The recovery of the river Twymyn from lead mine pollution and the zinc loading of the recolonising fauna

Comparison of the present study with historical records of the distribution of animal life in the Twymyn indicated that the recovery of parts of the river reported in previous years has continued and that macro-invertebrates have completely recolonised the river up to the spoil heaps at Dylife, the source of the pollution. The number of species at the source of the pollution was, however, still 50% of the number found downstream where the effects of the pollution were diluted. Although invertebrate recolonisation has been complete in all but diversity the Twymyn is still fishless above a point where residual heavy metal pollution restricts brown trout populations through acute zinc toxicity and chronic lead toxicity. Nevertheless brown trout have moved further upstream than was recorded previously and over the long term may continue to do so if the diminution of residual lead and zinc in the Dylife spoil heaps also continues.A gradient of dissolved environmental zinc concentrations existed within the Twymyn system at the time of the study as a consequence of ancient mining activities. A direct result of animals recolonising against this zinc gradient has been an increased body loading of zinc in both macro-invertebrates and brown trout tissues which was dependent upon environmental zinc concentrations.