04 May 2023
 | 04 May 2023
Status: this preprint is currently under review for the journal HESS.

The seasonal origins and ages of water provisioning streams and trees in a tropical montane cloud forest

Emily I. Burt, Gregory R. Goldsmith, Roxanne M. Cruz-de Hoyos, Adan Julian Ccahuana Quispe, and A. Joshua West

Abstract. Determining the sources of water provisioning streams, soils, and vegetation can provide important insights into the water that sustains critical ecosystem functions now and how those functions may be expected to respond given projected changes in the global hydrologic cycle. We developed multi-year time series of water isotope ratios (δ18O and δ2H) based on twice monthly collections of precipitation, lysimeter, and tree branch xylem waters from a seasonally dry tropical montane cloud forest in the southeastern Andes mountains of Peru. We then used this information to determine indices of the seasonal origins, the young water fractions (Fyw), and the new water fractions (Fnew) of soil, stream, and tree water. There was no evidence for intra-annual variation in the seasonal origins of lysimeter and stream waters, which were predominantly comprised of wet season precipitation, even during the dry seasons. However, branch xylem waters demonstrated an intra-annual shift in seasonal origin: xylem waters were comprised of wet season precipitation during the wet season, and dry season precipitation during the dry season. The young water fractions of lysimeter (< 15 %) and stream (5 %) waters were lower than the young water fraction (37 %) in branch xylem waters. The new water fraction (an indicator of water 2 weeks old) was estimated to be 12 % for branch xylem waters, while there was no significant evidence for new water in streams. Our results indicate that the source of water for trees in this system varied seasonally, such that recent precipitation may be more immediately taken up by shallow tree roots. In comparison, the source of water for soils and streams did not vary seasonally, such that precipitation may mix and reside in soils and take longer to transit into the stream. Our insights into the seasonal origins and ages of water in soils, streams, and vegetation in this tropical montane cloud forest adds to understanding of the mechanisms that govern the partitioning of water moving through different ecosystems.

Emily I. Burt et al.

Status: open (until 29 Jun 2023)

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  • RC1: 'Comment on hess-2023-75', Anonymous Referee #1, 15 May 2023 reply

Emily I. Burt et al.

Emily I. Burt et al.


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Short summary
When it rains, water remains in the ground for variable amounts of time before it is taken up by plants or becomes streamflow. Understanding how long water stays in the ground before it is taken up by plants or becomes streamflow helps predict what will happen to the water cycle in future climates. Some studies suggest that plants take up water that has been in the ground for a long time; in contrast, we find that plants take up a significant amount of recent rain.