Journal of Conference Abstracts

Comparative Measurements of Carbon Exchange
Between Peatlands Systems, the Atmosphere and
Streams in Scotland

Michael F. Billett¹ (m.billett@abdn.ac.uk), Diane Hope¹ (di.hope@abdn.ac.uk),
Ken J. Hargreaves² (kenh@ite.ac.uk) & David Fowler² (d.fowler@ite.ac.uk)

¹ Department of Plant & Soil Science, Cruickshank Building, University of Aberdeen,
Aberdeen, AB24 3UU, Scotland, U.K.

² Institute of Terrestrial Ecology, Edinburgh Research Station, Bush Estate, Penicuick,
Midlothian, EH26 0QB, Scotland, U.K.

Recent research has shown that on a national basis riverine losses of organic C in the UK (0.9 Mt yr^-1) are of a similar magnitude to C uptake by wetlands and afforestation (Hope et al., 1997). In the context of global climate change, it is therefore important to establish the magnitude of riverine fluxes to other important pathways in the C cycle, such as the exchange of C between the land surface and the atmosphere. Quantification of riverine fluxes involves the measurement of various components including dissolved and particulate organic/inorganic C and free CO₂ and CH₄. Gas exchange at the land surface involves measurement of fluxes of CO₂ and CH₄.

This paper aims to combine flux measurements traditionally made by atmospheric physicists at the land-atmosphere interface (typically carried out over a few days), with those made by hydrochemists (carried out over a year or more). In a regional context Scottish soils contain 71 % of the total UK soil carbon pool (Milne and Brown, 1997) and therefore represent the major C pool in the UK.

The study sites are located in 2 contrasting regions of Scotland where comparative measurements of C exchange between peatlands, the atmosphere, and streams are currently being made. The 2 study sites are at Auchencorth Moss in Central Scotland and Bealach Burn in Northern Scotland. The former is an undisturbed lowland, peatland catchment covering an area of 2.3 km² and the latter a disturbed upland catchment, with a catchment area of 1.7 km², which has recently been ploughed for forestry.

At Auchencorth Moss, simultaneous measurements of CO₂ fluxes from the land surface to the atmosphere and C losses in streamwater began in August 1996. Carbon dioxide land-atmosphere fluxes are being measured with an eddy covariance measurement system using a LICOR gas analyser (Fowler, et al. 1995). Streamwater C fluxes are being estimated from weekly sampling for DOC, DIC, POC, CO₂ and CH₄. Discharge at the site is also measured on a weekly basis. At Bealach Burn simultaneous measurements of riverine and land-atmosphere fluxes were carried out over a 48 hour period in February 1997. These were based on the same methods as used at Auchencorth Moss, with streamwater fluxes calculated from samples collected every 4 hours and continuous discharge measurements.

Initial results suggest that at Auchencorth Moss the net annual CO₂ flux from the atmosphere to the land surface is ca. 250 kg C ha^-1; this compares to streamwater DOC losses estimated at ca. 300 kg C ha^-1. These results will be compared to flux estimates from the disturbed system in Northern Scotland and the findings discussed in terms of the role which streams may play in the regulation of C accumulation in the soil-plant system.

References

Fowler, D., Hargreaves, K.J., MacDonald, J.A. & Gardiner, B. Forestry 68, 327-334 (1995).

Hope, D., Billett, M.F., Milne, R. & Brown, T.A.W. 1997. Hydrol. Proc. (in press).

Milne, R. & Brown, T.A. W. 1997. J. Environ. Manage. (in press).