Fluorescence spectroscopy reveals accompanying occurrence of ammonium with fulvic acid-like organic matter in a fluvio-lacustrine aquifer of Jianhan Plain
2016
Huang, Shuangbing | Wang, Yanxin | Ma, Teng | Wang, Yanyan | Zhao, Long
This study is the first to investigate the simultaneous presence of NH₄ ⁺ and fluorescent organic matter components (FOCs) from a fluvio-lacustrine aquifer in Central Jianghan Plain. Sediment, groundwater, and surface water samples were collected for the sediment organic matter extraction, 3D fluorescence spectroscopy characterization, and/or hydrochemical analysis. NH₄ ⁺ and dissolved organic carbon was ubiquitous in the groundwater. The fluorescence spectroscopy revealed good relationships between NH₄ ⁺ and fulvic acid-like components (FALCs) in the groundwater and sediment-extracted organic matter (SEOM) solutions. NH₄ ⁺ also exhibited significant positive correlation with protein-like component (PLC) (p < 0.001), with the stronger in the SEOM solutions than that in groundwater. Comparisons of spectroscopic indices [e.g., humification index (HIX), biological index (BIX), spectra slope (S₂₇₅–₂₉₅), and specific UV absorbance (SUVA₂₅₄)] between the groundwater and SEOM solutions revealed more labile properties of SEOM. This result indicates that the decreasing NH₄ ⁺–FOCs correlations of groundwater relative to sediments may be attributed to microbial degradation. Factor analysis identifies important factors that cause NH₄ ⁺ occurrence in the groundwater. The accompanying increase of FALC (C1) and NH4–N with the mole concentration of the normalized HCO₃ ⁻/(Ca²⁺+Mg²⁺) and [H⁺] suggests that couple effects of various biodegradations simultaneously occur in the aquifer, promoting the occurrence of NH₄–DOMs.
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