『Abstract
To quantify and explain the contributions by pollution and chemical
weathering to their compositions, we studied the chemistries of
springs and surface waters in the mountainous part of the Vouga
River basin. Water samples were collected during a number of consecutive
summer campaigns. Recharge rates were derived from monitored discharge
rates within the basin. Very large contributions by meteoric,
agricultural and domestic sources to the water chemistries were
found, identified by the chloride, sulfate and nitrate concentrations:
on average only 1/4 to 1/3 of the solutes could be attributed
to chemical weathering. Two petrologic units characterize the
river basins: granites and metasediments. The waters collected
within metasediment units are distinct from those in granite terrain
by a higher magnesium concentration. On that basis, it could be
estimated that the Rio Vouga, when leaving the mountainous part
of the basin, has for some 2*5 a signature determined by chemical
weathering in the metasediments. The dominant primary minerals
subject to chemical weathering are plagioclase (Pl) and biotite
(in granite) or Pl and chlorite (in metasediment). Kaolinite,
gibbsite and vermiculite are the major weathering products where
annual precipitation (P)＞1000 mm y-1, and kaolinite,
vermiculite and smectite where P was lower. Using an algorithm
based on the ratio of dissolved silica to bicarbonate, the contributions
of chemical weathering of primary minerals could be unraveled.
The results show that in granite the export rate (as mol ha-1
y-1 wt％ mineral-1) of oligoclase (Pl with
An10-30) was 5.0±2.6 and of biotite 3.2±2.6,
while in metasediment these rates for albite (Pl with An0-10) are 16.5±8.9 and for chlorite are 0.5±0.5.
The observed decrease of dissolved silica in surface waters relative
to springs was ascribed to (summer) uptake by aquatic biota.』
1. Introduction
2. Regional setting
2.1. Geology, petrology, mineralogy
2.2. Morphology and climate
2.3. Hydrology
2.4. Soils and land use
3. Materials and methods
4. Results and discussion
4.1. Total concentrations
4.2. Atmospheric and anthropogenic contributions
4.3. Natural contributions
4.4. Vouga water
5. mineral weathering
5.1. Modeling assumptions
5.2. Results of the SiB algorithm - springs
5.3. Results of the SiB algorithm - stream(let)s
6. Conclusions
Acknowledgements
Appendix 1. Brief outline of the Kille method
Appendix 2. Vouga data set
Appendix 3. Brief outline on the SiB algorithm
References