The Manso River Drainage System in the Northern Patagonian Andes: Hydrological, Hydrochemical and Nutrient Dynamics

Abstract

The Manso River system is a mountainous basin fed by rain, snow andglacier meltwater from the Patagonian Andes. Glaciers located in the uppermostbasin have shown a significant retreat though the last decades. Most of the annualprecipitation occurs during austral winter and, together with meltwater, generatesa bimodal annual hydrograph. Mean annual discharge increases from 12.5 m3 s−1in the upper basin, to ~80 m3 s−1 in the lower basin. The historical discharge ofthe Manso Superior (i.e. Upper) River shows a significant positive trend due tomeltwater discharge increase, generating the growth of the Proglacial lake. LakeMascardi and the Manso Inferior (i.e. Lower) River show a negative statistical trendin their respective mean discharges. The hydrochemical signal of theManso River isdetermined by dominating geochemical processes along the basin: the upper basin ishighly influenced by the Manso Glacier dynamics, where pyrite oxidation generatessulfate-calcic waters, and it is responsible for the scavenging of phosphorous fromthe solution, causing a lowsoluble reactive phosphorous/total phosphorous ratio. Thelow N:P ratio indicates that nitrogen limits algal growth. In the middle and lowerbasin, the silicate hydrolysis is the dominant process, generating bicarbonate waters.The Manso River system appears to be highly sensitive to climate change, which isan attribute influencing both, the hydrological and geochemical signals.