Influence of hydrological regime of an Andean river on salinity, temperature and oxygen in a Patagonia fjord, Chile

Abstract

Patagonian fjord ecosystems might experience new scenarios due to climate variability (decreasing annual precipitation and glacier melting) in the short term. Herein, we studied the seasonal variability of the Puelo River regime (North Patagonia, 1944–2007, mean streamflow: 650 m3/s) and analyses its influence on surface salinity, temperature and dissolved oxygen in the well-stratified Reloncaví Fjord (41.5°S). Our results show a decreasing trend in the Puelo River streamflow since the late 1970s that is frequently associated with regimes lacking a defined interannual pattern. During the study period, years with prolonged periods of low streamflows in autumn and winter were common. On a scale of hydrological years, the influence of the Puelo River on the surface layer of the Reloncaví Fjord varied strongly in function of both the river's streamflow level and regimes. Years with markedly mixed regimes (rainfall/snowmelt), high autumn and spring streamflows (Q>1000 m3/s) resulted in significantly cooler, fresher conditions in the fjord. These temporal patterns, in turn, determined high, constant saturations (100%) and concentrations (10 mg/l) of surface dissolved oxygen. By contrast, the discharge pattern of 2007 led to stable, low streamflows in autumn and winter (Q=250 m3/s) that did not influence temperature or salinity. A significant association was found between the temporal variability of the salinity (increasing from 6 to 28 psu) and low dissolved oxygen saturation (<50%) and concentration (<5 mg/l), largely dominated by wind events.