SCALING UP: ESTIMATES OF BASIN-SCALE RIPARIAN NITROGEN FLUX IN THE RIO ICACOS, PUERTO RICO

Carbon (C) and Nitrogen (N) flux and uptake rates from groundwater at the riparian interface were determined at plot, reach, and basin scale along a 1.6 km third-order tropical stream in the Caribbean National Forest, Puerto Rico. At the basin scale, TDN and DOC flux rates were 3.63 ug N m-1s-1, and 168 kg C ha-1yr-1. 36% of TDN and 60% of DOC was removed from groundwater passing through the riparian zone and entering the stream. Since riparian N uptake was strongly correlated with DOC uptake (R2=0.70, p<0.005), it is likely that denitrification is an important component of riparian N uptake/loss in the Icacos. Modeling of N flux through the Icacos basin indicated that N flux rates through the riparian zone increased with stream size, and 74-82% of groundwater N entered the Icacos through the third-order main stem. This finding highlights the importance of controlling N flux to higher order streams in tropical areas, as they function less effectively as sinks/removal points for the increased fluxes of N.