An account is given of methods developed to monitor heavy metals in rivers by measuring the concentration of these metals in Fontinalis antipyretica Hedw. Key features of the standard method recommended include the harvesting of materials from microhabitats with fast current speeds wherever possible, thorough washing in field and laboratory, use of terminal 2-cm lengths of shoot, drying at 1050C and digestion in 2 M HNO 3 . In order to establish the extent to which this species is useful and to provide baseline data with which others can compare their own observations, samples of moss, water and sediments were harvested for analysis from 52 different sites in northern England and Belgium. Significant positive correlations were obtained between Cu and Zn in 2-cm tips and in both (total) water and sediment, but in the case of Cd and Pb only between 2-cm tips and sediment. Multiple stepwise regression was used to quantify the apparent influence of environmental variables. For instance, with Pb in the moss as the dependent variable, significant influences were found for Zn in the moss (+ve) aqueous Mn (+ve) and filtrable reactive phosphate (-ve). Variables which were significant were incorporated in each case into equations to predict the concentration of metal that would be expected if allowance was made for the concentrations of all these variables at each site. In the case of Pb, r 2 = 0.075 for metal in moss versus aqueous metal, whereas r 2 = 0.879 for metal in moss versus the predicted value for metal in moss. This suggests that the lack of correlation between Pb in moss and Pb in water was probably due largely to the influence of other variables. For Cd, the difference was less: r 2 = 0.013 and r 2 = 0.47, respectively. A principal components analysis was also carried out, with measurements of water and moss as the variables ordinated. An example is given of the use of the moss to monitor intermittent Zn pollution in R. Wear.

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An account is given of the chemistry and floristic composition of stream sites in a small catchment (1.2 km 2 ) with extensive waste from disused lead mines in the upper part of the catchment. One stream sequence provided a gradient of aquatic zinc levels from very high (R = 25.6 mg I' after passing through a filter) to relatively low ( = 1.2 mg I'). There was a negative correlation between the number of photosynthetic species present in a reach and the logarithm of the concentration of zinc. The flora at the site with the highest level of zinc was nevertheless comparatively rich, with 25 species, as opposed to a maximum of 41 species in any reach with elevated zinc. A reach in an unpolluted tributary had 61 species, I I of which were absent at all other reaches. A discussion is included of the extent to which the various floristic changes observed are likely to be a direct result of changes in zinc levels rather than of correlated changes such as flow regime.