ALBERT

Notes: During the period April 1967-ApriI 1968 the phytoplankton production and respiration of the River Thames and its tributary, the River Kennet, were measured at approxi-mately 2-week intervals using the light and dark bottle technique. Concentrations of chlorophyll and pheopigment were determined weekly. On fourteen occasions sets of light and dark bottles were rotated in a specially designed apparatus, and production and respiration values obtained were found to be 1·38 ± 0·31 times higher than in stationary bottles at identical depths over the same period. There was little horizontal, vertical or diurnal variation in chlorophyll concentration showing that the water was well mixed. Peaks of chlorophyll were found in spring, summer and autumn in the Thames (max. 219 mg/m3) but there was very little variation in the Kennet (max. 38·2 mg/m3). In both rivers lowest concentrations were found during winter. Pheo-pigment concentration was low in both rivers for most of the period although in the Kennet this represented on average 50% of the pigments present. In the Thames a peak of pheopigments(1·33–5 mg/m3) was associated with the autumnal bloom and repre-sented 61 % of the total pigments. No pheopigments were detected during the spring bloom. The average concentration of suspended organic matter was identical in both rivers but in the Thames over 25 % was due to phytoplankton and in the Kennet almost 95 % was non-algal.In the Thames, net oxygen production reached a peak in May (10·81 gO2/m2/day) and was negative from November to February (min. −0·45 gO2/m2/day). In the Kennet, maximum production also occurred in May (0·85 gO2/m2) but was negative from the middle of May until the following March. The average annual net production was 1250 and −78 g O2/m2 in the Thames and Kennet respectively.Respiration rates showed similar fluctuations being 4·59 g O2/m2/day in spring in the Thames to 0·09 g O2/m2/day in November. The Kennet was almost always lower (1·05–0·34 g O2/m2/day. The average annual respiration was almost three times higher in the Thames than in the Kennet (641–228 g O2/m2).Various factors which might influence production are discussed. The average net efficiency ofthe Thames phytoplankton fell within ranges described from other rivers. Net efficiencies ofthe Kennet were almost always negative.In the Thames it appeared that net production could be explained as a function of solar radiation, chlorophyll concentration and euphotic depth.