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MEET A LEAF: GE SUN

11/29/2021

Dr. Ge Sun is Research Hydrologist and Project Leader at the Southern Research Station, USDA Forest Service, Research Triangle Park, NC.

What does ecohydrology mean to you?
Ecohydrology means how forests influence water resources and how water availability affects forest ecosystem functions and services.

What are your undergraduate and graduate degrees in?
I attended Beijing Forestry University for my undergraduate majoring in soil and water conservation (1985) and then a master degree program (1988) in forest hydrology in the same university. Then I moved all the way to the West, and got my Ph.D in forest hydrology (1995) from the University of Florida in Gainesville.

How did you arrive at working in/thinking about ecohydrology?
Forest hydrology studies the interactions between forests, a long-lived organism, and the water cycles, so forest hydrology is ecohydrology. Forest hydrology was rooted in serving the needs of watershed management and solving emerging environmental issues in the 1960s from soil erosion to acid rain. I have enjoyed doing forest hydrology work since I was undergraduate student. One of the reasons I got interested in this field might be that forest hydrology was full of controversy (mystery) over the past century. For instance, how reforestation will affect river flow in different regions? Would revegetation revive the lost springs in many parts of the world? Forest hydrology is getting more important given the importance of forests in carbon sequestration addressing global climate change today.

What do you see as an important emerging area of ecohydrology?
The world is changing rapidly and unpredictably. However, one thing is certain that clean water is in much demand with the rise of human population. With global warming intensifies, so is the water needs by trees and forests. Consequences are dare when the needs by either humans or the ecosystems that people depend on, are not met. Water uses by ecosystems, or the evapotranspiration process, was the center of ecohydrology from the beginning of the ecohydrological science. We have a lot to learn in ET from different perspectives, energy balance, biological, and hydrological processes as influenced by humans. Many of the controversies arise from our inability to quantify ET everywhere (from the leaf to global) and all the time (from minute to millennium).

Do you have a favorite ecohydrology paper? Describe/explain.
My hero in forest hydrology is John Hewlett, the ‘God father’ of forest hydrology. Hewlett’s paper published in the first international symposium on forest hydrology in 1967 opened my minds while I was a graduate student working in the deep subtropical mountains in southern China.
Hewlett, J.D. and Hibbert, A.R., 1967. Factors affecting the response of small watersheds to precipitation in humid areas. Forest hydrology, 1, pp.275-290.

This paper explains the ‘Variable Sources Area Concept’, a stream flow generation theory describing the hydrologic processes in humid small headwater forested watersheds. Forested watersheds have high infiltration rate due to the porous soils with extensive root network and also the high evapotranspiration rate (thus drier soils), so overland flow in forests is rare. However, quick flow or torrent stormflow can be generated in saturated riparian areas near stream channels that grow their length and width during storms. This theory represents a shift of traditional flow generation doctrine (Hortonian flow) to one that reflects the role of vegetation covers, thus the biological processes, in modifying the physical processes of water movement.

What do you do for fun (apart from ecohydrology)?
Taking road trip to national forests and parks with families in different seasons has been fun; Other ‘free’ times, I like cooking following YouTube; I also enjoyed chatting with friends over the internet sharing life experiences.

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MEET A LEAF: Erica L. McCormick

11/22/2021

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Erica L. McCormick is a Research Scientist Assistant at the Jackson School of Geoscience, University of Texas at Austin. Twitter: @McCormickEricaL

What does ecohydrology mean to you?
Ecohydrology is an invitation to think complexly about Earth as a whole system, without the confines of traditional disciplines. As so many other “Leafs” have discussed, there is an invitation in ecohydrology to consider processes from the single plant level photosynthetic chemistry all the way to global hydrology. With this breadth comes expertise in topics ranging from mycorrhizal and plant physiology to atmospheric turbulence to hard-core geology and fluid mechanics (not to mention so much more!). I also love how ecohydrology embraces how the “answers” we seek are likely to be complex, nonlinear, and potentially context dependent, which in turn motivates the use of many exciting methods which ecohydrologists are free to use, including field work, remote sensing, modeling, and more!

What are your undergraduate and graduate degrees in?
I got my B.S. in Environmental Science, Geology from the Jackson School of Geoscience at UT Austin. I am applying to U.S. PhD programs right now after COVID-19 messed up my plans to work with Sally Thompson in Perth, Australia.

How did you arrive at working in/thinking about ecohydrology?
For most of my pre-college life, I was heart set on being an astronomer. It wasn’t until I went to the Milton Mountain School, a small forestry and farming semester school in rural Vermont, that I was exposed to geoscience. One of our teachers was a self-described geologist, but instead of studying rocks (as I assumed all geologists did), she studied glaciers! This was my first taste of “Earth science.” This realization, coupled with an entire semester spent in the forest, changed my direction entirely. I came to UT ready to find my place in environmental science.

My first exposure to ecohydrology came during a course in my undergrad taught by Ashley Matheny. I loved basically everything about it, from the questions themselves to the field work and coding we employed to answer them. I have had the opportunity to continuously confirm that this field is a good fit for me during my research with Dr. Matheny, Dr. Daniella Rempe, and others since then. I am fully hooked on ecohydro and can’t wait to see what sorts of things I get involved with during my PhD!

What do you see as an important emerging area of ecohydrology?
I’m very early on in my scientific career, but my recent involvement with Daniella Rempe’s lab has convinced me that in order to better understand above-ground plant behavior, we need to better constrain uncertainty in the subsurface, especially with regards to water storage. I am definitely biased because of my excitement about our recent work on bedrock water storage and rock moisture as an important contribution to ET. However, there seems to be a consensus among many ecohydrologists that we need more data and a better understanding of the subsurface. I am excited about several aspects of this “subsurface” focus, and my recent fascinations include understanding how lithologic and soil properties interact with climate to mediate plant water access as well as how plants leverage their below-ground carbon allocation, rooting strategies, and fungal interactions to sustain ET during dry periods.

Do you have a favorite ecohydrology paper? Describe/explain.
“Beyond isohydricity: the role of environmental variability in determining plant drought response” by Xue Feng et al. is my favorite paper, in part because it was one of the first ecohydrology papers I ever read! This paper really kickstarted my ongoing fascination with the way that “categorizing” behaviors we think see in nature (like iso/anisohydricity) can be duped by uncertainties in the myriad environmental factors and the setting in which those behaviors manifest.

My hope is that the difficulty we have in nailing down plant drought response is secretly holding a wealth of information about subsurface and water storage dynamics that we can leverage for better understanding of the whole water and carbon cycle. This paper was my first taste of that way of thinking!

Feng, Xue, David D. Ackerly, Todd E. Dawson, Stefano Manzoni, Blair McLaughlin, Robert P. Skelton, Giulia Vico, Andrew P. Weitz, and Sally E. Thompson (2019). "Beyond isohydricity: the role of environmental variability in determining plant drought responses." Plant, cell & environment.

What do you do for fun (apart from ecohydrology)?
Like most ecohydrologists, I love to be outside whenever possible! I especially love to run, swim, cycle, and hike with my dog, Hamilton (though I will report that he much prefers hiking and swimming to running and biking)! During the pandemic, I took up triathlon training, which has been a wonderful distraction as well as a great real-world example of an activity being “about the journey” and not the result. I had the pleasure of running my first race a few months ago, and although I had a blast, it was nowhere near as fun as the daily training. When I’m forced to be indoors, I also like to play bluegrass and americana music and make pottery.

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MEET A LEAF:

11/15/2021

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Dr. Ciaran J. Harman is an Associate Professor in Environmental Health and Engineering at Johns Hopkins University.

What does ecohydrology mean to you?
Someone once described ecohydrology to me (Paul Brooks I think) as the study of how plants muck up a perfectly good physics problem. I think there’s some humorous truth to that. It is possible to do a lot of interesting hydrology without really thinking about plants and life in general, and considering only the fluid mechanics. You can even go a long way understanding the role of plants in evapotranspiration as merely a kind of ‘wick’ that allows soil water to be drawn into the atmosphere. The result of that approach is inevitably that plants (and ecosystems in general) are reduced to a set of empirical parameters (rooting depth, max stomatal conductance, canopy roughness, etc.) that we can measure and catalog, and which must be estimated in any given applied situation.

That way of doing things has proved to be something of a dead-end. Rarely can these parameters be predicted with fidelity (and their fidelity is rarely checked). Their variability is overwhelming, even within a single plant species sometimes. And it is difficult to anticipate how these parameters will change under changing conditions.

To me, ecohydrology is the project of going beyond that reductive approach and instead engaging with plant physiology, evolution, and ecosystems more deeply. It is the search for a deeper understanding of how life on earth has evolved complex adaptations that enmesh it with its thermodynamic and material environment. It seeks to understand the role of water in how life reacts to its environment and manipulates it to its own ends.

On a more personal level, ecohydrology is a dimension of my 20-year fascination with the coevolution of hydrologic systems and the broader landscapes that they are part of.

What are your undergraduate and graduate degrees in?
I have a B.Eng in Environmental Engineering and a B.A. in Asian Studies from the University of Western Australia. I graduated in 2002. I went to the University of Illinois for grad school in 2005, starting with a Masters in Geography (2008), and a PhD in Civil and Environmental Engineering (2011).

How did you arrive at working in/thinking about ecohydrology?
It was something I was exposed to in grad school, particularly though my advisor, Siva Sivapalan, and through some influential peers – particularly Sally Thompson. Stan Schymanski’s PhD work on stomatal optimization was particularly formative – it helped me understand how the water balance was linked to evolutionary demands and plant physiology at a deep level.

I muddled into doing ecohydrology myself mostly through work on the water balance. Peter Troch and Paul Brooks helped a group at the NSF synthesis summer school in 2010 use the MOPEX dataset to better understand the imprint of ecohydrology on the water balance, showing how annual ET responded to variations in annual precip in a surprisingly consistent way across many watersheds. I’ve also spent a LOT of time thinking and talking about the Budyko curve, much more than appears in publications (which is probably for the best).

More recently I have been returning to ecohydrology along different avenues. I’m having a wonderful time interacting with Kanishka Singh at Cornell who is doing some very cool experiments looking at tracer transport through trees. I think his results are going to be transformative. My own PhD student David Litwin has been working on ‘hydrologically-explicit’ landscape evolution and is starting to think about how water balance partitioning might play an important role in that. It has been a great opportunity to dust off some ideas in that area that have been laying around for too long.

What do you see as an important emerging area of ecohydrology?
I feel like I have such a limited view – there’s a lot of cool things out there, and it is hard to keep up with more than the small niche I’m invested in!

Something that I do think is important is the increasing understanding of how vegetation interacts with the shallow subsurface. There was a paper by Blair McLaughlin last year that showed nicely how subsurface architecture controlled variations in plant responses to drought within and across species. I’m part of a critical zone project at the moment that is trying to understand this kind of issue using geophysical imaging. There is also a lot of really cool work being done by geomorphologists and geochemists interested in understanding how vegetation drives the evolution of the critical zone. I think so much of what happens above ground is linked to things underground, but our limited ability to ‘see’ underground has resulted in these interactions being discounted.

Do you have a favorite ecohydrology paper? Describe/explain.
Cripes, this is a hard one. OK I’ll go with favorite of the moment – ask me again tomorrow and I’ll say something different.

I really like this paper by Jochen Schenk presenting “The Shallowest Possible Water Extraction Profile:
A Null Model for Global Root Distributions” (https://acsess.onlinelibrary.wiley.com/doi/10.2136/vzj2007.0119).
It is such an elegant model that makes startlingly good predictions about ecosystem-level root depth distributions from climate alone. Rumor has it that Schenk came up with the idea in grad school but his advisor didn’t like it, and so he published it on his own. I think it is terribly underappreciated. Ying Fan was inspired by it for this excellent paper (https://www.pnas.org/content/pnas/114/40/10572.full.pdf) though ultimately used a more sophisticated resistance formulation.

At the moment we are using Schenk’s model to capture the effect of root water uptake from the vadose zone on landscape evolution. This allows us to avoid having to specify a rooting depth, and instead assume a climate-adapted one. I sat down and worked out analytical solutions for the root depth distribution a few months ago, though I have no idea what to do with them. If anyone thinks they’ll be useful let me know!

What do you do for fun (apart from ecohydrology)?
I’m at that stage of life where I don’t have much time outside of family and work. I have cycled through a LOT of different hobbies over the years though, including photography, swing dancing, rock climbing, choral singing, roller derby, recreational math, and gardening. I have pretty severe ADHD, and switching hobbies a lot is common for people like me. Hopefully I’ll have more time soon and can take up a new hobby – any suggestions?

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MEET A LEAF: Bhaskar Mitra

11/8/2021

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Dr. Bhaskar Mitra is currently research scientist at Northern Arizona University.

What does ecohydrology mean to you?
For me ecohydrology is the framework that would allow us to explore the comprehensive soil-plant-water relationship. The primary aim is to understand soil carbon sequestration capacity in relation to climate change and other anthropogenic perturbations.

What are your undergraduate and graduate degrees in?
I pursued my engineering studies from Bengal Engineering and Science University (BE) in India and my MS from University of Kentucky. However, I always wanted to pursue my studies in Environmental Science and my MS thesis explored acid drainage treatment using surface treatment technology. I was lucky to pursue my doctoral studies at State University of New York, Buffalo, under the guidance of Dr D.S. Mackay. Essentially, I identify myself as a carbon cycle and environmental data scientist.

How did you arrive at working in/thinking about ecohydrology?
My research in ecohydrology started with simulating eddycovariance-derived carbon and water flux across the cold semi-arid sagebrush ecosystem in Wyoming using the process-based ecosystem model TREES. The data was provided by Dr Elise Pendall and Dr Brent Ewers from University of Wyoming from their sagebrush-steppe ecosystem research site. While simulating carbon and water fluxes, I designed geostatistical and climate change manipulation experiment to explore different hypothesis about model failure in simulating both the fluxes. These experiments were conducted by me at Saratoga, Wyoming.

These studies set up the foundation for me explore the linkage between different exogeneous and endogenous drivers that simulate greenhouse gas emission (soil respiration, methane) across managed and natural coastal wetland ecosystem in North Carolina.

Overall, I would state that quantitative analysis of greenhouse gas emission has been a key theme of my research for the last 15 years. To that end, I have incorporated extensive field work along with ecosystem models and different statistical techniques (parametric and non-parametric) to analyze control of vegetation activity on greenhouse gas emission at different spatial (leaf, plant, landscape) and temporal (sub-daily, diurnal, diurnal, synoptic, monthly) resolution.

What do you see as an important emerging area of ecohydrology?
Identifying causality in complex ecohydrological processes. Simply put, nonlinear dynamics are ubiquitous across ecohydrological systems.

For example, soil respiration and wetland methane emission are important metrics of ecosystem metabolism. Both these processes are multivariate, multidimensional and non-linear. Ideally, ecosystem manipulation experiment can help us to explore causation. However, that may not always be the case.

My two recent papers (Mitra et al., 2019; Mitra et al., 2020), under the supervision of Dr Asko Noormets (Texas A & M University) and Dr John King (North Carolina State University) explored causality within a spectral modeling and information theory framework. The study explored how the different drivers of soil respiration and wetland methane emission are sometime positively and negatively coupled with different biotic and abiotic drivers at different temporal resolution across the coastal wetland ecosystem in North Carolina. Radically different control regimes for soil respiration and methane, depending on time and temporal scale (diurnal, synoptic etc) is characteristics of complex non-linear systems.

Variables which may be positively coupled can become decoupled during certain time periods. This definitely creates an issue while fitting functional relationship to observed data. One must also exercise caution in differentiating between correlation and causation as the former remains ingrained in our heuristic thoughts. Lack of correlation does not necessarily imply lack of causation.
Overall, causal analysis point highlights the need to develop “spectrally-truthful” ecosystem models that can potentially reduce the uncertainty with estimation of greenhouse emission across different ecosystems.

Do you have a favorite ecohydrology paper? Describe/explain.

While there are many, I would likely refer to Dr Gabriel Katul’s paper as highlighted below:

Katul, G., C.-T. Lai, K.V.R. Schäfer, B. Vidakovic, J.D. Albertson, D.S. Ellsworth and R. Oren. 2001. Multiscale analysis of vegetation surface fluxes: from seconds to years. Adv. Water Resour. 24: 1119-1132.

I consider this paper to be the fundamental reference for the application of wavelet techniques in ecosystem science. Subsequent 20 years of study by different researchers on control on eddy fluxes by different physical and biological processes is heavily inspired by this paper.

What do you do for fun (apart from ecohydrology)?
Simply chatting with my mother, my friends, going out for occasional swim, playing soccer and cricket, watching movies and reading fiction literatures. Jane Austen and Rabindranath Tagore are my favorite novelists and William Wordsworth remain my favorite poet.

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MEET A LEAF: Shuyu Chang

11/1/2021

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Shuyu Chang is a Ph.D. Student in the Department of Geography at the Penn State University, studying with Dr. Kimberly Van Meter. Follow her on Twitter @shuyo5

What does ecohydrology mean to you?
I think ecohydrology is an interdisciplinary field sitting across hydrology and ecology. It allows hydrologists, biochemists, ecologists, and geologists to work together to better understand the environmental systems and processes under Anthropocene.

What are your undergraduate and graduate degrees in?
I received my bachelor's degree in Hydraulic and Hydropower Engineering from China Agricultural University (CAU). During my senior year as an undergraduate, I also received one-year training in GIS and Remote Sensing at the University of Connecticut (UCONN). Shortly after UCONN, I received a M.S. degree in Water Resources Engineering from Johns Hopkins University (JHU). I have finished two-year study for my Ph.D. degree at the University of Illinois at Chicago (UIC), and just transferred to the Penn State University (PSU) this semester.

How did you arrive at working in/thinking about ecohydrology?
In my master’s study, I was drawn to Dr. Ciaran Harman’s Landscape Hydrology lab, and I started my first research to understand how farmers adapt to climate change and how these altered practices coupled with climate shifts affect water quality at the watershed scale. When I presented the research at the Chesapeake Biannual Meeting, I met with my Ph.D. advisor, Dr. Kimberly Van Meter. I was fascinated by her talk about the effects of nitrogen legacies on delaying the improvement of water quality. Management practices implemented by us, have significant, but quite unknown effects on the next generations. I found myself motived in ecohydrology, since I can solve real problems, and at the same time there are more unknowns remaining on the earth that are calling to me.

What do you see as an important emerging area of ecohydrology?
New techniques and the availability of large volumes of data allow us to move beyond traditional ecohydrology, which has focused on data collection at single sites and the development of small-scale models. I am looking forward to using new-generation, data-driven approaches, coupled with process-based models to better understand how human perturbations affect the water quality across different.

Do you have a favorite ecohydrology paper? Describe/explain.
Shen, 2018 is eye opening and enlightening for me to overview and study the technical summaries, progress updates, further challenges, and limitations about the applications of Deep Learning (DL) to Hydrology. “For water sciences, DL could help tackle several major challenges, old or new”. It triggered me thinking about the direction of my own research.

Shen, C. (2018). A transdisciplinary review of deep learning research and its relevance for water resources scientists. Water Resources Research, 54(11), 8558-8593.

What do you do for fun (apart from ecohydrology)?
I like various water activities, kayaking, swimming, and paddle boarding…This summer, I learned how to surf by the Venice beach, LA. I enjoyed both riding the waves and falling into the Pacific Ocean.

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MEET A LEAF: GE SUN

MEET A LEAF: Erica L. McCormick

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MEET A LEAF: Bhaskar Mitra

MEET A LEAF: Shuyu Chang

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