Abstract
Abstract. There is increasing recognition of the role that groundwater plays in the maintenance of ecosystem structure and function. As a result, water resources planners need to develop an understanding of the water requirements for these ecosystems. In this study we reviewed estimates of groundwater discharge from terrestrial vegetation communities around Australia and explored this data set for empirical relationships that could be used to predict groundwater discharge in data poor areas. In particular we explored how leaf area index and the water balance of groundwater systems conformed to two existing ecohydrological frameworks; the Budyko framework, which describes the partitioning of rainfall into evapotranspiration and runoff within a simple supply and demand framework, and Eagleson's theory of ecological optimality. We demonstrate strong convergence with the predictions of both frameworks. Terrestrial groundwater systems discharging groundwater lie above the water limit line as defined in the Budyko framework. However, when climate wetness was recalculated to include groundwater discharge there was remarkable convergence of these sites along this water limit line. Thus, we found that there was a strong correlation between estimates of evapotranspiration derived from the Budyko's relationship with observed estimates of evapotranspiration. Similarly, the LAI of ecosystems with access to groundwater have higher LAI than those without access to groundwater, for a given climatic regime. However, again when discharge was included in the calculation of climate wetness index there was again strong convergence between the two systems, providing support for ecological optimality frameworks that maximize LAI under given water availability regimes. The simplicity and utility of these simple ecohydrological insights potentially provide a valuable tool for predicting groundwater discharge from terrestrial ecosystems, especially in data poor areas.
Highlights
Applying the definition proposed by Budyko (1974), the Australian landscape is predominantly water-limited
In this paper we have examined the relationships between Leaf area index (LAI), climate and the water balance of ecosystems dependent on groundwater
We identified 17 water balance studies that included measured ET and LAI and a further six where no groundwater discharge was identified
Summary
Applying the definition proposed by Budyko (1974), the Australian landscape is predominantly water-limited. There has been considerable focus on understanding the water balance in Australian landscapes, driven by a motivation to ensure that this valuable and limiting resource is used sustainably and that sufficient water resources are allocated for the maintenance and protection of key environmental assets and services. In recent years there has been increasing recognition of the role that groundwater plays in the maintenance of ecosystem structure and function (Eamus and Froend, 2006). Recognition of the importance of this water resource to vegetation functioning imposes an imperative on water
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