A novel in-situ biomonitor using alginate immobilised algae (Scenedesmus subspicatus) for the assessment of eutrophication in flowing surface waters

A technique has been developed using alginate-immobilised algae that is suitable for in-situ biomonitoring of flowing waters. This approach will facilitate the site-specific assessment of eutrophication in running waters and the prediction of ecosystem response to altered nutrient inputs. Effects of the cell immobilisation process were assessed and it was demonstrated that entrapment increased the rate of response to, and growth in, increased nutrient supply compared to free cells, although this effect was not significant at environmentally relevant nutrient concentrations. Significant differences in growth were detected when nutrients were supplied at a constant concentration but at different flow rates (0.5, 16 and 230 cm3 min−1). Growth was determined as the rate of change in algal biomass measured using a non-destructive, automated scan of the absorbance (650 nm) across thin ( 0.75–1 mm) nylon-supported films of immobilised algal cells. This novel technique was compared with the established methodologies of chlorophyll-a extraction and cell enumeration as measurements of algal biomass. All three methods showed that algal growth was inversely related to flow rate of growth medium over the immobilised cells. These results demonstrate the value of this technique as a tough, durable and sensitive method for the continuous, or “on-line”, water monitoring of algal growth potential in running waters.