Downstream and seasonal changes of lithium isotope ratios in the Ganges‐Brahmaputra river system

Abstract

The Li isotope ratio (δ7Li) is expected to be a useful tracer of silicate weathering in river and groundwater systems, which is an important contributor to the seawater compositional changes that accompany the evolution of the Earth's surface environment. To obtain accurate estimates of continental Li fluxes to the ocean, we determined δ7Li values of dissolved Li in the lower Ganges‐Brahmaputra river system in both the dry and rainy seasons, and in deep groundwater in the Bengal basin. Dissolved Li and δ7Li values in the lower reaches of the rivers (0.04–0.66 µmol kg−1 and +19.1‰ to +34.2‰, respectively) were predominantly derived from silicate weathering, as is the case in the upper parts of these rivers. We observed large changes in δ7Li over a distance of more than 1000 km downstream that were due mainly to Rayleigh‐type removal of Li from river water. Extremely high Li concentrations (1.15–1.67 µmol kg−1) and low δ7Li values (+5.1‰ to +11.6‰) in groundwater samples indicate congruent isotope leaching and dissolution of silicate minerals in the deep aquifer, where the water residence time is long. In the rainy season, Li concentrations and δ7Li values were lower than in the dry season, owing to the shorter residence time of river water and the substantial input of local subsurface flow through lowland alluvium. These results suggest that accurate estimation of continental Li fluxes to the ocean should take account of downstream and seasonal changes, as well as aquifer depth variations, in δ7Li values.

Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

“…Open symbols represent VMR rivers draining south-facing catchments. Huh et al, 1998a); the Mackenzie River (Millot et al, 2003;Millot et al, 2010); Antarctic rivers (Witherow et al, 2010); Greenland (Wimpenny et al, 2010b); the High Himalayas (Huh et al, 1998a;Kısakűrek et al, 2005); the Ganges-Brahmaputra (Huh et al, 1998a;Kısakűrek et al, 2005;Bagard et al, 2015;Frings et al, 2015;Manaka et al, 2017;Pogge von Strandmann et al, 2017); the Amazon (Huh et al, 1998a;Dellinger et al, 2015); the Orinoco (Stallard et al, 1995;1996;Huh et al, 1998a); the Congo (Henchiri et al, 2016); Changjiang (Yangtzee) River (Huh et al, 1998a;Liu et al, 2011;Wang et al, 2015); and basalts from Iceland, the Azores and the Columbia River Basalts (Pogge von Strandmann et al, 2006;Vigier et al, 2009;Pogge von Strandmann et al, 2010;Liu et al, 2015). Figure 7: Histograms summarising dissolved δ 7 Li compositions from large global rivers, and rivers draining basaltic terrains.…”

“…High riverine d 7 Li values have been interpreted as reflecting less complete weathering, greater secondary mineral formation and thus greater 'weathering intensity' (i.e., the ratio of chemical to physical denudation; Bouchez et al, 2013;Dellinger et al, 2015). There have been a number of large global rivers in tropical and temperate environments where the behaviour of Li isotopes has been studied: e.g., the Amazon River (Chan et al, 1992;Huh et al, 1998a;Dellinger et al, 2014Dellinger et al, , 2015; the Orinoco River (Huh et al, 1998a;Huh et al, 2001); rivers in the high Himalayas and the Ganges-Brahmaputra (Huh et al, 1998a;Kısakűrek et al, 2005;Bagard et al, 2015;Manaka et al, 2017;Pogge von Strandmann et al, 2017) the Changjiang (Yangtzee)…”

Monthly changes in <I>p</I>CO₂ in the Ganges River: implications for carbon release from soil to the atmosphere via inland waters

“…Some river water data before September 2012 BD11-3, RBD11-5, GBD12-12, FBD12-6 were first reported in Manaka et al 2015 . Some groundwater data BD11-12 and RBD11-2, -7, and -8 were reported in Manaka et al 2017 . polypropylene bottles under cool and dark conditions.…”

Li and U Isotopes as a Potential Tool for Monitoring Active Layer Deepening in Permafrost Dominated Catchments

“…The two studied catchments are situated next to each other (Figure 1) in the Paleogene sedimentary Central Basin of Svalbard. The sedimentary formations exposed in the catchments are from the Van Mijenfjorden group, which is Paleocene to Eocene in age (66-33.9 Ma) and contain sandstones, siltstones, and shale (Major et al, 2000). There is negligible soil formation in either catchment and the surface is dominated by moraine material and glacial sediment in the glaciated catchment and by frost-shattered shale in the unglaciated catchment (Figure 1).…”