STREAM SOLUTE EXPORT AND BIOGEOCHEMISTRY IN THE LUQUILLO MOUNTAINS, PUERTO RICO

Researchers in the 326-ha Rio Icacos watershed, located in the tropical wet forest of the Luquillo Mountains, northeastern Puerto Rico, have compiled a long-term stream chemistry record revealing the catchment’s overall patterns and short-term dynamics of solute export. Stream solute concentrations reflect sea salt inputs and the rapid weathering of the underlying granodiorite. During storms solute dilution values captured in this study were among the highest in the literature. DOC evinced a unique “boomerang” pattern of concentrations increasing with discharge to a threshold and then decreasing at the highest flows. The data sets also provide context for further studies in the catchment’s nitrogen biogeochemistry. Nitrate concentrations match throughfall, suggesting steady-state nitrogen cycling. Three hurricanes passed over this watershed over the study period, after which stream nitrate concentrations increased threefold and then returned to baseline over several years. Stream N concentrations are strongly controlled by watershed N cycling, including high retention or removal in riparian floodplains. A new study of groundwater flowpaths and N transformations in these riparian biogeochemical hotspots will also be discussed.