PRIMARY PRODUCTION STUDIES IN 2 LINKED BUT CONTRASTING WELSH LAKES

SUMMARY. Llyn Padarn and Llyn Peris have distinct phytoplankton populations. During 1975–76, the standing crop measured as chlorophyll‐a was 5.5 times greater in Padarn than in Peris and the production rate, determined by the 14CO2 method, was faster by 3.4 times. These differences were attributed to the higher concentrations of phosphorus in the lower lake caused by treated sewage effluent. Incident light intensity, which was slightly lower in Peris due to mountain shading, and temperature, which was 1–4°C higher in Padarn, made little significant contribution to these differences during the summer. The reduced transparency of Padarn water, compared with that of Peris, resulted from denser phytopiankton crops in Padarn. During the summer, Padarn exhibited carbon dioxide depletion which correlated with the chlorophyll concentration. Light inhibition at the surfaces of both lakes correlated with solar radiation intensity. However, the relationship between pigment content and maximum photosynthetic rate was poor. Extracellular products accounted for about 16% of the total production in the lakes. Uptake of 14C‐labelled acetate was low compared with that of 14CO2 uptake. Copyright © 1978, Wiley Blackwell. All rights reserved