Potamon: A dynamic model for predicting phytoplankton composition and biomass in lowland rivers

POTAMON is a unidimensional, non-stationary model, designed for simulating potamo-plankton from source to mouth. The forcing variables are discharge, river morphology, water temperature, available light and nutrient inputs. G iven the description of several algal categories, POTAMON allows to simulat e algal "successions" at a particular site, as well as longitudinal changes of potamoplankton composition and biomass. The algal categories differ by their physiology, their loss rates, and their sensitivity to grazing by zoo plankton. Two zooplankton categories were considered, Brachionus-like and K eratella-like. which differ by their clearance rate, their incipient limiti ng level, their selectivity towards phytoplankton, and their growth yield. The model simulates satisfactorily the onset and the magnitude of the phyto plankton spring bloom in the Belgian part of R. Meuse, the biomass decrease in early summer, and the autumn bloom. It also renders the major variation s of algal assemblages along the river. The model allows to confirm that th e main driving variables of potamoplankton dynamics in a eutrophic river ar e physical factors: discharge and related variables (e.g. retention time), light and temperature. In addition, the simulations confirm that the zoopla nkton-phytoplankton interaction may result in phytoplankton biomass fluctua tions and compositional changes. POTAMON can be useful to explore plankton dynamics in a large river, and it may become a tool to test various managem ent measures. (C) 2001 Published by Elsevier Science Ltd.