Impact Type: Direct exposure to pollutant
Studies in relation to nitrogen oxide pollution gradients are limited and the is a need for further research (Mulgrew & Williams 2000). Morgan et al. (1992) have shown that exposure to NOX can affect the assimilation of wet deposited nitrogen in a range of bryophyte species (Ctenidium molluscum, Homalothecium sericeum, Pleurozium schreberi and Hylocomium splendens). However, these plants can recover their normal nitrogen metabolism after a pollution-free period. In the long term it is unlikely that NOX will be a major cause of toxicity problems at typical rural concentrations, but deposition of NOX will add to overall nitrogen loading (Lee et al. 1993). The accumulation of the isotope 15N in mosses close to roads has been suggested as an indicator of NOX exposure (Pearson et al., 2000).
One of the few studies which has been carried showed that the distribution of epiphytic bryophytes was less where NO2 levels were > 0.02 ppm (Inui and Yamaguchi, 1996).
|Critical Load/ Level|
No estimate available