A mass‐balance approach to estimate in‐stream processes in a large river |
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Authors: | Samuel Teissier Sabine Sauvage Philippe Vervier Frédéric Garabétian José‐Miguel Sánchez‐Pérez |
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Institution: | Laboratoire d'Ecologie Fonctionnelle (ECOLAB), UMR 5245 CNRS‐UPS‐INPT Ecole Nationale Supérieure Agronomique de Toulouse (ENSAT), Avenue de l'Agrobiopole BP 32607 Auzeville Tolosane 31326 CASTANET TOLOSAN Cedex, France |
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Abstract: | A mass‐balance approach was used to estimate in‐stream processes related to inorganic nitrogen species (NH4+, NO2? and NO3?) in a large river characterized by highly variable hydrological conditions, the Garonne River (south‐west France). Studies were conducted in two consecutive reaches of 30 km located downstream of the Toulouse agglomeration (population 760 000, seventh order), impacted by modification of discharge regime and high nitrogen concentrations. The mass‐balance was calculated by two methods: the first is based on a variable residence time (VRT) simulated by a one‐dimensional (1‐D) hydraulic model; the second is a based on a calculation using constant residence time (CRT) evaluated according to hydrographic peaks. In the context of the study, removal of dissolved inorganic nitrogen (DIN) for a reach of 30 km is underestimated by 11% with the CRT method. In sub‐reaches, the discrepancy between the two methods led to a 50% overestimation of DIN removal in the upper reach (13 km) and a 43% underestimation in the lower reach (17 km) using the CRT method. The study highlights the importance of residence time determination when using modelling approaches in the assessment of whole stream processes in short‐duration mass‐balance for a large river under variable hydrological conditions. Copyright © 2007 John Wiley & Sons, Ltd. |
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Keywords: | mass balance in‐stream processes inorganic nitrogen hydraulic perturbations large river |
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