DOI: 10.6073/pasta/1e72d716e065aecd20f9633c0ba00024
title: Dissolved Organic Carbon Stable Isotopes and Lignin Phenols from Everglades National Park (FCE LTER), South Florida, USA, 2018-ongoing

description: Estuarine and coastal waters are home to more than half of the world's population and provide many social and economic benefits to society. Additionally, these ecosystems are sites of intense carbon cycling and are under pressure from changing land uses and climate. DOM is functionally defined as the OM passed through a 0.7 µm borosilicate glass fiber filter (GF/F) and is primarily made up of viruses, bacteria, colloids, lignins, humic substances, organic acids, and other small organic compounds (Repeta, 2015). Approximately 50% of DOM is generally considered to be dissolved organic carbon (DOC) (Stedmon and Nelson, 2015). Thus, DOC can be used as a proxy for quantifying DOM. Whole water samples were collected monthly from three different transects representing marl-dominated (Taylor Slough), peat-dominated (Shark River Slough), and seagrass-dominated (Florida Bay) environments. The water was filtered using 0.7 µm porosity glass fiber filters, then acidified to pH 2 and stored at 4°C until processing occurred. DOC concentration and the stable isotope ratio of DOC (δ13C-DOC) was measured on an OI Analytical TOC analyzer coupled to an Agilent Delta V plus Isotope Ratio Mass Spectrometer using high-temperature combustion (Lalonde et al., 2014). Dissolved vanillyl (vanillin, acetovanillone, vanillin acid), syringyl (syringaldehyde, acetosyringone, syringic acid), cinnamyl (p-coumaric acid, ferulic acid), and 3,5-hydroxybenzoic acid lignin phenols were isolated from ~2 liters of 0.7 µm filtered, acidified (pH 2) water by solid phase extraction (SPE) using 1g PPL cartridges that were pre-conditioned using pH 2 water and methanol. SPE cartridges were extracted using methanol, then dried and redissolved in 2N NaOH. Cupric oxide oxidation and liquid-liquid ethyl acetate extraction were used to extract lignin oxidation products (Hedges and Ertel, 1982, modified by Goñi and Hedges, 1995; Louchouarn et al., 2000; Goñi and Montgomery, 2000; Benner and Kaiser, 2011). Briefly, NaOH dissolved samples were added to teflon vessels with CuO, ferrous ammonium sulfate, and glucose then oxidized in a muffle furnace for 150 minutes at 155C (5C/min ramp rate). Samples were then rapidly cooled, vortexed then transferred to centrifuge tubes and centrifuged, then the supernatant was transferred to a new centrifuge tube and internal lignin standards are added and then supernatant is acidified. Ethyl acetate is added to preform liquid-liquid extraction. Ethyl acetate extract is dried over a sodium sulfate column, then extracts are dried. Extracts are redissolved in pyridine then derivatized using BSTFA in a muffle furnace for 1 hr at 60C. Dertivatized samples are then dried and redissolved in dichloromethane then immediately quantified using an Agilent Gas Chromatograph-Mass Spectrometer (GC-MS) according to the method provided by Kaiser and Benner (2012). Benner, R., & Kaiser, K. (2011). Biological and photochemical transformations of amino acids and lignin phenols in riverine dissolved organic matter. Biogeochemistry, 102(1), 209-222. Goñi, M. A., & Hedges, J. I. (1995). Sources and reactivities of marine-derived organic matter in coastal sediments as determined by alkaline CuO oxidation. Geochimica et Cosmochimica Acta, 59(14), 2965-2981. Goñi, M. A., & Montgomery, S. (2000). Alkaline CuO oxidation with a microwave digestion system: Lignin analyses of geochemical samples. Analytical chemistry, 72(14), 3116-3121. Hedges, J. I., & Ertel, J. R. (1982). Characterization of lignin by gas capillary chromatography of cupric oxide oxidation products. Analytical Chemistry, 54(2), 174-178. Kaiser, K., & Benner, R. (2012). Characterization of lignin by gas chromatography and mass spectrometry using a simplified CuO oxidation method. Analytical chemistry, 84(1), 459-464. Lalonde, K., Middlestead, P., & Gélinas, Y. (2014). Automation of 13C/12C ratio measurement for freshwater and seawater DOC using high temperature combustion. Limnology and Oceanography: Methods, 12(12), 816-829. Louchouarn, P.; Opsahl, S.; Benner, R. 2000. Isolation and quantification of dissolved lignin from natural waters using solid phase extraction and GC/MS. Analytical Chem. 2000, 2780-2787 Repeta, D. J. (2015). Chemical characterization and cycling of dissolved organic matter. In Biogeochemistry of marine dissolved organic matter (pp. 21-63). Academic Press. Stedmon, C. A., & Nelson, N. B. (2015). The optical properties of DOM in the ocean. In Biogeochemistry of marine dissolved organic matter (pp. 481-508). Academic Press.