Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/21/2011
Publication Date: 10/22/2011
Citation: Bowen, G.J., Kennedy, C.D., Liu, Z., Stalker, J. 2011. Water balance model for mean annual hydrogen and oxygen isotope distributions in surface waters of the contiguous US. Journal of Geophysical Research-Biogeosciences. 116. DOI: 10.1029/2010JG001581. Interpretive Summary: The stable hydrogen and oxygen isotope composition of stream water provides a signature of the runoff sources and land/atmosphere water fluxes within the catchment, and is a potentially powerful tool for network-based monitoring of large ecohydrological systems. Models for predicting the isotopic composition of stream water, which is used for human drinking supplies and agricultural irrigation, were developed and validated against an existing stream-water isotope dataset. The stable isotope signature of stream water that is used for agricultural crops is preserved in the organic tissues of plants, providing a fingerprint of the source water of the plant. This isotopic signature may be used to screen for adulterated fruit juices, with a measured isotopic value that varies significantly from the modeled value indicating possible adulteration (e.g., European regulations state that juices having isotope values lower than delta18O = 0 and deletaD = -15 have been watered down). The newly-developed models make this type of authentication more accessible to smaller crops – such as for cranberries in Massachusetts – that may not have the financial resources for long-term hydrological monitoring of stream-water isotopes.
Technical Abstract: The stable H and O isotope composition of river and stream water records information on runoff sources and land/atmosphere water fluxes within the catchment, and is a potentially powerful tool for network-based monitoring of large ecohydrological systems. Process-based hydrological models, however, have thus far shown limited power to replicate observed large scale variation in USA surface water isotope ratios. Here we develop a geographic information system-based model to predict long-term annual average surface water isotope ratios across the contiguous USA. We use elevation-explicit, gridded precipitation isotope maps as model input and data from a United States Geological Survey monitoring program for validation. We find that models incorporating monthly variation in precipitation-evapotranspiration (P-E) amounts account for the majority (greater than 89%) of isotopic variation and have reduced regional bias relative to models that do not consider intra-annual P-E effects on catchment water balance. Residuals from the water balance model exhibit strong spatial patterning and correlations that suggest model residuals isolate additional hydrological signal. We use interpolated model residuals to generate optimized prediction maps for USA surface water deltaH-2 and deltaO-18 values. We show that the modeled surface water values represent a relatively accurate and unbiased proxy for drinking water isotope ratios across the USA, making these data products useful in ecological and criminal forensics applications that require estimates of the local environmental water isotope variation across large geographic regions.