Acidification in Three Lake District Tarns: Historical Iong term trends and modelled future behaviour under changing sulphate and nitrate deposition

Abstract. Three upland Lake District Tarns, Scoat, Greendale and Burnmoor, have been evaluated using MAGIC (Model of Acidification of Groundwater In Catchments) to reconstruct past, present and future chemical behaviour. The modelled historical changes in acidity are compared with palaeoecological estimation of pH to demonstrate model validity. Chemistry as simulated for all anions and cations and two of the three lakes are shown to have undergone significant acidification. The effects of changing atmospheric pollution levels on lake chemistry is evaluated and 80-90% sulphur reduction levels are required to achieve zero alkalinity. The impacts of increased nitrogen deposition are assessed and are shown to further delay reversibility.