24 Oct 2023
 | 24 Oct 2023
Status: this preprint is open for discussion.

Sorption of Colored vs Noncolored Organic Matter by Tidal Marsh Soils

Patrick J. Neale, J. Patrick Megonigal, Maria Tzortziou, Elizabeth A. Canuel, Christina R. Pondell, and Hannah Morrissette

Abstract. Tidal marshes are significant sources of colored (or chromophoric) dissolved organic carbon (CDOC) to adjacent waters and, as a result, contribute substantially to their optical complexity making CDOC a good indicator of water quality. Despite this, our mechanistic understanding of the processes that regulate the exchange and transformation of CDOC at the tidal marsh-estuarine interface remains limited. We hypothesized that tidal marsh soils regulate this exchange and transformation subject to soil mineralogy and salinity environment. To test this hypothesis, we generated initial mass sorption isotherms of CDOC and noncolored dissolved organic carbon (NCDOC) using anaerobic batch incubations with four tidal wetland soils, representing a range of organic carbon content (1.77 ± 0.12 % to 36.2 ± 2.2 %) and across four salinity treatments (0, 10, 20, and 35). CDOC sorption followed Langmuir isotherms that were similar in shape to those of total DOC, but with greater maximum sorption capacity and lower binding affinity. Like isotherms of total DOC, CDOC maximum sorption capacity increased and binding affinity decreased with greater salinity. Initial natively adsorbed colored organic carbon was low and increased with soil organic content. In contrast, NCDOC desorbed under all conditions with desorption increasing linearly with initial CDOC concentration. This suggests that for our test solutions (made from Great Dismal Swamp DOC), CDOC displaced NCDOC on tidal marsh soils. Parallel factor analysis of 3-D excitation emission matrices and specific ultraviolet absorbance measurements suggested that CDOC sorption was driven primarily by the exchange of highly aromatic humic-like CDOC. Taken together, these results suggest that tidal marsh soils regulate export and composition of CDOC depending on the complex interplay between soil minerology, water salinity, and CDOC vs NCDOC composition.

Patrick J. Neale et al.

Status: open (until 01 Jan 2024)

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Patrick J. Neale et al.

Patrick J. Neale et al.


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Short summary
Adsorption/desorption incubations were conducted with tidal marsh soils to understand the differential sorption behavior of colored vs non-colored dissolved organic carbon. The wetland soils varied in organic content and a range of salinities fresh to 35 was used.  Soils primarily adsorbed colored organic carbon and desorbed non-colored organic carbon. Sorption capacity increased with salinity, implying that salinity variations may shift composition of dissolved carbon in tidal marsh waters.