Characterization of dissolved organic matter from temperate wetlands: field dynamics and photoreactivity changes driven by natural inputs and diagenesis along the hydroperiod

Wetlands store large amounts of C in biomass, sediments and water. A major C fraction is in the dissolved organic matter (DOM) pool and has multiple regulatory functions in the ecosystem. Patagonian wetlands undergo profound changes in their water cycle due to warming and reduced precipitation, causing shorter hydroperiods and reduced landscape connectivity and overall affecting their C budgets. In this study we characterized the DOM pool of a temporary wetland of North Patagonia during a hydroperiod, using optical DOM proxies obtained by absorption and fluorescence spectroscopy. DOM components were modeled through EEM-PARAFAC. DOC varied between [~]4 and [~]9 mg L-1, displaying aromatic signals and terrestrial/sediment fingerprints. The humic components C1 (microbial and/or vegetation derived) and C2 (soil/sediment derived) prevailed in the DOM pool, whereas the non-humic component C3 (derived from aquatic production) showed lower contribution. Along the hydroperiod DOM optical proxies allowed identifying allochthonous inputs, degradation and an increasing contribution of the internal production to the DOM pool. Photodegradation experiments showed that exposure to PAR+UVR produced slight changes in the DOC concentration and a reduction in DOM molecular weight/size. The contribution of humic vs. non-humic components influenced DOM photoreactivity. The prevalence of humic components determined high DOM photorecalcitrance.