Nutrient balance in the Rio de la Plata River using mathematical modelling

摘要

A nutrient balance for the Inner Rio de la Plata River is performed. The river is segmented based on hydrodynamic and morphological considerations. Results from an existing 2D hydrodynamic model are used to generate data on the advective and diffusive fluxes. The nutrient balance is performed by means of a 2D water quality model. This model is calibrated using measured electrical conductivity distributions. It is then applied to perform the balance for nitrate, ammonia, total organic nitrogen, total phosphorous, phosphate phosphorous, and total organic carbon (through BOD data). Available measured concentration for the tributaries, effluents and the outer front (transition to outer river) are used to obtain the concentration distributions throughout the inner river, which are then compared with measured distributions within the river. A series of interesting conclusions regarding the system dynamics are drawn from the study: the identification of three adjacent flow ways, the evidence of a relatively strong longitudinal mixing at the outer front, the verification of two transformation processes (nitrification and biodegradation), for which rate constants are estimated, while the remaining nutrient species behave as conservative, and the establishment of the magnitude of the nutrient loads from the upper basin and fluxes from the coastal sources. The application illustrates the capacity of the used methodology to provide both qualitative and quantitative information about the systems dynamics. The results are of prime importance in order to develop management strategies.