Dissolved organic carbon (DOC) reactivity in aquatic systems is essentially dependent on DOC precursor material and on the processes regulating its bioavailability, especially photodegradation and microbial activity. We investigated temporal changes (from hours to weeks) in the reactivity of allochthonous and autochthonous DOC sources in a macrophyte-dominated shallow lake using a set of incubation experiments. Changes in DOC fluorescence and absorbance properties due to biodegradation (BD) and to the combined effect of photo- and biodegradation (UV + BD) were traced. Allochthonous DOC was more reactive than autochthonous DOC (AutoDOC), showing higher DOC losses (between 22 and 36 %) and faster changes in DOC properties than AutoDOC. The effect of UV + BD was larger than BD alone for both sources of DOC. The rates of change of DOC properties were stronger during the first days of incubation and showed no regular pattern for any of the treatments or DOC sources. Our findings highlight the relevance of the timescale when assessing changes in DOC quality under different degradation pathways, as well as the need of discussing the labile character usually attributed to autochthonous DOC in systems dominated by submerged vegetation, as many shallow lakes or lagoons. © 2013 Springer Basel.

This study was funded by the project CGL 2008-05095/BOS, from the Ministerio de Ciencia e Innovación (Spain). NC holds a doctoral fellowship (FI 2010–2013) from the Generalitat de Catalunya.

Peer reviewed