CURRENT AND HISTORICAL RELATIONSHIPS BETWEEN THE TISSUE NITROGEN-CONTENT OF A SNOWBED BRYOPHYTE AND NITROGENOUS AIR-POLLUTION

Snowbed vegetation is under threat from atmospheric pollution. Most of the late lying snowbeds in Britain are in the central highlands of Sc otland, coinciding with an area of very high deposition of nitrogenous air pollutants. Snow is a very efficient scavenger of atmospheric pol lution and, due to the dynamics of snowmelt, much of the pollution loa d of a snow pack is released at very high concentrations in episodes k nown as 'acid flushes'. This study demonstrates the existence of a pos itive relationship between duration of snow-lie and tissue nitrogen co ntent of Kiaeria starkei, a bryophyte characteristic of late snowbeds. An increase in the tissue nitrogen content of this bryophyte over thi s century is also shown, reflecting increasing air pollution. Maximum tissue nitrogen concentration in K. starkei is up to 50% greater than that recorded in other upland bryophyte species, demonstrating the exc eptional threat of pollution to snowbed bryophytes. This has implicati ons for the critical loads approach to pollution emission controls, as it indicates that some mountain communities are receiving higher poll ution loadings than previously realised and therefore current exceeden ce of critical loads is probably greater than recognised at present.