Small-catchment perspective on Himalayan weathering fluxes

Abstract

Weathering fluxes from four small catchments in the Himalayas, one forested, one agricultural, and two glacial, have been calculated by quantifying stream discharge, deposition, and biomass uptake of major ions. These fluxes were partitioned between silicate and carbonate sources by using a mineral mass-balance model. This approach provides the first well-defined estimates of Himalayan weathering fluxes from small catchments. Silicate weathering rates are highest in the favorable weathering environment of the Middle Hills catchments, despite higher dissolved fluxes in the High Himalayas attributed to high carbonate weathering. The silicate weathering fluxes for High Himalayan small catchments are similar to estimates from the chemistry of large rivers draining the same regions. Much higher silicate weathering intensity for the Ganges basin indicates that the silicate material eroded from the High Himalayas undergoes up to six times as much weathering in the Ganges Plain as in the High Himalayan mountains. Himalayan silicate weathering rates are higher than in equivalent continental settings and, on an area-normalized basis, are comparable to fluxes from weathering of basalts on ocean islands and tropical volcanic provinces.