The goal is to monitor, analyse and evaluate the biogeochemical recovery in the covered catchment G1 ROOF at Gårdsjön from the start of the experiment in 1991 up to 2001. This includes monitoring of deposition, runoff and soils. The cycling of sulphur in the catchment is studied in particular using the stable isotopes 34S. That makes it possible to estimate the relative importance of sorption processes compared to organic sulphur cycling, during the process of recovery from acidification.
During the summer 2001, the covered catchment project went into its new phase when the plastic cover of the roof was taken away. There were two key reasons for dismantling the roof: the deposition outside the roof decreased strongly over the 11 years of the experiment and therefore the roof was not making as big difference in 2001 as in 1991. Furthermore the catchment will be studied for two years without roof in order to investigate the possible interference from the roof itself.
Some major findings from the the covered catchment experiment to date are:
· Deposition reduction under the roof was followed by rapid and strong improvement of the runoff water quality. However, the recovery was after 11 years not complete and the water did not reach desirable quality with respect to e.g pH or inorganic A1 concentrations.
· No major improvement was observed after deposition reduction in parameters commonly used to indicate tree vitality (crown density and discoloration, tree growth). There was a slight improvement of the fine roots vitality. There was no increase in soil base saturation.
· Sulphur dynamics in the soil and sulphate desorption in particular has been identified as crucial factors, which caused a certain lag time after the deposition has decreased.
Filip Moldan
IVL Swedish Environmental Research Institute
filip.moldan@ivl.se