Speculations on the application of foliar &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C discrimination to reveal groundwater dependency of vegetation and provide estimates of root depth and rates of groundwater use

Rizwana Rumman,Tonantzin Tarin,Rachael H Nolan,Derek Eamus,James Cleverly

doi:10.5194/hess-22-4875-2018

Speculations on the application of foliar &lt;sup&gt;13&lt;/sup&gt;C discrimination to reveal groundwater dependency of vegetation and provide estimates of root depth and rates of groundwater use

Rizwana Rumman, Tonantzin Tarin + Show 3 more

Open Access

https://doi.org/10.5194/hess-22-4875-2018

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Abstract

Abstract. Groundwater-dependent vegetation is globally distributed, having important ecological, social, and economic value. Along with the groundwater resources upon which it depends, this vegetation is under increasing threat through excessive rates of groundwater extraction. In this study we examined one shallow-rooted and two deep-rooted tree species at multiple sites along a naturally occurring gradient in depth-to-groundwater. We measured (i) stable isotope ratios of leaves (δ13C), xylem, and groundwater (δ2H and δ18O); and (ii) leaf-vein density. We established that foliar discrimination of 13C (Δ13C) is a reliable indicator of groundwater use by vegetation and can also be used to estimate rooting depth. Through comparison with a continental-scale assessment of foliar Δ13C, we also estimated the upper limits to annual rates of groundwater use. We conclude that maximum rooting depth for both deep-rooted species ranged between 9.4 and 11.2 m and that annual rates of groundwater use ranged from ca. 1400 to 1700 mm for Eucalyptus camaldulensis and from 600 to 900 mm for Corymbia opaca. Several predictions about hydraulic and leaf traits arising from the conclusion that these two species made extensive use of groundwater were supported by additional independent studies of these species in central Australia.

Highlights

Drylands cover 41 % of the earth’s total land area (Reynolds et al, 2007) and are sub-categorized as hyper-arid, arid, semi-arid, and dry sub-humid areas
As a consequence of these patterns in 13C, water-use efficiency (WUEi) did not vary significantly for A. aneura across sites differing in DTGW (Fig. 4a) despite the large variability in WUEi across sites and seasons
We confirmed that access to shallow groundwater by E. camaldulensis and C. opaca (DTGW ca. 0–11 m) resulted in smaller WUEi than A. aneura

Summary

Introduction

Drylands cover 41 % of the earth’s total land area (Reynolds et al, 2007) and are sub-categorized as hyper-arid, arid, semi-arid, and dry sub-humid areas. 40 % of the world’s population reside in drylands and groundwater represents a major water resource for human consumptive use, and for groundwater-dependent ecosystems (GDEs, Eamus et al, 2006). Sustainable management of both groundwater and GDEs requires identification of the location of GDEs, rooting depth of vegetation, and rates of groundwater use, but attaining such information presents significant technical and cost challenges (Eamus et al, 2015).

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