Abstract
Abstract. Wetlands provide quintessential ecosystem services such as maintenance of water quality, water supply and biodiversity, among others; however, wetlands are also among the most threatened ecosystems worldwide. Natural dissolved organic matter (DOM) is an abundant and critical component in wetland biogeochemistry. This study describes the first detailed, comparative, molecular characterization of DOM in subtropical, pulsed, wetlands, namely the Everglades (USA), the Pantanal (Brazil) and the Okavango Delta (Botswana), using optical properties, high-field nuclear magnetic resonance (NMR) and ultrahigh-resolution mass spectrometry (FT-ICRMS), and compares compositional features to variations in organic matter sources and flooding characteristics (i.e., differences in hydroperiod). While optical properties showed a high degree of variability within and between the three wetlands, analogies in DOM fluorescence properties were such that an established excitation emission matrix fluorescence parallel factor analysis (EEM-PARAFAC) model for the Everglades was perfectly applicable to the other two wetlands. Area-normalized 1H NMR spectra of selected samples revealed clear distinctions of samples while a pronounced congruence within the three pairs of wetland DOM readily suggested the presence of an individual wetland-specific molecular signature. Within sample pairs (long- vs. short-hydroperiod sites), internal differences mainly referred to intensity variations (denoting variable abundance) rather than to alterations of NMR resonances positioning (denoting diversity of molecules). The relative disparity was largest between the Everglades long- and short-hydroperiod samples, whereas Pantanal and Okavango samples were more alike among themselves. Otherwise, molecular divergence was most obvious in the case of unsaturated protons (δH > 5 ppm). 2-D NMR spectroscopy for a particular sample revealed a large richness of aliphatic and unsaturated substructures, likely derived from microbial sources such as periphyton in the Everglades. In contrast, the chemical diversity of aromatic wetland DOM likely originates from a combination of higher plant sources, progressive microbial and photochemical oxidation, and contributions from combustion-derived products (e.g., black carbon). FT-ICRMS spectra of both Okavango and Pantanal showed near 57 ± 2 % CHO, 8 ± 2 % CHOS, 33 ± 2 % CHNO and < 1 % CHNOS molecules, whereas those of Everglades samples were markedly enriched in CHOS and CHNOS at the expense of CHO and CHNO compounds. In particular, the Everglades short-hydroperiod site showed a large set of aromatic and oxygen-deficient “black sulfur” compounds whereas the long-hydroperiod site contained oxygenated sulfur attached to fused-ring polyphenols. The elevated abundance of CHOS compounds for the Everglades samples likely results from higher inputs of agriculture-derived and sea-spray-derived sulfate. Although wetland DOM samples were found to share many molecular features, each sample was unique in its composition, which reflected specific environmental drivers and/or specific biogeochemical processes.
Highlights
Natural dissolved organic matter (DOM) is a critical component of the global carbon cycle (Battin et al, 2009)
This study describes the first detailed, comparative, molecular characterization of DOM in subtropical, pulsed, wetlands, namely the Everglades (USA), the Pantanal (Brazil) and the Okavango Delta (Botswana), using optical properties, high-field nuclear magnetic resonance (NMR) and ultrahigh-resolution mass spectrometry (FT-ICRMS), and compares compositional features to variations in organic matter sources and flooding characteristics
SR and fluorescence index (FI) values were quite similar for all sample pairs and among samples, suggesting that the molecular weight distribution and the soil/higher plant vs. microbial contributions were quite similar among these samples, or that the mineralization of wetland DOM leads to similar compositional features for systems with different organic matter sources
Summary
Natural dissolved organic matter (DOM) is a critical component of the global carbon cycle (Battin et al, 2009). While optical properties have been widely applied for DOM bulk characterizations (Jaffé et al, 2014; Fellman et al, 2010) and allow large sample throughput at low cost, more advanced molecular level characterization techniques such as NMR provide unsurpassed insight into closerange molecular order (Hertkorn et al, 2006, 2013; Lam et al, 2007; McCaul et al, 2011; Woods et al, 2011, 2012; Zhang et al, 2014; Bell et al, 2015), while FT-ICRMS provides depiction of the compositional space with exceptional resolution (Kujawinski, 2002; Sleighter and Hatcher, 2007; D’Andrilli et al, 2010; Hertkorn et al, 2008, 2013; Kaiser et al, 2003; Minor et al, 2014; Koch et al, 2005, 2007) The combination of such techniques in the assessment of DOM dynamics has become more frequent (e.g., Tfaily et al, 2015; Jaffé et al, 2012), and the association between optical properties and the molecular characteristics of DOM have recently become an active research endeavor in an attempt to better link these parameters (Stubbins et al, 2014; Kellerman et al, 2015; Wagner et al, 2015a). DOM samples from three of the largest and most important subtropical, pulsed wetlands – the Everglades (USA), the Pantanal (Brazil) and the Okavango Delta (Botswana) – were collected and analyzed on a comparative basis using optical properties, including EEM-PARAFAC, high-field 1H NMR, 13C NMR and FT-ICRMS, in order to assess similarities and differences in DOM composition and molecular structure in such vital ecosystems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
