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| Eight PARAFAC components used in this study. In specific, C1-C4 and C6 are classified as terrestrial humic-like components, and C5 as a microbial humic-like component. In addition, C7 is designated as a tryptophan-like component, and C8 is generally a protein-like component. The PARAFAC model has been validated and cross-checked with other published studies, showing no overfitting. Fluorescence intensities are normalized to Raman units (r.u.). Detailed information can be found in Xue et al., 2022.
Source publication
Although river mixing occurs widely in nature, the corresponding evolution of dissolved organic matter (DOM) composition remains poorly understood. Here, surface water samples were collected at multiple transects in the lower Athabasca River (LAR) under base-flow conditions. Asymmetric flow field-flow fractionation (AF4) coupled to online excitatio...
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The current study investigates the combined treatment of wastewater of anaerobic digestate and landfill leachate, using deammonification and coagulation/flocculation processes. The deammonification section studies the performance of a full-scale deammonification plant in nitrogen and chemical oxygen demand (COD) removal, monitored over 2 years. For...
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Citations
Over the past few decades, asymmetric flow field-flow fractionation (AF4) has emerged as a robust technique for the
separation of colloid-associated trace elements (TEs) in aqueous samples. Nevertheless, little is known about potential artifacts and
how to control them when measuring the concentrations of colloid-associated elements at low (μg L−1) or ultralow concentrations
(ng L−1) using AF4-UV-ICP-MS. Water from a boreal river was selected as a challenging test material due to its high concentrations of dissolved organic matter (DOM) and Fe-rich colloids. These colloids are expected to be significant contributors to artifact occurrence, even in a metal-free, ultraclean laboratory. The results show that the adsorption of Mn, Co, Ni, Cu, and Pb onto acidcleaned, non-channel surfaces (such as connection tubing and autosampler) accounted for up to 48% of TE loss. These losses on
non-channel surfaces also represent potential sources of cross-contamination for Co, Ni, Cu, and Pb. New, uncleaned poly(ether
sulfone) membranes are also sources of contamination for Ni and Cu. Analytical bias may exist in the measured concentrations of
TEs, primarily due to the potential carryover of weakly adsorbed TEs (e.g., Ni and Cu) on the system surfaces by colloids in the
samples (e.g., DOM). On the other hand, colloids in the samples can also act to gradually remove contaminants from the surfaces.
For these types of DOM-rich waters, preconditioning the AF4 system using 40 mg C L−1 of Suwannee River Natural Organic Matter (SRNOM, pH = 7) is recommended to mitigate the impact of membrane fouling and carryover. A comprehensive strategy for
minimizing instrumental artifacts is presented and discussed.
This chapter reviews and synthesizes key advances in our understanding of organic carbon (OC) cycling in estuaries over the past decade, combining a discussion of both particulate and dissolved OC (POC and DOC). Estuaries receive OC from terrestrial and oceanic sources as well as internal production, and this OC is highly diverse in chemical composition and biogeochemical reactivity. We review methodological advances as well as key established techniques that are used to quantify OC, distinguish OC sources, and track OC transformations. We also examine the different sources themselves and how their OC fluxes are controlled. Estuaries have high rates of OC transformation, and we examine the effects of flocculation, sorption to minerals, and microbial and photochemical degradation. We discuss how advances in our knowledge are applied in biogeochemical ocean models of estuaries and coastal zones, and examine the challenges in modeling OC across the interface from land to ocean. We conclude by evaluating how our understanding of the carbon budget for the coastal zone has evolved, highlighting key challenges for the future.
The molecular mass distribution (MMD) and fluorescence properties of dissolved organic matter (DOM) are important characteristics for tracing and predicting its pathways, processes, and fate in aquatic systems. For the first time, asymmetrical flow field-flow fractionation (AF4) with coupled absorbance and fluorescence detectors was used to determine the contribution of endmembers to three mixtures of leaf leachate and riverine DOM in various proportions. Parallel factor analysis (PARAFAC) and fractogram deconvolution were used to decompose and distinguish the size distributions and fluorescence excitation-emission matrices (EEMs) of mixture constituents. It was determined that: 1) Both size and optical properties were conservative tracers in mixtures; 2) Fractogram deconvolution was extremely helpful for discriminating endmember size properties; 3) The contributions of endmembers to overall DOC concentration were accurately estimated using both the proportion of a humic-like PARAFAC component (0.93 < R2 < 1.00), and the ratios of deconvoluted peaks (0.88 < R2 < 0.98). The fluorescence at the peak maximum of the MMD was lacking in protein-/polyphenol-like and microbial humic-like fluorescence compared to the whole sample (−11 ± 9 and −10 ± 7%, respectively); however, the contribution of endmembers to the MMD (A254) were also effectively predicted using both the proportion of a microbial humic-like PARAFAC component (0.91 < R2 < 0.98) and the ratio of deconvoluted peaks (0.94 < R2 < 0.98).
