Field comparison of methods for estimating groundwater discharge by evaporation and evapotranspiration in an arid-zone playa Margaret Shanafield a,⇑ , Peter G. Cook a,b,1 , Hugo A. Gutiérrez-Jurado a,1 , Ralph Faux c , James Cleverly c , Derek Eamus c a National Centre for Groundwater Research and Training, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia b Water for a Healthy Country National Flagship, Commonwealth Scientific and Industrial Research Organisation, Division of Land and Water, Glen Osmond, Adelaide, SA 5064, Australia c National Centre for Groundwater Research and Training and School of the Environment, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia article info Article history: Received 2 January 2015 Received in revised form 16 May 2015 Accepted 2 June 2015 Available online 7 June 2015 This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of Markus Tuller, Associate Editor Keywords: Evaporation Evapotranspiration Isotopes Playa Salt pan Groundwater discharge summary Evaporative losses typically play a substantial role in the water balances of arid regions. However, they are often poorly understood due to low flux rates and difficulty in direct measurement. We compared six field methods to quantify groundwater discharge due to evaporative and evapotranspirative fluxes from Stirling Swamp, a playa in central Australia; Bowen ratio–energy balance (BREB), maximum entropy production (MEP), chloride and stable isotope profiling, change in groundwater level, and 14 C profiles within the aquifer. The latter method has not been previously used to determine groundwater discharge. Evaporative groundwater discharge estimates varied between 0 and 300 mm/y, partly due to variability in spatial and temporal scales captured by the individual methods. Within playa systems where evapo- transpiration within the soil is negligible but the depth to groundwater is small, land surface energy bal- ances were found to have the advantage of integrating over hundreds of metres, and when upscaled to annual estimates they agreed well with expected evaporative flux values. Soil profile methods yielded a wide range of results depending on the values of several constants that must be assumed, and the assumption of steady state was found to be a disadvantage. Groundwater methods also had the advan- tage of integrating over some distance within the aquifer; however, advective transport in the subsurface may have led to under-estimation of evaporative flux with these methods. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Use of groundwater in arid regions is increasing worldwide, in response to a growing global population (Seely et al., 2003). To determine the impacts of this groundwater use on the long-term viability of the resource, as well as on the flora and fauna in these fragile arid ecosystems, accurate water budgets must be devel- oped. Many arid environments are found in closed basins, where water lost to the combined processes of transpiration by plants and evaporation from bare surfaces can account for up to 95% of the total annual rainfall (Wilcox and Thurow, 2006). In playas or salt pans where water tables are shallow, diffuse discharge of groundwater is typically considered to be a large component of the water balance (Thorburn et al., 1992; Holland, 2002). However, evaporative loss through these features can be difficult to quantify due to harsh conditions and low evaporative fluxes (Tyler et al., 1997). Due to these difficulties, relatively few field studies have been conducted in natural playa ecosystems to determine evaporative fluxes. Tyler et al. (1997) estimated mean groundwater evapora- tion from the playa surface at Owens Lake, California to be in the range of 88–104 mm/y using lysimeters and eddy correlation, but only 17–22 mm/y using chloride profiles. Malek et al. (1990) reported groundwater evaporation of 229 mm/y from a playa sur- face in eastern Utah. At the dry, saline bed of Lake Frome in South Australia, an early study using isotope and chloride profiles esti- mated an annual evaporation rate of 50–240 mm/y (Allison and Barnes, 1985). At the nearby dry, saline Lake Eyre, Ullman (1985) estimated a lower annual evaporation rate of only 9–28 mm/y using chloride and bromide soil profiles. Ullman (1985) attributed the low evaporative flux at Lake Eyre to the mulching effect and higher albedo associated with the salt crust at the soil surface. Also in this general region, Costelloe et al. (2014) estimated evap- oration rates of approximately 7–79 mm/y using soil profiles. In a http://dx.doi.org/10.1016/j.jhydrol.2015.06.003 0022-1694/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +61 8 82012193. E-mail address: Margaret.shanafield@flinders.edu.au (M. Shanafield). 1 Tel.: +61 8 82012193. Journal of Hydrology 527 (2015) 1073–1083 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol