Element Budgets in Catchments
285
For marine-derived elements, net throughfall fluxes mostly represent dry
deposition onto canopies because they are scarcely leached from plants. We
thus considered all Na+ in net throughfall, and the corresponding sea-salt
proportion for CI-, to represent dry deposition. This amounted (Chap. 15) to
0.4 and 0.6 kg ha- l yearl respectively at Montseny, and 0.7 and 1.2 kg ha- l
year- l respectively at Prades (Tomers). These fluxes were added to bulk
deposition inputs to give the total Na+ and CI- inputs to our catchments.
Other elements were not corrected for dry deposition. For a wider discussion
of the inputs see Chapters 14 and 15.
20.3 Output Fluxes
Output fluxes were measured for two catchments at Montseny (see site description in Chap. 2), named TM9 and TMO (TM9 for the period 1984-1994
and TMO for the period 1990-1994) and at the Avic catchment in Prades for
the period 1982-1994. Montseny data have been reported in Avila (1988) and
Avila and Rodii (1988) for the period 1983-1985. The Prades series has been
partly analysed by Lled6 (1990), Pinol (1990) and Bellot et al. (1992). Some
data exist for two other catchments at Prades (Teula and Saucar) but will not
be discussed here. Element budgets for the Teula catchment are described for
the period 1986-1988 in Pinol (1990).
20.3.1 Streamwater Chemistry
The main chemical features of these streamwaters are summarized here.
Prades and Montseny catchments produced highly buffered streamwaters
(Table 20.1): pH was rarely below 7 in weekly samples. At the observed pH
values, alkalinity corresponds to HC03 -, and the dominant anion at all sites
was bicarbonate which accounted for 76% of the total anion concentration at
Avic, and 55 and 52% at TM9 and TMO, respectively. In the Prades catchment,
the dominant cation was Ca 2 +, in similar proportion to HC03 -, At Montseny,
Na+ and Ca2+ codominated. The streamwater of the Prades catchments was
more mineralized than that of the Montseny streams: the total flow-weighted
mean ion content was 10.6 meq L- 1 at Avic, and only 1.4 and 1.1 meq L- 1 for
TM9 and TMO (Table 20.1). The higher mineralization of Prades streamwater
results from the higher residence time of water within the catchment, and
from a concentration effect due to a higher ratio of precipitation to runoff
(Pinol et al. 1992; Chap. 19). Weathering rates are probably enhanced at
Prades due to the mentioned longer residence time of the water and to
higher pC02 in the soils compared to Montseny (Pinol et al. 1995). The very
high concentrations of HC03 - and Ca2+ at Avic give a calcite-saturated character to these waters: calcite precipitated at some points in the channel where
285
For marine-derived elements, net throughfall fluxes mostly represent dry
deposition onto canopies because they are scarcely leached from plants. We
thus considered all Na+ in net throughfall, and the corresponding sea-salt
proportion for CI-, to represent dry deposition. This amounted (Chap. 15) to
0.4 and 0.6 kg ha- l yearl respectively at Montseny, and 0.7 and 1.2 kg ha- l
year- l respectively at Prades (Tomers). These fluxes were added to bulk
deposition inputs to give the total Na+ and CI- inputs to our catchments.
Other elements were not corrected for dry deposition. For a wider discussion
of the inputs see Chapters 14 and 15.
20.3 Output Fluxes
Output fluxes were measured for two catchments at Montseny (see site description in Chap. 2), named TM9 and TMO (TM9 for the period 1984-1994
and TMO for the period 1990-1994) and at the Avic catchment in Prades for
the period 1982-1994. Montseny data have been reported in Avila (1988) and
Avila and Rodii (1988) for the period 1983-1985. The Prades series has been
partly analysed by Lled6 (1990), Pinol (1990) and Bellot et al. (1992). Some
data exist for two other catchments at Prades (Teula and Saucar) but will not
be discussed here. Element budgets for the Teula catchment are described for
the period 1986-1988 in Pinol (1990).
20.3.1 Streamwater Chemistry
The main chemical features of these streamwaters are summarized here.
Prades and Montseny catchments produced highly buffered streamwaters
(Table 20.1): pH was rarely below 7 in weekly samples. At the observed pH
values, alkalinity corresponds to HC03 -, and the dominant anion at all sites
was bicarbonate which accounted for 76% of the total anion concentration at
Avic, and 55 and 52% at TM9 and TMO, respectively. In the Prades catchment,
the dominant cation was Ca 2 +, in similar proportion to HC03 -, At Montseny,
Na+ and Ca2+ codominated. The streamwater of the Prades catchments was
more mineralized than that of the Montseny streams: the total flow-weighted
mean ion content was 10.6 meq L- 1 at Avic, and only 1.4 and 1.1 meq L- 1 for
TM9 and TMO (Table 20.1). The higher mineralization of Prades streamwater
results from the higher residence time of water within the catchment, and
from a concentration effect due to a higher ratio of precipitation to runoff
(Pinol et al. 1992; Chap. 19). Weathering rates are probably enhanced at
Prades due to the mentioned longer residence time of the water and to
higher pC02 in the soils compared to Montseny (Pinol et al. 1995). The very
high concentrations of HC03 - and Ca2+ at Avic give a calcite-saturated character to these waters: calcite precipitated at some points in the channel where