The Stable Isotope Facility installed the Berry Prairie Precipitation Collector so every precipitation event could be captured and analyzed for stable isotopes. Here’s why:
Isotopes are atoms of the same element (think periodic table, like hydrogen, nitrogen, oxygen, etc.) that have different numbers of neutrons; that is, they have the same number of protons and electrons, but differ in molecular weight due to different numbers of neutrons. Radioactive, or unstable isotopes, decay (which makes them harmful), whereas stable isotopes do not decay. The stable isotopes for water are 2H and 18O. Stable isotopes are present everywhere, but the ratio of the lighter (common) and heavier (uncommon) isotopes (e.g., H : 2H) changes from place to place.
When water evaporates from the ocean, the water vapor travels away from the ocean and precipitation occurs (see figure). When precipitation happens, the rain (or snow) that condenses is enriched in the heavier isotopes – heavier isotopes fall out before lighter ones. The remaining water vapor in the airmass then is composed of lighter isotopes. Subsequent precipitation has an increasingly lighter stable isotope composition.
The stable isotope composition in the precipitation reflects both the origin of the water vapor (ocean, lake, river) and the conditions under which the condensation occurred (temperature, elevation, distance from the equator). Oxygen and hydrogen isotopes in water can be used to trace the hydrological cycle from evaporation in the oceans to local precipitation and groundwater. Monitoring the isotope ratios at a single location through different seasons and over a long period of time establishes a record of changes in air circulation patterns that produce precipitation, and is the foundation for understanding vegetation function, animal diet and migration.
Based on figure in Hoefs 1997 and Coplen et al. 2000
In the study of animal migration, using stable isotopes has an advantage in that it does not require initial marking of individuals (radio collars, bands, etc.); all that is required is that an animal moves from one isotopically distinct habitat to another. It is particularly informative for those animals that are too small to attach transmitters, for example insects.
To understand the approach, let’s look at hydrogen. Hydrogen occurs in two stable isotopes: 1H and 2H. Both forms, when combined with oxygen, create water. But water created from 2H is heavier and condenses to form rain faster than water created from 1H. Because there is more precipitation near the equator, and less near the poles, ratios of the hydrogen isotopes (δ2H, said as “delta H 2”) vary by latitude. In other words, the further away from the equator, the less 2H is found in the precipitation.
When rain falls in an area, the plants absorb the rainfall, and the plants, as well as animals that consume the plants or drink from a nearby pond, reflect the isotopic ratio of the precipitation. Thus, a researcher can use the δ2H measured values to help determine the geographic origin of a plant, or of an insect and even a bird that ate that plant or insect. . One requirement of such studies is having a database of the δ2H in the regional precipitation, a project not yet completed for Wyoming.
Above is a map, often called an isoscape, showing a model of the isotope bands within the US. This modeling was based on hair collected from barber shops in 65 cities across the country. Although this gives a good idea of the isoscape of the country, it is not very specific to Wyoming and its geographic variances. Once the waters are collected from around the state, a more detailed isoscape can be mad
Scientists collected summer-grown feathers from American Redstarts in their winter range (Central America and Caribbean). Based on measurements of the H isotopic composition of the feathers, they were able to predict where in North America the birds had spent the summer breeding season. In the figure (below), horizontal bars show the fraction of individuals collected at each wintering site (dots) assigned to each breeding range (colored polygons) based on feather isotopic composition and an isoscape predicting compositions of locally grown feathers (background color field). This example shows a pattern of chain migration, where birds breeding in the northern part of the breeding range, for example, tend to migrate to the northern part of the wintering range.
Several scientists at the University of Wyoming are interested in calculating the contribution of melting glaciers to streams in Wyoming. This is not a purely academic question—it has been estimated that about one sixth of the world’s people rely on glacial melt for a significant portion of their water needs.
In 2011, Dr. Dave Williams and his colleagues, working in the Wind River Range, used the stable isotopes of water to describe the contribution of glacier water to streamflows leaving the Wind River Range. For two years they sampled meltwater directly from Dinwoody Glacier and from melting winter snowfall, and collected summer rain and winter ground water. These first three sources have different δ2H and δ18O due to the different climatic conditions during precipitation. As you’d expect, glaciers and annual snow are more similar to each other than to summer rain, but because the glacier formed during colder conditions than generally exist in Wyoming today, the glacial meltwater is relatively enriched in heavy isotopes compared to snow. Summer precipitation is much lighter; ground water, not surprisingly, is a mixture of all three sources.
Using a complex model, the scientists showed that glacial meltwater accounts for approximately half of the late summer flow of Dinwoody Creek. This means that a decline in the overall size of the glaciers of the Wind River Range due to increasing global temperatures is expected to have a negative long-term effect on streamflow, potentially impacting fisheries, recreation and agricultural use of the region, especially during low-snowfall years.
Our surface waters are largely derived from snowmelt, but many towns use a mixture of surface and deep water. For example, Laramie takes water from the Laramie River and from the Casper aquifer, the proportion of each varying both across the city and seasonally. In Wyoming, where water is a scarce commodity, the sourcing and usage of water is an important concern for managers and users of water—in other words, for everybody.
Together, we can learn a lot!
By collecting precipitation at your school, you can help the Stable Isotope Facility create a map of the δ2H and δ18O signature of meteoric water across Wyoming. Having access to such data will help researchers to better understand vegetation functions and local animal migratory patterns. These data are available for anyone’s use—what questions would you like to answer? In exchange for your help, the Biodiversity Institute will provide a rain gauge for your school, instructions, training and vials, and provide a prepared introductory lecture suitable for your classroom. Data from your school and other stations across Wyoming will be made available, along with the expertise of researchers who use stable isotope analysis in their work. For more information on how your school can participate contact Dorothy Tuthill at 307-766-6279 or firstname.lastname@example.org.
Many of the Next Generation Science Standards for middle and high school students can be met with projects involving stable isotope analysis. Closely related Disciplinary Core Ideas include:
The Stable Isotope Facility and the Biodiversity Institute can help you design and conduct an experiment for school or science fair. Contact Dorothy Tuthill (email@example.com) for more information.
The Knowledge Project has nice introduction to the use of isotopes in migration studies at http://www.nature.com/scitable/knowledge/library/the-use-of-stable-isotopes-in-the-96648168.
Bowen, G.J. 2010. Isoscapes: Spatial Pattern in Isotopic Biogeochemistry. Annual Review of Earth and Planetary Sciences 38: 161-187.
Cable, J., K. Ogle and D. Williams. 2011. Contribution of glacier meltwater to streamflow in the Wind River Range, Wyoming, inferred via a Bayesian mixing model applied to isotopic measurements. Hydrological Processes 25: 2228–2236.
Coplen TB, Herczeg AL, Barnes C. 2000. Isotope engineering — using stable isotopes of the water molecule to solve practical problems. In Environmental Tracers in Subsurface Hydrology, Cook PG, Herczeg AL (eds). Kluwer Academic Publishers: Boston; 79 – 110.
Ehleringer JR, Bowen GJ, Chesson LA, West AG, Podlesak DW, Cerling TE. 2008. Hydrogen and oxygen isotope ratios in human hair are related to geography. Proc. Natl. Acad. Sci. USA 105:2788–93
Hoefs, J. 1997. Stable Isotope Geochemistry. Springer-Verlag, Berlin.
© 2017 University of Wyoming Biodiversity Institute.