a Data for Planktothrix is per 1 mm length of filament.

b From compilation of previously unpublished measurements of field-collected material, as specified in Reynolds (1984a). c From Nalewajko (1966). d From later data of Reynolds (see 1997a).

Source: List assembled by Reynolds (1984a) from thitherto unpublished field data, and from data of Nalewajko (1966).

planktic cells will be equivalent to between 0.41 and 0.47 pg ^m-3. In fact, the data suggest an order-of-magnitude range, from 0.10 to 1.65 pg ^m-3. In part, this reveals an inherent danger in the interpretation of a wide spread of raw data through log/log representations. Caution is required in interpolating species-specific derivations from a general statistical relationship. However, the additional difficulty must also be recognised that the regression is fitted to phytoplank-ton of considerable structural variation (vacuole space, carbonate or silica impregnation of walls). Accumulated dry mass is also influenced by the physiological state of cells and the environmental conditions obtaining immediately prior to the harvesting of the analysed material. It is, perhaps, surprising that the data used to construct Table 1.3 and Fig. 1.8, based on analyses of material drawn largely from wild populations, should show any consistency at all. Thus, the patterns detected are worthy of slightly deeper investigation.

For instance, the variation in the percentage ash content (where known) appears to be considerable. Nalewajko (1966; see also Table 1.3) found that ash accounted for between 5.3% and 19.9% (mean 10.2%) of the dry weights of 16 species of planktic chlorophytes but for between 27% and 55% (mean 41.4%) of those of 11 silicified diatoms.

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