Agricultural crops such as fruits take up irrigation and meteoric water and
incorporate it into their tissue (“fruit water”) during growth, and the
geographic origin of a fruit may be traced by comparing the H and O stable
isotope composition (
Teaching of environmental science and enhancement of student engagement with associated disciplines is a key focus of science education efforts in the United States and worldwide (Quinn et al., 2012). Because human activity and climate change combine to create new pressures on water resources (Pachauri et al., 2014), a comprehensive understanding of how water moves between reservoirs in Earth's subsurface, surface, and atmosphere (“the water cycle”; e.g., Oki and Kanae, 2006) is critical knowledge for students in any field of study. The economic and ecological implications of changes to the water cycle provide motivation for increased focus on environmental sciences and improvement in the teaching of these sciences in K–12 (from kindergarten to grade 12) and undergraduate science education curricula in the United States and internationally (Osborne and Dillon, 2008; Quinn et al., 2012; Ruddell and Wagener, 2013; Wagener et al., 2007). However, the invisibility of some components of the water cycle, such as inter-reservoir fluxes (e.g., atmospheric water vapor transport) is a fundamental challenge in teaching the concepts of the global water cycle (Bar, 1989; Rappaport, 2009). Anthropogenic forcings, such as transfers between watersheds in the form of water diversions for irrigation and drinking water (Good et al., 2014), further complicate the already-complex natural system.
Students' most direct connections to the water cycle are the water they drink and the food they eat. These existing connections may be a novel entry point for education. Existing studies of food provenance have been forensic studies of counterfeiting and ingredient substitutions (Cerling et al., 2016). This present work relies on the fact that agricultural crops such as fruits and vegetables take up precipitation and irrigation water during growth and incorporate it into their tissue (“fruit water”; Kramer and Boyer, 1995), which may have a specific geochemical signature in the form of its hydrogen and oxygen isotopic composition (detailed below). Therefore, if the fruit water can be linked to its source water, the geographic origin of the fruit may be determined, and the complex relationship between agriculture, transportation of crops to market, and consumption becomes more apparent.
The distance between food source and consumption represents the movement of
water out of source watersheds via trucks and trains, rather than inside
pipes, a concept known as a “virtual water footprint”, which is another
nearly invisible water transport mechanism (Hoekstra and Mekonnen, 2012;
Chen and Chen, 2013). For example, in California in 2015, 2.3
We designed a 1-day teaching activity within the context of a week-long outreach workshop that was centered on helping aspiring science, technology, engineering, and math (STEM) students and high school science teachers gain insight into the practice of science and to engage the participants in hands-on hydrological research. For this teaching activity, we developed introductory lecture materials, in-class participatory demonstrations of fruit water isotopic measurement in real time, and a computer lab exercise to couple actual fruit water isotope data with open-source online geospatial analysis software. The goals of the teaching activities were to introduce and establish key water cycle concepts, reveal human modification of the natural water cycle, introduce core concepts of stable isotope hydrology, and link these concepts together through scientific data analysis and synthesis in the context of a food sourcing study. Additionally, because the week-long workshop was conducted as outreach from large teaching and research universities towards ambitious students and teachers, an over-arching goal of the workshop activities (and this paper) was to inspire and nurture scientific interest in the participants by exposing them to a variety of environmental science activities.
In this paper, we describe how we (1) developed teaching modules about isotope hydrology and the water cycle, (2) developed novel laboratory and computer demonstrations and exercises to link water cycle components to the investigation of food sourcing, and (3) evaluated the efficacy of these teaching activities and materials. To do so, we first discuss the scientific background for this teaching activity, and provide a dataset of fruit source water H and O stable isotope values for use in the teaching activities. We then provide and discuss teaching materials in the form of lecture materials, as well as laboratory exercises and datasets, and provide results and discussion on the evaluation of the lesson's efficacy in achieving learning outcomes. The teaching materials are publicly available to the teaching community for nonprofit use, and are included in the accompanying Supplement.
Isotopes are atoms of the same chemical element (defined by the number of
protons in the nucleus) that differ in the number of neutrons. In the case
of the water molecule (H
The
The generalized relationship between
Because plants take up soil water during growth, the H and O stable isotope
composition (
A potential caveat of directly linking fruit water to a source region using
precipitation is that evaporation may occur from the soil water before plant
uptake, after plant uptake and during fruit growth, or after harvest. Water
that has undergone evaporation will have higher
Water
Labeled origins, average measured
Photograph of membrane-inlet probe (opaque white tubing) partially inserted into a tomato.
Briefly, the analytical system consists of a microporous membrane probe
attached to a laser spectrometer instrument (L2130-i, Picarro, Inc., USA)
that simultaneously measures water vapor concentration ([H
It was necessary to measure several (
Values of
This teaching and outreach activity took place in the context of a week-long outreach workshop for nine high school students with an interest in pursuing environmental science, nine undergraduate students who are actively studying environmental science and water issues, and nine high school teachers who teach physical science subjects such as chemistry and earth science. Day one of the workshop consisted of a field-based environmental sampling session where the participants collected water samples from a small creek and documented their sampling activities. Day two involved the isotope hydrology activity discussed herein. Day three consisted of collecting responses to a short survey of questions on water-related issues in an urban setting. On day four, the students self-selected into three equally sized groups divided amongst the three days' concept areas, with the goal of producing a poster exhibit communicating the scientific results of their activities. Each group was guided by a PhD-level scientist who specialized in that area of research (and who had guided that day's lesson and sampling activities). Day five consisted of a lunchtime poster exhibition where each group presented their research to a scientific audience. The workshop was designed holistically to expose students to several types of water-related research, but each component of the workshop could be a standalone activity.
The teaching activities described below consist of three components: (1) an introductory lecture on the water cycle and isotope hydrology general concepts with a participatory demonstration of fruit water isotopic measurements in real time, (2) a computer-based laboratory exercise using the fruit water H and O stable isotope dataset, and (3) learning effectiveness evaluations consisting of pre- and post-tests (Supplement Material File 4) aligned with learning objectives for activities 1 and 2 (Table 2) . The learning objectives are tied to the three dimensions of the Next Generation Science Standards (NGSS Lead States, 2013), which are science curriculum guidelines for grades K–12 in the United States. The NGSS dimensions and the teaching activity associated with each component are as follows: (A) Disciplinary Core Ideas: The Water Cycle and stable isotope hydrology, (B) Science and Engineering Practices: data collection and analysis, (C) Crosscutting Concepts: using data and geospatial relationships to evaluate food sourcing.
Learning objectives with pre- and post-test assessment
results. Asterisks indicate level of statistical significance
(
A live demonstration of the use of the isotope analyzer system to make measurements of fruit water isotopic composition as described above and utilization of student participation could be repeated in situations where the instrumentation is available, but is not required. The dataset shown in Table 1 can provide the basis for implementing the following teaching activities and materials in any teaching setting.
The first activity consists of a lecture introducing basic water cycle and stable isotope concepts, and linking them with stable isotope hydrology. The content of the introductory lesson is focused on teaching to learning objectives 1–4 (Table 2). The presentation slides used in the teaching session are available for public, not-for-profit use and are provided in the Supplement. The following discussion in Sect. 3.2 and 3.3 can be utilized as a teaching guide to accompany the introductory lesson materials. Supplement Material File numbers referenced in the following discussion refer to slide numbers in the introductory lesson presentation slides (Supplement Material File 1).
The introductory lecture begins with a presentation of the water cycle (Supplement Material File 1.2). The oceans, atmosphere, and subsurface water are all introduced as “reservoirs” where water resides for some length of time. The processes such as evaporation and runoff associated with movement between reservoirs are introduced as “fluxes”. The ways in which human activity and built infrastructure can alter the size of water cycle components are illustrated in Supplement Material File 1.3.
The chemical formula of the water molecule is introduced in Supplement Material File 1.4,
and Supplement Material Files 1.4–1.7 illustrate how atoms are composed of protons in
the nucleus with orbiting electrons, using hydrogen as an example. Isotopes
are introduced and illustrated in Supplement Material Files 1.8–1.14, again using
hydrogen as the example. The important concept for isotopes is that they are
atoms of the same element because they have the same number of protons, but
differ in the number of neutrons in the nucleus, with
The concept of stable isotope notation is introduced in Supplement Material Files 1.21–1.23,
and which can be an obstacle for comprehension and could potentially
divert a student's learning progression because the notation is represented
by a mathematical equation, the use of a Greek symbol (
Supplement Material Files 1.24–1.25 show that
In Supplement Material File 1.39 the concept of the water cycle is returned to, and includes the routing of water through plants as they use soil water to form new plant tissue, including fruits and vegetables. The table in Supplement Material File 1.40 emphasizes the amount of water in common fruits and vegetables. This is a good time to point out the fact that by harvesting fruits and vegetables and bringing them to market to be sold and later consumed, we are transporting water. The example of a tomato truck is useful in this context: a tomato truck is effectively a water truck. This is also a good opportunity to introduce the idea that irrigation is necessary to grow food crops in regions where there is not enough precipitation. The map in Supplement Material File 1.41 shows that in the arid western United States, much more water is used for irrigation than falls as rain or snow. This implies that ground water or river water must be transported from a wetter region to the agricultural region. This is an explicit anthropogenic alteration to the water cycle through exporting or importing water.
Finally, the concepts of the water cycle, stable isotope hydrology, and water in fruits and vegetables can be applied to the overarching research question (Supplement Material File 1.42): Can we use the stable isotopes of hydrogen and oxygen in water as “fingerprints” to determine the origin of fruits and vegetables? The general approach to using fruit and vegetable water to identify source regions is shown in Supplement Material File 1.43.
The computer-based laboratory exercise was designed to reinforce the
concepts covered in the introductory lecture and promote hands-on learning
using fruit water stable isotope data. The laboratory exercise materials are
made available as Supplement Material File 2 for public, nonprofit use. The
laboratory exercise makes use of the IsoMAP online isotope mapping software
and resulting data products that are publicly available under a
noncommercial reuse and attribution license (
The students are provided with detailed handouts giving step-by-step
instructions for completing the laboratory exercise, which may be worked
individually or in small groups. The exercise begins with a brief review of
concepts covered in the introductory lecture, and the material is made
available again as a reference to use in completing the exercises. The
sequence of measurement activities that yields fruit water isotope data is
reviewed, and the method for converting the measured
The students are directed to a website that hosts downloadable html files (included as Supplement Material Files 3.1–3.4) that are interactive maps allowing the student to use their mouse pointer to hover over a spot on the map and the isotope values of that spot appear. These interactive maps provide a good opportunity for the students to synthesize what they have learned about what controls the spatial distribution of stable isotopes in precipitation (e.g., temperature and geographic location) as they explore the maps. The students can also use the interactive maps to quickly survey a geographic area and identify potential growing regions for each fruit.
Graphical method of fruit source water determination by back-projecting regression line through
Next, the students are asked to use the online mapping software at
We assessed learning outcomes with evaluation pre- and post-tests (Supplement Material File 4) tied to learning objectives (Table 2), as well as participant feedback surveys. The pre- and post-tests were developed by preliminary testing beforehand on an audience with similar demographics to that of the anticipated students. Problematic questions and terminology in terms of “guessability” and embedded contextual clues on the pre- and post-tests were corrected through iterative rephrasing and testing prior to administering the evaluation tests to the participant group. The pre- and post-tests consisted of identical multiple-choice questions with four candidate answers. The tests were anonymized by having each participant label their tests with a unique four-digit number (the last four digits of their phone number). With this system, there could be a possibility to track individual learning gains, though we did not do so. Instead we assessed the learning effectiveness of the group as a whole. Calculation of statistical results was done with IBM SPSS version 23 software.
Example of an assignment map created with IsoMAP software.
Warm colors (red to orange) indicate higher probability that the fruit water
was sourced from that location, while cooler colors (blue, exclusive of
ocean area) indicate lower probability. Fruit source water
Table 1 lists the range of fruit water
Figure 3 shows example fruit water H and O stable isotope data from
apricots, bananas, oranges, and tomatoes from varied source regions in North
and South America. A primary observation is that the fruit waters are
distinct from each other when plotted in
Another important observation from Fig. 3 is that all samples within a
fruit type have generally similar
When the known source regions (from store labeling) of the apricots,
oranges, and tomatoes are combined with the source water information derived
from isotope measurements discussed above, several key water cycle concepts
can be synthesized to provide the following teaching example. The low
Having students utilize either their own pre-existing knowledge, or
knowledge gained during the teaching activity through online or literature
research, can enable better source water interpretations of the isotope data.
For example, a map of the likelihood of water source locations in North
America for the tomato water data shown in Fig. 4 is shown in Fig. 5
(data in Fig. 4 and Table 1). The red regions on the map indicate a higher
probability that the calculated fruit source water
This lack of a clear-cut geographical source solution requires the students to synthesize some of the concepts introduced in the water cycle portion of the introductory lecture and include outside information in their evaluation of the map results. For example, the prediction map in Fig. 5 shows high probabilities for tomato source water in regions of high-latitude Canada, the Laurentian Great Lakes, mountainous areas of western North America and Appalachia, as well as parts of California and Mexico. This example of a scientific analysis not yielding an unambiguous result is a useful aspect to the teaching activities. In this instance, the students must assimilate external information to determine if these are likely tomato-growing regions. In practice, similar situations are common in science, when the investigator must ask themselves if their results are reasonable, and if not, what other evidence should be collected to answer the question at hand.
The student group was reconvened after the three 1-day activity modules were completed (stream sampling for water quality, this stable isotope hydrology activity, and social science activity with surveys) and the group was asked to partition themselves into equally sized groups according to individual subject matter interest. Each group was tasked with creating a poster presentation summarizing that day's scientific activities and findings. Mentoring of the stable isotope hydrology group by one of the authors (E. Oerter) during the poster creation yielded the following qualitative observations. The participants were generally in agreement on which aspects of the water cycle and stable isotope hydrology concepts to include in the introduction portion of the poster. The participants all seemed to understand how the water cycle works and how the stable isotope signature of H and O in the fruit water could give information on where the fruit was grown. There was also general agreement about what parts of the methods were necessary to include and that photographs and conceptual plots similar to Figs. 1 and 2 would communicate what was done during the laboratory exercise. There was less agreement on what the conclusions should consist of, with roughly half of the participants feeling that a straightforward presentation of confirming the labeled origin of each food was a sufficient conclusion, while the balance of the group felt that there needed to be a stronger tie between the food sourcing aspect and general water cycle themes. Ultimately, the poster conclusions were focused largely on the food sourcing results with minor mention of the water cycle.
The teaching activities as a whole can be viewed through the lens of experiential learning theory, which is based on an iterative cycle of grasping a new concept (concrete experience and abstract conceptualization) followed by transformation of the new concept (active experimentation and reflective observation; Kolb et al., 2001; Kolb, 2014). The grasping phase consisted of the introductory lecture and fruit water isotopic measurement demonstration, followed by the transformation phase where students worked with data and explored results in the laboratory exercise. The poster creation session provided an extension to this iterative cycle, where the students were forced to articulate their new knowledge, and in so doing confront where the gaps were in their understanding and work with their peers and the instructor to fill those gaps.
The posters were presented to the entire workshop participant group with a 20 min talk where each member of the poster group focused on a particular aspect with which they felt comfortable. The presentations were followed by a brief question-and-answer period with the audience. The presentations largely confirmed observations of learning outcomes made during the small group poster creation session, with the group again divided about how far to extend the conclusions of their findings beyond simple issues of food sourcing. The question-and-answer period revealed individuals' nuanced strengths and weaknesses in specific subject areas. Audience questions that targeted tangential concepts from, or extensions of, the presented topic sometimes received answers that combined newly learned vocabulary terms in nonsensical ways. This type of response was common for questions that were at the edge of newly acquired knowledge areas, and was not limited to any particular participant demographic group. These responses suggest that the students, regardless of their age, scientific background, or public speaking experience, had not yet reached a threshold of enough exposure and usage of the new and unfamiliar knowledge of stable isotope hydrology. Threshold concept theory (Meyer and Land, 2003, 2005) posits that unfamiliar concepts without an established analogue for the student (e.g., ranges of negative numbers, such as for stable isotope values, in which the relative magnitude of each are inverse compared to that of positive numbers) can be troublesome knowledge and require sustained exposure and usage to surpass the threshold of familiarity. This outcome implies that the instructor or discussion leader should focus on core concepts over details or implications, and that more exercises in which the students work with the unfamiliar concepts are necessary to realize more learning gains.
However, presenting the activities described here in a 1 day format may be fundamentally limiting to surpassing the learning thresholds that would allow each student to transform the troublesome knowledge into tractable and readily useable concepts. A way this limitation could be overcome in a 1-day setting would be for the instructor and the course content to focus on strengthening the participants' understanding of core concepts framed in the context of pre-existing analogues. For example, stable isotope values and their relative differences could be discussed in terms of which values are “higher” and which are “lower”, instead of numerical (negative) values. Additionally, the instructor should train the students to rely on their solid understanding of the basic concepts to answer questions, and to understand and acknowledge the limits of their new knowledge.
The evaluation pre- and post-tests (Supplement Material File 4) consisted of four
questions with multiple choice answers tied to the learning objectives in
Table 2. Tests were scored by tallying the number of correct responses out
of the total possible (e.g.,
A paired-samples
Because of the small sample size, nonparametric analyses, using the
related-sample McNemar test, were also performed. Results confirmed the
significant
The evaluation pre- and post-tests were anonymized for participant identity, and we did not follow individual participant's learning progress through the exercises. In the context of a 1-day course, tracking individuals would probably be of limited value, as individualized instruction would need several sessions to implement. However, if the lessons and laboratory exercises were conducted over the course of several sessions, as would be the case in a conventional course setting, individual participant progress tracking would be beneficial and could provide improved learning outcomes for each participant.
Informal, qualitative participant feedback was solicited from participants after the conclusion of the teaching activities in the form of post-participation surveys and was combined with informal observation during the teaching activities by one of the authors (E. Oerter). These results indicated that the audience demographic groups (high school students, high school teachers, and undergraduate students) responded to the teaching approaches differently.
Interestingly, high school teachers
Contrasting learning styles extended to the structure of the lessons, with commonalities again between high school teachers and students, but not between teachers and undergraduate students. One high school teacher suggested that the teaching model, “I do, we do, you do” (i.e., the instructor first demonstrates, then the instructor and students repeat the activity together, and finally the students perform the activity unguided) would be more effective. Undergraduate students were able to follow the lab exercise instructions without guidance, but asked clarifying questions. Perhaps these results are not surprising or unexpected as the teachers have become subconsciously accustomed to how they themselves construct learning activities, while the undergraduates are currently immersed in classes that utilize the same teaching approach as the “lecture then laboratory” model used here. These disparities in pedagogic receptiveness suggest that lesson plans and approaches need to be expressly tailored to each demographic group, and that age or education level is not a good grouping denominator.
It is also worthwhile to consider potential applications for extending the teaching activities beyond that described here as a way to increase student motivation and interest. Possibilities could include the investigation of whether fruits found at local farmer's markets are sourced as claimed by a vendor, as well as applications making use of the geographical information provided by the sourcing analysis. For example, food transportation to market may involve fossil fuel resources, and therefore the carbon cycle could be tied to the water cycle. In this way, the teaching materials discussed here provide a versatile foundation to extend or build upon.
We developed, described here, and provided teaching materials in the Supplement for an education and engagement activity that introduces hydrologic concepts using H and O stable isotope measurements in fruit water. The fruit water isotope dataset provided in this paper is a useful dataset for teaching data analysis and interpretation. The core scientific disciplinary areas of hydrology, isotope geochemistry, and predictive mapping were introduced to the students through the teaching activities and laboratory exercises. We found that students gained effective learning outcomes as measured by assessment metrics, though feedback indicated that pedagogic tailoring may be a way to increase teaching effectiveness.
This pilot study provides an example of ways that real scientific data resulting from research activities can be incorporated into teaching activities. The study described here can be used as a foundation for further development of outreach materials that may effectively engage a range of participant groups in learning about the water cycle and the ways in which humans modify the water cycle through agricultural activity.
No data sets were used in this article.
The authors declare that they have no conflict of interest.
We appreciate the classroom assistance of Griffin Siebert. This research was supported by NSF EPSCoR grant IIA 1208732, awarded to Utah State University as part of the State of Utah Research Infrastructure Improvement Award. Erik Oerter's preparation of this paper was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, release number LLNL-JRNL-725565. Constructive comments by Sally Male and an anonymous reviewer helped improve this paper. Edited by: Anas Ghadouani Reviewed by: Sally Male and one anonymous referee