Systematic errors of determination of pigments are also based on 

 incomplete collection of plant material by filtration. In particular, 

 some of the chlorophyll _a and its derivates pass through the No. 5 

 membrane filters used in the USSR (Koblentz-Mishke, Konovalov, 1974). 

 The magnitude of this error has never been estimated, but it is probably 

 not great, since the filters used by specialists of different countries 

 produce practically identical results, although their pore diameters are 

 significantly different (SCOR UNESCO, 1966). 



In the lower layers of the euphotic zone, one serious source of 

 systematic errors, leading to overestimation of the results of 

 determination of the content of photosynthetically active pigments, may 

 be the presence in samples of products of the transformation of these 

 pigments. Upon loss of the central Mg atom, chlorophyll is converted to 

 phaeophytin, upon loss of phytol--to chlorophyllide and upon loss of 

 phytol and Mg--to phaeophorbide. The absorption spectra in extracts 

 practically coincide for chlorophyll a_ and chlorophyllide £ and also for 

 phaeophytin a and phaeophorbide^ (Holt, Jacobs, 1954; Strickland, 1965; 

 Lorenzen, 19'67); therefore, standard spectrophotometric methods can 

 determine only the sum of chlorophyll plus chlorophyllide. If a sample 

 contains phaeophytin a^ or phaeophorbide a^, calculations by the standard 

 equations will lead to the overestimation of chlorophyll _a by a quantity 

 equal to 59% of the content of phaeopigments. Recording of the spectrum 

 of an extract after acidification (Lorenzen, 1967) allows a correction 

 to be introduced for the content of phaeopigments but cannot allow 

 separate determination of chlorophyll and chlorophyllide. 



Random errors in the determination of pigments, using the standard 

 spectrophotometric method, consist basically of errors in the reading of 

 transmission or extinction spectra. 



With the identical concentration of pigments, the accuracy of 

 determination of chlorophyll a^ is 2-3 times greater than that of 

 chlorophyll b_ and 4-6 times greater than that of chlorophyll c_. The 

 shortcomings of the standard method lead in many cases to great errors 

 in the determination of the content of chlorophyll h_ and chlorophyll _c 

 in phytoplankton (Strickland, Parsons, 1965; Madgwick, 1966; Wauthy, Le 

 Bourhis, 1966; Pyrina, Yelizarova, 1971). 



Chlorophyll a is the only pigment which is determined with 

 sufficient reliability by the standard method. If the samples contain 

 no products of decomposition of chlorophyll a^, parallel measurements of 

 its content by chromatographic and spectrophotometric methods yield 

 identical results (Madgwick, 1966). The systematic errors in deter- 

 mination of chlorophyll ^ by the fluorometric and spectrophotometric 

 methods usually lead to "overestimation of the results (if phaeopigments 

 are not determined). The relative random error of determination of this 

 pigment, as of primary production, increase with a decrease in its 

 concentration. 



Phytoplankton . Data on phytoplankton are required for physiologic 

 interpretation of the results of determination of primary production. 

 Of particular significance are data on the biomass (B) of phytoplankton, 

 expressed as primary production in mg C/m^ (^nhyt^' ^^ ^^^ present 



232 



