1. General Model Information
Name: MAGIC, Model of Acidification of Groundwater in Catchments
Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: Landscape
Type of model: not specified
Keywords: Soil, acidification, catchment scale, sulfur adsorption, weathering, cation exchange, aluminium dynamics
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
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
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
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.
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
Operating System(s): DOS
Programming Language(s): FORTRAN
III. Mathematical Information
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