[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-P25] Hydrogeochemical evolution mechanisms of groundwater in the Semarang Coastal Zone, Java Island, Indonesia

*Rizka Maria Maria^1,6, Anna Fadliah Rusydi^2,6, Shin-ichi Onodera³, Mitsuyo Saito⁴, Seiichiro Ioka⁵, Robert Muhammad Delinom⁶, Wahyu Purwoko⁶, Dadi Sukmayadi⁶, Hendarmawan Hendarmawan¹ (1.Faculty of Geological Engineering, Padjadjaran University, Indonesia, 2.Graduate School of Integrated Arts and Sciences, Hiroshima University, Japan, 3.Graduate School of Advance Science and Engineering, Hiroshima University, Japan, 4.Graduate School of Environmental and Life Science, Okayama University, Japan, 5.Research Institute for Sustainable Energy, Hirosaki University, Japan, 6.Research Center for Geotechnology, Indonesian Institute of Sciences, Indonesia)

Keywords:hydrogeochemical, saline groundwater, anthropogenic, groundwater evolution mechanisms, coastal aquifers

Semarang city, the capital of Central Java Province is the coastal area in the Java island has the problem of saline groundwater in the coastal region and the high land subsidence rate that influence groundwater condition. Groundwater vulnerabilities in Semarang are influenced by internal factors such as geological type of marine clay and anthropogenic. Based on the problems, it is necessary to conduct a study on hydrogeochemical evolution mechanisms of the groundwater quality. Sixteen dug wells samples, nine bore wells samples, one spring sample and two surface water samples were collected during a field investigation. The Methods including ionic ratios, statistics, Piper diagram, bivariate ion analyses and Gibbs diagrams were used to analyses the hydrogeochemical characteristics and evolution mechanisms. The spatial distribution of key parameters was assessed using a GIS-based simple natural neighbour technique. Results showed that dendrogram statistics of the major hydrogeochemical parameters, including conductivity, Na⁺, Cl⁻, Ca²⁺ and Mg²⁺ displayed similar trend distributions, increasing gradually from the southern to northern regions of the study zone; HCO₃⁻ and SO₄ ²⁻ have a similar trend. High NO₃⁻–N and NH₄⁺–N concentration comes from the influence of settlements and agriculture. The hydrochemistry of the groundwater consists of Na-Cl type, Na-Cl-HCO₃ type, Na-HCO₃ type, Ca-HCO₃ type and Ca-Mg-HCO₃ type. The coastal aquifers are influenced by seawater intrusion, mineral dissolution and ion exchange processes, impacting groundwater evolution.

This studio is supported by the Asia-Pacific Network for Global Change Research (APN) under Grant No. CRRP2019-09 MY-Onodera (funder ID: http://dx.doi.org/10.13039/100005536).