Underestimation of primary production as indicated by measurements with size-fractionated phytoplankton in Lake Maarsseveen I (The Netherlands)

Primary productivity of four size classes of phytoplankton (<150μm, <50μm, <20μm and <5μm) was measured from March through October 1986 in Lake Maarsseveen I with an incubator technique. The mean column production was approximately 400 mg C.m−2.day−1, with a range of values between 150 and 750 mg C.m−2.day−1. The mean contribution of the size fractions <50μm, <20μm and <5μm to the size fraction<150μm was 80%, 60% and 35%, respectively. During their appearance the grazing impact of small herbivorous zooplankton,e.g. rotifers, can give an underestimation of the size fraction <150μm. An indication of this phenomenon is given