Abstract
The Chubut River’s mean annual discharge is ~1.1 km3 (~35 m3 s−1), contributes ~2% to Patagonia’s total freshwater discharge, and ranks far behind the mighty Negro River (~32 km3 y−1). In a semiarid scenario, the river has a mountainous active basin, low runoff (<3.5 mm y−1), and a scanty specific water yield (1.1 L s−1 km−2). The seasonal Kendall trend test shows that discharges during the low-water months (Jan.–Mar., May) have been significantly decreasing during the last decades. Ca2+–HCO3− are the governing ions in the headwaters but the composition gradually shifts to a Na+-type toward the lowermost reaches. Numerous Andean glaciers suggest that subglacial oxidation of pyrite may be an active solute-supplying mechanism. Silicate hydrolysis and limestone dissolution—implied by non-radiogenic 87Sr/86Sr ratios—are the processes ruling chemical weathering. The Chubut is a mesotrophic river, with a moderate organic load (mean TOC ~290 µmol L−1, and mean yield ~10.5 mmol m−2 y−1; ~60% accounted for by DOC). Suspended sediment yield at Los Altares (~14 T km2 y−1) and in the lowermost reach (~25 T km2 y−1) indicate a relatively low denudation. The alteration index of riverbed sediments (mean CIA ≈ 55) suggests scarce weathering; REE spider diagrams of sediments shows a signature compatible with continental island arcs.
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Notes
- 1.
Chubut comes from the aboriginal (i.e. tehuelche) word chupat, which means “transparent”. Welsh settlers called the river “Afon camwy”, meaning “twisting river”.
- 2.
According to Argentina's glacier inventory (https://www.argentina.gob.ar/ambiente/agua/glaciares/inventario-nacional), there are over 1500 ice and rock glaciers and snow buildups in Chubut's Andean region, covering a surface area of ~225 Km2.
- 3.
Also reported as particulate organic matter or POM.
- 4.
The global DOC average concentration fluctuates between ~400 and 480 µmol L−1 (Perdue and Ritchie 2005).
- 5.
DIC = (CO2*) + (HCO3−) + (CO32−), where (CO2*) = (CO2) + (H2CO3).
- 6.
Mean POC/PN ≈ 10, thus suggesting a dominant origin in the terrestrial environment.
- 7.
The Los Altares gaging station is 230 km upstream from the city of Trelew and over 250 km from the estuary.
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Depetris, P.J., Pasquini, A.I. (2021). Patagonia’s Chubut River: Overview of the Main Hydrological and Geochemical Features. In: Torres, A.I., Campodonico, V.A. (eds) Environmental Assessment of Patagonia's Water Resources. Environmental Earth Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-89676-8_6
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