During the 1st GAP Workshop at Konstanz in April 1982 comparative measurements of phytoplankton primary production by several techniques were conducted simultaneously at an offshore station in Lake Konstanz and an experimental algal pond. Suspended glass bottle exposure techniques using 14C and 13C uptake gave Pz (mg C m−3 h−1) values which varied considerably near-surface, but estimates of areal rates for the euphotic zone ΣPcu(mg C m−3 h−1) which were reasonably close. In the lake, ΣPz, from a vertical tube exposure (with 14C uptake) was greater than rates derived for integrated bottle samples. The oxygen bottle method permitted a good estimate of compensation depth, corresponding to in situ growth studies. There were difficulties in direct comparison between O2 and carbon methods. Correlation between them for Pz was good in the lake but poor in the pond, both for suspended bottle and vertical tube methods. This series demonstrates that despite reasonable overall estimates, comparatively minor methodological differences in experimental technique can cause large variatio
