Twenty playas that could be easily accessed were selected from 30
monitored playas on the Jornada Experimental Range as part of another
study on carbon and nitrogen storage in playas (JRN package
210420001). We used the chloride mass balance (CMB) approach to
empirically estimate groundwater recharge rates beneath playa
surfaces. CMB is the most common method for estimating ground-water
recharge in unsaturated soil zones. Surface inputs of chloride and
precipitation are balanced by the mass out beneath the playa via
chloride in the unsaturated zone deep percolation that results in
groundwater recharge.
Recharge mm/yr=(Chloride inputs (mg/L) * precipitation
(mm/yr))/Chloride in Unsaturated Zone (mg/L)
We used values of annual precipitation and wet and annual dry
deposition values from JRN data. We calculated mean annual
precipitation from the 100 year record (1914–2015) of the centrally
located Jornada weather station. We calculated annual rates of wet and
dry deposition using a 30-year record (1983–2013) in which wet and dry
deposition of Chloride were measured monthly at the same centrally
located weather station using Aero ChemMetrics collector. To estimate
chloride in soils, we sampled at the lowest topographic point of each
playa, because this area is flooded most frequently. We collected each
core in August 2014 when playas were not flooded. We took five 100 g
soil samples from below the core at 1 meter increments (1–5 m). Soils
were homogenized and 3 subsamples were taken from each 1 meter depth.
We combined gravimetric water content with soil bulk density
measurements to calculate volumetric soil water content. Chloride was
measured using an ion selective electrode. The concentration of
chloride per gram of soil was estimated after subtracting out water
content.
For further information on methods, refer to: McKenna, O. P. and O. E.
Sala. 2018. Groundwater recharge in desert playas: current rates and
future effects of climate change. Environmental Research Letters 13:
014025.
