Dynamics of Spring Flow and Recharge in Tropical Volcanic Springs Based on Hydrogeochemical and Isotope Data in Bandung, Indonesia
The research conducted in Bandung, the third largest city in Indonesia, situated on volcanic rock and characterized by a tropical climate, focused on the analysis of the hydrogeochemistry of groundwater springs. The aim was to base spring conservation efforts on this analysis and enhance the understanding of volcanic springs dynamics through the lens of hydrochemistry and isotopes. The methodology involved field observation of spring yields, examination of the physiochemical properties of spring water, and water sampling for major elements and isotopes. The results revealed that the Electrical Conductivity (EC) and Total Dissolved Solids (TDS) values of the spring ranged between 80-417 μS/cm and 40-209 mg/l respectively, signifying a moderate level of mineral concentration in the water. The dominant facies of the spring water were identified as Calcium Bicarbonate (CaHCO3) and Calcium Magnesium Chloride (CaMgCl). These findings provide critical insights for conservation strategies, affirming the importance of maintaining these springs due to their role in the area's water supply and their potential impacts on public health and the local ecosystem.
Bandung is a metropolitan city situated in a volcanic area with hundreds of springs that serve as clean water sources. This research focuses on the analysis of recharge dynamics of mesothermal volcanic springs based on hydrogeochemistry and isotope data. The study aims to enhance the understanding of volcanic spring flow dynamics and recharge, serving as a foundation for spring water conservation.
The methods include spring yield measurement, physical and hydrochemical assessments, and isotope analysis. Measurements were conducted monthly from April 2021 to June 2022. Physical assessments included pH, electric conductivity (EC), and total dissolved solids (TDS). Hydrochemical assessments involved major ion analysis and water facies identification using a Piper diagram. The isotope data included δ18O, δ2H, and δ13C.
The results showed that the EC and TDS ranged between 80-417 μS/cm and 40-209 mg/l, respectively. The spring water facies were Ca2+HCO3‾ and Ca2+Mg2+Cl‾. The chloride facies were influenced by agriculture and human activity. The tropical climate affected the spring system's recharge and discharge processes, and it also had an impact on the environment.
Article highlights:
The Indonesian statistical agency (BPS) data from 2002-2016 states that about 12% of Indonesians rely on springs for clean water supply. Indonesia is a tropical archipelago with hundreds of active volcanoes. In tropical areas, rainwater becomes a large source of groundwater supply. These volcanoes produce volcanic deposit materials with productive aquifers and many springs (Irawan 2009). Volcanic deposits are a product from the volcano eruptions such as pyroclastic, tuff, and sand. This has resulted in many cities in Indonesia being located on the slopes of volcanoes, one of them being the city of Bandung. This city is located in a basin surrounded by volcanoes. The center of Bandung city is located on the north side of the slope from the active volcano Tangkuban Perahu. Bandung was developed into a metropolitan city and has attracted migration in the last 200 years (Tarigan et al., 2016). One of the clean water sources utilized in Bandung is springs. Communities in North Bandung areas utilize springs for clean water (Nastiti et al. 2017).
Springs have a vital role in Bandung, so it is crucial to maintain the springs for future water sustainability. However, on the other hand, spring flows are dynamic, influenced by (1) changes in land use (Valdiya and Bartarya, 1991); (2) groundwater pumping (Fensham et al., 2016; Dragoni et al., 2013); (3) mining (Fan et al., 2018); (4) climate change (Ma et al., 2004; Tambe et al., 2012; Hao et al., 2016); (5) earthquakes (Valigi et al., 2017). These various factors can generally be divided into two, namely human activities and natural. Understanding the spring flow system will help determine the conservation area and potential groundwater pollution. This is necessary because in urban areas there are many human activities that have the potential to disrupt the sustainability of springs.
Research of spring water in North Bandung has been conducted since 1921 (Pulawski and Obro, 1976) which analyzed the groundwater recharge area. Furthermore, Hendarmawan (2002) and Hendarmawan et al. (2005) state that spring water in Bandung comes from local to intermediate flow systems. This conclusion is based on physical parameters EC and pH. Hendrasto and Sunarwan (2013) and Sunarwan (2014) analyzed groundwater recharge based on isotope 18O and 2H. Based on field observations and interviews with the community, several springs during the dry season have stopped flowing, where previously they flowed all year round. Excessive groundwater extraction and changes in land use in the spring recharge area potentially threaten the sustainability of springs. Changes in land cover to built-up land in Bandung are increasing every year and are predicted to reach 14.5% by 2050 (Yulianto et al., 2019).
Based on these conditions, conservation efforts for springs are very much needed with the first step of understanding their recharge-discharge process. A comprehensive flow system analysis by combining various methods will produce more accurate data. Hydrogeochemical data provide a deeper understanding of spring characteristics based on the interaction of water and rocks, also giving an understanding of the recharge-discharge process (Irawan et al., 2009). Stable isotopes have been proven to be capable and have been widely used to determine groundwater recharge (Hao, 2019; Mao 2021). Stable isotopes 2H and 18O are conservative and record the characteristic of initial meteoric water in the absence of water rock interaction and significant evaporation (Yeh, et al 2011). Carbon isotope 13 is a parameter needed to determine chemical reactions in the aquifer from the recharge process (Gastman and Chang, 2010). The combination of hydrogeochemical data, isotopes, and carbon isotopes will strengthen the analysis of the dynamics of the spring flow system in the research area.