Nutrient concentrations and N speciation in an unpolluted tropical forested watershed, Panama

Human activities have considerably increased the availability of reactive nitrogen. Now, many streams carry large nitrate loads to inland and coastal waters. Nevertheless, mass balance studies have shown that a significant portion of the terrestrial N load does not reach coastal systems, suggesting the existence of important N removal processes. Denitrification has been suggested as an important sink of N in inland waters, which is true in temperate regions of the Northern Hemisphere where most streams contain high nitrate concentrations. However, the global distribution of reactive nitrogen is far from uniform. Recent studies have shown that nitrogen loss from pristine watersheds occurs mainly via dissolved organic compounds, and that the amount of inorganic nitrogen is only a fraction of the total dissolved nitrogen. Herein we present chemistry data from streams within the upper Rio Chagres watershed, a pristine, densely forested watershed in the humid tropics of central Panama. Contrary to that observed in temperate watersheds of the Northern Hemisphere, DIN concentrations in the Rio Chagres and tributaries were low (mostly 10 uM.