Analysis of growing season carbon and water fluxes of a subalpine wetland in the Canadian Rocky Mountains: Implications of shade on ecosystem water use efficiency

Abstract

Mountain regions are an important regulator in the global water cycle through their disproportionate water contribution. Often referred to as the “Water Towers of the World”, mountains contribute 40%–60% of the world's annual surface flow. Shade is a common feature in mountains, where complex terrain cycles land surfaces in and out of shadows over daily and seasonal scales, which can impact water use. This study investigated the turbulent water and carbon dioxide (CO2) fluxes during the snow‐free period in a subalpine wetland in the Canadian Rocky Mountains, from 7 June to 10 September 2018. Shading had a significant and substantial effect on water and CO2 fluxes at our site. When considering data from the entire study period, each hourly increase of shade per day reduced evapotranspiration (ET) and gross primary production (GPP) by 0.42 mm and 0.77 g C m−2, equivalent to 17% and 15% per day, respectively. However, the variability in shading changed throughout the study, it was stable to start and increased towards the end. Only during the peak growing season, the site experienced days with both stable and increasing shade. During this time, we found that shade, caused by the local complex terrain, reduced ET and potentially increased GPP, likely due to enhanced diffuse radiation. The overall result was greater water use efficiency during periods of increased shading in the peak growing season. These findings suggest that shaded subalpine wetlands can store large volumes of water for late season runoff and are productive through short growing seasons.

The dependence of evaporative efficiency of vegetated surfaces on ground cover mass fractions in vegetated soils in mesic ecosystems

“…The mean temperature from 2011 to 2021 recorded at the nearest long‐term climate station (ID: 305MGFF, ~2543 m), at a distance of 13.7 km, is −1.2 °C. No long‐term precipitation record was found, but the mean temperature and rainfall measured during June to August in 2018 at the site was 9 °C and 339 mm, respectively (Hrach et al, 2022). Vegetation comprises two distinct groups: sparsely distributed overstory species (e.g., Salix spp., Larix spp., and Abies spp.)…”

“…Vegetation comprises two distinct groups: sparsely distributed overstory species (e.g., Salix spp., Larix spp., and Abies spp.) and abundant understory species including Erigeron spp., parnassia spp., and Equisetum spp (Chau, 2023; Hrach et al, 2022 ) . The average height is around 0.8 m for overstory canopy and 0.1 m for understory canopy.…”

“…Near the stream, there is a thin layer of sand above a semi‐pervious layer of very fine silt, while at the centre of the meadow, soils are defined by silt and clay (Christensen, 2017). More site information can be found in Hrach et al (2022).…”

Quantifying relative contributions of source waters from a subalpine wetland to downstream water bodies

“…The importance of snow and snowmelt, however, is heavily documented in the Canadian Rocky Mountains (Fang et al, 2013;Hayashi & Farrow, 2014;Hrach et al, 2022;Mercer, 2018;Pomeroy et al, 2016). In glacier-fed catchments of the Canadian Rockies, streams originate from glacial meltwater and snow that recharges aquifers during late spring (Penna et al, 2013).…”

Water use patterns of dominant species of riparian wetlands in arid areas

“…Due to limited precipitation and strong evaporation in arid areas, water resources are an important limiting factor affecting plant survival, growth and sustainability of vegetation restoration (Austin et al, 2004; Wang, D'Odorico, et al, 2012). In recent years, due to more frequent extreme weather events such as high temperature and drought, land degradation has intensified (IPCC, 2019), and the riparian wetland ecosystem has been faced with drought problems such as reduced precipitation and water level decline in different degrees (Hrach et al, 2022). Extreme drought will reduce the availability of water resources and vegetation productivity and bring irreversible death risk to plants (Chen et al, 2010; Wang et al, 2011).…”