Characterisation and reactivity continuum of dissolved organic matter in forested headwater catchments of Andean Patagonia

GARCIA, ROBERTO DANIEL; DIÉGUEZ, MARÍA DEL CARMEN; GEREA, MARINA; GARCIA, PATRICIA ELIZABETH; REISSIG, MARIANA

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 vol. 63 p. 1049 - 1062

0046-5070

Abstract1. Terrestrial inputs of dissolved organic matter (DOM) make a significant contributionto the carbon pool of headwaters and the reactivity of this pool depends on its sourceand diagenetic state, being influenced by photochemical and biological processes.The main goal of this study was to characterise the composition and reactivity of soiland leaf litter DOM from a native forest of Nothofagus pumilio (Nothofagaceae), andfrom natural stream water, evaluating the effect of degradation processes.2. Photo- and biodegradation laboratory experiments were conducted using DOMleached from soil and leaf litter, while the impact of photodegradation alone wasalso analysed through laboratory assays using stream water. The effects ofphoto- and biodegradation were evaluated through changes in the concentrationof dissolved organic and inorganic carbon (DOC and DIC, respectively) and opticalDOM proxies (absorbance and fluorescence).3. In the initial characterisation, DOM from soil and water leachates showed naturallyhigh humification, aromaticity and lignin content compared with the DOMof leaf litter leachate rich in non-humic compounds.4. Photo- and biodegradation increased humification of the DOM. DOM from leaf litterleachate was more bioavailable than DOM from soil leachate, as reflected by thehigher growth of bacteria, DOC consumption and DIC production. In general,biodegradation increased DOM molecular weight, aromaticity and lignin content.Changes in fluorescent DOM (FDOM) showed a trend characterised by the loss oflabile protein-like compounds and an increase in refractory humic-like components.5. Long-rod shaped bacteria were more abundant in leaf litter leachate, suggestingtheir preference for labile DOM, whereas cocci dominated in the humic andmore biorecalcitrant DOM from soil leachate.6. This study showed a continuum of DOM humification, with decreasing DOM reactivityfrom leaf litter leachate towards soil leachate and stream water. Soil leachateDOM was probably the main source of stream water DOM, as reflected by theirsimilar signatures and close positioning in the reactivity continuum, although carbonmineralisation was much lower in soil leachate than stream water.