the laboratory assistance from Han Yinchou. Finally, we thank Rajasekhar Balasubramanian for the constructive comments/suggestions given on an earlier manuscript draft.
Funding Information:
This research was conducted as part of ?Drivers and Consequences of Water Acidification in Singapore's Nature Streams? supported by Singapore's National Parks Board. Field work was conducted under research permit NP/RP17-040. We thank the hard work of the core team of research assistants: Khairun Nisha Binte Mohamed Ramzdan, Valerie Lee, Dawn Ho, Jocelyn Lim Shi Hui. We also acknowledge the research of several students: Pak Hui Ying; Thio Eng Loon; Chia Jia Min, Sandra; Bian, Ruoyi; Tan Rou Ming and Chua Yan Yi Alvina. We are grateful for the laboratory assistance from Han Yinchou. Finally, we thank Rajasekhar Balasubramanian for the constructive comments/suggestions given on an earlier manuscript draft.
Publisher Copyright:
© 2021 John Wiley & Sons Ltd.
PY - 2022/1
Y1 - 2022/1
N2 - We investigated processes contributing to periodic acidification events in headwater streams of Nee Soon Forest Catchment (NSFC) in Singapore by monitoring hydrochemical changes in response to rainfall inputs. Stream chemistry response to most rainfall events was characterized by decreases in pH from means ranging from 5.1 to 5.3 to below 4.8–5.0 and corresponding increases in specific electrical conductivity from baseflow values of 15–30 to 50–80 μS cm−1, indicative of low-total dissolved solids in stormflow. The decreases in pH in the streams, which are typically acidic year-round, were related to occasional highly acidic rainfall inputs (pH ~4.05) and likely the flushing of organic acids into the stream by shallow subsurface flow interacting with surface litter and/or organic-rich soil horizons. The interaction of rainwater runoff with organic matter in the soil matrix possibly alters the chemical composition of stormflow, influencing pH. Decomposition of instream organic matter also reduces stream water pH. Leaching experiments revealed that the overland flow passing through organic matter and A horizon material has the potential to lower stream water pH by approximately a half unit or more, in part, by flushing nitrates that were produced by microbial decomposition of organic matter and/or precipitated sulphur that enterred the forest by wet or dry atmospheric deposition. The observed periodic acid events are a natural phenomenon in the stream system in this urban environment because of naturally acidic rainfall and granitic soils with low buffering potential. However, acid events are likely amplified in frequency and magnitude by anthropogenic pollution emissions of sulphur and nitrogen species (e.g., SO2 and NOx) from local and regional sources that lower rainfall pH. Although, acid runoff events are typically short-lived (<12–24 h), further longitudinal monitoring and experimental studies are needed to investigate the long-term implications on sensitive taxa in the NSFC streams. Finally, understanding the flow pathways of stormflow water in the nested system was critical for deciphering the mechanisms driving stream acid events at the site.
AB - We investigated processes contributing to periodic acidification events in headwater streams of Nee Soon Forest Catchment (NSFC) in Singapore by monitoring hydrochemical changes in response to rainfall inputs. Stream chemistry response to most rainfall events was characterized by decreases in pH from means ranging from 5.1 to 5.3 to below 4.8–5.0 and corresponding increases in specific electrical conductivity from baseflow values of 15–30 to 50–80 μS cm−1, indicative of low-total dissolved solids in stormflow. The decreases in pH in the streams, which are typically acidic year-round, were related to occasional highly acidic rainfall inputs (pH ~4.05) and likely the flushing of organic acids into the stream by shallow subsurface flow interacting with surface litter and/or organic-rich soil horizons. The interaction of rainwater runoff with organic matter in the soil matrix possibly alters the chemical composition of stormflow, influencing pH. Decomposition of instream organic matter also reduces stream water pH. Leaching experiments revealed that the overland flow passing through organic matter and A horizon material has the potential to lower stream water pH by approximately a half unit or more, in part, by flushing nitrates that were produced by microbial decomposition of organic matter and/or precipitated sulphur that enterred the forest by wet or dry atmospheric deposition. The observed periodic acid events are a natural phenomenon in the stream system in this urban environment because of naturally acidic rainfall and granitic soils with low buffering potential. However, acid events are likely amplified in frequency and magnitude by anthropogenic pollution emissions of sulphur and nitrogen species (e.g., SO2 and NOx) from local and regional sources that lower rainfall pH. Although, acid runoff events are typically short-lived (<12–24 h), further longitudinal monitoring and experimental studies are needed to investigate the long-term implications on sensitive taxa in the NSFC streams. Finally, understanding the flow pathways of stormflow water in the nested system was critical for deciphering the mechanisms driving stream acid events at the site.
UR - http://www.scopus.com/inward/record.url?scp=85123768711&partnerID=8YFLogxK
U2 - 10.1002/hyp.14467
DO - 10.1002/hyp.14467
M3 - Article
AN - SCOPUS:85123768711
SN - 0885-6087
VL - 36
JO - Hydrological Processes
JF - Hydrological Processes
IS - 1
M1 - e14467
ER -