INTERSPECIFIC DIFFERENCES IN METAL BIOACCUMULATION AND PLANT WATER CONCENTRATION RATIOS IN 5 AQUATIC BRYOPHYTES

We studied the capacity of five species of aquatic bryophyte to accumu late metals, and the relationship between plant metal content and wate r composition, on the basis of 170 samples taken from 32 rivers in Gal icia (NW Spain). In all cases, only the final two centimetres of the a pex were analysed. Scapania undulata was the species with the highest accumulatory capacity, and Fissidens polyphyllus was that with the low est. Fontinalis antipyretica, Rhynchostegium riparioides and Brachythe cium rivulare displayed intermediate capacities for metal accumulation , but showed a broader range of variation in body concentration in com parison with similar contamination levels. This resolution capacity, t ogether with a greater resistance to pollution and, in the study regio n, a wider distribution and higher abundance, suggests that the latter two species are the most useful for bioindication studies. Bioaccumul ation factors were high for all metals studied, tending to increase wi th increasing body concentration but decreasing with increasing water concentration. The relationship between metal in plant and filtrable m etal in water was low, but statistically significant for all the metal s studied except Co in F. antipyretica and Cd, Pb and Co in S. undulat a, F. polypllyllus and B. rivulare. The influence of physical and chem ical variables of the water on bioaccumulation was evaluated using ste p-wise multiple correlation analysis. Bioaccumulation is largely gover ned by physical and chemical factors, by the concentration of metal in the water and by the bioaccumulation factor of the bryophyte species. Sulphate concentration, pH and to a lesser extent nitrite, ammonia an d FRP (filtrable reactive phosphate) appear to be the most important p hysical and chemical variables governing metal bioavailability.