My definition of Ecohydrology is that of a discipline that concerns all ecological processes that are relevant for Hydrology and water resources, and investigates their effect on hydrological processes and vice versa. An important example is the effect of vegetation processes on transpiration rates and water resources, but I would also include effects of e.g. earth burrowing organisms on soil water retention and drainage properties. I like to distinguish Ecohydrology from Hydro-ecology, which I would define as a sub-discipline of Ecology that focuses on the effect of hydrological processes on freshwater ecosystems.
What are your undergraduate and graduate degrees in?
My undergraduate degree is in Geobotany from the University of Freiburg in Germany. I did my PhD in Environmental Engineering at the University of Western Australia.
How did you arrive at working in/thinking about ecohydrology?
I always loved plants, water and the outdoors. For my undergrad thesis in Geobotany, I did a lot of field work on Middle European peat bogs, trying to understand if their decay had to do with facilitated drainage due to historical peat removal and drainage channels. My supervisors, Dr. Arno Bogenrieder and Dr. Pascal von Sengbusch, hypothesised that in a peat bog, initial drainage can stimulate tree growth and therefore water extraction, leading to a positive feedback between decreasing water tables and further enhancing tree water use. This motivated me to learn more about vegetation-hydrology feedbacks.
I started off my post-graduate path at a forestry research institute (FVA), investigating the flood tolerance of the common ash in Southern Germany. At the same time, I met my wife Emma, who was on exchange from Australia to do her undergraduate thesis in Freiburg. When she returned to Australia, I revived my interest to go abroad for a PhD project and extended my search to Australia. As it turned out, one of Emma's professors at the University of Western Australia, Dr. Sivapalan, was looking for a PhD student to investigate Eagleson's Ecological Optimality hypotheses. A few more lucky coincidences brought me to Perth on an international scholarship and support by the CRC for Greenhouse Accounting, which gave me the opportunity to learn about hydrology from Siva and about ecology from my external advisor, Dr. Michael Roderick and colleagues at the Australian National University. This inspiring mentoring team was complemented by generous support from Dr. Lindsay Hutley from Charles Darwin University and Dr. Jason Beringer, then from Monash University, who taught me about the intricacies of tropical savannas and shared their eddy covariance measurements with me.
I found the transfer from a then rather descriptive discipline (Geobotany) to a very quantitative discipline (Environmental Engineering/Hydrology) very challenging and stimulating at the same time. I found out that my naive questions about hydrology sometimes inspired hydrologists as much as their seemingly naive questions about plants inspired me to dig deeper and question my intuitive understanding of the underlying processes. At the same time, Mike Roderick exposed me to a very quantitative view of plant ecophysiology and ecology, while Jason Beringer and Lindsay Hutley kept us all close to the ground using their detailed site-specific knowledge. Since then, I have been exploring the boundaries of Ecohydrology, by venturing into thermodynamics and environmental physics and extending my tool set by lab experiments and open science approaches.
If I had to summarize everything I learned during that time in one point, it would be that in order to understand the vegetation and catchment response to environmental forcing, we need to understand the hydrological system, the physics of vegetation-environment interactions and the ecology determining vegetation dynamics. This inseparability of Ecology and Hydrology in water-limited systems is to me the main pillar of of Ecohydrology.
What do you see as an important emerging area of ecohydrology?
Environmental change, such as increasing atmospheric CO2 concentrations, changing climate patterns and increasing nitrogen deposition can have a strong indirect effect on water resources by their direct effect on vegetation. We are only at the beginning of understanding how vegetation responds to these environmental changes at different spatial (leaf-individual-ecosystem) and temporal (seasonal, annual, decadal, centennial) scales. With new sensing techniques, both at the macro (satellites) and micro-scale (distributed networks of micro-sensors, high-resolution and high-frequency sampling etc.), we will be able to test more details of our understanding and formulate new, more relevant questions about hydro-ecosystem functioning. This testing of our understanding will also benefit from improved modelling capabilities, linked to freely available, open-science community models permitting to test one component at a time and the effect of feedbacks between different domains (soil-vegetation-atmosphere, groundwater-soil moisture-surface water etc).
Do you have a favorite ecohydrology paper? Describe/explain.
My favorite paper is:
Cowan, I. R. and Farquhar, G. D.: Stomatal Function in Relation to Leaf Metabolism and Environment, in: Integration of activity in the higher plant, edited by D. H. Jennings, pp. 471–505, Cambridge University Press, Cambridge, 1977
In this paper, Cowan and Farquhar link leaf transpiration to photosynthesis, arguing that plants tend to maximise photosynthetic carbon uptake per unit of water lost. This enables predictions of stomatal dynamics and transpiration at the diurnal scale, essentially linking vegetation water use to atmospheric CO2 concentrations, a link that is missing in many hydrology-originated approaches to ecohydrology. They also discuss the necessity for day-to-day water use optimisation in the context that water used early on in a dry period may be lacking towards the end of the dry period, essentially linking plant water use to water resources from a purely ecological perspective. The paper also demonstrates the benefits of interdisciplinarity, as Cowan and Farquhar use a concept from economy to derive a solution to the ecological optimisation problem.
What do you do for fun (apart from ecohydrology)?
I love spending time in nature with my wife and my son, either hiking, paddling, mountain biking or skiing. I also enjoy more dangerous endeavors with friends, such as whitewater kayaking, backcountry skiing or trail biking. I played international level ultimate frisbee for many years, which I like for its emphasis on team spirit, fair play and hard work.