Some Observations on the Effects of Water Inflow and Outflow on the Plankton of Small Lakes

Abstract

1. Four years' observations on the plankton populations of four Scottish hill lochs have shown that their density tends to be highest and that they are most stable in lochs with a low rate of water replacement. 2. Detailed studies were made during the spring and summer of 1954 on the plankton and replacement of water in one of these lochs having a low rate of replacement and in another with a high rate in order to determine more precisely the influence of this factor. 3. These studies indicated that at times the rate of replacement may be a factor of over-riding importance and may produce not only quantitative but also qualitative differences in the plankton. 4. Some observations have been made on the effectiveness with which different species and age-groups of individual species of zooplankton can avoid being carried down the outflows of lochs. 5. The results of this investigation indicate that the standing crop of plankton cannot be used as a measure of the productivity of small lakes, particularly where the replacement of water may be considerable.