Predicting watershed acidification under alternate rainfall conditions

• Published in: Water, air, and soil pollution Vol. 90; no. 3/4; pp. 429 - 450
• Main Author: Huntington, T.G
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 1996
• Subjects: acid deposition; acidification; acidity; air pollution; alkalinity; base saturation; bases; climate change; deposition; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Geochemistry; Hydrology; Hydrology. Hydrogeology; magic model; Mathematical models; Mineralogy; prediction; Q1; Rain; seasonal variation; Silicates; simulation models; soil water; sulfates; sulfur; Water geochemistry; Water quality; Watersheds; Georgia; United States; North America; models; adsorption; software; simulation; ground water; runoff; vegetation; acidification; evapotranspiration; sulfates; alkalinity; forests; drainage basins; climate modification; hydrochemistry; pore water; acid rains; prediction; sulfur; soils; calibration; seasonal variations
• ISSN: 0049-6979; 1573-2932
• DOI: 10.1007/BF00282660

Long term catchment response to chronic sulphur loadings under alternate rainfall scenarios was evaluated using the model of acidification of ground water in catchments (MAGIC). MAGIC is a lumped parameter, soil orientated, charge balance model which reacts precipitation, dry deposition and weathering inputs with soil matrix. The model was calibrated with measured soil properties, wet and dry deposition and modelled hydrologic routing, at the Panola Mountain Research Watershed, Atlanta. Calibration used 140-year hindcast data. Model inputs for 140-year forecast simulations included a constant average annual sulphur deposition of 97.3 meq per m2.year and a sulphate concentration in precipitation of 43.6 ueq per litre. Forecast simulations were evaluated to compare alternate temporal averaging of rainfall inputs, variations in amounts of rainfall and seasonal distribution. Model sensitivities to averaging hydrologic conditions, total annual rainfall, seasonal rainfall distribution and soil water flux are presented. Predicted soil water alkalinity as a function of sulphate deposition and water flux is presented. Alkalinity was predicted to decrease with a decrease in rainfall and when rainfall occurred during the growing season. Changes in rainfall distribution resulting in a decreased net soil water flux would temporarily delay acidification, although decreased net soil water flux would eventually increase soil adsorbed sulphur and surface water sulphate, and decrease the alkalinity. Net soil water flux changes caused by changes in rainfall, seasonal distributions of rainfall or evapotranspiration (associated with climate change) would affect the dynamics of acidification response to continued sulphate loading.