Phytoplankton in the English Lakes: I. The Proportions in the Waters of Some Dissolved Substances of Biological Importance

Abstract

SINCE 1920, large numbers of observations have been made on the phytoplankton of the English lakes in the attempt to correlate its distribution and periodicity with the environmental factors. The main features were determined in 1921 and 19221 (12) and some attempt was made to determine the nature of the factors involved (9, 10). The methods available at that time for the estimation of the dissolved substances in the lake waters proved barely adequate or too cumbersome for the purpose, and in particular the phosphate content was too small for precise determination. Since then the valuable work of Atkins (1, 2) has brought into prominence refined and rapid methods of estimating phosphate and silica, and in 1928 a series of combined observations on the phytoplankton and the dissolved substances of the lake waters was carried out, in order to ascertain if any correlation could be traced between them'. The present paper deals with the water analyses. The collections were made at intervals of about six weeks (or less in summer) from nine lakes, the samples being obtained on two successive days. Each sample, of about two litres, was obtained from near the outlet of the lake-except those from Ullswater, which were collected off Stybarrow Crag. The samples were conveyed in bottles, which had been previously used for some time for the same purpose, and no material change in composition was detected. The analyses were started on the third day after collection. Regular determinations of phosphate, nitrate, silica, iron carbonate hardness and hydrogen-ion concentration were made. In addition, determinations of ammonia, albuminoid ammonia and calcium have been made when required. The methods used were as follows: Phosphate. The colorimetric method of Deniges as modified by Atkins (1) was employed, using tall clear glass tubes for the comparisons and 200 c.c. of water when the phosphate content was low. A blank determination was, with the reagents used, indistinguishable from 0*0005 part per million of phosphate P. It was found advisable always to employ two drops of stannous chloride to obviate the possible effects of occasional high nitrate. The figures, given as P, may be turned into P205 by multiplying by 4-59. For estimating phosphate in peaty waters, standards tinged to an appropriate colour with Bismarck Brown was used.