UMB-WEST: Second Week in Mexico 

Hola amigos!

After a week of familiarizing the group to the food, culture, language and climate of Sonora, UMB-WEST participants traveled to Rayon, Sonora to begin field work. The town, which is a two-hour drive northeast of Hermosillo, has a population that nears 1,000 residents. It is a traditional pueblo with stucco homes and lazy afternoons; a place with few stores, but many homes operating as cheese and tortilla vendors. This locale was chosen for field work because the environment is a reflection of the US-Mexico border region and is heavily affected by the summer monsoons.

Sunrise at the tower site in Rayon

The experiments implemented during this summer 2012 campaign included the following:

Collecting stem samples from Ocotillo

Isotopic Partitioning of Evapotranspiration

Because water vapor from plant transpiration and soil evaporation has unique isotopic signatures, measurements of the two can help separate the relative contribution of transpiration and evaporation at the ecosystem scale. Soil and stem samples were collected to determine the corresponding isotopic compositions of the relative proportions of evapotranspiration.

Water Vapor Isotope Analyzer

Stem samples were taken from nine representatives species of the shrubland: Prosopis velutina, Fouquieria macdougalii, Acacia cochliacantha, Jatropha cordata, Parkinsonia praecox, Mimosa distachya, Ambrosia cordifolia, Encelia farinosa and Lycium sp. A Water Vapor Isotope Analyzer (WVIA) was installed on site to analyze water vapor isotopes.

Plant Water Potential

Here, the role of the plant in ecohydrology was examined. The water potential of a plant is a sensitive indicator of the water stress of a plant, and ultimately a sign of an ecosystem’s overall health. A Scholander pressure chamber was used to measure water potential. Stems of nine different representative species were collected twice a day, before sunrise and during the afternoon.

Observing water potential of stems.

Stomatal Conductance

Measuring stomatal conductance of a mesquite tree

In another ecohydrological experiment, students used a leaf porometer to measure the stomatal conductance of nine representative plants species. Vapor loss from leaf area affects numerous terrestrial processes, even the development of the climate itself, and is a direct response to water availability. Measurements were taken daily in the early morning and afternoon.

Ecosystem Gas Exchange Measurements with Dome Structure

This experiment was by far the most foreign looking. Several students were in charge of using a large-scale static chamber to measure ecosystem fluxes of carbon dioxide and water vapor in the arid shrublands. The dome experiment was performed in natural shrubland scenery and at a buffel grass site.

Students carrying the dome at the buffel grass site.

Sap Flow Measurements

Measurements of transpiration based on sap flow allow the continuous monitoring of the physiological stage of vegetation and estimate the amounts of transpired water per unit of ground area. In this experiment, whole-water plant use in trees was quantified by measuring xylem sap  flow with Granier’s Thermal Dissipation Probe. Individual Mesquite trees were chosen for the installation of new sensors and maintenance was conducted on previously installed sensors.

Measurements of Vegetation Cover, Leaf Area Index and Vegetation Reflectance

The goal of this experiment was to validate vegetation-related Leaf Area Index (LAI) and reflectance products in MODIS/LANDSAT using a line intercept/transect method, a ceptometer and a spectroradiometer.

Soil Moisture Sampling Plots

Though most experiments were conducted at a tower site in natural vegetation, this experiment was conducted on a field of buffel grass. This year was the first time experiments were conducted near buffel grass, an invasive species grown for cattle grazing. The purpose of this experiment was to study soil variability in terms of soil moisture.

Using moisture probes at the buffel grass site.

A circular grid was created with transects spanning north, south, northeast, southeast, northwest and southwest, each venturing out 300 m. Teams were sent out to dig 60 cm holes and probe moisture at various depths. The resulting data also served as a comparative tool for the new COSMOS instrument which also aims to measure soil moisture.

The buffel grass digging crew.


A COsmic-ray Soil Moisture Observing System (COSMOS) was installed at the buffel grass site. This method of measuring soil moisture takes advantages of solar radiation and the resulting neutrons released from soil. The data collected from the instrument was compared to the soil moisture data collected from the aforementioned experiment.

COSMOS at the Buffel grass site

Overall, the science was performed smoothly. There were a few hiccups with testy equipment and the language barrier was frustrating at times, but the general feeling at the end was one of satisfaction. The first week in Mexico laid the groundwork of the whole UMB-WEST experience but the blood, sweat and tears shed during the second week really bonded the group of students and faculty. Much was learned regarding the ecohydrology of the Sonoran region and now Arizona State students can bring back the knowledge to improve situations here in the U.S. and call for a more collaborative effort between borders.

Sunset from the Rayon tower site

Final Group Photo

Thanks for reading,

Sarah Cronk
SESE Geological Sciences Undergraduate
Barrett Honors College

For more information on the hydrology program at Arizona State, visit the webpage.