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Updated: May 2, 2026

Watershed Planning within a Quantitative Scenario Analysis Framework
Published on: July 24, 2016
REEs-HNMD weakens riverine N-sink function through suppressed sediment denitrification in a rare-earth mining
Yingxue Xuan1, Qianyi Zhou2, Xiankai Lu3
1Guangdong Provincial Key Laboratory of Applied Botany, Key Laboratory of National Forestry and Grassland Administration on Plant Conservation and Utilization in Southern China, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China; School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou 510006, China.
Abstract:
Mining of rare earth elements (REEs) in regolith-hosted ion-adsorption clay deposits generates REE-rich, high-nitrogen mining drainage (REEs-HNMD), yet whether this coupled stressor weakens riverine nitrogen (N)-sink function remains unclear. We investigated a river network draining an ion-adsorption rare-earth mining region across a contamination gradient during wet and dry seasons. Sediment denitrification and anammox were quantified using 15N isotope-tracer incubations and integrated these rates with water and sediment chemistry, microbial community profiles, denitrification genes (nirS, nirK, nosZ), and dual nitrate isotopes (δ15N-NO3- and δ18O-NO3-). Denitrification dominated benthic N loss (0.01-63.50 nmol N g-1 h-1) but responded non-linearly to REEs-HNMD, peaking at moderately polluted sites and declining sharply under high contamination, especially in the wet season. Anammox was rarely detectable (0-0.83 nmol N g-1 h-1) and contributed little. Under high contamination, denitrification-gene abundance declined, the (nirS+nirK)/nosZ ratio decreased, and nitrate isotopes showed a weak watershed-scale expression of denitrification. Structural equation modeling further indicated that REEs-HNMD constrained denitrification mainly through microbial bottlenecks, with stronger net inhibition in the wet season than in the dry season. These results show that REEs-HNMD not only increases N loading, but also weakens riverine N-sink function by suppressing sediment denitrification.
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