Impact of elevation and weather patterns on the isotopic composition of precipitation in a tropical montane rainforest

Abstract

This study presents the spatial and temporal variability of δ<sup>18</sup>O and δ<sup>2</sup>H isotope signatures in precipitation of a south Ecuadorian montane cloud forest catchment (San Francisco Catchment). From 2 September to 25 December 2010, event sampling of open rainfall was conducted along an altitudinal transect (1800 m a.s.l. to 2800 m a.s.l.) to investigate possible effects of altitude and weather conditions on the isotope signature. <br> The spatial variability is mainly affected by the altitude effect. The event based δ<sup>18</sup>O altitude effect for the study area averages −0.22‰ × 100 m<sup>−1</sup> (δ<sup>2</sup>H: −1.12‰ × 100 m<sup>−1</sup>). The temporal variability is mostly controlled by prevailing air masses. Precipitation during the times of prevailing southeasterly trade winds is significantly enriched in heavy isotopes compared to precipitation during other weather conditions. In the study area, weather during austral winter is commonly controlled by southeasterly trade winds. Since the Amazon Basin contributes large amounts of recycled moisture to these air masses, trade wind-related precipitation is enriched in heavy isotopes. We used deuterium excess to further evaluate the contribution of recycled moisture to precipitation. Analogously to the δ<sup>18</sup>O and δ<sup>2</sup>H values, deuterium excess is significantly higher in trade wind related precipitation. Consequently, it is assumed that evaporated moisture is responsible for high concentrations of heavy isotopes during austral winter

Tropical West Pacific moisture dynamics and climate controls on rainfall isotopic ratios in southern Papua, Indonesia

“…The mean weighted d values range from 13.35‰ at KK to 17.10‰ at GRS (Table 2), which demonstrate an increase of d value with elevation at a rate of 0.68‰/km. Increasing d values with elevation have also been reported in the tropical montane rainforest of the Amazon Basin [e.g., Windhorst et al, 2013]. The d values tend to increase with elevation at high relative humidity [Gonfiantini et al, 2001], which is prevalent in the Papua region.…”

“…The mean d value of all samples is~15‰, which is greater than the GMWL intercept of 10‰ [Craig, 1961]. The possible cause of the high d value in this region is a land surface recycling through the surrounding tropical rainforests during transport to the collection sites [Salati et al, 1979;Windhorst et al, 2013]. As with δ 18 O, the daily d variations at all stations show similar patterns suggesting relatively similar moisture sources and transport pathways into the region (Figure 3b).…”

“…The additional moisture from land surface recycling during transport from oceanic sources to the precipitation sites can have considerable impact on isotopic composition in precipitation [Salati et al, 1979]. The land surface recycling has been shown to yield precipitation with higher d values over the Amazon Basin [Gat and Matsui, 1991;Windhorst et al, 2013]. Additional recycled moisture within the air masses over the Amazon Basin also contributes to 18 O-enriched rainfall during austral winter when the southeast trade wind-related precipitation prevails [Windhorst et al, 2013].…”

“…The amount effect in rain has been ascribed to fractionation processes that occur on both local [Vuille et al, 2005;Lee et al, 2009] and larger spatial scales [Cobb et al, 2007;Risi et al, 2008a;Kurita et al, 2009Kurita et al, , 2011Fudeyasu et al, 2011;Tremoy et al, 2012;Moerman et al, 2013;Kurita, 2013]. However, previous studies also have linked rainfall isotopic composition to moisture sources, moisture transport history, and/or prevailing weather patterns [Rhodes et al, 2006;Scholl et al, 2007Scholl et al, , 2009Kurita et al, 2009;Breitenbach et al, 2010;Fudeyasu et al, 2011;Crawford et al, 2013;Suwarman et al, 2013;Windhorst et al, 2013].…”

Advancing ecohydrology in the changing tropics: Perspectives from early career scientists

“…tems, a few have been carried out in tropical regions to (a) estimate mean transit times of water(Mosquera, Célleri, et al, 2016;Muñoz- Villers, Geissert, Holwerda, & McDonnell, 2015;Timbe et al, 2014), (b) explore the influence of topographic and weather patterns on the isotopic composition of precipitation(Sánchez-Murillo et al, 2016;Vimeux, Tremoy, Risi, & Gallaire, 2011;Windhorst, Waltz, Timbe, Frede, & Breuer, 2013), and (c) calibrate hydrological models(Birkel & Soulsby, 2016;Windhorst, Kraft, Timbe, Frede, & Breuer, 2014).…”