The timescales associated with precipitation moving through watersheds reveal processes that are critical to understanding many hydrologic systems. Measurements of environmental stable water isotope ratios (δ 2H and δ 18O) have been used as tracers to study hydrologic timescales by examining how long it takes for incoming precipitation tracers become stream discharge, yet limited measurements both spatially and temporally have bounded macroscale evaluations so far. In this observation driven study across North American biomes within the National Ecological Observation Network (NEON), we examined δ 18O and δ 2H stable water isotope in precipitation (δP) and surface water (δQ) at 26 co-located sites. With an average 54 precipitation samples and 139 surface water samples per site, assessment of local meteoric water lines (LMWL) and local surface water line (LSWL) showed geographic variation across North America. Taking the ratio of estimated seasonal amplitudes of δP and δQ to calculate young water fractions ( Fyw), showed a Fyw range from 1% to 93% with most sites having Fyw below 20%. Calculated mean transit times (MTT) based on a gamma convolution model showed a range from 0.10 to 13.2 years, with half of the sites having MTT estimates lower than 2 years. Significant correlations (r) were found only between the Fyw and watershed area, longest flow length, and the longest flow length/slope, whereas the only significant correlation observed for MTT was with site latitude. The estimated Fyw and MTT provide information describing hydrologic processes at NEON sites, however limited correlations of Fyw and MTT with the environmental characteristics we analyzed demonstrate that these quantities are primarily driven by site or area specific factors. The analysis of isotope data presented here provides important constraints on isotope variation in North American biomes and the timescales of water movement through NEON study sites.

Catchment studies provide foundational scientific knowledge that is relevant to policy, resource management, education, outreach, and public awareness of the environment and environmental problems. Through a concerted effort to highlight the catchments and catchment studies behind a rich legacy of scientific findings, we have led several efforts to promote long-term and place-based research at monitoring, observatory, and ecosystem study sites. Our efforts have included sessions at AGU and other professional meetings, a special issue of Hydrological Processes, and a CUAHSI Cyberseminar series on monitoring and observation at research catchments that span the globe. In this poster, we continue to promote the catchments and innovative research at those sites by summarizing our efforts and updating a map of the catchment studies that we have identified. Our primary objective is to stimulate discussion about the vibrant state of the catchment sciences, the sites that make the science possible, and how to move forward in coming decades.