Jaivime Evaristo


Photo of Jaivime Evaristo

Assistant Professor

Department of Natural Resources and Environmental Science
University of Nevada/Mail Stop 186
1664 N. Virginia Street
Reno,  Nevada   89557

Office: (775)
Email: jevaristo@unr.edu
Building: Max Fleischmann Agriculture,  Office 119
Personal Web: http://envisoapp.weebly.com/

Download Electronic Business Card OR vCard

EDUCATION
B.S. University of the Philippines, 2001
M.S. University of Pennsylvania, 2013
Ph.D. University of Saskatchewan, 2016

ACADEMIC & RESEARCH INTEREST

My primary research interest is in understanding the spatial and temporal linkages between earth, atmosphere, and biosphere processes. My overarching research theme is the contribution of vegetation to water, nutrient, and carbon cycles in natural and in coupled human-environmental systems.

My research program -- Environmental Isotope Applications (EnvIsoApp) Lab -- is interested in identifying sources of water and solutes, understanding nutrient and water cycling, and testing hydrologic and water quality hypotheses with experiments and models. My research integrates laboratory and field studies with quantitative data science methodologies linking geology, ecology, biology, biogeochemistry, and hydrology. My spatial scales of interest range from pore- and rhizosphere-scale processes to watershed- and continental-scale patterns. Such an integrated perspective enables exploration of connections between subsurface architecture and hydrologic fluxes, influenced by processes that are modulated largely by primary productivity.

COURSES & TEACHING RESPONSIBILITIES

NRES 3XX: Environmental Physics
NRES 400/600; GEOG 400/600: International Issues for Water Development (Fall, even years)

ACCOMPLISHMENTS

2016-2017: Postdoctoral Fellow, Global Institute for Water Security

2014-2016: Teaching Assistant, Global Institute for Water Security

2012-2013: Research Fellow, Luquillo Critical Zone Observatory, University of Pennsylvania

AWARDS, HONORS, & PROFESSIONAL RECOGNITION

2017: Farley Mowat Award, School of Environment and Sustainability, University of Saskatchewan

2017: Best Doctoral Thesis Award in Water Security Research

2015: Saskatchewan Innovation and Opportunity

2014: Saskatchewan Innovation and Opportunity

2013: Dean’s Scholar Award, University of Pennsylvania

2012: Graduate Research Fellowship, National Critical Zone Observatory Program

REPRESENTATIVE PUBLICATIONS

Journals
Evaristo, J. and McDonnell, J.J. 2017, A role for meta-analysis in hydrology, Hydrological Processes
Abstract:

Research in hydrology has evolved from a rich history of site based (usually catchment-based) field data collection. These studies typically have a small sample size—i.e. one study hillslope or catchment and usually no replication. While different to many other scientific fields where replication is sacrosanct, such field-based discovery science has driven much of what we know about infiltration, runoff processes, and ecohydrological dynamics. But while field work at single sites continues to unearth new forms of hydrological behavior—and this is much needed to understand better ‘how catchments work’—process inference by one-off field experiments has significant limitations. While some of these limitations can be mediated by replication and stronger adherence to the scientific method and formal hypothesis testing, many limitations remain. One tool that has not yet been fully exploited in hydrology is meta-analysis.

Daly, K.R., Cooper, L.J., Koebernick, N., Evaristo, J., Keyes, S.D., Van-Veelen, A. and T. Roose 2017, Modelling water dynamics in the rhizosphere, Rhizosphere
Abstract:

We review the recent progress in the use of image based modelling to describe water dynamics in the rhizosphere. In addition, we describe traditional modelling and experimental methods, and how images obtained from X-ray Computed Tomography can be used in combination with direct pore-scale modelling to answer questions on water movement in the rhizosphere. The focus of this review is on the need for micro-scale experiments to parameterize image-based modelling on the pore-scale, and to show how variations in these parameters can lead to different macroscopic parameters when considering the movement of water on the plant scale. We finish the review with an illustrative example which highlights the importance of fluid-to-fluid contact angle, and the need for care in image preparation when using detailed models of this type.

Evaristo, J., McDonnell, J.J., and Clemens, J. 2017, Plant source water apportionment using stable isotopes: A comparison of simple linear, two-compartment mixing model approaches, Hydrological Processes
Abstract:

Plant source water identification using stable isotopes is now common practice in ecohydrological process investigations. Notwithstanding, little critical evaluation of the approaches for source apportionment have been conducted. Here we present a critical evaluation of the main methods used for source apportionment between vadose and saturated zone water: simple mass balance and Bayesian mixing models. We leverage new isotope stem water samples from a diverse set of tree species in a strikingly uniform terrain and soil conditions at the Christchurch Botanic Garden, New Zealand. Our results show that using δ2H alone in a simple, two-source mass balance approach leads to erroneous results; particularly an apparent overestimation of groundwater contribution to xylem. Alternatively, using both δ2H and δ18O in a Bayesian inference framework improves the source water estimates and is more useful than the simple mass balance approach, particularly when soil and groundwater contributions are relatively disproportionate. We suggest that plant source water quantification methods should take into consideration the possible effects of 2H/1H fractionation. The Bayesian inference approach used here may be less sensitive to 2H/1H fractionation effects than simple mass balance methods.

Evaristo, J. and McDonnell, J.J. 2017, Prevalence and magnitude of groundwater use by vegetation: a global stable isotope meta-analysis, Scientific Reports 7, 44110
Abstract:

The role of groundwater as a resource in sustaining terrestrial vegetation is widely recognized. But the global prevalence and magnitude of groundwater use by vegetation is unknown. Here we perform a meta-analysis of plant xylem water stable isotope (δ2H and δ18O, n = 7367) information from 138 published papers – representing 251 genera, and 414 species of angiosperms (n = 376) and gymnosperms (n = 38). We show that the prevalence of groundwater use by vegetation (defined as the number of samples out of a universe of plant samples reported to have groundwater contribution to xylem water) is 37% (95% confidence interval, 28–46%). This is across 162 sites and 12 terrestrial biomes (89% of heterogeneity explained; Q-value = 1235; P < 0.0001). However, the magnitude of groundwater source contribution to the xylem water mixture (defined as the proportion of groundwater contribution in xylem water) is limited to 23% (95% CI, 20–26%; 95% prediction interval, 3–77%). Spatial analysis shows that the magnitude of groundwater source contribution increases with aridity. Our results suggest that while groundwater influence is globally prevalent, its proportional contribution to the total terrestrial transpiration is limited.

Brantley, S. L., Eissenstat, D. M., Marshall, J. A., Godsey, S. E., Balogh-Brunstad, Z., Karwan, D. L., Papuga, S. A., Roering, J., Dawson, T. E., Evaristo, J., Chadwick, O., McDonnell, J. J., and Weathers, K. C. 2017, Reviews and syntheses: on the roles trees play in building and plumbing the critical zone, Biogeosciences
Abstract:

Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. The hypotheses are roughly divided into those about the architecture (building) and those about the water (plumbing) in the CZ, but the two functions are intertwined. Depending upon one's disciplinary background, many of the nine hypotheses listed below may appear obviously true or obviously false. (1) Tree roots can only physically penetrate and biogeochemically comminute the immobile substrate underlying mobile soil where that underlying substrate is fractured or pre-weathered. (2) In settings where the thickness of weathered material, H, is large, trees primarily shape the CZ through biogeochemical reactions within the rooting zone. (3) In forested uplands, the thickness of mobile soil, h, can evolve toward a steady state because of feedbacks related to root disruption and tree throw. (4) In settings where h « H and the rates of uplift and erosion are low, the uptake of phosphorus into trees is buffered by the fine-grained fraction of the soil, and the ultimate source of this phosphorus is dust. (5) In settings of limited water availability, trees maintain the highest length density of functional roots at depths where water can be extracted over most of the growing season with the least amount of energy expenditure. (6) Trees grow the majority of their roots in the zone where the most growth-limiting resource is abundant, but they also grow roots at other depths to forage for other resources and to hydraulically redistribute those resources to depths where they can be taken up more efficiently. (7) Trees rely on matrix water in the unsaturated zone that at times may have an isotopic composition distinct from the gravity-drained water that transits from the hillslope to groundwater and streamflow. (8) Mycorrhizal fungi can use matrix water directly, but trees can only use this water by accessing it indirectly through the fungi. (9) Even trees growing well above the valley floor of a catchment can directly affect stream chemistry where changes in permeability near the rooting zone promote intermittent zones of water saturation and downslope flow of water to the stream. By testing these nine hypotheses, we will generate important new cross-disciplinary insights that advance CZ science.

Berry, Z.C., Evaristo, J..+13 co-authors 2017, The two water worlds hypothesis: Addressing multiple working hypotheses and proposing a way forward, Ecohydrology
Abstract:

Recent studies using water isotopes have shown that trees and streams appear to return distinct water pools to the hydrosphere. Cryogenically extracted plant and soil water isotopic signatures diverge from the meteoric water lines, suggesting that plants would preferentially use bound soil water, while mobile soil water that infiltrates the soil recharges groundwater and feeds streamflow all plots on meteoric water lines. These findings have been described under the “two water worlds” (TWW) hypothesis. In spite of growing evidence for the TWW hypothesis, several questions remain unsolved within the scope of this framework. Here, we address the TWW as a null hypothesis and further assess the following: (a) the theoretical biophysical feasibility for two distinct water pools to exist, (b) plant and soil processes that could explain the different isotopic composition between the two water pools, and (c) methodological issues that could explain the divergent isotopic signatures. Moreover, we propose a way forward under the framework of the TWW hypothesis, proposing alternative perspectives and explanations, experiments to further test them, and methodological advances that could help illuminate this quest. We further highlight the need to improve our sampling resolution of plants and soils across time and space. We ultimately propose a set of key priorities for future research to improve our understanding of the ecohydrological processes controlling water flows through the soil–plant-atmosphere continuum.

Zhang, Z., Evaristo, J., Si, B., Li, Z., and McDonnell, J.J. 2017, Tritium analysis shows apple trees may be transpiring water several decades old, Hydrological Processes 31:1196–1201
Abstract:

Recent work has shown evidence of ecohydrological separation whereby plants appear to use a less mobile soil water pool that does not mix with more mobile soil water, groundwater, and streamflow. Although many elements of this two water worlds hypothesis remain to be tested and challenged, one key question is “how old might the less mobile water used by plants be?” Such a question is methodologically difficult to answer: stable isotope tracing makes it difficult to resolve any water age older than a few years since the signal gets so damped. Tritium—a useful radiogenic isotope and age dating tool, is now difficult to use in natural systems because most bomb tritium has washed out of soil profiles. Here, we leverage new data from an unusually deep, homogenous soil profile that preserves the mid-1960s tritium bomb signal. We sample the Fuji apple trees (Malus pumila Mil) growing on this site that have root systems that penetrate over 15 m and utilize water from within the bomb peak soil water distribution (extracted via cryogenic extraction). Our data show that water used by these trees is on average 29 years old. Bayesian mixing analysis suggests that 40 ± 30% of fruit tissue water came from depths between 4 and 9 m within the soil profile (36 ± 9 years old); 60 ± 29% was equally divided between 0 and 4 m and 9–15 m ranges (13 ± 5 years old). These findings suggest that trees can use quite old less mobile water, highlighting the separation in ages between more mobile soil water and water in transit in sap flow.

Evaristo, J. and McDonnell, J.J. 2016, Carbon, nitrogen, and water stable isotopes in plant tissue and soils across a moisture gradient in Puerto Rico, Hydrological Processes 31:1558–1559
Abstract:

Stable isotopes in the water molecule (2H or D and 18O), carbon, and nitrogen are useful tracers and integrators of processes in plant ecohydrological systems across scales. Over the last few years, there has been growing interest in regional to continental scale synthesis of stable isotope data with a view to elucidating biogeochemical and ecohydrological patterns. Published datasets from the humid tropics, however, are limited. To be able to contribute to bridging the “data gap” in the humid tropics, here, we publish a relatively novel and unique suite of δ13C, δ15N, δ2H, and δ18O isotope data from three sites across a moisture gradient and contrasting land use in Puerto Rico. Plant tissue (xylem and leaf) samples from two species of mahogany (Swietenia macrophylla and Swietenia mahagoni) and soil samples down to 60 cm in the soil profile were collected in relatively “wet” (July 2012) and “dry” (February 2013) periods at two sites in northeastern (Luquillo) and southwestern (Susua) Puerto Rico. The same sampling suite is also being made available from a highly urbanized site in the capital San Juan. Leaf samples taken in July 2012 and February 2013 were analyzed for δ13C and δ15N; all xylem and bulk soil samples were analyzed for δ2H and δ18O. Soil samples taken in July 2012 were analyzed for δ13C and δ15N. Leaf δ15N and δ13C dataset showed patterns that are possibly associated with site differences. While spatial patterns were also apparent in soil δ15N and δ13C dataset, the positively linear δ15N –δ13C relationship tends to weaken with site moisture. Soil depth and site moisture patterns were also observed in the δ2H and δ18O datasets of bulk soil and xylem samples. The purpose of these datasets is to provide baseline information on soil–plant water (δ2H and δ18O, N = 319), δ13C (N = 272), and δ15N (N = 269) that may be useful in a wide range of research questions from ecohydrological relations to biogeochemical patterns in soils and vegetation.

Evaristo, J., McDonnell, J.J., Scholl, M.A., Bruijnzeel, L.A., and Chun, K.P. 2016, Insights into plant water uptake from xylem-water isotope measurements in two tropical catchments with contrasting moisture conditions, Hydrological Processes 30: 3210–3227
Abstract:

Water transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree-transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany (Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley-bottom, riparian trees than for ridge-top trees. Groundwater contribution was also greater at the xeric site than at the mesic–hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgement that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales.

Evaristo, J., Jasechko, S., and McDonnell, J.J. 2015, Global separation of plant transpiration from groundwater and streamflow, Nature 525, 91–94
Abstract:

Current land surface models assume that groundwater, streamflow and plant transpiration are all sourced and mediated by the same well mixed water reservoir—the soil. However, recent work in Oregon1 and Mexico2 has shown evidence of ecohydrological separation, whereby different subsurface compartmentalized pools of water supply either plant transpiration fluxes or the combined fluxes of groundwater and streamflow. These findings have not yet been widely tested. Here we use hydrogen and oxygen isotopic data (2H/1H (δ2H) and 18O/16O (δ18O)) from 47 globally distributed sites to show that ecohydrological separation is widespread across different biomes. Precipitation, stream water and groundwater from each site plot approximately along the δ2H/δ18O slope of local precipitation inputs. But soil and plant xylem waters extracted from the 47 sites all plot below the local stream water and groundwater on the meteoric water line, suggesting that plants use soil water that does not itself contribute to groundwater recharge or streamflow. Our results further show that, at 80% of the sites, the precipitation that supplies groundwater recharge and streamflow is different from the water that supplies parts of soil water recharge and plant transpiration. The ubiquity of subsurface water compartmentalization found here, and the segregation of storm types relative to hydrological and ecological fluxes, may be used to improve numerical simulations of runoff generation, stream water transit time and evaporation–transpiration partitioning. Future land surface model parameterizations should be closely examined for how vegetation, groundwater recharge and streamflow are assumed to be coupled.

Audio/Visual
Evaristo, J. 2015, Earth’s separate water worlds, Nature Podcast