Abstract
While it is critical to accurately understand the sources and transformation of sulfate based on time-series analysis, there are limited studies on temporal variation of sulfate in rivers and on rock weathering by sulfuric acids. We conducted a monthly sampling campaign in the Beipan, Nanpan, and Hongshui Rivers over the course of one hydrological year. This study examined seasonal variations in riverine sulfate impacted by the monsoon climate in the upper reaches of the Xijiang River basin. In general, the SO42− contents in these rivers dropped from relatively high levels to low values during the high-flow season, in response to increasing discharge. The sulfate was generally enriched in heavy isotopes during the low-flow season compared to the high-flow season. The calculated results indicate that the riverine sulfate was mainly derived from sulfide oxidation, but that evaporite dissolution could be an important source during the low-flow season, based on isotopic evidence. Mine drainage is likely an important source of sulfate to these rivers during the high-flow season due to contributions from fast surface flow, which responds to frequent heavy rain in monsoonal climate regions. A relatively high proportion of HCO3− was found to be derived from rock weathering by sulfuric acid during the high-flow season when compared to that observed during the low-flow season. The results suggest that approximately one quarter of the HCO3− in the Hongshui River originated from carbonate weathering by sulfuric acid derived from the oxidation of sulfide. Such information on the specific dual isotopic characteristics of riverine sulfate throughout a hydrological year can provide unique evidence for understanding the temporal variability of sulfate concentrations and weathering processes in rivers.
Highlights
Sulfate attracts widespread attention as the dominant form of sulfur in riverine systems
The results suggest that approximately one quarter of the HCO3- in the Hongshui River originated from carbonate weathering by sulfuric acid derived from the oxidation of sulfide
We examined the effects of seasonal variations on the sulfate sources of the upper reaches of the Xijiang River
Summary
Sulfate attracts widespread attention as the dominant form of sulfur in riverine systems. Riverine sulfate generally originates from precipitation and from the weathering of sulfide-bearing minerals and evaporite minerals, as well as from fertilizer and industrial inputs (Yang et al 1996; Krouse and Mayer 2000; Pawellek et al 2002; Brenot et al 2007; Rock and Mayer 2009). The temporal and spatial variation of sulfate in river systems can reflect geological characteristics, environmental changes, and anthropogenic inputs (Dogramaci et al 2001; Jiang et al 2007). It is necessary to understand riverine sulfate biogeochemistry in the context of the terrestrial system
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