A Hydrological and Biogeochemical Appraisal of Patagonia’s Río Gallegos

Abstract

The Gallegos is the southernmost river of continental Patagonia. It has the smallest drainage basin of all the main rivers in the region. Moderate atmospheric precipitations (~500 mm y−1 in the uppermost catchments) determine discharge maxima in austral winter (rainfall/snowfall) and spring (snowmelt), delivering ~0.573 km3 y−1 of freshwater (i.e. ~57 L m2 y−1) into an ample estuary in the SW Atlantic Ocean. The Gallegos stands out among the remaining Patagonian rivers for its connection (~18-month significant squared coherency) with the Southern Annular Mode, and due to its biogeochemistry, which appears affected by groundwater and debris, both associated to some degree with Eocene bituminous coal beds. The relevant factors seem to be: (a) the marked prevalence of NO3−–N among nutrients (N:P = 50:1–60:1); (b) the mean DOC concentration (~500 µmol L−1), higher than all remaining Patagonian rivers (mean of ~300 µmol L−1), and linked to river discharge; (c) high DIC, correlated with high pCO2 (probably groundwater-supplied); (d) mean POC/PN molar ratio of ~8:1 (the highest in Patagonia’s rivers), leading to infer a terrigenous source with some planktonic contribution. High DOC concentrations (~1000 µmol L−1) are associated with low δ13CDIC (~−11 per mil), probably controlled by carbonate dissolution. Mean TOC in the Gallegos River is ~700 µmol L−1, 70% of which is accounted for by DOC.