Distribution Characteristics and Formation Mechanism of Strontium-Enriched Groundwater in the Taxiutan of Gonghe Basin, Qinghai Province

Qinghai Province possesses abundant high-quality natural mineral water resources, particularly characterized by strontium-enriched mineral waters. However, previous studies have primarily focused on strontium-enriched water bodies in karst regions, with limited understanding of the hydrochemical characteristics, spatial distribution patterns of strontium, and enrichment mechanisms in pore-type strontium-enriched groundwater within unconsolidated rock formations. Therefore, this study selected the Taxiutan area in Qinghai’s Gonghe Basin as the research site. A total of 156 water samples and 38 rock and soil samples were collected. By comprehensively applying methods such as the Piper three-line diagram, Pearson correlation analysis, principal component analysis (PCA), and spatial interpolation, this study systematically revealed the hydrochemical characteristics, spatiotemporal distribution patterns, and dominant formation mechanisms of strontium-enriched groundwater in loose rock formations. Results indicate: (1) The groundwater chemistry exhibits significant spatial differentiation, transitioning from HCO₃-Ca·Mg type in the foreland to HCO₃·SO₄-Ca·Mg type at the plain's edge, with median TDS increasing from 113.65 mg/L to 352.95 mg/L. Strontium concentrations in groundwater increased along the runoff path from 0.11 mg/L in the recharge zone to a peak of 2.46 mg/L in the discharge zone, with high-strontium areas primarily distributed in the Xilongqu—Mangla River confluence zone; temporally, groundwater strontium concentrations peaked during normal flow periods and were lowest during high-flow periods, whereas surface water concentrations peaked during low-flow periods. (2) Strontium in water primarily originates from Triassic limestone and Quaternary silt, with release mechanisms including dissolution of carbonate and silicate minerals and cation exchange; At the groundwater system scale, strontium-enriched bedrock in the southern mountainous area releases strontium through dissolution. This strontium enters the loose aquifers of the plain via lateral groundwater recharge, where it undergoes further enrichment through cation exchange and retention processes, ultimately reaching peak concentrations in the foreland discharge zone. This study systematically elucidates the distribution characteristics and formation mechanisms of strontium-enriched groundwater in porous loose rocks within the Gonghe Basin at the northeastern margin of the Tibetan Plateau. The findings provide scientific basis for the exploration and sustainable development of this high-quality mineral water resource.