Open AccessREY‐Th‐U Solute Dynamics in the Critical Zone: Combined Influence of Chemical Weathering, Atmospheric Deposit Leaching, and Vegetation Cycling (Mule Hole Watershed, South India)
Author(s) -
Braun JeanJacques,
Riotte Jean,
Battacharya Shrema,
Violette Aurélie,
Prunier Jonathan,
Bouvier Vincent,
Candaudap Frédéric,
Maréchal JeanChristophe,
Ruiz Laurent,
Panda Smruthi Rekha,
Subramanian S.
Publication year - 2017
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2017gc007158
Subject(s) - weathering , authigenic , groundwater , geology , hydrology (agriculture) , leaching (pedology) , geochemistry , cycling , watershed , soil science , sedimentary rock , soil water , history , geotechnical engineering , archaeology , machine learning , computer science
The source and proportion of REY, Th, and U exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the subhumid tropical forested CZO of Mule Hole, Southern India. The study relies on a pluriannual hydrogeochemical monitoring combined with a hydrological model. The significant difference between the soil input (SI) and output (SO) solute fluxes (mmol/km 2 /yr) of LREE (SI‐SO = 13,250‐1,500), HREE (1,930‐235), Th (64‐12), and U (63‐25) indicates a strong uptake by roots carried by canopy and forest floor processes. The contribution of atmospheric dust leaching can reach about 60% of LREE and 80% of HREE. At the watershed scale, the U solute flux exported by groundwater (180 mmol/km 2 /yr) mainly originates from the breakdown of primary U‐bearing accessory minerals and dominates by a factor of 25 the stream flux. The precipitation of authigenic U‐bearing phases and adsorption onto Fe‐oxides and oxyhydroxides play a significant role for limiting the U mobility. In the groundwater, the plagioclase chemical weathering is efficiently traced by the positive Eu‐anomaly. The very low (REY) to nil (Th) contents are explained by the precipitation of authigenic phases. In the stream flow, dominated by the overland flow (87% of the yearly stream flow), the solute exports (in mmol/km 2 /yr) of REY (1,080 for LREE and 160 for HREE) and of Th (14) dominate those by groundwater. Their mobility is enhanced by chelation with organic ligands produced by forest floor and canopy processes.