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

Abstract

Terrestrial inputs of dissolved organic matter (DOM) make a significant contribution to the carbon pool of headwaters and the reactivity of this pool depends on its source and diagenetic state, being influenced by photochemical and biological processes. The main goal of this study was to characterise the composition and reactivity of soil and leaf litter DOM from a native forest of Nothofagus pumilio (Nothofagaceae), and from natural stream water, evaluating the effect of degradation processes. Photo‐ and biodegradation laboratory experiments were conducted using DOM leached from soil and leaf litter, while the impact of photodegradation alone was also analysed through laboratory assays using stream water. The effects of photo‐ and biodegradation were evaluated through changes in the concentration of dissolved organic and inorganic carbon (DOC and DIC, respectively) and optical DOM proxies (absorbance and fluorescence). In the initial characterisation, DOM from soil and water leachates showed naturally high humification, aromaticity and lignin content compared with the DOM of leaf litter leachate rich in non‐humic compounds. Photo‐ and biodegradation increased humification of the DOM. DOM from leaf litter leachate was more bioavailable than DOM from soil leachate, as reflected by the higher 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 of labile protein‐like compounds and an increase in refractory humic‐like components. Long‐rod shaped bacteria were more abundant in leaf litter leachate, suggesting their preference for labile DOM, whereas cocci dominated in the humic and more biorecalcitrant DOM from soil leachate. This study showed a continuum of DOM humification, with decreasing DOM reactivity from leaf litter leachate towards soil leachate and stream water. Soil leachate DOM was probably the main source of stream water DOM, as reflected by their similar signatures and close positioning in the reactivity continuum, although carbon mineralisation was much lower in soil leachate than stream water.

Experimental evaluation of the role of inorganic phosphorus for terrestrial carbon degradation in stream hyporheic zones

“…In fact, we did not measure a decrease in oxygen at 100% DOM soil , which suggests that the extracted DOM soil did not stimulate microbial activities. This is in line with studies from pelagic waters(Garcia et al, 2018;Hansen et al, 2016) and the oxic HZ(Wagner et al, 2014), which postulate that terrestrial DOM extracted from soils generally is less degraded in aquatic systems than DOM algal . By contrast,Fellman et al (2009) found high proportions of bioavailable DOC in the pore water of different soils, often exceeding those of the stream water.…”

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

“…2011), and the leaching that occurs on inundation sends an initial pulse of DOC into the water column of wetlands. Accordingly, the initial DOM pool of FP showed optical signatures indicative of high humic content and prevalence of compounds of high molecular weight/size and aromaticity (Table S1), resembling terrigenous inputs (García et al . 2018).…”

“…Other investigations focusing on the photoreactivity of DOM in running waters and shallow permanent lakes in the same catchment have also reported high recalcitrance of the humic component C2 (or A+C peaks) (Soto Cárdenas et al . 2017; García et al . 2018).…”

Biosolids leachate variability, stabilization surrogates, and optical metric selection

“…S9†). 57 While these environmental associations can be made, PARAFAC components are statistically derived and do not have established, explicit chemical meaning for a given component. Further work is needed to do so.…”