Potamoplankton and primary productivity in the River Danube

Abstract

Autochthonous production of potamoplankton has recently attracted greater interest as it was incorporated into expanded river concepts such as the flow pulse concept or the riverine productivity model (RPM). This review assembles data on primary production from the River Danube to evaluate the importance of productivity in large rivers. Results indicate positive net production in the middle reach of the river and in impoundments. These sections are characterised by favourable conditions for algal growth. Reduction in flow, reduced concentrations of suspended solids and improved under-water light result in significant increase in plankton biomass. Maximum chlorophyll concentrations were below 20 mg m−3 in 2007 but concentrations up to 130 mg m−3 have been recorded in the past. Since nutrients are not limiting, as in most large rivers, net primary production is largely controlled by availability of photosynthetic active radiation under water, chlorophyll-a, water depth and discharge. Hourly carbon uptake rates of 3–130 mg C m−3 h−1 observed in the Danube are well within the range of 0–790 mg C m−3 h−1 for large rivers of the world. Autochthonous autotrophic production must be regarded as an important feature of large rivers supporting the RPM concept.