Studies of tolerance to heavy metals in the flora of the rivers Ystwyth and Clarach, Wales

Summary A survey of the river Ystwyth demonstrated that it was polluted with metals especially below the areas of old lead mines. Hormidium spp. Kütz in particular Hormidium rivulare Kütz were the most tolerant filamentous green algae present. Scapania undulata (L.) Dum. was a tolerant bryophyte on the Ystwyth and Clarach rivers and was found alone in polluted sites, but was less frequent in cleaner areas. Metal extracts of this bryophyte mirrored the variation in metal concentrations of the environment to some extent. In general, lower levels of Fe, Pb and Mn were found in Scapania as compared with the less tolerant Fontinalis squamosa Hëdw. When the latter was transplanted to polluted sites an increase in its Pb, Cu, Zn and Mn content occurred within 6 weeks and the plant started to die and decay after 18 weeks. Scapania survived when it was transplanted from its natural polluted habitat to a less polluted area, and there was no marked change in its metal content. Zn 65 tracing experiments, in the laboratory, demonstrated that both plants had similar uptake patterns for the metal, but that the amount taken up was slightly higher in the less tolerant Fontinalis . There was no change in the number of diatoms found upon Scapania when it was transplanted, but a reduction in numbers occurred on the transplanted Fontinalis when it started dying. The composition of these diatom floras was different in polluted sites as compared to that in the cleaner areas.