High-frequency monitoring reveals how hydrochemistry and dissolved carbon respond to rainstorms at a karstic critical zone, Southwestern China

Hydrogeochemical Dynamics and Response of Karst Catchment to Rainstorms in a Critical Zone Observatory (CZO), Southwest China

“…This phenomenon indicates their large potential supplements with increasing discharge. Other ions in this study display weaker chemostatic behavior, especially Na + and NO − 3 in SU and Na + , SO 2− 4 and NO − 3 in SP, implying that the pool of these ions is more susceptible to dilution, which is mainly due to their slower release or lower quantities along flowing pathways (Qin et al, 2020). SO 2− 4 in SP is more sensitive to hydrological variation than that in SU.…”

“…At the second sampling (D), large inputting water in W3 diluted solute concentrations, excluding [NO − 3 ], which may be affected by fertilizer application and some biological processes (Yue et al, 2020). The highest CV of [HCO − 3 ] in W3 at this time is possibly caused by the variation of dissolved soil CO 2 and soil respiration during infiltration processes (Qin et al, 2020). At the third sampling (A), the relative ratio of vertical flow to lateral flow might remain constant or infiltration water might dominate discharge, leading to small profile variation for solute concentrations in W3.…”

“…As rainstorms go on, rainfall is enough to generate hillslope runoff and surface runoff, and "old" water is extruded and gradually replaced by the percolating "new" water. At this stage, the dominant pathway of underground flow is likely to change from matrix to conduit after saturating epikarst aquifer; the supplementary sources of solutes in spring can be quickly mobilized by the increasing discharge along pathways (Qin et al, 2020); the excess infiltration water would quickly pass through conduits and flow out at the outlet (Trček, 2007). This process can shorten the available time for both spring transportation and fluid-rock interaction (Tipper et al, 2006;Chen et al, 2018), generating differences on the transportation of both fluid and solutes (Bakalowicz, 2005;Bowes et al, 2005).…”

“…The pH value of RA in this study is higher than that of other karst or forest regions in Southwest China, e.g., Guiyang of 4.5 (Han and Liu, 2006) and Chongqing of 4.75 (Ma et al, 2017), but it is lower than that of some areas in Northwestern China, e.g., Alxa Desert Plateau of 7.6 (Rao et al, 2017) and Urumqi River Valley of 7.0 (Zhao et al, 2008). This is most likely attributed to active carbon circulation and intense carbonate weathering within this karst depression (Qin et al, 2020). These processes can release some alkaline products (e.g., CaCO 3 and MgCO 3 ) into the atmosphere, neutralizing rainwater acidity (Tang and Han, 2019).…”

A Forty-Year Karstic Critical Zone Survey (Baget Catchment, Pyrenees-France): Lithologic and Hydroclimatic Controls on Seasonal and Inter-Annual Variations of Stream Water Chemical Composition, pCO2, and Carbonate Equilibrium

“…Lastly, the rise in ion concentrations observed in stream water during autumn with the first stormflow events occurring after the strong summer evaporation period, is supposed to come from soil horizons and epikarst drainage. This "flushing effect" was evidenced by Walling and Foster [145] and later on by several authors on catchment draining various lithologies and under various climate conditions: on silicate basins such as the Mont-Lozère, the Strengbach and Ringelbach [72,111], the silicate-rich Chari-Logone River catchment in Chad [146], the Vantaa River boreal catchment in southern Finland [147], the Heidingzi agricultural catchment in China [137], and also on calcareous basins such as the Oka River forested catchment in Spain [148], the Middle Bussento Karst System in Italy [149], and the Chenqi agricultural karstic catchment [150].…”