No abstract

Wetlands play a central role in the global C cycle since they are sites of intensive C sequestration and fixation, storing large amounts of C in biomass, sediments and water. A major fraction of this C is present in the pool of dissolved organic matter (DOM), contributed by the terrestrial and aquatic production and with multiple regulatory functions in the aquatic ecosystem. Patagonian wetlands are undergoing profound changes in their water cycle due to warming and reduced precipitation, which has led to shorter hydroperiods and reduced landscape connectivity, affecting their C budgets. In this study we characterized the dynamics and reactivity of the DOM pool in a temporary temperate wetland of North Patagonia during a hydroperiod, using optical DOM proxies obtained through absorption and fluorescence spectroscopy. EEM-PARAFAC analysis was applied to model DOM components. DOC varied between ~4 and ~9 mg L-1, displaying aromatic signals and soil/sediment and terrestrial fingerprints. The humic fluorescent 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. In the course of the hydroperiod different DOM optical proxies allowed identifying allochthonous inputs, the progression of 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 relative contributions of humic vs. non-humic components influenced the photoreactivity of the DOM throughout the hydroperiod. The prevalence of humic components determined the high photorecalcitrance of the DOM pool.