Stable hydrogen and oxygen isotopes reveal aperiodic non-river evaporative solute enrichment in the solute cycling of rivers in arid watersheds

Highly Contrasted Geochemical Pattern in Sediments of the Okavango Delta, Botswana Driven by Dust Supply, Hydrological Heritage and Biogeochemical Reactions

“…Though the incoming floodwater has low pH and conductivity (Dauteuil et al, 2021), Oromeng et al (2021) estimated that it brings annually about 329,200 Mg/y of dissolved solutes in the Delta. From these, 21% are removed, flushed out of the system by the flood or rainwater, leaving 260,960 Mg/y of solute in the Delta (Letshele et al, 2023;Oromeng et al, 2021;Ramatapleng et al, 2021Ramatapleng et al, , 2023. However, the fate of these solutes remains to be understood.…”

Reply to Comment by Terence McCarthy and Marc Humphries on “Highly Contrasted Geochemical Pattern in Sediments of the Okavango Delta, Botswana Driven by Dust Supply, Hydrological Heritage and Biogeochemical Reactions”

“…The swamps, and the shores are vegetated, mostly with grass and reeds but also with bushes and sometimes trees. Several authors suggested that these salts, as well as solutes concentrated in the swamps, are washed out of the Delta during the rainy season (November to March) and annual flooding (June to September) when hydraulic connectivity is established between the rivers and the swamps (Letshele et al, 2023;Ramatlapeng et al, 2021Ramatlapeng et al, , 2023. This may partly explain the fate of the solutes entering the Delta, although we agree that the model should be further developed, especially by establishing the final sink of those solutes.…”

Groundwater-surface water interactions in a semi-arid irrigated agricultural valley: A hydrometric and tracer-aided approach

“…Stable isotopic composition of hydrogen ( 2 H/ 1 H, δ 2 H) and oxygen ( 18 O/ 16 O, δ 18 O) provide information about the origin, transport and phase change processes to which the water molecule has been exposed (Gat, 1996). These tracers have been applied to understand hydrological processes by identifying water sources and losses along catchments, as well as prevailing pathways (e.g., Yang and Han, 2020;Letshele et al, 2023). In arid/semi-arid regions, where evaporation and mobilization of soil-stored salts, and therefore soil and water salinization, are important processes (Benyamini et al, 2005;Estévez et al, 2018), measurements of salinity serve as powerful tracers of hydrological processes.…”

“…They cause freshwater pulses that flush stored salts in both the underlying sediments and water column. In addition, increased runoff during rainfall events can increase surface water inflows that are higher in salinity than under natural conditions (Jolly et al, 2008;Letshele et al, 2023). The Chubut River within the irrigated valley is sensitive to local rainfall events in terms of flow, but its behavior related to river EC was variable.…”