1. General Model Information

Name: MAGIC, Model of Acidification of Groundwater in Catchments

Acronym: MAGIC


Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: Landscape
Type of model: not specified
Main application:
Keywords: Soil, acidification, catchment scale, sulfur adsorption, weathering, cation exchange, aluminium dynamics

Contact:

Dr. Richard F. Wright
Norwegian Istitute for Water Research
NIVA, P.O. Box 69, Korsvoll
N-0808 Oslo, Norway
Phone: +47 22 18 51 00
Fax : +47 22 18 52 00
email:

Dr. Bill J. Cosby
Dept. of Environmental Sciences
University of Virginia
Charlottesville, VA 22903, USA
Phone: +1 804-924-7787
Fax : +1 804-982-2300
email:

Author(s):

Abstract:

MAGIC is a lumped-parameter model of intermediate complexity (Cosby et al. 1985a,b) that is calibrated to the watershed of an individual lake or stream and then used to simulate the response of that system to changes in atmospheric deposition. MAGIC includes a section in which the concentration of major ions is governed by simultaneous reactions involving sulfur adsorption, cation weathering and exchange, aluminum dissolution/precipitation/speciation, and dissolution/speciation of inorganic carbon. A mass balance section of MAGIC calculates the flux of major ions to and from the soil in response to atmospheric inputs, chemical weathering inputs, net uptake in biomass and losses to runoff.
Model calibration to a specific catchment is accomplished by specifying deposition and hydrological forcing functions, setting the values of those parameters that can be measured (fixed parameters), and determining the values of the remaining parameters that cannot be measured (adjustable parameters) through an optimization routine. The adjustable parameters are modified to give the best agreement between observed and predicted surface water and soil chemistry (Cosby et al. 1985a,b).
MAGIC is based on simultaneous reactions describing sulfate adsorption, cation exchange, dissolution -precipitation-speciation of aluminium, dissociation of organic acids and dissolution-speciation of organic carbon. Mass balances are controlled by atmospheric inputs, chemical weathering inputs, net uptake in biomass and losses to runoff. At the heart of MAGIC is the size of the pool of exchangeable base cations in the soil. As the fluxes to and from this pool change over time in response to changes in atmospheric deposition, the chemical equilibria between soil and soil solution shift producing changes in surface water chemistry. Cation exchange is modeled using equilibrium (Gaines-Thomas) equations for each base cation and aluminium. Sulfate adsorption is represented by a Langmuir isotherm. Aluminium dissolution-precipitation is assumed to be controlled by equilibrium with a solid phase of aluminium trihydroxide. Aluminium spaciation is calculated by considering hydrolysis reactions as well as complexation with sulfate and fluoride.

Model purpose
MAGIC (Model of Acidification of Groundwater in Catchments; Cosby et al., 1985a,b,c) was development to simulate the effects of acidic deposition on soils and surface waters. The model operates at the catchment scale. Simulation typically involve seasonal or annual time steps and are implemented on decadal or centennial time scales.

Abstract References:

  • MAGIC documentation
  • Joergensen S.E., B. Halling-Soerensen and S.N Nielsen (Edts.) 1996: Handbook of Environmental and Ecological Modelling. CRC Press Boca Raton et al. 672 pp.

    II. Technical Information

    II.1 Executables:

    Operating System(s): DOS

    II.2 Source-code:

    Programming Language(s): FORTRAN

    II.3 Manuals:



    II.4 Data:



    III. Mathematical Information


    III.1 Mathematics


    III.2 Quantities


    III.2.1 Input

    III.2.2 Output


    IV. References

    Cosby, B.J., Hornberger, G.M., Galloway, J.N., Wright, R.F., 1985.a Modelling the effects of acid deposition: assessment of a lumped-parameter model of soil water and streamwater chemistry. Water Resour. Res., 21,51.
    Cosby, B.J., Wright, R.F., Hornberger, G.M., Galloway, J.N., 1985.b Modelling the effects of acid deposition: estimation of long-term water quality responses in a small forested catchment. Water Resour. Res., 21, 1591.
    Sullivan, T.J., B.J. Cosby, C.T. Driscoll, H.F. Hemond, D.F. Charles, S.A. Norton, H.M. Seip, andG. Taugbl. 1994. Confirmation of the MAGIC Model Using Independent Data: Influence ofOrganic Acids on Model Estimates of Lakewater Acidification. Report No. DOE/ER/30196-4.Final Report prepared for The U.S. Department of Energy, under Agreement No.DE-FG02-92ER30196.
    Norton, S.A., R.F. Wright, J.S. Kahl, and J.P. Scofield. 1992. The MAGIC simulation of surfacewater at, and first year results from, the Bear Brook Watershed Manipulation, Maine, USA.Environ. Pollut. 77:279-286.
    Rajarishi Sinha History of Lake Acidification Modelling: An Overview.


    V. Further information in the World-Wide-Web



    VI. Additional remarks


    Last review of this document by: T. Gabele: 24. September 1997 -
    Status of the document:
    last modified by Tobias Gabele Wed Aug 21 21:44:45 CEST 2002

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