Technical note: Effects of iron(II) on fluorescence properties of dissolved organic matter at circumneutral pH

Jia, K, Manning, CCM, Jollymore, A and Beckie, RD 2021 Technical note: Effects of iron(II) on fluorescence properties of dissolved organic matter at circumneutral pH. Hydrology and Earth System Sciences, 25 (9). 4983-4993.

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Modern fluorescence spectroscopy methods, including excitation–emission matrix (EEM) spectra parsed using parallel factor analysis (PARAFAC) statistical approaches, are widely used to characterize dissolved organic matter (DOM) pools. The effect of soluble reduced iron,Fe (II), on EEM spectra can be significant but is difficult to quantitatively assign. In this study, we examine the effects of Fe(II) on the EEM spectra of groundwater samples from an anaerobic deltaic aquifer containing up to 300 mg L−1 Fe(II), located a few kilometres from the ocean and adjacent to the Fraser River in Richmond, British Columbia, Canada. We added varying quantities of Fe(II) into groundwater samples to evaluate Fe(II)–DOM interactions. Both the overall fluorescence intensity and the intensity of the primary peak, a humic-like substance at excitation and emission wavelengths of 239 and 441–450 nm (peak A), respectively, decreased by approximately 60 % as Fe(II) concentration increased from 1 to 306 mg L−1. Furthermore, the quenching effect was non linear and proportionally stronger at Fe(II) concentrations below 100 mg L−1. This nonlinear relationship suggests a static quenching mechanism. In addition, DOM fluorescence indices are substantially influenced by the Fe(II) concentration. With increasing Fe(II), the fluorescence index (FI) shifts to higher values, the humidification index (HIX) shifts to lower values, and the freshness index (FrI) shifts to higher values. Nevertheless, the 13-component PARAFAC model showed that the component distribution was relatively insensitive to Fe(II) concentration; thus, PARAFAC may be a reliable method for obtaining information about the DOM composition and its redox status in Fe(II)-rich waters. By characterizing the impacts of up to 300 mg L−1 Fe(II) on EEMs using groundwater from an aquifer which contains similar Fe(II) concentrations, we advance previous work which characterized impacts of lower Fe(II) concentrations (less than2 mg L−1) on EEMs.

Item Type: Publication - Article
Divisions: Plymouth Marine Laboratory > National Capability categories > National Centre for Earth Observation
Plymouth Marine Laboratory > Science Areas > Earth Observation Science and Applications
Plymouth Marine Laboratory > Science Areas > Marine Biochemistry and Observations
Depositing User: S Hawkins
Date made live: 28 Sep 2021 15:14
Last Modified: 28 Sep 2021 15:14

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