| 摘 要： |
The geochemistry of rare earth elements (REEs) in riverine suspended particle matter (SPM) is an important role in indicating rock weathering processes. However, it has been unclear whether reservoirs can cause variations of geochemical characteristics and behaviors of REEs in SPM. In the present study, the REE contents and fractionations in SPM were investigated passing through cascade reservoirs in the Lancangjiang River. Large-sized reservoirs affected riverine temperature, pH, and dissolved oxygen, but did not affect electric conductance, total dissolved solids, and HCO3- concentration. Reservoirs affected the compositions of major elements in SPM by the redistribution of different minerals passing through dams. For the large-sized reservoirs, the REE contents in SPM showed a sharp decline ( n-ary sumation REE content decreased by 102 mg kg(-1) in the Xiaowan reservoir and decreased by 204 mg kg(-1) in the Nuozhadu reservoir) and then increased continuously after passing through dams. The variations of REE contents in SPM passing through dams are closely linked to the redistribution of clay minerals because clay minerals derived from feldspar weathering are the main carriers of REEs in SPM. The REE fractionation indexes, including the ratios of PAAS-normalized La/Yb (1.1-1.4), La/Sm (0.8-1.0), Sm/Yb (1.3-1.7), delta Ce (0.9-1), delta Eu (1.0-1.4), and delta Gd (1.3-1.5) in SPM slightly varied along the flow direction of the main stream and were not affected by dams. These results indicated that cascade reservoirs can affect REE contents in SPM by the redistribution of clay minerals when riverine water passes through dams, but cannot cause REE fractionations. |
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