Jeffrey McDonnell

University of Saskatchewan | U of S · Global Institute for Water Security

The short-term dynamics of tree water use strategies for neighbouring co-occurring species are poorly understood. Here, we quantify the high frequency changes in water sources and sap flux patterns of two commonly co-occurring tropical rainforest tree species: Dendrocnide photinophylla (Kunth; Chew) and Argyrodendron peralatum (F.M. Bailey; Edlin e...

Clarifying the water-root-carbon nexus in the entire root zone is crucial for unlocking the potential of afforestation in mitigating climate change. But the nexus in deep soil (depth > 1 m) remains poorly understood. Here we report contrasts in deep soil water and root distributions across 72 paired sites of adjacent farmlands, representing typical...

Stable isotope studies (δ2H and δ18O) of water within plants are providing new information on water sources, competitive interactions and water use patterns under natural conditions. This is based on the assumption that there is no fractionation at the time of water uptake or during its transport within trees. However, previous studies have found f...

Plain Language Summary While paleoclimate reconstructions have been made with ice cores, tree rings, lake sediments and other proxies, few if any studies have explored the potential use of soil cores from the unsaturated zone to tease out paleoclimate information. Here, we report the soil water stable isotope data for an unusually deep, unsaturated...

Field-based assessment of transpiration phenology in boreal tree species is a significant challenge. Here we develop an objective approach that uses stem radius change and its correlation with sapwood temperature to determine the timing of phenological changes in transpiration in mixed evergreen species. We test the stem-temp approach using a five...

Groundwater is one of the largest reservoirs of water on Earth but has relatively small fluxes compared to its volume. This behavior is exaggerated at depths below 500 m, where the majority of groundwater exists and where residence times of millions to even a billion years have been documented. However, the extent of interactions between deep groun...

Water transit time is now a standard measure in catchment hydrological and ecohydrological research. The last comprehensive review of transit time modeling approaches was published 15+ years ago. But since then the field has largely expanded with new data, theory and applications. Here, we review these new developments with focus on water‐age‐balan...

Ecohydrological investigations commonly use the stable isotopes of water (hydrogen and oxygen) as conservative ecosystem tracers. This approach requires accessing and analyzing water from plant and soil matrices. Generally, there are six steps involved to retrieve hydrogen and oxygen isotope values from these matrices: (1) sampling, (2) sample stor...

Studies of tree water source partitioning have primarily focused on the growing season. However, little is yet known about the source of transpiration before, during, and after snowmelt when trees rehydrate and recommence transpiration in the spring. This study investigates tree water use during spring snowmelt following tree's winter stem shrinkag...

Little is known about the short‐term dynamics of tree water use strategies particularly for neighbouring co-occurring species. Here, we quantify the high frequency changes in water sources and sap flux patterns of two commonly co-occurring tropical rainforest tree species: Dendrocnide photinophylla (Kunth; Chew) and Argyrodendron peralatum (F.M. Bai...

Groundwater is one of the largest reservoirs of water on Earth but has relatively small fluxes compared to its volume. This behaviour is exaggerated with depth where the majority of groundwater exists at depths below 500 m and where residence times of millions to even a billion years have been documented. However, the extent of interactions between...

Plant transpiration plays a significant role in the terrestrial cycles, but the spatiotemporal origins of water used by plant remains highly uncertain. Therefore, the missing link to fully characterize the water mass balance, for any control volume including significant vegetated surfaces, is identifying and quantifying the key factors that control...

Study region This study was conducted at an oil sands operation in the Athabasca Oil Sands Region (AOSR), northeastern Alberta, Canada. The mine comprises open pit excavation of bituminous sands at two sites (Mildred Lake, ML, and Aurora North, AN), with a single hot-water extraction circuit connecting extraction plants at each mine. Study focus W...

The stable isotopes of hydrogen and oxygen in xylem water are often used to investigate tree water sources. But this traditional approach does not acknowledge the contribution of water stored in the phloem to transpiration, and how this may affect xylem water and source water interpretations. Additionally, there is a prevailing assumption that ther...

Determining the sources and mean transit times (MTTs) of water that generates streamflows is important for understanding and managing headwater catchments. The sources and especially the MTTs of water that contributes to streamflow in seasonally intermittent streams are far less studied than for perennial streams. Here we use major ions, dissolved...

Regional scale distributed conceptual models are typically developed with a bottom-up approach, which is process-inclusive but prone to over-parameterization. Here we demonstrate a proof of concept top-down approach for distributed conceptual model development, intended to emphasize dominant streamflow generating processes and to fulfill the princi...

Perceptual catchment models are a key first step towards hydrologic synthesis and provide the process foundation of predictive models. However, their development is usually limited to the headwater catchment scale where field work can be done. Here develop a perceptual model approach for a regional scale catchment. We use a systematic “top-down” ap...

Plant transpiration is the dominant water flux in the global terrestrial water balance and a key process in the hydrological sciences. Stable isotopes have contributed greatly to this understanding but one difficult assumption for plant water source quantification using hydrogen and oxygen isotopes is that no isotopic fractionation occurs during wa...

Global groundwater volumes in the upper 2 km of the Earth's continental crust—critical for water security—are well estimated. Beyond these depths, a vast body of largely saline and non‐potable groundwater exists down to at least 10 km—a volume that has not yet been quantified reliably at the global scale. Here, we estimate the amount of groundwater...

Study region United Kingdom (UK). Study focus Natural flood management (NFM) schemes are increasingly prominent in the UK. Studies of NFM have not yet used natural tracers at catchment scale to investigate how interventions influence partitioning during storms between surface rainfall runoff and water already stored in catchments. Here we investig...

Studies of plant water sources generally assume that xylem water integrates the isotopic composition (δ²H and δ¹⁸O) of water sources and does not fractionate during uptake or transport along the transpiration pathway. However, woody xerophytes, halophytes, and trees in mesic environments can show isotopic fractionation from source waters. Isotopic...

Stable isotope tracing of plant water use can illuminate plant water sources. But to date, the number of species tested at any given site has been minimal. Here, we sample 46 tropical hardwood tree species in a 0.32 ha plot with uniform soils. Soil water was characterized at 6 depths at 0.2 m intervals down to 1 m and showed simple and predictable...

Descriptions of runoff generation processes continue to grow, helping to reveal complexities and hydrologic behavior across a wide range of environments and scales. But to date, there has been little grouping of these process facts. Here, we discuss how the “fill‐and‐spill” concept can provide a framework to group event‐based runoff generation proc...

Rationale: Hydrogen and oxygen stable isotope ratios (δ2 H, δ17 O, and δ18 O values) are commonly used tracers of water. These ratios can be measured by isotope ratio infrared spectroscopy (IRIS). However, IRIS approaches are prone to errors induced by organic compounds present in plant, soil, and natural water samples. A novel approach using 17 O...

Closure of the soil water balance is fundamental to ecohydrology. But closing the soil water balance with hydrometric information offers no insight into the age distribution of water transiting the soil column via deep drainage or the combination of soil evaporation and transpiration. This is a major challenge in our discipline currently; tracing t...

The interior of western Canada, like many similar cold mid- to high-latitude regions worldwide, is undergoing extensive and rapid climate and environmental change, which may accelerate in the coming decades. Understanding and predicting changes in coupled climate–land–hydrological systems are crucial to society yet limited by lack of understanding...

The Panola Mountain Research Watershed (PMRW) is a 41‐hectare forested catchment within the Piedmont Province of the Southeastern United States. Observations, experimentation, and numerical modeling have been conducted at Panola over the past 35 years. But to date, these studies have not been fully incorporated into a more comprehensive synthesis....

Source water apportionment studies using the dual isotopes of oxygen and hydrogen have revolutionized our understanding of ecohydrology. But despite these developments—mostly over 26 the past decade—many technical problems still exist in terms of linking xylem water to its soil water and groundwater sources. This is mainly due to sampling issues an...

Our understanding of the source of transpiration and how phenological and hydrological processes affect tree water use are based mainly on temperate and tropical zones. In cold regions, as trees emerge from winter dormancy, tree water storage refilling sinks large volume of water. Understanding the timing of snowmelt, tree water storage refilling,...

Accurate travel time estimation by hydrological models is of significant importance as it is key to understand biogeochemical processes in the subsurface. In particular, our understanding of how plants rely on water from previous precipitation events remains poor and mainly based on streamflow and soil water data. In this study, we quantify the age...

The stable isotopes of hydrogen and oxygen (δ2H and δ18O, respectively) have been widely used to investigate tree water source partitioning. These tracers have shed new light on patterns of tree water use in time and space. However, there are several limiting factors to this methodology (e.g. the difficult assessment of isotope fractionation in tre...

The interior of western Canada, like many similar cold mid- to high-latitude regions worldwide, is undergoing extensive and rapid climate and environmental change, which may accelerate in the coming decades. Understanding and predicting changes in coupled climate–land–hydrological systems are crucial to society, yet limited by lack of understanding...

This repository holds data collected during the “SPIKE II” tracer experiment. The experiment was carried out on a large vegetated lysimeter (2.5 m3) planted with two willow trees (clones) (Salix viminalis) within the EPFL campus (CH), in Switzerland. SPIKE II took place from May 10 to June 29 in 2018. This composite dataset contain stable isotopic...

Watersheds have served as one of our most basic units of organization in hydrology for over 300 years (Dooge, 1988, https://doi.org/10.1080/02626668809491223; McDonnell, 2017, https://doi.org/10.1038/ngeo2964; Perrault, 1674, https://www.abebooks.com/first-edition/lorigine-fontaines-Perrault-Pierre-Petit-Imprimeur/21599664536/bd). With growing inte...

The depth distribution of soil water contributions to plant water uptake is poorly known. Here we evaluate the main water sources used by plants at the global scale and the effect of climate and plant groups on water uptake variability and depth distribution. The global meta‐analysis is based on isotope data (δ ² H and δ ¹⁸ O) extracted from 65 pee...

The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and, ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives only provide a low temporal resolution (ca. 15 years), precluding the ability to identify changes on inter-ann...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The American Geophysical Union (AGU) and other scientific societies have recently been promoting policies on scientific ethics. This chapter presents some of AGU members’ personal experiences that they hope might stimulate discussion and debate and might be a way for more groups to begin discussions about scientific ethics in their professional soc...

Sixty seemed an impossibly long way away when the author was an early‐career scientist. The forces that are changing the academic career are indeed tectonic. Stay focused and on course, there are so many forces to drive PhD students off course. PhD students should plan to be running with the same people for a very long time, so being nice to them a...

Interviews are strange. And department members may not know what they want from an incoming assistant professor, which can provide a huge advantage to the candidate who has the ability to connect with the department and hiring committee. Of course, there is more to the hiring process. This chapter explains what a PhD student needs to know: the job...

PhD programs are stressful. PhD students have crises. A recent survey of 3659 PhD students in the journal Research Policy showed that more than 50% of them struggled with their mental health during their PhD program. Such crises, from mild to major, are commonplace. In many ways, knowing that an upset or two will happen during a PhD program can hel...

The scientific enterprise needs leadership from researchers to advocate for science and evidence‐based, informed decision‐making. Early‐career scientists often think about leadership in a formal sense and at the highest levels, an appointed administrator at a university, and an elected leader of a scientific union. Incremental opportunities for inc...

The world has problems; universities have departments. Many early‐career scientists coming into their first department imagine that, like first love, it will sustain them. While some departmental situations will be better than others, most new faculty is confronted with some issues in early career. Blissfully unaware of such things and floating thr...

Beyond professors' love of their science, the rejection of the conventional workplace structure is perhaps the most common reason that academics love academia, despite its adverse effect on work–life balance. There is almost no work–life balance in the pre‐tenure years. Apart from the often‐discussed hubbub of faculty and committee meetings, an aca...

Everyone has heard of the Matthew Effect, the well‐known axiom, “The rich get richer; the poor get poorer.” Networks and the Matthew Effect also explain why some research groups become such dominant forces. Research in the 1960s by Robert Merton on scientific communities showed that renowned scientists and institutions tend to attract “inordinate a...

Beyond the individual output of the graduate students and post‐docs lies a parallel universe of teamwork, peer‐to‐peer mentoring, and, most important, discovery for the research group as a whole. Research group members will have their own theses, projects, and papers, but one can orchestrate a group dynamic that promotes discussion about where the...

Lab members were hydrologists, but most were trained from a completely different academic tradition from those in North America and Europe. Doing an academic visit takes active planning. Research visits, especially to foreign labs, accomplish more than the obvious and tangible. For early‐career scientists especially, academic visits afford great ne...

A life in academia is a life in sales, of proposal writer ideas through their proposals. And writing proposals is a different kettle of fish than writing journal articles. The proposed research for any competition must be fundable, laudable, and achievable. Writing a proposal for a detailed call means reading that call over and over and submitting...

Writing papers is easiest when the PhD student or postdoc spends considerable thought and time stacking all these pieces first. The author calls it the top–down writing approach. Each of his group's papers starts with a storyboard session at a whiteboard. He pretends to be a big‐time Hollywood producer and asks the PhD student or postdoc to play th...

The author has in no way mastered the writing game, but his 1‐hour workday has certainly increased his academic output. And by keeping him focused and in practice, it has improved the quality of his writing and made the process much more enjoyable. It also offers an opportunity for deep thinking. When the author strings together days of successful...

As the author entered his first faculty position, he thought that the only real trait needed to be a successful scientist was academic brilliance. He believed that science was an IQ meritocracy. He has since realized that soft skills are crucial to navigating and enjoying an academic career. He has seen tenure denials handed down in the same week t...

A sustainable professor is still a hard‐working professor. Combining hard work with laser‐like focus and ruthless time management is an important step toward making PhD student or postdoc's life sustainable. Even more important is opportunity management. Developing a personal work philosophy can help the student or postdoc allocate his/her most pre...

A research brand identity, in the best scientific sense, is a PhD Student or Postdoc's central mission: the particular branch of research he/she would like to be truly excellent in and known for. Equal parts research focus and career vision, a brand identity is a map of a few key subareas where he/she strives to make a difference over a sustained p...

When the author mentors mid‐career colleagues, he tells them about his experience and tries to help them to understand the differences between early‐career expectations, which tend to center on numbers of papers, numbers of grants, numbers of students supervised for earning tenure, and the new set of leadership expectations that define mid‐career a...

The relationship between streamwater mean transit time (MTT), catchment geology and landscape structure is still poorly characterized. Here we present a new simple index that builds on the Jackson et al. (2014) index that focuses specifically on permeability contrasts at the soil‐bedrock interface and DEM‐based physical flowpath measurements to ide...

Forest cover has a significant effect on hillslope hydrological processes through its influence on the water balance and flow paths. However, knowledge of how spatial patterns of forest plots control hillslope hydrological dynamics is still poor. The aim of this study was to examine the impact of an across-slope forest strip on sub-surface soil moi...

Integrated surface‐subsurface hydrological models (ISSHMs) are well established numerical tools to investigate water flow and contaminant transport processes over a wide range of spatial and temporal scales. However, their ability to correctly reproduce the response of hydrological systems to natural and anthropogenic forcing depends largely on the...

Abstract. The stable isotopes of oxygen and hydrogen (δ²H and δ¹⁸O) have been widely used to investigate plant water source partitioning. These tracers have shed new light on patterns of plant water use in time and space. However, this black box approach has limited our source water interpretations and mechanistic understandin...

An Addendum to this paper has been published and can be accessed via a link at the top of the paper.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Long records of hillslope runoff and nutrient concentrations are rare – on seasonally frozen ground they are almost non-existent. The Swift Current hillslopes at the Swift Current Research and Development Centre on the Canadian Prairies provide such a long-term hydrological record. Runoff, runoff nutrient concentration, snowpack depth, density and...

The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives provide only low temporal resolution (ca. 15 years) precluding the ability to identify changes on inter-annual...

The time that water takes to travel through the terrestrial hydrological cycle and the critical zone is of great interest in Earth system sciences with broad implications for water quality and quantity. Most water age studies to date have focused on individual compartments (or subdisciplines) of the hydrological cycle such as the unsaturated or sat...

We present a new controlled experiment using a 2 m3 lysimeter planted with a small willow tree (Salix viminalis) to explore how plant water status affects water source partitioning and uptake. We combine high resolution sampling of tree and soil water isotopic composition with measurements of tree hydrodynamics, soil matric potential and climate da...

Intercomparison of soil pore water extraction methods for stable isotope analysis has been a focus of recent studies in relation to plant source waters, which found a wide isotopic variance depending on the extraction method. Few studies have yet explored extraction effects for mobile pore waters that relate to hillslope runoff. This is because it...

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, p...

Predicting the responses of streamflow to changes in forest management is fundamental to the sustainable regulation of water resources. However, studies of changes in forest cover have yielded unclear and largely unpredictable results. Here we compile a comprehensive and spatially distributed database of forest-management studies worldwide, to asse...

Recent field observations indicate that in many forest ecosystems, plants use water that may be isotopically distinct from soil water that ultimately contributes to streamflow. Such an assertion has been met with varied reactions. Of the outstanding questions, we examine whether ecohydrological separation of water between trees and streams results...

Rationale The stable isotope compositions of hydrogen and oxygen in water (δ²H and δ¹⁸O values) have been widely used to investigate plant water sources, but traditional isotopic measurements of plant waters are expensive and labor intensive. Recent work with direct vapor equilibration (DVE) on laser spectroscopy has shown potential to sidestep lim...