D665 D665A INDEX VS FREQUENCIES AS INDICATORS OF BRYOPHYTE RESPONSE TO PHYSICOCHEMICAL GRADIENTS/

The chlorophyll-to-phaeophytin (D665/D665a) ratio is an index of physi ological stress in aquatic bryophytes. In the present study, the usefu lness of this index for evaluating water contamination was investigate d. Samples of bryophytes and water were collected from 188 stretches o f river in northwest Spain. Water quality was characterized by standar d procedures. Ecological profile methods were used to investigate (for each species and each water quality variable) whether stress index or frequency of occurrence varied significantly along environmental grad ients. Most stress profiles showed significant departures from uniform ity, whereas many frequency profiles did not, indicating that the stre ss index approach is more sensitive to differences in water quality th an are approaches based simply on presence/absence data. To further in vestigate relationships between water quality variables and D665/D665a ratio, canonical correspondence analysis (CCA) was used. The first ax is extracted by CCA was clearly closely related to degree of organic p ollution. The second axis was most strongly correlated with pH. Taken together, these results suggest that D665/D665a ratio in aquatic bryop hytes may be of value as an indicator of river water pollution.