N deposition :: Baltic bog moss

Impact Type: Deposition of pollutant

Key Concerns:

Sphagnum balticum is a Red Data book species and is listed under the UK Biodiversity Action Plan (DoE 1994).
There is extensive evidence to suggest that increasing N deposition is affecting the growth and metabolism of ombrotrophic Sphagnum species (Press et al. 1986). Experimental additions of nitrate and ammonium within the range observed in rainfall in the southern Pennines, and the decline in health and survival of Sphagnum communities in areas of Wales and the southern Pennines have been related to increased atmospheric N deposition (Woodin & Farmer 1993). Tissue N content of ombrotrophic Sphagna is also related to N deposition, being much larger in areas of high N deposition (e g. Cumbria) than in the cleaner areas of North West Scotland (Pitcairn et al. 1995).

Additional Comments:

Different sphagnum species respond differently to NH₄⁺ and NO₃^- (Risager 1998). Carfrae et al 2002 showed changes in the ratio of oxidised to reduced Nitrogen could potentially alter the balance between different Sphagnum species growing in bogs. Response to nitrogen is dependent on the availability of Potassium, and is also influenced by the height of the water table (Williams et al 1999). Nitrogen tends to accumulate in the Sphagnum as amino acids so that initially almost none of the additional nitrogen is available to other plant species. Aerts et al (1992) recorded a 4 fold increase in the growth of S. balticum in response to additions of 20 and 40 kg N in Sweden (background 0.4 kg N ha^-1 yr-1). Growth stimulation is phosphorous dependent.