Molecular Characterization of Dissolved Organic Matter from Subtropical Wetlands: A Comparative Study Through the Analysis of Optical Properties, NMR and FTICR/MS

Abstract:

Dissolved organic matter (DOM) is a critical component of the carbon cycle in freshwater systems and its elemental composition and molecular features determine its reactivity and thus its stability in the environment. DOM is particularly prominent in wetland ecosystems and can be exported through drainage into streams and ultimately the ocean. While DOM has been characterized through a great variety of analytical techniques, much focus has been placed on characterizations in oceanic environments and large river systems. In addition, multi-analytical approaches using advanced analytical techniques for the characterization of DOM in wetlands have been sparse. Here we present a comparative study of DOM from three, large, subtropical wetlands, the Everglades (USA), the Pantanal (Brazil) and the Okavango Delta (Botswana), applying a combination of optical properties (EEM-PARAFAC), high field NMR and FT-ICRMS. We basically confirm findings of other reports that many of the bulk molecular characteristics in freshwater DOM are shared by diverse aquatic ecosystems that can be very different in their environmental character. However, detailed analyses reveal significant variations in the molecular composition that can in most cases be controlled by site-specific ecological processes and watershed dynamics including fire regimes, external sources of sulphur, and hydrological drivers such as hydroperiod or degree of inundation. Differences and similarities between selected sites from the three abovementioned wetland systems will be presented in relation to their specific environmental characteristics.