248
Nuria Melia, Juan Bellot and V. Ramon Vallejo
floor (Table 17.2), and followed similar temporal patterns related to enrichment by throughfall, leaching and dissolution of decomposition products.
Differences between sites become apparent at lower depths, as can be seen
in the cation abundances and ion ratios of the soil solution (Tables 17.1 and
17.2). Montseny soil solution was proportionally poorer in K+ compared to
Prades, and each site followed a cation abundance sequence according to that
found in their respective cation exchange complexes.
Water that has entered the soil can either bypass the soil matrix through
preferential flow pathways or infiltrate the soil micropore system, increasing
its residence time and, consequently, the interaction with the soil matrix .
.Avila et al. (1995) showed that the chemical composition of the deep subsurface flow at Montseny was intermediate between that from the water collected below the forest floor and that coming from the soil solution sampled
with low-tension lysimeters. From this observation, they suggested that freeflowing water collected in the lower levels of the soil profile is a mixture of
the macropore water flow coming from the forest floor and pre-event displaced soil solution from the deeper horizons. Ion ratios in these three water
types broadly support this interpretation (Table 17.2).
Table 17.2. Mean ion ratios, on equivalent basis, in gravitational soil water, soil solution, and
streamwater at Montseny and Prades. Gravitational waters are underlined
Ca 2 +/ Mi+ Ca 2 +/ K+
Ca 2 +/ Cl -
K+/Cr
Montseny
Below forest floor·
3.99
4.77
6.04
1.60
Soil solution
20cm b
2.05
19.7
3.18
0.37
40cm b
2.02
96.9
2.72
0.25
160 em·
2.40
29.3
2.98
0.19
Baseflow"
1.53
31.4
3.97
0.13
Prades
Below forest floor
4.19
4.30
7.04
1.62
Soil solution
0-2.5 cm d
4.22
6.26
4.88
1.02
2.5-15 cm d
3.78
10.5
2.21
0.36
30 em
3.63
2.70
2.79
1.00
Streamwater e
4.74
78.4
8.09
0.10
• Arithmetic mean ratios from throughflow collectors (Bonilla 1990), May 1985 to May 1988.
b Arithmetic mean ion ratios from low-tension lysimeters (Bonilla 1990), December 1984 to
June 1986.
C Ion ratios of volume-weighted means in streamwater of the TM9 catchment (Avila et al.1995).
d Arithmetic mean ion ratios from centrifuge soil solution.
e Ion ratios of volume-weighted means in streamwater of the Avic catchment (Pinol and Avila
1992).
Nuria Melia, Juan Bellot and V. Ramon Vallejo
floor (Table 17.2), and followed similar temporal patterns related to enrichment by throughfall, leaching and dissolution of decomposition products.
Differences between sites become apparent at lower depths, as can be seen
in the cation abundances and ion ratios of the soil solution (Tables 17.1 and
17.2). Montseny soil solution was proportionally poorer in K+ compared to
Prades, and each site followed a cation abundance sequence according to that
found in their respective cation exchange complexes.
Water that has entered the soil can either bypass the soil matrix through
preferential flow pathways or infiltrate the soil micropore system, increasing
its residence time and, consequently, the interaction with the soil matrix .
.Avila et al. (1995) showed that the chemical composition of the deep subsurface flow at Montseny was intermediate between that from the water collected below the forest floor and that coming from the soil solution sampled
with low-tension lysimeters. From this observation, they suggested that freeflowing water collected in the lower levels of the soil profile is a mixture of
the macropore water flow coming from the forest floor and pre-event displaced soil solution from the deeper horizons. Ion ratios in these three water
types broadly support this interpretation (Table 17.2).
Table 17.2. Mean ion ratios, on equivalent basis, in gravitational soil water, soil solution, and
streamwater at Montseny and Prades. Gravitational waters are underlined
Ca 2 +/ Mi+ Ca 2 +/ K+
Ca 2 +/ Cl -
K+/Cr
Montseny
Below forest floor·
3.99
4.77
6.04
1.60
Soil solution
20cm b
2.05
19.7
3.18
0.37
40cm b
2.02
96.9
2.72
0.25
160 em·
2.40
29.3
2.98
0.19
Baseflow"
1.53
31.4
3.97
0.13
Prades
Below forest floor
4.19
4.30
7.04
1.62
Soil solution
0-2.5 cm d
4.22
6.26
4.88
1.02
2.5-15 cm d
3.78
10.5
2.21
0.36
30 em
3.63
2.70
2.79
1.00
Streamwater e
4.74
78.4
8.09
0.10
• Arithmetic mean ratios from throughflow collectors (Bonilla 1990), May 1985 to May 1988.
b Arithmetic mean ion ratios from low-tension lysimeters (Bonilla 1990), December 1984 to
June 1986.
C Ion ratios of volume-weighted means in streamwater of the TM9 catchment (Avila et al.1995).
d Arithmetic mean ion ratios from centrifuge soil solution.
e Ion ratios of volume-weighted means in streamwater of the Avic catchment (Pinol and Avila
1992).