paired-watershed budget study to quantify interbasin groundwater flow in a lowland rain forest, Costa Rica

A paired-watershed budget study was used to quantify the annual water and major ion (sodium, potassium, magnesium, calcium, chloride, and sulfate) budgets of two adjacent lowland rain forest watersheds in Costa Rica. Interbasin groundwater flow (IGF) accounted for about two thirds of the water input and about 97% of the solute input (an average over the six major ions) to one watershed but little or none of the inputs to the adjacent watershed in which IGF was at most marginally distinguishable from zero. Results underscore the significance of IGF as a potential control on the hydrology and water quality of lowland watersheds, the spatial complexity of its occurrence in lowlands (where its influence may range from dominating to negligible on adjacent watersheds), and the importance of accounting for IGF in the design and execution of watershed studies and in water management.