AN EVENT BASED GEOCHEMICAL ASSESSMENT OF THE TROPICAL DRY TO WET SEASON TRANSITION UNDER FOREST AND MIXED LAND USES IN THE PANAMA CANAL WATERSHED

The effects of land use and land cover on tropical hydrology is an important topic, yet these effects are poorly understood. Many tropical watersheds support large populations, and are susceptible to floods and droughts, which lends special importance to improve understanding of land use and land cover effects to inform management decisions. A prototypical tropical watershed with a significant period of hydrological record is the Panama Canal Watershed. The Smithsonian Tropical Research Institute’s Agua Salud Project was designed to test hypotheses regarding the effects of land use and land cover on hydrological and other ecosystem services. Preliminary hydrological results indicate that land use and land cover have extensive effects on hydrological response, yet the mechanisms are poorly understood. This study investigates stable water isotopes in rainfall and various stores of water, and major ion hydrogeochemistry in runoff during a dry to wet seasonal transition. Event-based geochemical results from groundwater, streamflow, and rainwater are coupled with physical observations in streamflow and rainfall. Hydrologic and geochemical behavior is compared and contrasted amongst mature forest, secondary forest, and pasture with the goal of observing changes in flow path and residence times.