310
Anna Avila
year 2045, as well as forest clear-cuts every 60 years. Finally, scenario 5 considered a 30% increase in atmospheric input without forest clear-cutting.
All simulations predicted a decrease in the soil base saturation: the input
of base cations in atmospheric deposition was not enough to compensate for
the depletion of the soil base cations due to forest growth in scenarios either
with or without forest clear-cut. When forest felling was simulated, the decrease in base saturation was steeper, an indication that plant regrowth was
consuming base cations at a faster rate than when the forest was left undisturbed. However, even with forest felling the base saturation in year 2045 was
estimated to be around 75%, a value too high to pose problems of acidification.
Streamwater response under the different future scenarios is not shown
here: until now, no good results were obtained at Prades because of the need
to modify the model in order to account for the precipitation-dissolution of
calcite. The calcite precipitated in the streambank in conditions of high alkalinity and Ca 2 + concentration and decreasing pC02 may well dissolve when
base cation concentrations and alkalinity decrease steeply in scenarios of
pollution or forest management. Therefore, the calcite solubility product has
to be introduced in the model for it to be able to reproduce accurately the
hydrochemical dynamics of the Prades streamwaters.
21.5 Concluding Remarks
The application of MAGIC to Montseny and Prades has shown that high atmospheric pollutant sulphur loadings have not resulted in significant
changes in the quality of the streamwater at both sites. At Montseny, atmospheric deposition was responsible of a slight decrease in alkalinity and base
cations. Forest management produced a wave-like pattern in streamwater
chemistry, reflecting the phase in the forestry cycle, with no consistent trend
toward acidification. This simulation confirmed the sustainability of the actual regime of forest harvest currently practised at Montseny.
At Prades, MAGIC was successfully fitted to a catchment of very high soil
base saturation and very mineralized streamwaters. However, the solubility
product of calcite needs to be included in the model to account for the calcite
precipitation/dissolution in these highly mineralized streamwaters. Historical
and future changes in soil base saturation showed that vegetation uptake was
the main process of depletion of the base saturation for the Prades soils.
Anna Avila
year 2045, as well as forest clear-cuts every 60 years. Finally, scenario 5 considered a 30% increase in atmospheric input without forest clear-cutting.
All simulations predicted a decrease in the soil base saturation: the input
of base cations in atmospheric deposition was not enough to compensate for
the depletion of the soil base cations due to forest growth in scenarios either
with or without forest clear-cut. When forest felling was simulated, the decrease in base saturation was steeper, an indication that plant regrowth was
consuming base cations at a faster rate than when the forest was left undisturbed. However, even with forest felling the base saturation in year 2045 was
estimated to be around 75%, a value too high to pose problems of acidification.
Streamwater response under the different future scenarios is not shown
here: until now, no good results were obtained at Prades because of the need
to modify the model in order to account for the precipitation-dissolution of
calcite. The calcite precipitated in the streambank in conditions of high alkalinity and Ca 2 + concentration and decreasing pC02 may well dissolve when
base cation concentrations and alkalinity decrease steeply in scenarios of
pollution or forest management. Therefore, the calcite solubility product has
to be introduced in the model for it to be able to reproduce accurately the
hydrochemical dynamics of the Prades streamwaters.
21.5 Concluding Remarks
The application of MAGIC to Montseny and Prades has shown that high atmospheric pollutant sulphur loadings have not resulted in significant
changes in the quality of the streamwater at both sites. At Montseny, atmospheric deposition was responsible of a slight decrease in alkalinity and base
cations. Forest management produced a wave-like pattern in streamwater
chemistry, reflecting the phase in the forestry cycle, with no consistent trend
toward acidification. This simulation confirmed the sustainability of the actual regime of forest harvest currently practised at Montseny.
At Prades, MAGIC was successfully fitted to a catchment of very high soil
base saturation and very mineralized streamwaters. However, the solubility
product of calcite needs to be included in the model to account for the calcite
precipitation/dissolution in these highly mineralized streamwaters. Historical
and future changes in soil base saturation showed that vegetation uptake was
the main process of depletion of the base saturation for the Prades soils.