Distinct variations in fluorescent DOM components along a trophic gradient in the lower Fox River-Green Bay as characterized using one-sample PARAFAC approach

Hui Lin; Sarah L Bartlett; Laodong Guo

doi:10.1016/j.scitotenv.2023.165891

Distinct variations in fluorescent DOM components along a trophic gradient in the lower Fox River-Green Bay as characterized using one-sample PARAFAC approach

Sci Total Environ. 2023 Dec 1:902:165891. doi: 10.1016/j.scitotenv.2023.165891. Epub 2023 Aug 5.

Authors

Hui Lin¹, Sarah L Bartlett², Laodong Guo³

Affiliations

¹ School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E. Greenfield Ave., Milwaukee, WI 53204, USA; Polar Research Institute of China, 1000 Xuelong Road, Pudong, Shanghai 201209, China.
² NEW Water/Green Bay Metropolitan Sewerage District, 2231 N. Quincy Street, Green Bay, WI 54302, USA.
³ School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E. Greenfield Ave., Milwaukee, WI 53204, USA. Electronic address: guol@uwm.edu.

PMID: 37544441
DOI: 10.1016/j.scitotenv.2023.165891

Abstract

Variations in molecular weight distributions of dissolved organic matter (DOM) and PARAFAC-derived fluorescent components were investigated along a transect in the seasonally hypereutrophic lower Fox River-Green Bay using the one-sample PARAFAC approach coupling flow field-flow fractionation for size-separation with fluorescence excitation-emission matrix (EEM) and PARAFAC analysis. Concentrations of dissolved organic carbon and nitrogen, chromophoric-DOM, specific UV absorbance at 254 nm, and humification index all decreased monotonically from river to open bay, showing a strong river-dominated DOM source and a dynamic change in DOM quality along the river-lake transect. The relative abundance of colloidal DOM (>1 kDa) derived from ultrafiltration exhibited minimal variation, averaging 71 ± 4 % of the bulk DOM, across the entire estuarine transect although the colloidal concentration decreased in general. Using the one-sample EEM-PARAFAC approach, the identified major fluorescent components were distinct between stations along the river-estuary-open bay continuum, with four components in river/upper-estuary but three components in open bay waters. Among the four common fluorescent components (C₄₇₅, C₄₁₀, C₃₂₀ and C₂₉₀), the most abundant and refractory humic-like component, C₄₇₅, behaved conservatively and its relative abundance (%ΣF_max) remained fairly constant (50 ± 4 %) along the transect, while the semi-labile humic-like component, C₄₁₀, consistently decreased from river to estuary and eventually vanished in open Green Bay. In contrast, the two autochthonous protein-like components (C₃₂₀ and C₂₉₀) increased from river to open bay along the trophic gradient. The new results presented here provide an improved understanding of the diverse and fluctuating characteristics in DOM composition, lability, and estuarine mixing behavior across the river-lake interface and demonstrate the efficacy of the one-sample PARAFAC approach.

Keywords: Dissolved organic matter; Estuarine processes; Flow field-flow fractionation; Fluorescence EEM; Fox River-Green Bay; Lake Michigan.