Testing the MAGIC acid rain model in highly organic,low-conductivity waters using multiple calibrations |
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Authors: | Ian?F?Dennis Email author" target="_blank">Thomas?A?ClairEmail author Bernard?J?Cosby |
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Institution: | (1) Environment Canada-Atlantic Region, P.O. Box 6227, Sackville, N.B. E4L 1G6, Canada;(2) University of Virginia, P.O. Box 400123, Clark Hall, Charlottesville, VA 22904-4123, USA |
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Abstract: | Accurate predictions of acid precipitation effects on water resources are important in order to allow a better understanding
of various pollution control strategy outcomes. Dynamic geochemical models have been developed to address this need, but have
to be tested under a variety of environmental conditions to provide confidence in their predictions. The most commonly used
aquatic acidification model in North America and Europe is the model of acidification of groundwater in catchments (MAGIC).
Though extensively used, MAGIC has never been tested in catchments with extremely low ionic strength water and high in natural
organic acids (NOAs) from wetlands, two conditions which are common in large parts of Canada. We calibrated the model for
two catchments located in Nova Scotia, Canada, which had some of the most dilute freshwaters reported in the literature and
very high NOA. We also evaluated the variability inherent in calibration data sets by using five separate data sets collected
over a 15-year period at the same sites. We show good model simulations for the main cations and anions in catchment waters.
However, modeling pH is more difficult in the highly organic waters and requires modification to the acid dissociation constants.
Calculated acid neutralization capacity can also be more difficult to model due to the low ion content making small errors
more important. In theory, multiple calibrations of a model at a same site should produce identical hindcasts and predictions.
In reality, the multiple calibrations produced a series of similar, but not identical outcomes which give a probable range
of past values and future outcomes. We feel that this practical approach to validation is a useful addition to the arsenal
of model testing tools. |
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Keywords: | MAGIC model water acidification Nova Scotia multiple calibrations |
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