Temporal Variation in the Water Quality Index of Baron Tropical Karst Spring, Gunungsewu Karst Area, Indonesia

Baron Springs is the largest karst spring in the Gunungsewu Karst Area, playing a significant role in supplying approximately 33.96% of the clean water needs in Gunungkidul Regency, Yogyakarta, Indonesia. This study aimed to analyze the temporal variations of the water quality index at Baron Spring, representing a tropical karst area with a predominantly ideal rural landscape. Water quality parameters assessed include pH, TDS, Na+, HCO3-, K+, Mg2+, Ca2+, Cl-, and SO42-. Water quality analysis was determined by comparing analysis results with water quality standards from the World Health Organization (WHO). Water quality index analysis was performed on 24 samples taken biweekly over one year (February 2020 until January 2021). The groundwater chemistry types, processes, and factors affecting water quality were analyzed using Schoeller-Berkaloff diagrams, Piper diagrams, bivariate analysis, Pearson correlation analysis, and multiple linear regression analysis. Results indicated that HCO3- and Ca2+ are the most dominant parameters exceeding quality standards due to the limestone dissolution process. Furthermore, it is also indicated that water pollution has occurred due to anthropogenic activities, although it did not exceed the quality standards. Water quality index temporally showed good water quality (50-100) during the dry period and improved to excellent water quality (<50) during the wet period due to dilution by rainfall. Statistical analysis revealed that HCO3-, Ca2+, TDS, K+, SO42-, and Na+ has a significant influence on the water quality index values at Baron Springs.