Sensitivity of chemical weathering and dissolved carbon dynamics to hydrological conditions in a typical karst river

Abstract

To better understand the mechanisms that hydrological conditions control chemical weathering and carbon dynamics in the large rivers, we investigated hydrochemistry and carbon isotopic compositions of dissolved inorganic carbon (DIC) based on high-frequency sampling in the Wujiang River draining the carbonate area in southwestern China. Concentrations of major dissolved solute do not strictly follow the dilution process with increasing discharge, and biogeochemical processes lead to variability in the concentration-discharge relationships. Temporal variations of dissolved solutes are closely related to weathering characteristics and hydrological conditions in the rainy seasons. The concentrations of dissolved carbon and the carbon isotopic compositions vary with discharge changes, suggesting that hydrological conditions and biogeochemical processes control dissolved carbon dynamics. Biological CO2 discharge and intense carbonate weathering by soil CO2 should be responsible for the carbon variability under various hydrological conditions during the high-flow season. The concentration of DICbio (DIC from biological sources) derived from a mixing model increases with increasing discharge, indicating that DICbio influx is the main driver of the chemostatic behaviors of riverine DIC in this typical karst river. The study highlights the sensitivity of chemical weathering and carbon dynamics to hydrological conditions in the riverine system.

Climate Variability Controls on CO2 Consumption Fluxes and Carbon Dynamics for Monsoonal Rivers: Evidence From Xijiang River, Southwest China

“…The total dissolved solutes vary from 110 to 227 mg/L, with a discharge‐weighted average (∑ C × Q /∑ Q ) of 160.1 mg/L, where C represents the concentration of various dissolved solutes and Q is the instantaneous discharge. It is about twice the global discharge‐weighted average (i.e., 97 mg/L; Li & Bush, ) but much lower than that of the Wujiang River in the karst area in Southwest China (i.e., 265 mg/L; Zhong, Li, Tao, Yue, et al, ). The total cationic charge (TZ + = Na + + K + + 2Ca 2+ + 2Mg 2+ ) varies from 1,401 to 3,138 μeq, which is about 1–3 times the average value of global large rivers (i.e., 1,250 μeq; Meybeck ()).…”

“…A positive correlation between TZ + Carb /TZ + Sil ratios and normalized discharge is observed (Figure a), and TZ + Sil has a stronger dilution effect and higher sensitivity to changes in river discharge than TZ + Carb (Figure S2). Concentrations of carbonate weathering products show relatively little variations with discharge change, possibly due to higher mineral dissolution rates (Calmels et al, ; Tipper et al, ; Zhong, Li, Tao, Yue, et al, ). Similar behavior was observed in climatically diverse global rivers (Calmels et al, ; Moon et al, ; Tipper et al, ).…”

“…Major ion compositions and the carbon isotope compositions of dissolved inorganic carbon (DIC; δ 13 C DIC ) reflect dominant biological and chemical weathering processes (Barth et al, ; Hélie et al, ; Jin et al, ), which can be used to provide important information on carbon sources and chemical weathering in a catchment (Li et al, , ; Marx et al, ; Telmer & Veizer, ; Zhong, Li, Tao, Yue, et al, ). Waldron et al () found that climate variability could alter the carbon mixed source compositions by controlling physical and biological processes in catchments.…”

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

“…The δ 13 C‐DIC values (+0.16 to −14.2‰) measured in the Great Barrier Reef rivers were at the higher (enriched) end of the literature range, suggesting a dominant geogenic source (Alling et al, ; Amiotte‐Suchet et al, ; Campeau et al, ). The power‐diluted relationship of DIC and river discharge further supports a geological source of DIC (Zhong et al, ). In the Burdekin and Fitzroy rivers, DIC concentration and δ 13 C relationships indicate a DIC source from carbonate dissolution by respiration‐derived H 2 CO 3 (Figure ).…”

“…River inorganic carbon concentration and discharge commonly follow power law trends, suggesting that the slope is representative of the degree of dilution (Joesoef, Kirchman, Sommerfield, & Cai, ; Zhong, Li, Tao, Yue, & Liu, ). Accordingly, the daily concentration ( C d ) of the studied rivers was calculated based on the regression equation of the relationship of measured concentration and daily river discharge ( Q d ) in each river system: where a is the coefficient and b the intercept of the regression equation (Figure ).…”