Applications of spatial water isotope data to basic and applied science

Hydrology:

• Stable water isotopes provide an incredibly useful tool for establishing connectivity of water resources. Hydrologists and hydrogeologists have been using water isotopes as a component of mixing and recharge models for decades, and a variety of intellectual and practical applications have been developed. Spatial analysis of water isotope data in a GIS environment, however, is a new endeavor, and current developments in this area are well-timed to take advantage of the recent emphasis on catchment to basin-scale hydrology. Our work has involved studies of the geospatial distribution of surface water (Dutton et al., 2005) and tap water (Bowen et al., 2007) isotope ratios to investigate the hydrological connectivity between water resources and hydro-climatic sources.

(Paleo)climatology:

• Studying the modern geospatial and temporal distribution of precipitation water isotopes can improve our understanding of how features of the climate are represented in water isotope data. Two approaches can be applied: we can study the static representation of mean climatic patterns in modern water isotope data to understand what salient features of the climate system are recorded, or we can study temporal patterns in stable water isotope distributions to understand what climate phenomena strongly affect water isotope ratios. I am pursuing both approaches in my work, with an emphasis on representation of climate seasonality (Bowen, 2008) and atmospheric circulation in spatial stable isotope fields.
• Geospatial interpretation of paleo-archive proxy data for water isotope ratios is still in its infancy. Increased understanding of the features of the modern spatial fields of water isotope ratios and recent advances in the analysis of H and O isotopes in organic compounds should lead to developments in this field over the next 5 years.

Ecology:

• Stable water isotopes are increasingly used in wildlife forensics studies, most commonly in studies of animal migration. A number of important studies have been published since 1997. My work has explored the basic premise that information on the geographic origin of migrant animals is recorded in the stable water isotope composition of their body tissues, and developed guidelines for applying this method in wildlife forensic studies. This work is described in two papers published in Oecologia. In the first, we use a new dataset of hydrogen and oxygen isotopes in European bird feathers to investigate the potential for identifying the wintering sites of European migrant birds using stable isotopes, with reference to spatial water isotope grids created using a variety of methods (Hobson et al., 2004). In the second, we adopt a broader focus, presenting the first global maps of growing season water isotope values and describing how they can be used to statistically constrain the location of origin of animal or plant samples (Bowen et al., 2005). We have applied these methods to study the migratory (Bearhop et al., 2005) and the dietary ecology of Pleistocene raptors (Fox-Dobbs et al., 2006).

Forensics:

• The use of hydrogen and oxygen isotope ratios as forensic tracers of biological tissues, foods, and manufactured materials has exploded in recent years. Body tissues like human hair and tooth enamel serve as an archive of information on a person's life and travel history. Research is ongoing to develop generalizable models and isoscapes describing the spatial patterns of water isotopes in such tissues. Increasingly, these approaches are being translated to practice. Companies like Oritain, FloraTrace, and Eurofins are working with governments and corporations to use water isotope data to trace the origin of foods and other products. Independent researchers and practitioners are both developing and providing expert advise - for example, through my consulting company Bowen Scientific, I work with law enforcement agencies, companies, and attorneys to support isotope applications. The growing isotope forensics community is supported through a professional organization, the Forensic Isotope Ratio Mass Spectrometry Network, which organizes conferences, provides training and accrediation programs, and issues best practices guidelines for isotope forensics.