Peatlands play an important role in modulating the climate, mainly through sequestration of carbon dioxide into peat carbon, which depends on the availability of reactive nitrogen (Nr) to mosses. Atmospheric Nr deposition in the UK has been above the critical load for functional and structural changes to peatland mosses, thus threatening to accelerate their succession by vascular plants and increasing the possibility of Nr export to downstream ecosystems. The N balance of peatlands has received comparatively little attention, mainly due to the difficulty in measuring gaseous N losses as well as the Nr inputs due to biological nitrogen fixation (BNF). In this study we have estimated the mean annual N balance of an ombrotrophic bog (Migneint, North Wales) by measuring in situ N2 + N2O gaseous fluxes and also BNF in peat and mosses. Fluvial N export was monitored through a continuous record of DON flux, while atmospheric N deposition was modelled on a 5 × 5 km grid. The mean annual N mass balance was slightly positive (0.7 ± 4.1 kg N ha−1 y−1) and varied interannually indicating the fragile status of this bog ecosystem that has reached N saturation and is prone to becoming a net N source. Gaseous N losses were a major N output term accounting for 70% of the N inputs, mainly in the form of the inert N2 gas, thus providing partial mitigation to the adverse effects of chronic Nr enrichment. BNF was suppressed by 69%, compared to rates in pristine bogs, but was still active, contributing ~2% of the N inputs. The long-term peat N storage rate (8.4 ± 0.8 kg N ha−1 y−1) cannot be met by the measured N mass balance, showing that the bog catchment is losing more N than it can store due its saturated status.
|Number of pages||11|
|Journal||Science of the Total Environment|
|Early online date||15 May 2021|
|Publication status||Published - 15 Sept 2021|
Bibliographical noteFunding Information:
The authors wish to acknowledge and thank staff at the UK Centre for Ecology & Hydrology (Bangor), who deployed and maintained instream optical sensors and Dwr Cymru Welsh Water (DCWW) for allowing access to the data. This research draws upon published datasets available through the Environmental Information Data Centre (hosted by UKCEH), funded under the Natural Environment Research Council (NERC) Macronutrient Cycles Programme. Stage discharge data along with the sampling and analysis of instream chemical variables were conducted under ‘Turf 2 Surf’ project (NERC; NE/J011991/1). Measurements of N 2 and N 2 O along with atmospheric deposition data were funded under the LTLS project (NERC; NE/J011541/1, NE/J011533/1 and NE/J011703/1 respectively). A special thanks goes to Edward Tipping and Hannah Toberman who carried out all the sampling and analysis in peat cores collected in the Migneint.
© 2021 The Authors
- N isotopes
- Atmospheric N deposition
- Biological nitrogen fixation
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal