Barium in the Yamuna River System in the Himalaya: sources, fluxes, and its behavior during weathering and transport

Abstract

Systematic measurements of Ba in waters and bed sediments of the Yamuna and many of its tributaries in the Himalaya (Yamuna River System) have been carried out. Dissolved Ba in the Yamuna River System (YRS) ranges from 17 to 871 nM. Streams near the source region draining predominantly granites/gneisses have lower abundance of Ba, <100 nM compared with those in the lower reaches. These data, coupled with those available for major ion composition of these rivers and their sediments, have been used to determine the contributions of silicates and carbonates, the two major lithologies in the drainage basin, to dissolved Ba in YRS. In YRS, dissolved Ba shows significant covariations with Na, Si, Ca, and Mg. Using Na as an index, it is estimated that silicates are an important source of Ba to many of the rivers; in a few streams in the lower reaches, however, they account for only <20% of measured Ba. Carbonate weathering, which dominates the major ion composition of YRS rivers, contributes on average ~30% of dissolved Ba. Together, silicates and carbonates roughly balance measured Ba in many of the rivers, whereas in a few streams, Ba contributions from additional sources are needed to balance the budget. Prospective sources include organic matter/phosphorites. Plot of 1/Ba versus ⁸⁷Sr/⁸⁶Sr shows a two-component mixing trend, one with low Ba-high ⁸⁷Sr/⁸⁶Sr (silicates) and the other with high Ba-low ⁸⁷Sr/⁸⁶Sr (carbonates, phosphorites). Ba also shows significant positive correlation with dissolved Re and SO₄. A likely explanation for the Ba-Re-SO₄ association is that they are supplied from organic matter/phosphorites/carbonates assemblages through H₂SO₄ weathering. In YRS bed sediments, Ba shows significant correlation with K and Al. Ba/Na and Ba/Sr in these sediments are higher than those in granites of the Higher Himalaya. These observations can be explained in terms of (1) differential release of these elements during weathering, Ba being less mobile because of its association with weathering resistant minerals or (2) "nonconservative" behavior of Ba in rivers resulting in its removal from dissolved to particulate phases. Either way, these results indicate that Ba is less mobile relative to Na and Sr. Dissolved Ba flux from the YRS basin is ~5 times more than that from the Ganga headwaters, a result consistent with higher physical and chemical erosion in the YRS basin. The Yamuna and the Ganga together transport ~5.4 × 10⁶ mol yr-1 of Ba out of the Himalaya, which is ~10% of the dissolved Ba flux from the Ganga at Bangladesh, roughly the same as their contribution to water discharge. The rate of Ba mobilization in the Yamuna and the Ganga basins in the Himalaya is a factor of ~2 higher than the global average.