Topography and Land Use Modulate Hydrological and Nutrient Export Dynamics in two Andean Streams

Abstract

Fluvial dynamics are driven by multiple environmental factors and scales. Studies coupling hydrological and nutrient dynamics of Andean streams are almost nonexistent. We characterized two adjacent streams with contrasting drainage basins: Casa de Piedra, originating in a small mountain lake and running through a pristine landscape, and Gutierrez, originating in a large piedmont lake and running through an anthropized landscape. Despite both drainage basins sharing geology and climate, we found that the streams presented contrasting hydrological and nutrient dynamics. Casa de Piedra had higher discharge flashiness with shorter response delays to precipitation. Interestingly, Gutierrezs hydrology was buffered by the upstream lake, but its nutrient exports were not. Differences observed in quality and timing of coarse particulate organic matter export and basal export levels of phosphorus and nitrogen could be explained by human activities affecting Gutierrez but not Casa de Piedra. Moreover, nitrogen:phosphorus ratio indicates a possible future shift to phosphorus as the limiting nutrient as Andean basins become more densely populated. In summary, our annual basis study shows that even under a common geology and climate, stream dynamics of adjacent basins can be starkly different due to differences in topography and land use.