Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake

1. Pelagic and epipelic microalgal production were measured over a year in a pre-defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata. 2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m(-2) year(-1)) than in the clearwater lake (141 g C m(-2) year(-1)). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake. 3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11-25%), when the water was relatively clear, than during summer (0.7-1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid-summer, when phytoplankton production was constrained either by nutrients or grazing. 4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes. 5. The study supports the theory of a competitive and compensatory trade-off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.