Abstract
This paper presents a hydrogeochemical modeling code HYDROS, which combines the multi-component transport model with equilibrium speciation module MINTEQA2. The processes of adsorption, aqueous speciation and mineral precipitation/dissolution are represented in the model. The numerical model uses a sequential iterative approach for solving the solute transport and the equilibrium geochemistry modules. Further the transport part is solved using an operator split approach wherein a finite volume method is used for solving the advective equations while a classical finite difference method is employed for solving the dispersive equations. The model performance is evaluated by comparing it with MINTOX for a literature problem. HYDROS is then applied to the case study of the transfer of transition metals with organic colloids in the swamp groundwater system of the experimental Nsimi watershed, representative of the humid tropical ecosystem of the South Cameroon Plateau. Field observations at the site swamp system suggest that the carbon is mainly transferred as organic colloids (i.e., dissolved organic carbon) produced by the slow biodegradation of the swamp organic matter. Using HYDROS, the behaviour of Al(III) and Fe(III) elements in the base flow system is simulated during inter rain events of a short rainy season (May–June 1996). The elemental time-series for Al, Fe, Cl, pH compare well with the simulation results. The colloids are found to have a strong impact on the mobilization and transfer of Al(III) and Fe(III), which are considered to have low mobility in weathering environment.
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Acknowledgments
The Nsimi experimental watershed is part of the programme ORE funded by INSU, IRD, OMP, MRT (http://www.ore-bvet.fr). Apart from the specific support from the French Institute of Research for Development (IRD), our project benefited from funding from the national programs PROSE/PEGI and PNSE. These programs were funded both by IRD and INSU/CNRS. The multidisciplinary research carried on the Nsimi watershed began in 1994 under the control of IRD and IRGM-CRH. We thank Mathieu Zang, Mathurin Amougou, Patrice Messi, Claude Akono of the Nsimi village and Justin Nlozoa (IRGM-CRH) for the care that they took in the set up of the watershed and to maintain it. Jacques Bodin is acknowledged for his help during the fieldwork. We are grateful to Michel Valladon and Bernard Reynier for their assistance during the ICP-MS measurements at LMTG (Toulouse).
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Sekhar, M., Braun, JJ., Hayagreeva Rao, K.V. et al. Hydrogeochemical modeling of organo-metallic colloids in the Nsimi experimental watershed, South Cameroon. Environ Geol 54, 831–841 (2008). https://doi.org/10.1007/s00254-007-0866-8
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DOI: https://doi.org/10.1007/s00254-007-0866-8