Bog habitats

The Ecosystem Overviews provide a summary introduction to the main habitat types covered in APIS and the main air pollutant pressures to those habitats in the UK. In specific locations, e.g.. close to a major source, other pollutants may be a concern for a habitat and the user should use the searches by location or by habitat/pollutant in these cases.

Introduction

The UK has over 2 million hectares of blanket and raised bogs making up significant proportion of the world's resource (BAP website) . Bog habitats divide into two types, raised bogs and blanket bogs. These are both priority habitats under the UK Biodiversity Action Plan. Raised bogs are typically described as being a discrete single dome of peat with a "halo" of lagg fen (Bragg & Tallis 2001). Blanket bog may consist of morphological units similar to raised bogs, but they are typically joined together by thin areas of peat at the edges. These ecosystems - often described as 'ombrotrophic' (rain-fed) mires - are especially sensitive to nitrogen air pollutants, and may be sensitive to ozone.

Typical bog species include the important peat-forming species, such as bog-mosses Sphagnum spp. and cottongrasses Eriophorum spp., or purple moor-grass Molinia caerulea in certain circumstances, together with heatherCalluna vulgaris and other ericaceous species.

BAP Habitats: Blanket bog (priority); Lowland raised bog (priority)

Main Pollutant Impacts

Nitrogen deposition

Bogs are highly sensitive to nitrogen deposition, as they derive all their nutrients from the atmosphere. In the UK around 50% of bog Broad Habitat exceeds the critical load for nutrient nitrogen (using 2006-2008 deposition data). Exceedance of the nitrogen critical load for bogs leads to preferential growth of more competitive nitrogen-loving species, especially grasses. For example, sphagnum mosses can be overgrown and shaded out by Calluna and hypnaceous mosses (Sheppard et al, 2008). This can have a substantial impact on the development of bog systems. Coupled to these changes, the presence of less dominant associated herbs, bryophytes and lichens may change accordingly.

Ammonia

Direct exposure to high concentrations of ammonia can lead to direct damage of sensitive bog species including leaf discolouration, and the bleaching of Sphagnum species and Cladonia. There is also an increase in algal growth on the thallus of lichens, and the Sphagnum hummock structure breaks down leading to bare patches of peat increasing the likelihood of erosion. Changes in the composition of groundflora, bryophyte and lichen communities are also observed.

Ozone

There are only a few studies on the sensitivity to ozone of species associated with bogs including Calluna vulgaris and some bryophytes species. There is some evidence that this habitat is sensitive. However, further studies of bog communities are essential to evaluate the longer-term effects on this community (Morrissey et al, 2007).

Acid Deposition

Over 75% of Bog Broad Habitat in the UK is exceeded for its acidity critical load (2006-2008 deposition data). Soil acidification affects the functioning of peat ecosystems including reduced decomposition, sulphate reduction, nitrate uptake, organic acid production, together with a decline in peat pH and drainage waters. An important consequence of acidification is an enhanced level of aluminium (Al3+) in the soil solution which can be toxic to plant roots at high concentrations. This has also led to the changes in vegetation composition including a decline in bryophytes (Sphagnum spp) and species diversity (Drosera spp).

Further information and resources:

JNCC habitat pages
UK Research on the Eutrophication and Acidification of Terrestrial Ecosystems.

References: 

Bragg, O.M.; Tallis, J.H. 2001 The sensitivity of peat-covered upland landscapes Catena 42 345-360
Morrissey, T.; Ashmore, M.R.; Emberson, L.D.; Cinderby, S.; Buker, P. 2007 The impacts of ozone on nature conservation JNCC 403
Sheppard, L.J.; Leith, I.D.; Crossley, A.; Dijk, N.; Fowler, D.; Sutton, M.A.; Woods, C. 2008 Stress responses of Calluna vulgaris to reduced and oxidised N applied under 'real world conditions' Environmental Pollution 154 404-413