Theses and Dissertations Collection

Effective watershed management is essential to maintain water quality and quantity and to protect drinking water for communities. To effectively manage water resources, managers need to understand local hydrologic processes and the temporal changes that influence these processes. However, local hydrologic processes can be complex, as a combination of many factors influences the hydrology of each watershed. In the tropics, the rainy and dry seasons lead to different hydrologic responses. This study addresses the following research questions: 1) how is spring flow generated? 2) how do stable isotopes inform our understanding of the seasonality in the tropics? and 3) does framing water resource issues in terms of spatial and temporal scales allow for new insights to identify, analyze, and resolve natural resource problems in social ecological systems? Answers to these questions are based on a combination of methodology, including stable isotope analysis, hydrometry, modeling in a microwatershed, and community interviews, to investigate hydrologic processes and watershed management in the Cartago province of Costa Rica.

The microwatershed (<1 km2) was a coffee agroforestry watershed in Aquiares, Cartago, Costa Rica. A dual stable isotope approach of oxygen-18 (δ18O) and deuterium (δ2H) was used to characterize precipitation influences in the watershed and to characterize hydrologic components. The physically based distributed Soil Moisture Routing (SMR) model was used to simulate water balance partitioning and hydrologic processes at the study site. A distinct isotopic seasonality in isotopic response was noted in this region, despite a weak hydrologic seasonality. Subsurface flow contributions were assessed to determine that lateral flow plays an important role in storm flow. The results of the SMR model showed that spring flow is an important contributor to stream flow in the study watershed. Finally, the interdisciplinary approach resulted in a tool to identify issues of scale mis-fit and for analysis of water resource management of springs in Costa Rica.