Peatland hydrology and carbon release: why small-scale process matters

Peatlands cover over 400 million hectares of the Earth's surface and store between one-third and one-half of the world's soil carbon pool. The long-term ability of peatlands to absorb carbon dioxide from the atmosphere means that they play a major role in moderating global climate. Peatlands can also either attenuate or accentuate flooding. Changing climate or management can alter peatland hydrological processes and pathways for water movement across and below the peat surface. It is the movement of water in peats that drives carbon storage and flux. These small-scale processes can have global impacts through exacerbated terrestrial carbon release. This paper will describe advances in understanding environmental processes operating in peatlands. Recent (and future) advances in high-resolution topographic data collection and hydrological modelling provide an insight into the spatial impacts of land management and climate change in peatlands. Nevertheless, there are still some major challenges for future research. These include the problem that impacts of disturbance in peat can be irreversible, at least on human time-scales. This has implications for the perceived success and understanding of peatland restoration strategies. In some circumstances, peatland restoration may lead to exacerbated carbon loss. This will also be important if we decide to start to create peatlands in order to counter the threat from enhanced atmospheric carbon

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Non peer reviewe

A video simulating the growth of a raised bog

The late Hugh Ingram (HAPI) contributed many things to our knowledge of peatlands. The two best known are probably the acrotelm/catotelm terminology (Ingram 1978), and the application of Childs & Youngs (1961) hemi-elliptical groundwater mound to the cross-section of raised bogs (Ingram 1982). As a tribute to HAPI, I combine these concepts with three others to create a video showing the development of a notional raised bog during 10,000 years. After that, I consider some of the limitations of this simplistic model and why, nevertheless, it is still useful

Why are there few gas bubbles in deep peat in British raised and blanket peat bogs?

(1) There is evidence of gas-filled voids - ‘bubbles’ - in deep (> 50–100 cm) peat in North America. (2) I used corers, designed to collect samples of accurately known volume, to sample peat profiles down to maximum depth 700 cm at five varied bog sites in northern England and southern Scotland, and measured the proportion of space apparently occupied by bubbles. (3) Of 126 samples in peat below 50 cm depth, three had bubbles occupying 12–15 % of the volume (and one of these was at only 55 cm depth). The other 123 had apparent bubbles distributed in Gaussian fashion, positively and negatively, about zero proportion of total volume and with standard deviation less than 2 %, consistent with these ‘bubbles’ being measurement error. (4) In northern England and southern Scotland, compared with North America, less variable temperature and cooler summers may lead to concentrations of dissolved gas that are generally too low to allow bubbles to form. Even where bubbles do form in summer, they may re-dissolve at winter temperatures

Diffusion and mass flow of dissolved carbon dioxide, methane, and dissolved organic carbon in a 7-m deep raised peat bog

In 65 samples, we got values (unusually replicable and consistent for this type of work) of concentration, 14C/13C (AMS) age, and δ13C for: peat, dissolved organic carbon (DOC), peat fractions, and dissolved CO2 and CH4 at 50-cm intervals down to 700 cm in Ellergower Moss, a rainwater-dependent raised (domed) bog in southwest Scotland. (1) We attribute the consistency of the results to Ellergower Moss being unusually homogeneous, with unusually low hydraulic conductivity, and containing only a few gas spaces; and to the sampling methods including 18-month equilibration of in situ samplers. (2) The dissolved gas concentration depth profiles are convex and very similar to each other, though CO2 is 5–10 times more concentrated than CH4, while the profile of DOC is concave. (3) The age profile of peat is near linearly proportional to depth; that for DOC is about 500–1000 yr younger than the peat at the same depth; the dissolved gases are 500–4300 years younger than the peat. The age of the operational peat fractions humic acid and humin is similar to that of whole peat. (4) The δ13C profile for deep peat is almost constant; δ13C–CO2 is more enriched than the peat (δ13C–CO2 35‰ more); δ13C–CH4 is the same amount more depleted. Nearer the surface both dissolved gases become steadily more depleted, δ13C is about 20‰ less at the surface. (5) A simulation shows that mass flow can account for the concentration and age profiles of DOC, but for the gases diffusion and an additional source near the surface are needed as well, and diffusion accounts for over 99% of the dissolved gas movements. (6) The same processes must operate in other peatlands but the results for Ellergower should not be extrapolated uncritically to them

A tentative dry matter balance sheet for the wet blanket bog on Burnt Hill, Moor House NNR

A dry matter balance is made for some Spaghnum dominated areas of blanket bog at 575m altitude in the Pennine Hills of Great Britain. Productivity of Sphagnum in pools in about 2.9g dm-2 yr-1, on lawns about 3.4g dm-2 yr-1 and on hummocks about 1.8g dm-2 yr-1. Mean gas loss is about 1.5, 0.9 and 1.3g (CH2) dm-2 yr-1 from the corresponding habitats. Loss in solution averages about 0.2g dm-2 yr-1, but distinction between habitats is not made

An extraordinary peat-forming community on the Falkland Islands

Most of Beauchêne Island in the South Atlantic is covered by tussac, the tussock-forming grass Poa flabellata (Lam.) Rasp., which has produced a deep accumulation of exceptionally dense peat during ∼12,500 yr. The basal peat is lignitic, yet it is several hundred times too young to be a true lignite. During an ecological survey of the island in December 19801, one of us (R.I.L.S.) sampled an 11-m high peat face. The age against depth profile in the peat is consistent with a constant proportional rate of decay of 1.1–2.2×10−4 yr−1 and a constant rate of addition of dry matter to the peat of 430–720 g m−2 yr−1. This rate of decay is within the range recorded for peats in corresponding latitudes in the Northern Hemisphere, but the rate of addition of dry matter is about 10 times as great. This is not easy to accommodate within current hypotheses about peat formation. An unusual combination of biological, physical and chemical circumstances may be the cause. As the island is difficult to visit and no more information can be obtained in the near future, we now report these results, incomplete though they are