Assessing DOC export from a Sphagnum ‐dominated peatland using δ 13 C and δ 18 O–H 2 O stable isotopes

• Published in: Hydrological processes 2019-10, Vol.33 (21), p.2792-2803
• Main Authors: Buzek, Frantisek, Novak, Martin, Cejkova, Bohuslava, Jackova, Ivana, Curik, Jan, Veselovsky, Frantisek, Stepanova, Marketa, Prechova, Eva, Bohdalkova, Leona
• Format: Article
• Language: English
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.13528

Dissolved organic carbon (DOC) originating in peatlands can be mineralized to carbon dioxide (CO 2 ) and methane (CH 4 ), two potent greenhouse gases. Knowledge of the dynamics of DOC export via run‐off is needed for a more robust quantification of C cycling in peatland ecosystems, a prerequisite for realistic predictions of future climate change. We studied dispersion pathways of DOC in a mountain‐top peat bog in the Czech Republic (Central Europe), using a dual isotope approach. Although δ 13 C DOC values made it possible to link exported DOC with its within‐bog source, δ 18 O H2O values of precipitation and run‐off helped to understand run‐off generation. Our 2‐year DOC–H 2 O isotope monitoring was complemented by a laboratory peat incubation study generating an experimental time series of δ 13 C DOC values. DOC concentrations in run‐off during high‐flow periods were 20–30 mg L −1 . The top 2 cm of the peat profile, composed of decaying green moss, contained isotopically lighter C than deeper peat, and this isotopically light C was present in run‐off in high‐flow periods. In contrast, baseflow contained only 2–10 mg DOC L −1 , and its more variable C isotope composition intermittently fingerprinted deeper peat. DOC in run‐off occasionally contained isotopically extremely light C whose source in solid peat substrate was not identified. Pre‐event water made up on average 60% of the water run‐off flux, whereas direct precipitation contributed 40%. Run‐off response to precipitation was relatively fast. A highly leached horizon was identified in shallow catotelm. This peat layer was likely affected by a lateral influx of precipitation. Within 36 days of laboratory incubation, isotopically heavy DOC that had been initially released from the peat was replaced by isotopically lighter DOC, whose δ 13 C values converged to the solid substrate and natural run‐off. We suggest that δ 13 C systematics can be useful in identification of vertically stratified within‐bog DOC sources for peatland run‐off.