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

ABSTRACT

Wetlands store large amounts of C in biomass, sediments and water. A major C fraction is in the dissolved organic matter (DOM) with multiple regulatory functions. Patagonian wetlands undergo changes in the water cycle due to climate warming and lower precipitation, causing shorter hydroperiods and reduced landscape connectivity with effects on C budgets. This study focuses on the optical characterisation of the DOM of an ephemeral wetland of North Patagonia. Along the hydroperiod the DOM showed optical signatures indicating terrestrial inputs, degradation and internal production. Dissolved organic carbon (DOC) concentration ranged between ∼4 and ∼9 mg L⁻¹. The DOM pool displayed high molecular weight/size and aromatic fingerprints. Humic components C1 (microbial and/or vegetation derived) and C2 (soil/sediment) prevailed in the DOM, whereas the non-humic component C3 (from aquatic processes) increased from early spring. Experimental exposure to PAR + UVR produced slight changes in DOC and reduction in DOM molecular weight/size. The components showed distinctive photoreactivity/lability: C1 > C3 > C2. Along the hydroperiod the relative contribution of the humic vs. non-humic components (C1 and C3) determined the reactivity/lability of the DOM. In Fantasma pond, the DOM pool fluctuates in response to hydrology and degradation processes, and the alternance between dry and flooded periods determines C dynamics.

KEYWORDS:

• Patagonia
• temperate wetlands
• dissolved organic carbon
• photoreactivity/photolability
• hydroperiod

Acknowledgments

The authors thank the town council of San Carlos de Bariloche for granting permission to collect samples in Fantasma pond, and to Mrs Audrey Shaw for language revision of the manuscript. We are grateful to the reviewers who provided helpful suggestions that improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Agencia Nacional de Promoción Científica y Tecnológica [PICT 2019-0026 to PEG; PICT 2016-0499 and PICT 2021-0068 to MCD]. P. E. García and M. C. Diéguez are CONICET researchers and C. F. Mansilla Ferro is a CONICET fellow.