MAGIC (Model for Acidification of Groundwater In Catchments) is a process-oriented intermediate-complexity dynamic model by which long-term trends in soil and water acidification can be reconstructed and predicted at the catchment scale (Cosby et al., 1985a,b). MAGIC consists of :
- soil-soil solution equilibria equations in which the chemical composition of soil solution is assumed to be governed by simultaneous reactions involving sulphate adsorption, cation exchange, dissolution and precipitation of aluminium, and dissolution and speciation of inorganic and organic carbon;
- mass balance equations in which the fluxes of major ions to and from the soil and surface waters are assumed to be governed by atmospheric inputs, mineral weathering, net uptake in biomass, and loss in runoff.
MAGIC produces long-term reconstructions and predictions of soil and streamwater chemistry in response to scenarios of acid deposition and land use. MAGIC uses a lumped approach in two ways:
- a myriad of chemical and biological processes active in catchments are aggregated into a few readily described processes;
- the spatial heterogeneity of soil properties within the catchment is lumped into one set of soil parameters.
Schematic representation of the flows and stores in MAGIC
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