Modeling in-stream biogeochemical processes at catchment scale: Coupling SWAT and RIVE models

Representation of biogeochemical in-stream processes is complex, and requires use of models to understand factors controling the transfer of contaminants on watershed scale. The biogeochemical model RIVE was inte-grated into the SWAT model and was used, instead of the current QUAL2E subroutine, to calculate biogeo-chemical in-stream processes. The coupled model was applied to an 89-km section of the Garonne watershed, downstream of Toulouse, for the 2000-2010 period, with a daily time-step. An epilithic biofilm equation was added to represent the river's algae communities, dominated by drifted benthic diatoms. The model matched observed data for major variables of water quality. Dominant processes for nitrogen, phosphorus, silica and organic suspended matter were assessed. The aim of coupling RIVE to the SWAT model was to improve the biogeochemical representation of the river's in-stream ecological processes linked to C, N, P and Si elements and dissolved oxygen, with minimal calibration.