Biogeochemical Models
309
input and vegetation uptake were obtained from Bellot (1989) and Lled6
(1990) respectively. Net uptake at this site was calculated to be (in meq m- 2
year-I) 47 for Ca H , 5 for Mg2+ and 18 for K+. The main calibration problem
was in fitting the streamwater Ca 2 + concentrations because some calcite precipitates along the stream when the water flows from the soil to the channel
(with decreasing pC02) in an environment of very high alkalinity and Ca 2 +
concentrations (Pinol and Avila 1992). The simulated value of 3569 Jleq Ca H
L -I was proposed to account for the calcium in dissolved and precipitated
forms (Bellot et al. 1994). A very good fit was obtained for the rest of the
variables (Table 21.4).
21.4.1 Historical Sequences
The wet deposition sequence for sol-, also used for N03 - and NH4 +, was
based on the evolution of sulphur emissions in Europe. Note, however, that
increasing acid anions in the rainwater from 1845 to 1985 did not result in
acidic rain: rainfall alkaHnity was 19.6 Jleq L- 1 in 1985, corresponding to an
air-equilibrated pH of 6.6 (Table 21.1).
Typical forest use in the Prades mountains between 1845 and 1940 was
moderate felling for charcoal production. However, between 1940 and 1950
the forest was totally clear-cut except for a few seed-producing trees. Afterwards the forest in the Prades catchment was protected, producing a dense
forest of resprouts (9000 stems ha- I in the tree plus shrub layers). These
vegetation changes were simulated in MAGIC with an uptake sequence
varying from 3% of present-day uptake between 1845 and 1940,200% of present-day uptake between 1940 and 1950, and a linear decrease from 200 to
100% between 1950 and 1985.
The results for the historical changes of the base saturation in the soil indicated that from 1845 to 1985 tree felling reduced the base saturation from
84 to 82%, a very small change without acidification consequences. No
changes in response to the atmospheric deposition were found.
21.4.2 Forest Management and Atmospheric Deposition Scenarios
MAGIC was also applied to the Avic catchment for different scenarios of forest management and atmospheric deposition. Five scenarios combining different intensities of atmospheric inputs and forest management were devised, in an attempt to forecast the soil and streamwater response to pollution and forestry (Bellot et al. 1995). Scenario 1 was a projection into the future of present-day atmospheric input and forest growth. Scenario 2 considered present-day atmospheric inputs and forest clear-cuts every 60 years.
Scenario 3 considered an increasing trend of atmospheric inputs reaching a
30% increment by the year 2045, with the same clear-cuts as in scenario 2.
Scenario 4 considered a reduction of atmospheric inputs down by 30% by the
309
input and vegetation uptake were obtained from Bellot (1989) and Lled6
(1990) respectively. Net uptake at this site was calculated to be (in meq m- 2
year-I) 47 for Ca H , 5 for Mg2+ and 18 for K+. The main calibration problem
was in fitting the streamwater Ca 2 + concentrations because some calcite precipitates along the stream when the water flows from the soil to the channel
(with decreasing pC02) in an environment of very high alkalinity and Ca 2 +
concentrations (Pinol and Avila 1992). The simulated value of 3569 Jleq Ca H
L -I was proposed to account for the calcium in dissolved and precipitated
forms (Bellot et al. 1994). A very good fit was obtained for the rest of the
variables (Table 21.4).
21.4.1 Historical Sequences
The wet deposition sequence for sol-, also used for N03 - and NH4 +, was
based on the evolution of sulphur emissions in Europe. Note, however, that
increasing acid anions in the rainwater from 1845 to 1985 did not result in
acidic rain: rainfall alkaHnity was 19.6 Jleq L- 1 in 1985, corresponding to an
air-equilibrated pH of 6.6 (Table 21.1).
Typical forest use in the Prades mountains between 1845 and 1940 was
moderate felling for charcoal production. However, between 1940 and 1950
the forest was totally clear-cut except for a few seed-producing trees. Afterwards the forest in the Prades catchment was protected, producing a dense
forest of resprouts (9000 stems ha- I in the tree plus shrub layers). These
vegetation changes were simulated in MAGIC with an uptake sequence
varying from 3% of present-day uptake between 1845 and 1940,200% of present-day uptake between 1940 and 1950, and a linear decrease from 200 to
100% between 1950 and 1985.
The results for the historical changes of the base saturation in the soil indicated that from 1845 to 1985 tree felling reduced the base saturation from
84 to 82%, a very small change without acidification consequences. No
changes in response to the atmospheric deposition were found.
21.4.2 Forest Management and Atmospheric Deposition Scenarios
MAGIC was also applied to the Avic catchment for different scenarios of forest management and atmospheric deposition. Five scenarios combining different intensities of atmospheric inputs and forest management were devised, in an attempt to forecast the soil and streamwater response to pollution and forestry (Bellot et al. 1995). Scenario 1 was a projection into the future of present-day atmospheric input and forest growth. Scenario 2 considered present-day atmospheric inputs and forest clear-cuts every 60 years.
Scenario 3 considered an increasing trend of atmospheric inputs reaching a
30% increment by the year 2045, with the same clear-cuts as in scenario 2.
Scenario 4 considered a reduction of atmospheric inputs down by 30% by the