Yellow substance (gelbstoff) and its contribution to the attenuation of photosynthetically active radiation in some inland and coastal south-eastern Australian waters

Abstract

The absorption spectra relative to distilled water of samples from various inland and coastal waters in south-eastern Australia (New South Wales and the Australian Capital Territory) have been measured. Amongst the freshwater samples the level of dissolved yellow substance (gelbstoff) was found to vary seven-fold (the base-10 logarithm absorption coefficient at 440 nm ranged from 0.42 to 2.90 m-1). In coastal sea water the concentration was much lower than in any of the freshwater samples (absorption coefficient 0.01-0.08 m-1 at 440 nm). Calculations have been carried out of the contribution made by yellow substance to attenuation of photosynthetically active radiation (PAR). In the inland waters yellow substance has a dominating influence on light attenuation, reducing the amount of PAR many-fold, and the blue region of the spectrum is abolished at quite moderate depths. In all cases except sea water it was calculated that most (60-80%) of the quanta captured are absorbed by yellow substance rather than by water. An alternative name, 'gilvin' (Latin, gilvus = pale yellow), for the yellow pigments in natural waters, to replace 'yellow substance' or 'gelbstoff ', is suggested.