Distribution and geochemical processes of boron in the multimedia of Lake Qinghai, China

Lake Qinghai on the Qinghai-Tibet plateau is the largest lake in China. This study investigated the concentration and geochemical processes of boron (B) in lake water, lake sediment and river samples collected from Lake Qinghai and the Buha River. In addition, lake sediment pore water samples were analyzed. The concentrations of B and major ions, including K+, Na+, Ca2+, Mg2+, Cl− and SO42−, were analyzed in all the water samples. The average concentration of B was 0.07 mg L−1, 6.37 mg L−1, 12.79) mg L−1 and 59.42 mg kg−1 for river water, lake water, pore water, and sediment, respectively. There were significant (p < 0.05) and positive (r = 0.70) relationships between the B concentrations in bottom water of the lake and in lake sediment, indicating that B diffusion from the sediment plays an important role in the concentration of B in bottom lake water. The differences in B concentrations and B/major ion molar ratios of the river water, lake water, and pore water indicated the following geochemical processes: 1) B is enriched in the lake water through evaporative concentration; 2) B is removed from the lake water through mineral precipitation as well as sorption onto colloids; 3) Solid-phase B in sediments was released through dissolution driven by organic matter mineralization. B/Cl and Na/Cl molar ratios alone are not enough to identify the sources of B in the water of inland closed-basin saline lakes because of these processes.