This Major Research Instrumentation (MRI) program grant supports acquisition a cavity ring-down spectrometer (CRDS) for analysis of stable isotopes of H and O in water and solid geological and biological materials (e.g., sediments, soils, wood and plant tissues). The CRDS will support research and research training at Union College, a non-Ph.D. granting institution. The instrument will support undergraduate student training in methods of stable isotope analysis and related hydrological and paleoenvironmental research applications and the investigators plan regional K-12 outreach and teacher training in the fundamentals of watershed and isotope hydrology. The CRDS will support the investigations of a minimum of 22 faculty researchers from 15 institutions, the lab component of 12 courses, and upwards of 25 undergraduate research students annually, with findings from the proposed research disseminated through presentations at professional meetings and peer-reviewed publications. Proposed research projects align with NSFs mission of promoting the progress of science and advancing national health, prosperity, and welfare by supporting environmental research aimed at understanding the water cycle and the Earth?s climate, which have implications for water resource management and confronting challenges stemming from a changing climate. <br/><br/>The CRDS will enable a number of major research projects on the application of stable water isotopes to: (a) characterize aquifer systems and surface-water-groundwater interaction with the aim of assessing risks to water quality (with a focus on arsenic) and availability, (b) examine non-rainfall water (fog/dew) contributions to aquifers in coastal and mountains regions, (c) explore the role of catchment characteristics on streamflow ages and the attending implications for solute and contaminant fate and transport through watersheds. Other hydrologic research includes research on geothermal waters in the Caribbean ? work that has important implications for understanding and predicting volcanic unrest. The CRDS will also advance paleoclimate research, with projects on paleoclimate archives from the Peruvian Andes (lake cores and stalagmites), the development of bivalve shell proxies in several environments, and a detailed study on oxygen isotopes in tree rings. In addition, other research projects involving plant-soil water dynamics, terrestrial biogeochemistry, and a watershed isotope study will benefit from the proposed instrumentation. The CRDS system will allow for the high-volume throughput required of the ongoing and proposed research. Furthermore, the CRDS will add the capability to measure ?17O, allowing us to better characterize evaporative processes in the environment ? a capability critical to many hydrologic, ecologic, and climatologic studies.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.