Spatial and temporal patterns in the chemistry of temperate low order Andean streams: effects of landscape gradients and hydrology

Abstract

Cold-temperate headwaters of Patagonia are interdigitated in a narrow sector of the Andes mountains devoid of anthropogenic impacts and thus are suitable systems to evaluate the climate and landscape controls on terrestrial-aquatic fluxes. In this investigation we focused on evaluating dissolved organic matter (DOM) and nutrient dynamics in a stream born in a mountain lake draining a steep forested catchment, a typical configuration of Andean-Patagonian headwaters. Stream water chemistry was studied throughout the hydrologic year and at different sites along the altitudinal drainage gradient. The analyses showed extremely low nutrient and dissolved organic carbon (DOC) concentrations and low primary production within the ranges of ultraoligotrophy. Pulses of terrestrial DOM and nutrient inputs were detected during rainfall events and in snowmelt periods, shifting distinctively the nutrients as well as the DOC concentration and quality from baseflow conditions. Stream DOM pools, characterized through optical methods, showed the prevalence of terrigenous humic components (C1 and C2) and a small contribution of a non-humic component (C3), with rainfall runoff increasing the C2 and snowfall enhancing the C3. Stream sites at higher elevation were influenced by the upstream lake showing signatures of phytoplankton production and degradation in their DOM pools, whereas downstream points displayed higher terrestrial prints.The results presented here contribute to understanding carbon and nutrient dynamics in cold-temperate pristine freshwaters of the Southern Hemisphere, which are underrepresented in global studies and differ substantially from temperate systems of the Northern Hemisphere in terms of climate and anthropogenic pressures.