Solute behaviour and export rates in neotropical montane catchments under different land-uses
<jats:title>Abstract:</jats:title><jats:p>To improve our knowledge of the influence of land-use on solute behaviour and export rates in neotropical montane catchments we investigated total organic carbon (TOC), Ca, Mg, Na, K, NO<jats:sub>3</jats:sub>and SO<jats:sub>4</jats:sub>concentrations during April 2007–May 2008 at different flow conditions and over time in six forested and pasture-dominated headwaters (0.7–76 km<jats:sup>2</jats:sup>) in Ecuador. NO<jats:sub>3</jats:sub>and SO<jats:sub>4</jats:sub>concentrations decreased during the study period, with a continual decrease in NO<jats:sub>3</jats:sub>and an abrupt decrease in February 2008 for SO<jats:sub>4</jats:sub>. We attribute this to changing weather regimes connected to a weakening La Niña event. Stream Na concentration decreased in all catchments, and Mg and Ca concentration decreased in all but the forested catchments during storm flow. Under all land-uses TOC increased at high flows. The differences in solute behaviour during storm flow might be attributed to largely shallow subsurface and surface flow paths in pasture streams on the one hand, and a predominant origin of storm flow from the organic layer in the forested streams on the other hand. Nutrient export rates in the forested streams were comparable to the values found in literature for tropical streams. They amounted to 6–8 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for Ca, 7–8 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for K, 4–5 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for Mg, 11–14 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for Na, 19–22 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for NO<jats:sub>3</jats:sub>(i.e. 4.3–5.0 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>NO<jats:sub>3</jats:sub>-N) and 17 kg ha<jats:sup>−1</jats:sup>y<jats:sup>−1</jats:sup>for SO<jats:sub>4</jats:sub>. Our data contradict the assumption that nutrient export increases with the loss of forest cover. For NO<jats:sub>3</jats:sub>we observed a positive correlation of export value and percentage forest cover.</jats:p>