Modelling nutrient exchange at the sediment-water interface of river systems

Publication TypeJournal Article
Year of Publication2007
AuthorsThouvenot, M, Billen, G, Garnier, J
JournalJournal of Hydrology
Pagination55 - 78
Date Published07/2007
ISBN Number0022-1694
Mots-clésEarly diagenesis, nutrient, sediment, water quality

In-stream benthic processes can play a significant role on the water quality of overlying waters flowing through a river network. In order to better understand and quantify the fate of nutrients (nitrogen, phosphorus and silica) during their travel through the river continuum, a deterministic benthic sub-model was developed with the purpose of being connected to a drainage network model. This benthic sub-model resolves the differential equations representing early diagenesis in the sediment, linking the sedimentation rate of organic matter onto the sediment to the resulting flux of nutrients across the sediment–water interface. The model has been developed for conditions where sedimentation prevails as well as for situations where net erosion prevents the built-up of a significant sediment layer and where only a biofilm can develop, attached to solid substrates. The benthic model was tested independently of the main water column biological–hydrological model to which it is intended to be coupled. For this, three case studies were chosen from the literature representing various sedimentation/erosion conditions: the 8th order river Seine (France), the water storage basin of Méry s/Oise (France), and the headwater stream Orneau (Belgium). The general benthic model has been validated for ammonium, nitrate, oxygen and phosphorus fluxes across the sediment–water interface. The capability of the model to correctly predict the observed nutrients profiles within the sediment was also validated for organic carbon, ammonium and phosphorus. An uncertainty analysis showed that using two modelling objectives (observed fluxes and concentration profiles in the sediment) strongly reduces the uncertainty in parameters calibration. A sensitivity analysis illustrated the complexity of the interacting reactions driving each variable, and justifies the usefulness of the model as a tool for understanding and predicting the behaviour of the benthic compartment of river systems.