242
Nuria Melia, Juan Bellot and V. Ramon Vallejo
be distinguished in these holm-oak forests (Chap. 14). Bellot and Escarre
(1991) found higher ion concentrations in throughfall during the summer at
Prades and Rodil. et al' (1990) also reported a distinct maximum in net
throughfall fluxes of K+ in early summer at Montseny (Chap. 15). Furthermore, maximum litterfall was found in late spring or early summer at Prades
(Bellot et al. 1992) and at Montseny (Verdu 1984). The highest carbon dioxide efflux from soil at both areas was observed in late spring and late summer
(Pinol et al. 1995), suggesting that high decomposition rate occurs during
these periods. These results suggest that the ion enrichment of soil water
from throughfall and leaching from fresh litter may occur especially during
late spring and late summer rainfall events. Added to these processes, the
high decomposition rate occurring in late summer may provide an important
source of soluble ions for the first autumn rainfalls.
17.3 Soil Solution '
The chemistry of water held in the soil at low hydric potentials was studied at
Montseny with low-tension lysirnetry and at Prades with drainage centrifugation. At Montseny, soil solution was sampled weekly with ceramic-cup
lysimeters evacuated manually to -65 kPa. Replicate lysimeters were installed
at 20- and 40-cm depths in or near the permanent plot at La Castanya (Chap.
2). Detailed descriptions of this study were provided by Rodil. et al. (1990)
and Avila et al. (1995). At Prades, research into soil solution composition focused on the spatial variability within the Avic catchment (Chap. 2). Sixteen
pits at each altitudinal extreme of the catchment were sampled at 0- to 2.5cm, 2.5- to 15-cm and 15- to 30-cm depths. Field moist samples were centrifuged using double-bottomed cups (Gillman 1976) at an equivalent pressure
of 3 MPa and the extracted solutions were analyzed after filtration.
17.3.1 Low-Tension Lysirneter Solution at Montseny
The mean solution chemistry was similar at 20- and 40-cm depths (Table
17.1). The soil solution in the mineral soil was generally less concentrated,
and had more acidic pH values, than the gravitational water collected below
the forest floor (Fig. 17.1, Table 17.1). As in gravitational water, soil solution
was dominated by Ca2+ and sol-, which accounted for more than 50% of the
cation and anion charge respectively. Potassium and N03 - in soil solution
were the ions with the lowest mean concentrations (Table 17.1). The order of
abundance of cations followed the same sequence as that in the cation exchange complex of the soil (Avila et al. 1995): Ca 2 + > Mg2+> Na+ > K+. The
anion charge deficit computed from the analyzed ions was much lower than
that found in the soil water flow below the forest floor, but it still represented
Nuria Melia, Juan Bellot and V. Ramon Vallejo
be distinguished in these holm-oak forests (Chap. 14). Bellot and Escarre
(1991) found higher ion concentrations in throughfall during the summer at
Prades and Rodil. et al' (1990) also reported a distinct maximum in net
throughfall fluxes of K+ in early summer at Montseny (Chap. 15). Furthermore, maximum litterfall was found in late spring or early summer at Prades
(Bellot et al. 1992) and at Montseny (Verdu 1984). The highest carbon dioxide efflux from soil at both areas was observed in late spring and late summer
(Pinol et al. 1995), suggesting that high decomposition rate occurs during
these periods. These results suggest that the ion enrichment of soil water
from throughfall and leaching from fresh litter may occur especially during
late spring and late summer rainfall events. Added to these processes, the
high decomposition rate occurring in late summer may provide an important
source of soluble ions for the first autumn rainfalls.
17.3 Soil Solution '
The chemistry of water held in the soil at low hydric potentials was studied at
Montseny with low-tension lysirnetry and at Prades with drainage centrifugation. At Montseny, soil solution was sampled weekly with ceramic-cup
lysimeters evacuated manually to -65 kPa. Replicate lysimeters were installed
at 20- and 40-cm depths in or near the permanent plot at La Castanya (Chap.
2). Detailed descriptions of this study were provided by Rodil. et al. (1990)
and Avila et al. (1995). At Prades, research into soil solution composition focused on the spatial variability within the Avic catchment (Chap. 2). Sixteen
pits at each altitudinal extreme of the catchment were sampled at 0- to 2.5cm, 2.5- to 15-cm and 15- to 30-cm depths. Field moist samples were centrifuged using double-bottomed cups (Gillman 1976) at an equivalent pressure
of 3 MPa and the extracted solutions were analyzed after filtration.
17.3.1 Low-Tension Lysirneter Solution at Montseny
The mean solution chemistry was similar at 20- and 40-cm depths (Table
17.1). The soil solution in the mineral soil was generally less concentrated,
and had more acidic pH values, than the gravitational water collected below
the forest floor (Fig. 17.1, Table 17.1). As in gravitational water, soil solution
was dominated by Ca2+ and sol-, which accounted for more than 50% of the
cation and anion charge respectively. Potassium and N03 - in soil solution
were the ions with the lowest mean concentrations (Table 17.1). The order of
abundance of cations followed the same sequence as that in the cation exchange complex of the soil (Avila et al. 1995): Ca 2 + > Mg2+> Na+ > K+. The
anion charge deficit computed from the analyzed ions was much lower than
that found in the soil water flow below the forest floor, but it still represented