Concentrations and fluxes of uranium in two major Chinese rivers: The Changjiang River and the Huanghe River

Abstract

We collected samples from January 2010 to December 2011 to determine the concentrations and fluxes of uranium in the Changjiang (Yangtze) and Huanghe (Yellow) Rivers in China. The dissolved U concentrations (DUC) were measured by inductively coupled plasma mass spectrometry (ICP-MS) at the freshwater end members of the Changjiang and Huanghe Rivers. The DUCs ranged from 1.32 to 4.06 nmol/L and 13.85 to 29.99 nmol/L in the Changjiang and Huanghe Rivers, respectively. The temporal variations of DUC followed the seasonal change, with high values in the two rivers occurring during the dry seasons and low values during the flood seasons. A strong negative correlation was observed between DUC and discharge in the Changjiang River (R2 = 0.69), but a weak correlation (R2 = 0.35) was found in the Huanghe River. The correlations between the major ions and the U in the rivers indicated that the primary source of uranium was from the weathering of carbonate and evaporite in the Changjiang Basin. The weathering of evaporite-bearing sequences and the erosion of loess dominated the U sources of the Huanghe River. Carbonate ligands in the dry season and phosphate ligands in the wet season were the primary factors controlling the accumulation and transportation of dissolved uranium in the Changjiang River. The soils of the Huanghe Basin contained five times more leachable uranium compared to the soils of the Changjiang Basin, which may explain the high DUC in the Huanghe River. The weighted-mean-concentrations of uranium were 2.78 nmol/L in the Changjiang River and 22.07 nmol/L in the Huanghe River. This lead to annual dissolved U fluxes (DUF) of 2.3 × 106 mol/yr in the Changjiang River and 4.1 × 105 mol/yr in the Huanghe River. The sum of the U fluxes in the two rivers represented 11.9% of the global U riverine flux into the sea comparing with 2.5% of the global runoff into the sea. The 234U/238U activity ratio of the Huanghe River had higher values (1.455–1.418) compared to the Changjiang River (1.424–1.374) from the dry season to the wet season, respectively.