Sample collection
Out of 30 monitored playas in the Jornada Basin (see related EDI
package knb-lter-jrn.210420001), twenty playas that could be
easily accessed were selected for deep soil coring. We used a
Giddens hydraulic auger to collect one continuous 5 m soil core
from the center of each study playa (n = 20). Five 100 g soil
samples were taken from below the core at 1 m increments (1 - 5 m)
for estimation of soil water content and chloride concentration
(details below). We extracted cores from 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.
Chloride mass balance
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 an Aero Chem
Metrics precipitation collector (Havstad et al, 2006).
To estimate chloride in soils, we took five 100 g soil samples
from the 5 meter soil 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 (g/g) with soil bulk
density (g/m3) (Elliot et al. 1999) measurements to calculate
volumetric soil water content. Cl- was measured (mg/l) using an
ion selective electrode (Santoni et al. 2010). The concentration
of chloride per gram of soil was estimated after subtracting out
water content.
For further information on methods, refer to the McKenna and Sala
(2018) publication below.
References
Elliot E. T., Heil J. W., Kelly E. F., Monger H. C. Soil
structural and other physical properties. 74-88. In: Robertson G.
P., Bledsoe C. S., Coleman D. C., Sollins P. (eds). "Standard
soil methods for long-term ecological research". (Oxford
University Press, 1999).
Santoni, C. S., E. G. Jobbágy, and S. Contreras (2010),
"Vadose zone transport in dry forests of central Argentina:
Role of land use". Water Resour. Res., 46, W10541,
doi:10.1029/2009WR008784
Havstad, K. M., Huenneke, L. F. and Schlesinger, W. H. (2006),
"Structure and Function of a Chihuahuan Desert Ecosystem: the
Jornada Basin Long-term Ecological Research Site" (Oxford,
New York: Oxford University Press)
McKenna, Owen P., and Osvaldo E. Sala. "Groundwater recharge
in desert playas: current rates and future effects of climate
change." Environmental Research Letters 13, no. 1 (2018):
014025. https://doi.org/10.1088/1748-9326/aa9eb6
