Chemical characterization of DOM in channels of a seasonal wetland

Abstract

Although wetlands are known to be important sources of dissolved organic matter (DOM) within watersheds, production of DOM within wetlands is not well understood. In the Okavango Delta, a large wetland located in Botswana, large amounts of DOM produced in the wetland are transported in the river network and to the subsurface. The purpose of this study was to gain insight into environmental processing of DOM in wetland surface waters by examining chemical characteristics of plant litter leachates and fulvic acids isolated from two surface water sites in the Panhandle (PHFA) and Seasonal Swamp (SSFA) of the Okavango Delta. Spectroscopic properties measured over the course of leaching experiments indicated a greater abundance of plant-derived DOM over time. Results of elemental and 13CNMR analyses showed that aromaticities and C:N ratios of PHFA and SSFA and a Cyperus papyrus leachate fulvic acid (CPLFA) were in the range typical for fulvic acids derived from vascular plants. Fluorescence analyses of fulvic acids using parallel factor analysis (PARAFAC) further indicated the importance of plant litter sources in surface water DOM. Environmental processing of DOM in downstream surface waters by bacterial and photodegradation was suggested by higher N and S content for SSFA compared to CPLFA and by differences in δ15N, δ34S, δ13C and fluorescence signatures among the 3 fulvic acid samples. These chemical characterization results suggest that a progressive enrichment of DOM by plant-derived material occurs with distance downstream and that this DOM undergoes some environmental processing within the surface water system.