Dissolved Molybdenum in the Brahmani River System: Potential Sources and Implications

Singh, Naman Deep (2015) Dissolved Molybdenum in the Brahmani River System: Potential Sources and Implications. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Relative contributions of molybdenum (Mo) from various sources to river waters remain uncertain. In this study we report concentrations and distributions of dissolved Mo in the Brahmani river system. Mo concentrations and its relation with major ions in the river waters are examined to ascertain the contributions from natural and anthropogenic sources. Weathering of silicate rocks in the basin is the major process in governing the major ion abundance in the river waters. To determine the anthropogenic impact on the Mo budget in the river system, sampling is done upstream and downstream of the heavily industrialized areas of Talcher in Odisha. In the upstream samples, Mo concentrations are relatively low, 0.14 to 2.8 nM; and Mo-SO4 plot shows a well correlated variation and follows the trend reported for global rivers. In contrast, the downstream samples are characterized by 5 to 20 times higher Mo concentrations than the average Mo of upstream samples; and Mo-SO4 plots show more scatter. Lack of strong correlation between Mo with Na* (Na corrected for contributions from rainwater, saline soils and anthropogenic sources), [Ca*+Mg*] and HCO3 both in upstream and downstream samples suggests that silicate and carbonate weathering do not exert major control on Mo concentrations in river waters. Rather, weathering of sulphide minerals associated with ore deposits and carbonaceous sediments seems to be more important in contributing Mo to rivers as evident from the strong Mo-SO₄ correlation in the upstream samples. This process could be enhanced by anthropogenic activity through large scale mining of coal and sulphide minerals and coal fired power plants. High levels of dissolved Mo in streams carrying contributions from mining and industrial effluents support that anthropogenic sources are important suppliers of Mo to rivers waters. Detailed quantification is needed to assess to what degree the natural Mo fluxes are modified by anthropogenic activity.

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