SEASONAL-VARIATIONS IN ACIDIC POLLUTANT INPUTS AND THEIR EFFECTS ON THE CHEMISTRY OF STEMFLOW, BARK AND EPIPHYTE TISSUES IN 3 OAK (QUERCUS PETRAEA (MATTUSCHKA) LIEBL WOODLANDS IN NW BRITAIN

Rainfall, throughfall and stemflow chemistry, bark chemistry and gaseous air pollutant levels were monitored for one year within three Quercus petraea (Mattuschka) Liebl. woodlands in north west Britain. Tissue chemistry of the epiphytic lichen Lobaria pulmonaria (L.) Hoffm. and the moss Isothecium myosuroides Brid. were also studied at the sites in which they were abundant. The sites were found to differ in the levels of acidic and nutrient inputs, bark chemistry and levels of gaseous pollutants, although the latter were low at all the sites. The epiphyte tissue chemistry responded to changes in stemflow chemistry across the season. At Borrowdale, Cumbria, where acid sensitive lichens have declined, stemflow was always of a low pH (3.5-4.5) and low nutrient content. The tissues of I. myosuroides at this site had low concentrations of nutrient cations, but a high nitrogen content, possibly due to a high nitrate input in the rainfall. It is concluded that acid precipitation will affect epiphytes by reducing the bark's buffering capacity and increasing its acidity. The extent to which this occurs will depend on tree species, soil chemistry and the nature of the atmospheric inputs. This is discussed in the context of the concept of critical loads for acidifying deposition.