Use of Artificial Substrata to Estimate the Productivity of Periphyton1

Plexiglas plates were placed in laboratory streams and in a spring and removed at 2‐ to 4‐day intervals to determine the increase in standing crop of periphyton. The instantaneous growth rate, calculated from the growth curve of periphyton on plates in the streams, was 0.51 g m −2 day −1 as compared to an estimate of 0.60 g m −2 day −1 obtained by oxygen measurements for growth of periphyton on the stream bottom. The average growth rate of periphyton on plates in the streams over a single exposure period was 0.31 g m −2 day −1 . Under the conditions of this experiment, the instantaneous growth rate was a better estimate of productivity than the average growth rate.