​The Goldsmith Lab has been awarded the 2019 Ignacio Rodriguez-Iturbe award for an outstanding publication from the journal Ecohydrology for their article quantifying the spatial variation in stable isotopes of water in a forest ecosystem. The research establishes best practices for using stable isotopes of water as a tool for understanding the source of water used by different species of trees in forest ecosystems:
 
Spatial variation in throughfall, soil, and plant water isotopes in a temperate forest
by Gregory R. Goldsmith, Scott T. Allen, Sabine Braun, Nadine Engbersen, Clara R. González‐Quijano, James W. Kirchner, Rolf T.W. Siegwolf 
  
The results are part of a long-term collaboration designed to inform the sustainable management of Switzerland’s forests in the face of unprecedented rates of climate change.
 
The project was carried out in collaboration with researchers from the Institute for Applied Plant Biology, the Swiss Federal Institute for Forest, Snow and Landscape Research and ETH Zurich with funding from the Swiss Federal Office of the Environment.

We have a new preprint posted to Edarxiv from the teaching team in the Grand Challenges Initiative at Chapman University: 

Discussion can be an important and powerful tool in efforts to build a more diverse, equitable, and inclusive future for STEM. However, facilitating discussions on complex and uncomfortable issues, like racism and sexism, can feel daunting. We outline a series of steps that can be used in offices, laboratories, and classrooms to facilitate productive discussions that empower everyone to listen, contribute, learn, and ultimately act to transform STEM.

Read the full text here: FULL TEXT 

It is feeling like the end of an era in our lab. But so many great things are happening: 

Dr. Eleinis Àvila-Lovera has started an Earl S. Tupper Fellowship at Smithsonian Tropical Research Institute in Panama. We continue to collaborate on project funded by a USDA-AFRI grant designed to understand the effects of green stem photosynthesis on hydraulic functioning in avocados. 

Dr. Scott T. Allen has started a faculty position at the University of Nevada, Reno. We continue to collaborate on a project funded by the Swiss Federal Office of the Environment designed to understand the future of Switzerland's forest ecosystems. 

Dr. Carter Berry has moved back east to his old haunting grounds in North Carolina. We continue to collaborate on a project funded by a USDA-AFRI grant designed to understand the effects of diffuse light photosynthesis on plant gas exchange. 

Dr. Andrew Felton joins us from Peter Adler's laboratory at Utah State University. Andrew will bring together our research on wood water storage and satellite remote sensing, funded by grants from USDA-AFRI and NASA. We are so excited to have Andrew as part of our community. 

My student Alex Drivas (Biochemistry '21) has been spending part of his summer working on printing aluminum parts using our 3D printer. I encouraged Alex to try this approach because, if successful, it would transform our ability to make new equipment in the lab. Generally, if you need something made of metal, you send a drawing out to a company that uses a CNC mill to remove material from a block of metal until you have the desired shape. This is referred to as subtractive manufacturing. Now, our desktop 3D printers have the ability to print in metal or in plastics supplemented with metal at the click of a mouse. Instead of sending something off to an outside manufacturer and paying hundreds or thousands of dollars per piece, we can print a design in the lab in the matter of hours for just the cost of the printer (< $1000) and the cost of the filament (~$165 per kilo). The print does need to be de-bound and sintered offsite, so it's not instant gratification, but it is a huge step forward. 

Alex is at the cutting edge of using this technology (a future employer will be very lucky) and I asked him to write up his specifications and thoughts on printing for the benefit of the 3D printing community. Here's what he has to say: 

General Specifications 
Hot end: 240 °C
Bed temp: 100 °C
Layer thickness: 0.2mm
Perimeters: 4 count
Infill type: Concentric  

Speed
First layer print speed: 25mm/s
Print speed: 40mm/s
Travel speed: 125mm/s
Cooling Fan: off

Extrusion/Retraction
Extrusion multiplayer: 90%
First layer extrusion: 93%
Retraction length: 6mm
Retraction speed: 125mm/s

Adhesion
Dimafix
4 count brim 
Glass plate 

What I learned:

Adhesion and extrusion settings were the most important variables in printing. I had to apply more Dimafix around the corners of the print than the center and introduce a small brim to achieve proper layer adhesion through the print. I had to lower the Z offset (beyond what I would for PLA for ABS) to get better first layer adhesion. In following layers, I manually increased the Z offset just slight. If the nozzle was too far from the plate, the layer would not stick properly, however, if the Z offset was too low, the nozzle would grab material from the print as it extrudes. Improper adhesion would cause the corners of the print to curl and destroy the progress of the print. Applying too much Dimafix however, would make it close to impossible to remove from the bed.

Over-extrusion was a second variable adding to the debris build up around the nozzle. It was difficult at first to differentiate between the two. It will vary in printer type, but I narrowed ours down to the extrusion and retraction settings I had stated above. Decreasing the extrusion of the first layer however, made capturing the proper Z offset very important. Even with the successful print, I was still receiving a little over-extrusion and debris build up around the nozzle and had to pause the print to clean the nozzle. The debris did not build up over time, but rather varied based on contours and geometries at the specific stage of the print.   The green part coming off the bed is unclean and needs to be sanded and filed to clean up the past troubles with extrusion. 

In terms of the material and how it physically printed, I would compare it to trying to print clay. Coming out of the hot end, it does not stick to the bed as you would expect. Rather, it sticks to itself at times you don’t want it to and doesn’t when you do. Geometrically the material is very limited. Holes below a 10mm radius print unclean and inconsistent through layers. Thicker walls the better. Any internal fillets or contours are difficult and should be avoided. The optimal print for this material would be a gear or some small, geometrically uncomplex, internally uniform object. 

Alex's work was supported by a grant from the Center for Undergraduate Excellence at Chapman University. 

We are fortunate to have a Picarro L2130i cavity ringdown spectrometer in our new lab here in the Keck Center for Science and Engineering here at Chapman University. The instrument can analyze stable isotopes of oxygen and hydrogen in water vapor or liquid samples via the autosampler (with a dry nitrogen carrier gas). The lab has a number of in-house standards that span the range of typical waters at natural abundance. Many labs are not running highly enriched or depleted liquid samples right now due to memory effects; these problems can be solved with a particularly rigorous approach to sample injection and careful choice of standards; we are willing to take the time to run those samples. We are happy to serve as a resource for the community - please reach out if you have analyses in mind. 

We also have the ability to extract water from environmental samples (e.g. soil, plants, and other biological tissue) using the method proposed by Koeniger et al. (2011 in RCMS). The basic principle is that a sample under vacuum is heated in the dry block heater and the evaporated water is in turn condensed in liquid nitrogen. This approach has not been as widely applied as cryogenic vacuum distillation systems built with glass or metal manifolds; however, the principles of use are identical. Again, we are happy to serve as a resource for the community - please reach out if you have analyses in mind or if you would like the parts list that we developed for how to build this instrumentation. 

Folks in the lab are pursuing a number of different innovative projects right now, ranging from understanding how environment contributes to the evolution of new species in the Tropics to how water moves through landscapes. What is interesting is how many of those innovative projects are leaning on very classic methods - we are measuring soil texture, quantifying stem anatomical traits, and counting stomata. Looking forward to seeing the results! 

​How do we know that what we observe at one location holds true at another?
 
For the past three years, my collaborators and I have been studying the spatial patterns in stable isotopes of water as they move through forest ecosystems. My hope was that looking at variations in space would reveal something variations in time cannot – the application of stable isotopes water to ecohydrology has long been focused on repeatedly sampling the same location. The first three papers are now a matter of public record, largely thanks to the efforts of Scott Allen, Sabine Braun, James Kirchner and Rolf Siegwolf, with a few more papers on the way.
 
I had hoped that we would gain some fundamental insights into process. For instance, can sampling spatial variation in soil water isotopes tell us more about how soil characteristics contribute to variation? However, what has captured my attention is very different:
 
-Many applications of stable isotopes of water benefit from spatially and temporally explicit estimations of precipitation inputs. Interpolated maps of precipitation isotopes have become a fundamental tool. In a paper published in Geophysical Research Letters, Scott Allen develops a method using sine curve functions to describe the temporal patterns in precipitation isotopes across the entirety of Switzerland, then maps each of the three sine curve parameters (amplitude, phase, and offset). Each parameter contains compelling information: amplitude describes the strength of the seasonal cycle, phase describes the timing of the peak values, and offset describes the mean values. Beyond the many existing applications of precipitation “isoscapes,” I cannot wait to see how the community uses this new information.
 
-For a long time, we have been using variation in stable isotopes of water in the soil and comparing it to stable isotopes of water in plants as a means of inferring something about the depth of plant water uptake. In a paper in Hydrology and Earth Systems Sciences (currently in open review), Scott Allen develops a new index of plant source water that I believe much more accurately reflects what we are measuring – the seasonal origin of the water being taken up by plants. This approach is agnostic to the current debate about the methodological concerns of soil water isotope extraction. Moreover, I am hoping that it will reframe and advance the field in new directions. This is not to say that the results of the study– over 900 trees at 182 sites across the entirety of the country of Switzerland –are not incredibly compelling in and of themselves….
 
-At the beginning of this post, I posed a question. How do we know that what we observe at one location holds true at another? How do we know that the soil water isotopes sampled in one location are similar to those 5 m distant, 50 m distant, or 500 m distant. This is of critical import because we frequently use soil water isotopes sampled at one location as the foundation for inferring the depth of root water uptake among any number of neighboring trees. On average, studies have sampled 4 replicate individuals of 3 different plant species and matched them with 3 replicate soil profiles (n = 76 studies from 2010-2016; Evaristo & McDonnell, 2017). We hope that those 3 soil profiles are representative. In a study I led in the journal Ecohydrology, we demonstrate that accurately characterizing the spatial variation (both lateral and vertical) in soil water isotopes requires considerable sampling. Our simulations show that due to tremendous variability, inferences of root water uptake using two-end member mixing models (or really most of the methods reviewed in the compelling paper by Rothfuss and Javaux 2017) cannot be interpreted with confidence at our temperate forest site. We will have to hold ourselves accountable for this while interpreting research carried out to date and in designing new research in the future.
 
As always, I invite your comments and feedback. Many thanks to all of the individuals who have contributed to this research, the funding agencies that have made it possible, and the reviewers and the handling editors who have helped us effectively communicate it. 

In collaboration with Christian Ammendola from the incomparable 42Matters (Zurich, Switzerland), I recently presented at a poster on the citizen science ecosystem at the annual meeting of the AAAS. This work builds on my longstanding interest in the role of technology in facilitating informal science learning. The abstract follows below, but I'll reduce this to just a single sentence: 

There has been an incredible growth in mobile apps to facilitate citizen science, but most are unused and subsequently abandoned by the developers. 

Abstract: Citizen science has become an increasingly popular means of engaging the public in the collection of scientific data. In parallel, scientists are creating mobile platforms to facilitate their citizen science projects. Such mobile apps hold the potential to significantly increase our capacity to do scientific research, as well as our ability to provide informal science education to broad audiences. However, our understanding of the development, use, and efficacy of mobile applications for citizen science remains limited. How do we know what apps are available and how they are being engaged?  We used web crawlers to search for citizen science mobile applications on the Android and iOS platforms. We used a number of different keywords to capture all possible applications and then reviewed each one to ensure it met criteria for inclusion. We identified 138 unique citizen science mobile applications, including 48 common to both platforms. The median range of downloads for applications on the Android platform was 500-1000, indicating that very few experience widespread adoption. We also observed that more than 70% of the applications have not been updated for more than a year. This raises interesting questions regarding the return on the investment in developing these apps. As such, we searched for peer-reviewed science or science education literature associated with each application and found articles relating to only 15% of them to date. At this time, it appears that very few mobile citizen science applications are resulting in published data and that little is known about how those applications affect public engagement in science. However, of those applications with widespread adoption, analysis of the text of user reviews indicated that participants liked facilitating science, appreciated application functionality, and were engaging applications to seek scientific information. While such results are promising, there is clearly a critical need for the community to study how we engage technology for citizen science and science education, as well as translate these findings into best practices that can inform how we invest our resources in the future.