Studies on epilithic and epiphytic diatoms in a chalkstream: Comparative estimates of chlorophyllaand its derivatives

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Abstract
The nutrient-rich chalk streams of southern Britain are characterized by extensive spring growths of epilithic and epiphytic diatoms. The solids suspended in these waters reflect the diatom growth on the bed of the stream, and their growth was monitored from late winter to midsummer by estimating chlorophyll a and its most significant pigmented degradation products. During 1985, chlorophyll a concentration was lowest in winter (-1) and was highest at the end of April (c. 25 μg 1-1). Phaeopigments were highest in winter (c. 10 μg 1-1) and lowest in mid summer (60%). During winter phaeophytin a was the most significant breakdown product (>30%). In summer the relative importance of phoaeophorbide a increased (c. 25%) while that of phaeophytin a decreased (a, etc.) never accounted for more than a few % of the total chlorophyll pigments, even during the decline of the diatom population. The results suggest that in late spring, live cells rather than dead cells are being lost downstream in the suspended solids or into the sediment.