[A-HW32] Material transportation and cycling in aquatic ecosystems; from headwaters to coastal areas

[AHW32-P11] Phosphorus in groundwater in the coastal area of Mataram, Lombok Island, Indonesia

*Seiichiro Ioka¹, Shin-ichi Onodera², Mitsuyo Saito³, Anna Fadliah Rusydi^2,4, Sachi Wakasa¹ (1.Institute of Regional Innovation, Hirosaki University, Japan, 2.Graduate School of Integrated Arts and Sciences, Hiroshima University, Japan, 3.Graduate School of Environmental and Life Sciences, Okayama University, Japan, 4.Research Center for Geotechnology, Indonesian Institute of Sciences, Indonesia)

Keywords:Phosphorus, Groundwater, Mataram

Several previous studies of phosphorus in groundwater at highly contaminated sites exist. However, although studies on the behavior of phosphorus in pristine aquifers have been increasing, they are still limited. Urban development in Indonesia’s coastal areas may lead to an increase in groundwater contamination. Mataram City on Lombok Island is a developing area in terms of tourism, and it is important to evaluate the phosphorus in the groundwater prior to the expansion of urban development. Mataram City was therefore selected as the study area for this work and groundwater was sampled at 26 sites.
Our results show that the concentrations of PO₄^3– in groundwater analyzed using ion chromatography range from approximately 0.1 to 8.5 mg/L. Fe concentrations in groundwater at 21 sites was lower than 0.1 mg/L. No correlation was found between the Fe and PO₄^3– concentrations. In addition, no correlation was found between the DOC (dissolved organic carbon) and PO₄^3– concentrations. These results indicate that the DOC and Fe-(hydr) oxides cannot represent the source of P. However, the values of the saturation index of hydroxyapatite for some groundwater samples were close to equilibrium; Therefore, hydroxyapatite may represent the source of P.