Are metal ions accumulated by saxicolous lichens growing in a rural environment?

The levels of Mn, Cu, zn, Mg and Ca were measured in the lichens Xanthoparmelia conspersa (Ach.) Hale and Parmelia glabratula ssp. fuliginosa (Fr. ex Duby): Laund. growing on a steep slate rock surface in south Gwynedd, Wales, UK. The objective was to test the following hypotheses: 1) that foliose lichens growing in a rural environment concentrate metal ions relative to the substratum, 2) that the concentration of metal ions increases significantly with thallus size and 3) that individual ions accumulate preferentially either in the marginal lobes or thallus centre. Mg and Ca were present in rainfall whereas all ions were present in rock surface runoff and in the substratum. Levels of Mn, Mg and Ca were increased in runoff collected from the bottom compared with the top of the rock surface. In P. glabratula ssp. fuliginosa thalli, ions were present as follows, Mg > Ca=Mn=Zn>Cu, and there were no significant differences in thalli collected from the top and bottom of the rock surface. With the exception of Mg and Ca, ion levels in thalli were similar to or less than those in the substratum. The levels of Ca, Cu and Zn were similar in thalli from under 1 to over 4 cm in diameter. However, the level of Mg increased with thallus size in X. conspersa while the level of Mn decreased with thallus size in both species. Ion levels were similar in the marginal lobes and centres of large diameter (over 4 cm) and small diameter (under 2 cm) X. conspersa thalli. With the exception of Mg, there was no evidence for a significant accumulation of ions relative to the substratum or with thallus size. In addition, there was no evidence to suggest preferential accumulation of ions either in the thallus centre or marginal lobes.

The response of lichen growth to additions of distilled water, rainwater and water from a rock surface

Three lichen species were wetted in the field with distilled water, rainwater or water which had run off a rock surafce, during July 1974 to February 1975. The radial growth rate of Parmelia glabratula ssp. fuliginosa was not influenced by the wetting treatments. The radial growth rate of P. conspersa with the distilled water was greater than the control, rainwater and runoff treatments. The radial growth rate of Physcia orbicularis was lower with rainwater and runoff treatmentss than the control and distilled water treatment. These results may be explained by the effect of wetting on the carbon balance of the lichens and by the influence of water chemistry.

Pathways utilized by heavy metal pollutants in urban stormwater runoff

The research concerned the assessment of the pathways utilized by heavy metal pollutants in urban stormwater runoff. A separately sewered urban residential catchment of approximately 107 hectares in Chelmsley Wood, north-east Birmingham was the subject of the field investigation. The catchment area, almost entirely residential, had no immediate industrial heavy metal input, however, industry was situated to the north of the catchment. The perimeter of the catchment was bounded by the M6 motorway on the northern and eastern sides and was believed to contribute to aerial deposition. Metal inputs to the ground surface were assumed to be confined to normal suburban activities, namely, aerial deposition, vehicular activity and anthropological activities. A programme of field work was undertaken over a 12 month period, from July 1983 to July 1984. Monthly deposition rates were monitored using a network of deposit cannisters and roadside sediment and soil samples were taken. Stormwater samples were obtained for 19 separate events. All samples were analysed for iron, lead, zinc, copper, chromium, nickel and cadmium content. Rainfall was recorded on site with additional meteorological data obtained from local Meteorological Offices. Use was made of a simple conceptual model designed for the catchment to substantiate hypotheses derived from site investigations and literature, to investigate the pathways utilized for the transportation of heavy metals throughout the catchment.