A Further Study of the Zinc-Polluted River Ystwyth

Abstract

Zinc is present in the main stream near Aberystwyth in concentrations of 0.2-0.7 mg/l according to river level. The flora above the mines is rich, but below the sources of pollution, seems poor in quantity and variety. The fauna is almost entirely made up of lithophilous insects. Quantitative sampling of the stony stream-bed near Aberystwyth in the spring of 1953 indicated animal populations of 161 to 373/2500 sq cm Rhithrogena semicolorata, Heptagenia lateralis, Baetis rhodani, Chloroperla tripunctata and Esolus parallelopipedus are the chief species. Detritus appears to be the main food source. Only 17 of the 279 insects examined had green algae in the gut. Brown trout now occur in the river. Though limited in variety the invertebrate fauna seems quantitatively adequate to feed a reasonable number of fish.