Algal growth responses to waters of contrasting tributaries of the River Dee, north-east Scotland

Increasing legislative emphasis is being placed on the use of biological indices in water quality assessments. The majority of current techniques have been developed for use in standing waters. Similar techniques 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 which uses 3 alginate-immobilised algal species, and shows its practical use by measuring growth responses in two contrasting tributaries of the R. Dee. Growth was quantified using a non-destructive, automated absorbance scan (650 nm) across the surface of nylon-supported, thin ( 1 mm) films of alginate-immobilised algal cells. Significant differences (P<0.001) occurred between growth responses at the two sites, 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 either nitrogen or phosphorus added at 10 and 1 μg cm−3 respectively. The two methods provided consistent assessments of the water quality, although for different reasons; the eutrophic status of one river meant further N and P additions were not significant, and the chemical properties of a second river, such as pH, may have been the growth-limiting factors. This preliminary field assessment shows the alginate film method is sensitive, tough and durable, and allows continual, site-specific, assessment of water quality. We also discuss the adaptability and potential standardisation of this bioassessment method.