ALGAL GROWTH-RESPONSES TO WATERS OF CONTRASTING TRIBUTARIES OF THE RIVER DEE, NORTHEAST SCOTLAND

Increasing legislative emphasis is being placed on the use of biologic al indices in water quality assessments. The majority of current techn iques have been developed for use in standing waters. Similar techniqu es are needed which provide in situ biological assessments of flowing waters, which should intrinsically include all of the time-integrated factors controlling algal growth. This paper presents a biomonitor whi ch uses 3 alginate-immobilised algal species, and shows its practical use by measuring growth responses in two contrasting tributaries of th e R. Dee. Growth was quantified using a non-destructive, automated abs orbance scan (650 nm) across the surface of nylon-supported, thin (sim ilar to 1 mm) films of alginate-immobilised algal cells. Significant d ifferences (P < 0.001) occurred between growth responses at the two si tes, and between the responses of individual algal species. These data are compared with the results obtained from a laboratory-based, free- cell bioassay, which suggested that growth was not being limited by ei ther nitrogen or phosphorus added at 10 and 1 mu g cm(-3) respectively . The two methods provided consistent assessments of the water quality , although for different reasons; the eutrophic status of one river me ant further N and P additions were not significant, and the chemical p roperties of a second river, such as pH, may have been the growth-limi ting factors. This preliminary field assessment shows the alginate fil m method is sensitive, tough and durable, and allows continual, site-s pecific, assessment of water quality. We also discuss the adaptability and potential standardisation of this bioassessment method. (C) 1998 Elsevier Science Ltd. All rights reserved.