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Licentiate thesis, 2016

Holocene carbon and nitrogen accumulation rates and contemporary carbon export in discharge

Larsson, Anna;

Abstract

The contemporary role of mires in land-atmosphere exchange of carbon dioxide (CO₂) is the subject of intense scientific debate. Investigating patterns and mechanisms of variations in past carbon (C) accumulation rates as well as contemporary C fluxes of peatlands facilitates predictions of future mire C sink strength under a changing climate. Nitrogen (N) is an important macro-nutrient and thereby strongly coupled to the C accumulation rate. Thus, I have investigated Holocene C and N accumulation rates and their potential controls, and the annual and seasonal stream C export during the Holocene at the oligotrophic fen Degerö Stormyr in northern Sweden. The mean (±SD) long-term apparent rates of C and N accumulation (LORCA and LORNA) were estimated to 13.7±5.5 g C m⁻² yr⁻¹ and 0.28±0.14 g N m⁻² yr⁻¹, respectively. These rates were relatively low compared to those of other northern peatlands. Variations in C and N accumulation rates exhibited similar temporal patterns largely coinciding with major changes in botanical remains, and mainly primary production controlled the accumulation rates. The botanical composition had a major impact on the degree of decomposition, with indications of enrichment of recalcitrant compounds in highly degraded peat, as well as differences in ¹³C-¹²C composition of litter at the onset of decomposition. There were also indications of preferential plant uptake of ¹⁴N at higher N availability. Stream total C export was primarily driven by discharge, with average annual C export estimated to 12.2 g m⁻² yr⁻¹ over twelve years. This flux typically corresponded to 25-37% of the mean annual net uptake of CO₂ (NEE). However, during a year with a dry summer and wet autumn the discharge C export corresponded to as much as 90%, highlighting the importance of seasonality. The highest TOC export was exhibited during summer when accounting for differences in discharge, underlining the importance of timing of precipitation for the seasonal C export. Seasonal variations in C quality (SUVA₂₅₄) indicate different within mire sources of TOC during the year. In this thesis I conclude the importance of primary production for C and N accumulation rates, and highlight the importance of seasonality for stream C export from mires.

Keywords

peat; mire; carbon accumulation; nitrogen accumulation; δ¹³C; δ¹⁵N; TOC; DIC; CH₄; stream carbon export

Published in


ISBN: 978-91-576-9372-3, eISBN: 978-91-576-9373-0
Publisher: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences

Authors' information

Larsson, Anna
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management

UKÄ Subject classification

Climate Research
Other Earth and Related Environmental Sciences

URI (permanent link to this page)

https://res.slu.se/id/publ/69325