<![CDATA[This study aims to analyze the spatial variation of the physicochemical characteristics of Auya River water and its relationship to geological conditions in Paniai Regency, Central Papua. In situ measurements were conducted at 20 stations (ST01–ST20) from upstream to downstream for Total Dissolved Solids (TDS), pH, Electrical Conductivity (EC), and temperature. Based on field conditions, the stations were grouped into Intrusive Igneous Rock (ST01–ST05), Siltstone (ST06–ST10), and Sand (ST11–ST20). Data were analyzed using descriptive statistics, One-Way ANOVA, Welch ANOVA, Tukey HSD, Pearson correlation, and partial correlation by controlling for cumulative distance. The results showed TDS 25–153 mg/L, pH 6.50–7.77, EC 48–166 µS/cm, and temperature 16.80–20.20 °C, with an increasing trend from upstream to downstream. One-Way ANOVA showed significant differences between groups for TDS, pH, EC, and temperature (p < 0.001). Tukey's test showed that all pairs of groups differed significantly in TDS, pH, and EC, while temperature between Intrusive Igneous Rock and Siltstone was not significantly different (p = 0.073). Pearson's correlation showed a very strong positive relationship between parameters (r = 0.969–0.985; p < 0.001), but the coefficient decreased after cumulative distance was controlled. These findings suggest that the physicochemical characteristics of the water form spatial gradients that coincide with changes in geological conditions. Because the geological groups are also arranged in an upstream–downstream sequence, these statistical differences are interpreted as geological–spatial associations, not evidence of an independent influence of lithology. Thus, variations in the Auya River water likely reflect the combined contributions of geological conditions, longitudinal position, solute accumulation, elevation, and environmental factors along the river course, which also need to be considered in hydrogeochemical interpretations.]]>
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