| Description |
Previous stable isotope research identified a riparian meadow in the Rocky Mountains where streamside box elder (Acer negundo) trees did not use stream water, the most reliable and readily available source. Further dual isotope analysis showed that the water used by trees appeared to be more evaporatively enriched than all available measured sources, including stream water, precipitation-derived soil water, and groundwater. While it is unlikely that there is a missing pool of water accessed by the trees, they may be tapping into a distinct subset of the bulk soil water available, possibly derived from snowmelt from the preceding winter. In this study, we investigated whether snowpack sublimation and melt may impart an enriched isotopic signature that persists throughout the following growing season in less-mobile soil water pools. Depth profiles of snow, bulk melt water, and early season soil lysimeter water were collected throughout the winter and analyzed for hydrogen and oxygen stable isotopes. As snow began to melt in the spring, water samples for isotope analysis were taken from soil profiles, stream water, groundwater, and stems. Although sublimation may have occurred at the site, neither sublimation nor exchange between melt water and snow imparted an evaporative isotope enrichment signal on the snowpack. However, tree xylem water remained isotopically enriched relative to all sources during the following growing season. These findings suggest that snowpack sublimation and liquid-ice isotopic exchange are not the source of evaporative enrichment in tree xylem water. |
