Sources and composition of sediment pore-water dissolved organic matter in prairie pothole lakes

Sediment pore-water dissolved organic matter (DOM) in two North Dakota prairie pothole lakes was quantified by dissolved organic carbon analysis (DOC) and its composition was characterized as a function of sediment depth for molecular weight distribution (MWD), molar absorptivity at 280 nm (epsilon 280), and fluorescence properties. Fluorescence excitation emission matrices were further analyzed by creating a Parallel Factor Analysis (PARAFAC) model specific to sedimentary pore-water DOM. The range of absolute pore-water DOC concentrations (similar to 26-183 mg C L-1) greatly exceeded abundances reported for other wetlands and generally increased with depth. Significant changes occurred in epsilon 280 and fluorescence seasonally. Prairie pothole pore-water DOM is primarily allochthonous in nature and three 'humic-like' components explained similar to 90% of total sample fluorescence, while a single 'non-humic' component was responsible for the remaining 10%. The contribution of the non-humic component, however, was more significant in the top 7 cm of sediment in samples collected in early autumn and is presumably derived from algal precursor material produced by primary production in the water column over the summer. The PARAFAC results corroborate epsilon 280 and MWD changes in pore-water DOM composition over the growing season. This dynamic process could affect the type of DOM available for biogeochemical processes seasonally.