Water balance model for mean annual hydrogen and oxygen isotope distributions in surface waters of the contiguous United States

Abstract

[1] 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 ecohydrological systems. Process-based hydrological models, however, have thus far shown limited power to replicate observed large-scale variation in U.S. 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 United States. We use elevation-explicit, gridded precipitation isotope maps as model input and data from a U.S. Geological Survey monitoring program for validation. We find that models incorporating monthly variation in precipitationevapotranspiration (P-E) amounts account for the majority (>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 U.S. surface water d 2 H and d 18 O values. We show that the modeled surface water values represent a relatively accurate and unbiased proxy for drinking water isotope ratios across the United States, 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.Citation: Bowen, G. J., C. D. Kennedy, Z. Liu, and J. Stalker (2011), Water balance model for mean annual hydrogen and oxygen isotope distributions in surface waters of the contiguous United States,

The Global Network of Isotopes in Rivers (GNIR): integration of water isotopes in watershed observation and riverine research

“…Immerzeel et al, 2010;Huss, 2011). Especially in ungauged catchments, but also in addition to quantitative studies, this method may be applied to evaluate glacier or permafrost contributions, or to observe winter / summer runoff ratios, as proposed by Bowen et al (2011). Finally, the CC-RCWIP-modelled seasonal amplitude of δ 18 O P was not correlated to the seasonal amplitude of δ 18 O R , which confirmed the results from the direct comparison of GNIP and GNIR station data (Fig.…”

“…In general, the CC-RCWIP model results showed that averaged δ 18 O values in river water samples were strongly correlated with amount-averaged precipitation in the upstream catchment of a river station. This finding underscored that the average isotopic composition of river water reflected amountaveraged rainwater on a global scale, as was also observed regionally for the United States by Fekete et al (2006) and Bowen et al (2011). These model comparisons provided a comparative tool whereby isotopic deviations of rivers from average precipitation revealed natural or anthropogenic Figure 9.…”

“…One major challenge comparing terrestrial rainfall inputs with point-based river isotope locations was the fact there were usually few GNIP stations distributed across watersheds, and they were rarely in locations that may be considered representative of all precipitation in a watershed. Some have proposed mathematical models to derive the comparability of the isotopic composition of rivers to rainfall, but these models rely on discrete but sparsely distributed GNIP station data or were applied regionally (Landwehr and Coplen, 2006;Bowen et al, 2011). To overcome this GNIP coverage limitation, we used a catchment-constrained version of the regionalized cluster-based water isotope prediction (RCWIP) model based on GNIP data (Terzer et al, 2013).…”

“…The cumulative effect of catchment-scale evapotranspiration and instream evaporative processes may additionally increase δ 18 O and δ 2 H values in the downstream direction. Rivers that are hundreds of kilometres long may therefore have distinctive upstream versus downstream isotopic patterns as they accumulate discharge and integrate various hydrological processes from contributing subcatchments (Simpson and Herczeg, 1991;Gremillion and Wanielista, 2000;Ferguson et al, 2007;Bowen et al, 2011). Alpine or high-latitude rivers may be ephemeral, dominated mostly by isotopically depleted snowmelt events (e.g.…”

Willamette River Basin surface water isoscape (δ18O and δ2H): temporal changes of source water within the river

“…Because the stable isotope composition of precipitation varies geographically (Dansgaard 1964, Bowen andWilkinson 2002), variation in the stable isotope composition of river water indicates the volume-weighted integration of source water within the watershed (Bowen et al 2011). The spatial variation of river water stable isotopes has been characterized at the continental scale from the USGS National Stream Quality Accounting Network (NASQAN, Coplen 2001, Dutton et al 2005).…”