Associations Between the Molecular and Optical Properties of Dissolved Organic Matter in the Florida Everglades, a Model Coastal Wetland System

Sasha Wagner; Rudolf Jaffé; Kaelin Cawley; Thorsten Dittmar; Aron Stubbins

doi:10.3389/fchem.2015.00066

Associations Between the Molecular and Optical Properties of Dissolved Organic Matter in the Florida Everglades, a Model Coastal Wetland System

Front Chem. 2015 Nov 25:3:66. doi: 10.3389/fchem.2015.00066. eCollection 2015.

Authors

Sasha Wagner¹, Rudolf Jaffé², Kaelin Cawley³, Thorsten Dittmar⁴, Aron Stubbins¹

Affiliations

¹ Marine Sciences Department, Skidaway Institute of Oceanography, The University of Georgia Savannah, GA, USA.
² Southeast Environmental Research Center, Department of Chemistry and Biochemistry, Florida International University Miami, FL, USA.
³ Department of Civil, Environmental and Architectural Engineering, Institute of Arctic and Alpine Research, University of Colorado at Boulder Boulder, CO, USA.
⁴ Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg Oldenburg, Germany.

Abstract

Optical properties are easy-to-measure proxies for dissolved organic matter (DOM) composition, source, and reactivity. However, the molecular signature of DOM associated with such optical parameters remains poorly defined. The Florida coastal Everglades is a subtropical wetland with diverse vegetation (e.g., sawgrass prairies, mangrove forests, seagrass meadows) and DOM sources (e.g., terrestrial, microbial, and marine). As such, the Everglades is an excellent model system from which to draw samples of diverse origin and composition to allow classically-defined optical properties to be linked to molecular properties of the DOM pool. We characterized a suite of seasonally- and spatially-collected DOM samples using optical measurements (EEM-PARAFAC, SUVA254, S275-295, S350-400, SR, FI, freshness index, and HIX) and ultrahigh resolution mass spectrometry (FTICR-MS). Spearman's rank correlations between FTICR-MS signal intensities of individual molecular formulae and optical properties determined which molecular formulae were associated with each PARAFAC component and optical index. The molecular families that tracked with the optical indices were generally in agreement with conventional biogeochemical interpretations. Therefore, although they represent only a small portion of the bulk DOM pool, absorbance, and fluorescence measurements appear to be appropriate proxies for the aquatic cycling of both optically-active and associated optically-inactive DOM in coastal wetlands.

Keywords: EEM-PARAFAC; Florida coastal Everglades; absorbance; dissolved organic matter; fluorescence; subtropical wetland; ultrahigh resolution mass spectrometry.