Assessing the changes in river water quality across a land-use change (forest to oil palm plantation) in peninsular Malaysia using the stable isotopes of water and nitrate

Masayuki Itoh; Ken'ichi Osaka; Kotaro Iizuka; Yoshiko Kosugi; Marryanna Lion; Satomi Shiodera

doi:10.1016/j.scitotenv.2022.160319

Assessing the changes in river water quality across a land-use change (forest to oil palm plantation) in peninsular Malaysia using the stable isotopes of water and nitrate

Sci Total Environ. 2023 Feb 10;859(Pt 2):160319. doi: 10.1016/j.scitotenv.2022.160319. Epub 2022 Nov 19.

Authors

Masayuki Itoh¹, Ken'ichi Osaka², Kotaro Iizuka³, Yoshiko Kosugi⁴, Marryanna Lion⁵, Satomi Shiodera⁶

Affiliations

¹ School of Human Science and Environment, University of Hyogo, 670-0092, Hyogo, Japan; Center for Southeast Asian Studies, Kyoto University, Kyoto 606-8501, Japan. Electronic address: masayukiitoh@yahoo.co.jp.
² School of Environmental Science, The University of Shiga Prefecture, 522-8533, Shiga, Japan. Electronic address: osaka.k@ses.usp.ac.jp.
³ Center for Spatial Information Science, The University of Tokyo, Kashiwa, Chiba 277-8568, Japan. Electronic address: kiizuka@csis.u-tokyo.ac.jp.
⁴ Graduate School of Agriculture, Kyoto University, 606-8502 Kyoto, Japan. Electronic address: kosugi.yoshiko.4x@kyoto-u.ac.jp.
⁵ Forestry and Environment Division, Forest Research Institute, Malaysia. Electronic address: marryanna@frim.gov.my.
⁶ Center for Southeast Asian Studies, Kyoto University, Kyoto 606-8501, Japan; Department of Global Liberal Studies, Faculty of Global Liberal Studies, Nanzan University, Aichi 466-8673, Japan. Electronic address: sshiodera@gmail.com.

PMID: 36410477
DOI: 10.1016/j.scitotenv.2022.160319

Abstract

Land conversion from natural forests to plantations (e.g., oil palm) in Southeast Asia is one of the most intensive land-use changes occurring worldwide. To clarify the effects of oil palm plantations on water quality, we conducted multipoint river and stream water sampling in peninsular Malaysia at the end of the rainy season over a 3-year period (2013-2015). We measured the major dissolved ions and stable isotope ratios of water (δ²H-H₂O and δ¹⁸O-H₂O) and nitrate (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-) in water from the upper streams in mountainous forests to the midstream areas of two major rivers in peninsular Malaysia. The electrical conductivity increased, and the d-excess value (as an index of the degree of evaporation) decreased with increasing distance from the headwaters, suggesting the effect of evaporative enrichment and the addition of pollutants. We separated the sampling points into four groups (G1-G4) through cluster analysis of the water quality data. From the land use/land cover (LULC) classification maps developed from satellite images and local information, we found that G1 and G2 mainly consisted of sampling points in forested areas, while G3 and G4 were located in oil-palm-affected areas. The concentrations of major ions were higher in the oil palm areas, indicating the effects of fertilizer and limestone (i.e., pH adjustment) applications. The dissolved inorganic nitrogen concentration did not differ among the groups, but the dissolved organic carbon, total dissolved nitrogen, and δ¹⁵N-NO₃^- were higher in the oil palm area than in the forested area. Although the nitrogen concentration was low, even in the oil palm area, the significantly higher δ¹⁵N-NO₃^- in the oil palm area indicated substantial denitrification. This implies that denitrification contributed to the lowering of the NO₃^- concentration in rivers in the oil palm area, in addition to nutrient uptake by oil palm trees.

Keywords: Forest; Land-use change; Oil palm plantation; Peninsular Malaysia; Stable isotopes; Water quality.

MeSH terms

Environmental Monitoring / methods
Forests
Isotopes / analysis
Nitrates* / analysis
Nitrogen / analysis
Nitrogen Isotopes / analysis
Water Pollutants, Chemical* / analysis
Water Quality

Substances

Nitrates
Nitrogen
Isotopes
Nitrogen Isotopes
Water Pollutants, Chemical