Accumulation of heavy metals by aquatic bryophytes in streams and rivers in northern England
A Study was made of the ecology of aquatic bryophytes and their accumulation of metals in rivers of northern England. Field surveys and experiments in the field and laboratory examined the effectiveness of bryophytes as monitors of heavy metal pollution. A survey of 105 river sites (10-m reaches) with Rhynchostegium riparioides was carried out, together with a seasonal survey of this species at seven sites, which also included data for two other species. Details of the aquatic bryophytes present, water chemistry and metal concentrations in mosses are given. The ecological ubiquity of Rhynchostegium was described using principal components analysis and discussed in relation to other macrophytes. A biometric study revealed that marked interpopulation differences in gametophytic characters were correlated with water chemistry variables (NH(_4)-N, PO(_4)-P, Cl, Na) indicative of organic pollution. Significant linear regressions were found between accumulation and aqueous concentrations of Zn, Cd, Ba and Pb. A multiple regression of these and other chonical data suggested several factors had significant effects on accumulation. Seasonal effects were largely chemical in nature, rather than a function of the plants themselves. Experiments supported several findings from the surveys. Zinc uptake proceeded more rapidly than loss and was influenced by aqueous Mg, Ca and humic acids, but not PO(_4)-P, NO(_3)-N or Si. Accumulation was greater in tips of Rhynchostegium than Amblystegium riparium or Fontinalis antipyretica. Results indicate that bryophytes are useful as monitors of pollution. Rhynchostegium in particular is recommended for its ecological ubiquity, its presence in a wide range of aqueous metals and greater accumulation. Applications of bryophytes for specific uses are outlined, with recommendations for different situations. A new model, based on slopes of accumulation, is proposed as a predictive tool.