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Abstract:
Variation in the algal standing crop on different substrata in an upland stream was assessed using chlorophyll-a as a measure. Chlorophyll level were considerably higher on soft sediments than on natural stones or sandstones tiles, and often approached levels recorded in lowland streams, estuarine or marine coastal habitats. After the flood period, spring and autumn peaks were observed on the epipelon in the middle reach of the stream. A dramatic reduction in chlorophyll levels occurred in March/April due to the spate. Seasonal fluctuations in standing crop were less obvious on natural stones, but spate discharge had a similarly drastic effect on the epilithon. In the spring region epilithic populations were less affected by flood while no clear effect was observed on the epipelon. The use of sandstone tiles as a hard substratum revealed that algal accumulation varied within and between sites, and with season. This was to some extent related to grazing pressure.
