A δ18O and δ2H stable water isotope analysis of subalpine forest water sources under seasonal and hydrological stress in the Canadian Rocky Mountains

Lindsey E. Langs, Richard M. Petrone and John W. Pomeroy

Hydrological Processes
Volume 24, Issue 26
December 18, 2020
https://doi.org/10.1002/hyp.13986

Abstract:
Subalpine forests are hydrologically important to the function and health of mountain basins. Identifying the specific water sources and the proportions used by subalpine forests is necessary to understand potential impacts to these forests under a changing climate. The recent “Two Water Worlds” hypothesis suggests that trees can favour tightly bound soil water instead of readily available free‐flowing soil water. Little is known about the specific sources of water used by subalpine trees Abies lasiocarpa (Subalpine fir) and Picea engelmannii (Engelmann spruce) in the Canadian Rocky Mountains. In this study, stable water isotope (δ18O and δ2H) samples were obtained from S. fir and Engelmann spruce trees at three points of the growing season in combination with water sources available at time of sampling (snow, vadose zone water, saturated zone water, precipitation). Using the Bayesian Mixing Model, MixSIAR, relative source water proportions were calculated. In the drought summer examined, there was a net loss of water via evapotranspiration from the system. Results highlighted the importance of tightly vadose zone, or bound soil water, to subalpine forests, providing insights of future health under sustained years of drought and net loss in summer growing seasons. This work builds upon concepts from the “Two Water Worlds” hypothesis, showing that subalpine trees can draw from different water sources depending on season and availability. In our case, water use was largely driven by a tension gradient within the soil allowing trees to utilize vadose zone water and saturated zone water at differing points of the growing season.

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By Shannon Boklaschuk
College of Arts & Science News
December 3, 2020

The first university course Dr. Martyn Clark (PhD) ever taught is memorable for many reasons.

First, Clark started teaching the University of Saskatchewan (USask) graduate geography course—GEOG 825—in September 2020, when most USask classes moved online due to the global COVID-19 pandemic. Second, because the course was offered remotely, students from more than a dozen countries around the world signed up. Third, Clark employed innovative teaching and learning practices in the course, including cloud computing, super-computing and hands-on model development.

As a result, teaching GEOG 825 involved a lot of “learning by doing,” said Clark, a professor in the Department of Geography and Planning in USask’s College of Arts and Science and the associate director of the Centre for Hydrology. “It’s been a pretty wild ride,” he said.

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By Nick Skinner
Laurier Campus Magazine
Fall 2020

Nearly 4,000 km northwest of Wilfrid Laurier University’s southern Ontario campuses, where mainland Canada meets the Arctic Ocean, lies Trail Valley Creek Arctic Research Station. Located between Inuvik and Tuktoyaktuk, N.W.T., within the Inuvialuit Settlement Region, it is Laurier’s northern-most research station and this year marks its 30th anniversary.

Now the longest-running hydrologically focused Arctic research station in Canada, Trail Valley Creek has become a productive field site for Laurier’s Centre for Cold Regions and Water Science, which maintains more than 50 research sites north of Ontario’s Ring of Fire. It is also central to the university’s decade-long partnership with the Government of the Northwest Territories. Dedicated to understanding and predicting environmental changes near the treeline in the western Canadian Arctic, the research station is an interactive training ground for Laurier students and hosts international collaborators from organizations including NASA and the University of Edinburgh.

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