Water use in a riparian cottonwood ecosystem: Eddy covariance measurements and scaling along a river corridor

Flanagan, Lawrence B.; Orchard, Trina E.; Logie, Gordon; Coburn, Craig A.; Rood, Stewart B.

doi:10.1016/j.agrformet.2016.08.024

Cited by 30 publications

(38 citation statements)

References 72 publications

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“…That modelling indicated that the increased evaporation with climate warming would result in substantial water loss, resulting in regional river flow declines of ~10% to 20% through the nonwinter seasons. That modelling was still incomplete relative to transpirational water use by woodlands including riparian cottonwood forests, and that hydrologic component is advancing, following the regional applications of newer research tools including eddy covariance flux measurements (Flanagan, Orchard, Logie, Coburn, & Rood, ).…”

Section: Discussionmentioning

confidence: 99%

Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers

Philipsen

Gill

Shepherd

et al. 2018

Hydrological Processes

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The South Saskatchewan River Basin of southern Alberta drains the transboundary central Rocky Mountains region and provides the focus for irrigation agriculture in Canada. Following extensive development, two tributaries, the Oldman and Bow rivers, were closed for further water allocations, whereas the Red Deer River (RDR) remains open. The RDR basin is at the northern limit of the North American Great Plains and may be suitable for agricultural expansion with a warming climate. To consider irrigation development and ecological impacts, it is important to understand the regional hydrologic consequences of climate change. To analyse historic trends that could extend into the future, we developed century‐long discharge records for the RDR, by coordinating data across hydrometric gauges, estimating annual flows from seasonal records, and undertaking flow naturalization to compensate for river regulation. Analyses indicated some coordination with the Pacific decadal oscillation and slight decline in summer and annual flows from 1912 to 2016 (−0.13%/year, Sen's slope). Another forecasting approach involved regional downscaling from the global circulation models, CGCMI‐A, ECHAM4, HadCM3, and NCAR‐CCM3. These projected slight flow decreases from the mountain headwaters versus increases from the foothills and boreal regions, resulting in a slight increase in overall river flows (+0.1%/year). Prior projections from these and other global circulation models ranged from slight decrease to slight increase, and the average projection of −0.05%/year approached the empirical trend. Assessments of other rivers draining the central and northern Rocky Mountains revealed a geographic transition in flow patterns over the past century. Flows from the rivers in Southern Alberta declined (around −0.15%/year), in contrast to increasing flows in north‐eastern British Columbia and the Yukon. The RDR watershed approaches this transition, and this study thus revealed regional differentiation in the hydrological consequences from climate change.

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Section: Discussionmentioning

confidence: 99%

Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers

Philipsen

Gill

Shepherd

et al. 2018

Hydrological Processes

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“…We studied a riparian cottonwood forest within the Helen Schuler Nature Reserve (HSNR) in Lethbridge, Alberta, Canada (49.702°N, 112.863°W, elevation 928 m). This study site has been described in detail in our previous publications (Flanagan et al, ; Rood et al, ; Yang et al, ), and so we provide below only a short summary of the site characteristics. The average annual precipitation and temperature in Lethbridge during 1981–2010 were 380.2 mm and 5.9 °C, respectively (http://www.climate.weather.gc.ca/climate_normals/).…”

Section: Methodsmentioning

confidence: 99%

“…The herbaceous plant community was dominated by a range of grass species. The tree canopy and understory plants contributed approximately equally to the ecosystem leaf area index, which was measured at 1.8 ± 0.2 m 2 /m 2 in 2014 (Flanagan et al, ). The tree density was relatively low (276 ± 300 trees/ha, mean ± SD), with average tree height and tree diameter (at 1.35 m above ground) of 18 ± 5 m and 37 ± 15 cm, respectively (Flanagan et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…Comparison of cumulative evapotranspiration and precipitation in a riparian cottonwood forest during May–August in three different years with contrasting environmental conditions. Evapotranspiration was measured using the eddy covariance technique at the same location used in this study, as previously reported by Flanagan et al () and Yang et al (). No evapotranspiration measurements were conducted during 2016…”

Section: Introductionmentioning

confidence: 93%

“…The amount of river water (alluvial groundwater) that was used by riparian trees to support transpiration would depend on the amounts of water taken up from other sources, which in turn would depend on water potential gradients within the soil and the plant's functional rooting pattern (Bowling, Schulze, & Hall, ; Penna et al, ). It is clear that cottonwood riparian forests in semiarid western regions of North America do not receive sufficient growing season precipitation to completely support the relatively high transpiration requirements of these forests (Flanagan, Orchard, Logie, Coburn, & Rood, ; Scott et al, ; Yang, Rood, & Flanagan, ). For example, cumulative evapotranspiration in cottonwood riparian forests can exceed precipitation inputs substantially during the growing season (Figure ).…”

Section: Introductionmentioning

confidence: 99%

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Using stable isotopes to quantify water sources for trees and shrubs in a riparian cottonwood ecosystem in flood and drought years

Flanagan

Orchard

Tremel

et al. 2019

Hydrological Processes

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Riparian cottonwood forests in dry regions of western North America do not typically receive sufficient growing season precipitation to completely support their relatively high transpiration requirements. Water used in transpiration by riparian ecosystems must include alluvial groundwater or water stored in the potentially large reservoir of the unsaturated soil zone. We used the stable oxygen and hydrogen isotope composition of stem xylem water to evaluate water sources used by the dominant riparian cottonwood (Populus spp.) trees and shrubs (Shepherdia argentea and Symphoricarpos occidentalis) in Lethbridge, Alberta, during 3 years of contrasting environmental conditions. Cottonwoods did not exclusively take up alluvial groundwater but made extensive use of water sourced from the unsaturated soil zone. The oxygen and hydrogen isotope compositions of cottonwood stem water did not strongly overlap with those of alluvial groundwater, which were closely associated with the local meteoric water line. Instead, cottonwood stem water δ 18 O and δ 2 H values were located below the local meteoric water line, forming a line with a low slope that was indicative of water exposed to evaporative enrichment of heavy isotopes. In addition, cottonwood xylem water isotope compositions had negative values of deuterium excess (d-excess) and line-conditioned (deuterium) excess (lc-excess), both of which provided evidence that water taken up by the cottonwoods had been exposed to fractionation during evaporation. The shrub species had lower values of d-excess and lc-excess than had the cottonwood trees due to shallower rooting depths, and the d-excess values declined during the growing season, as shallow soil water that was taken up by the plants was exposed to increasing, cumulative evaporative enrichment. The apparent differences in functional rooting pattern between cottonwoods and the shrub species, strongly influenced the ratio of net photosynthesis to stomatal conductance (intrinsic water-use efficiency), as shown by variation among species in the δ 13 C values of leaf tissue. K E Y W O R D Shydrogen and oxygen isotopes, Populus sp, Shepherdia argentea, Symphoricarpos occidentalis

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Riparian cottonwood mortality following compound impacts from river water withdrawal and hydroclimatic variation

Rood

Mahoney

2023

Ecohydrology

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Originating in Glacier Park, Montana, the transboundary St. Mary River has provided a focus for international water sharing for a century. It was dammed and diverted in the USA, and more extensively in Alberta, where it supports Canada's centre for agricultural irrigation. Following water withdrawals, the riparian cottonwoods (Populus angustifolia) collapsed, and we assessed the woodland decline downstream from the St. Mary Dam, through eight sets of aerial photographs over seven decades. These revealed 88% woodland loss from 1951 to 1999 (R2 = 0.984), including a steeper decline with the 1980s drought. Following the implementation of an environmental flow regime that increased minimum flows after 1993, the remnant woodlands were stabilized, with a slight recovery by 2022. Analyses of the historical hydrology revealed compound contributions to the woodland mortality. (1) Annual river flows declined with increasing water diversion, and (2) late summer flows were particularly depleted. (3) Dam operations resulted in abrupt stage recessions and irregular spikes. (4) Accompanying climate warming, the spring snowmelt advanced and late summer flows declined. (5) The greatest climatic influence involved multiple‐year clusters with high versus low flows, corresponding with the Pacific decadal oscillation (PDO) from 1920 to 1990 (R2 = 0.365), but less coupled thereafter. This long‐term study demonstrates the coordination between hydroclimatic variation, water management and the fate of riparian woodlands, which reveal ecosystem health. An environmental flow regime provided benefit, and for other regulated rivers in dry ecoregions, we recommend functional flow regimes that provide sufficient minimum flows and avoid abrupt flow recession or irregular spikes.

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Water use in a riparian cottonwood ecosystem: Eddy covariance measurements and scaling along a river corridor

Cited by 30 publications

References 72 publications

Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers

Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers

Using stable isotopes to quantify water sources for trees and shrubs in a riparian cottonwood ecosystem in flood and drought years

Riparian cottonwood mortality following compound impacts from river water withdrawal and hydroclimatic variation

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