Magic modeling of long-term lake water and soil chemistry at Abborrtrasket, northern Sweden

The geochemical model MAGIC has been applied to the Abborrtrasket lake catchment in northern Sweden for the period 1843-2000. The two objectives were to 1.) simulate historical biogeochemical fluxes and pools and 2.) test whether the MAGIC model of biogeochemical cycling contradicts the published diatom record of a relatively stable pH (around 6) during the last two centuries in this weakly buffered, acid sensitive lake. Abborrtrasket has received elevated sulfur and nitrogen deposition in the second half of the 20th Century and had a large part of its catchment clearcut in 1975. The MAGIC simulation of very small pH decline from 6.1 to 5.9 between 1843 and 1987 was comparable to the published diatom reconstructions of almost stable lake water pH up until the lake was limed in 1988. MAGIC also simulated the modern soil and water chemistry, including lake liming. Thus the diatom indication of stable pH cannot be dismissed as necessarily incorrect.