Chromium, tungsten and vanadium sediment-porewater geochemistry under oxic and anoxic redox conditions: Implication...

Global chromium (Cr), tungsten (W), and vanadium (V) cycles are emerging concerns due to their toxicities to ecosystems. However, a comprehensive understanding of their geochemical reactions and controls at the sediment-water interface remains largely unknown. This knowledge gap hinders the assessment of their potential remobilization in Earth's surface environments threatened by hypoxic conditions. We collected pore water and sediment samples from the undisturbed Castle Lake, situated in the Klamath-Siskiyou Mountains of northern California, USA, to investigate the geochemical controls responsible for the fixation and release of Cr, W, and V under redox transitions from oxia to anoxia during early diagenesis. The results show that, under oxic conditions, authigenic Cr, W, and V ratios in porewater account for approximately 4.7 %, <0.1 %, and < 0.1 %, respectively, whereas their ratios display around ten times increase under anoxic conditions with average values of 62.4 % for Cr, 4.1 % for W, and 1.1 % for V. Our combined thermodynamic calculation and diagenetic analyses show that the sequestration and release of Cr, W, and V are intimately associated with Fe cycle under anoxic conditions. In contrast, under oxygenated conditions, only Cr and V geochemical behaviors are significantly affected by Fe cycle, while the adsorption of W to Fe minerals is probably inhibited by dissolved organic matter. Furthermore, we suggest that the Cr, W, and V pollution could become significant in coastal and inland water areas where redox conditions oscillate between oxia and anoxia, with intensified water deoxygenation, acidity, and eutrophication.