Modélisation de l'azote total en rivière à l'aide du modèle quantité–qualité CEQUEAU

Abstract

A model for nitrogen concentrations in running waters has been developed and associated with the hydrological model CEQUEAU. The model allows the simulation of total nitrogen concentrations at any point in a watershed during various hydrological event. The catchment area is first subdivided into discrete elements; each element is associated with a production function which quantifies the accumulation of nitrogen at the soil–atmosphere interface. Supplementary functions describe the transformations of nitrogen species in the soil and the transfer of the nitrogen load towards the hydrographic system by runoff (caused by rain and (or) snowmelt), and the transport of the different nitrogen compounds downstream. Another function is used to represent the in-stream transformation. Nitrogen data inputs to be modeled are those from precipitation dry deposition, diffuse sources due to agricultural practices, and industrial point sources. The model was applied to the Sainte-Anne River, Québec (catchment area, 2700 km2) in order to reproduce the observed nitrogen concentrations for 1978, 1979, and 1980. Model performance was judged to be promising and it is proposed to validate the model by the simulation of nitrogen concentration on the other rivers for which land use and industrial activity are well documented. Key words: modeling, river, nitrogen, supply, runoff, seepage, drainage.