Application of Three-Dimensional Hydrodynamic and Water Quality Models to Study Water Hyacinth Infestation in Lake Nokoué, Benin

Water hyacinth (Eichhornia crassipes) poses numerous water quality problems in many surface water bodies in tropical and sub-tropical regions. In this paper, a three-dimensional coupled hydrodynamic model in the Environmental Fluid Dynamics Code (EFDC) modeling framework and a water quality model using the Water Quality Analysis Simulation Program (WASP7.2) were developed for Lake Nokoué, Benin for the period of September 01, 2006 to December 31, 2007. A third predictive model that simulates the suitability of salinity, nutrient and temperature conditions in the lake for water hyacinth growth was developed. Results from this study showed that during the dry season no water hyacinth infestation was expected in the lake since the salinity was above the lethal level whereas in the rainy season, the environmental conditions in many parts of the lake were suitable for the weed's growth except in the Cotonou area where salinity remains limiting almost throughout the year. Investigation of the lake's response to removal of nutrients from the different sources showed that a maximum reduction of 17% in themulti-parameter suitability index was achieved when 66% of the nutrient loads from the Ouemé River and flooded marshes were removed.