Abstract
Global food systems rely on irrigated agriculture, and most of these
systems in turn depend on fresh sources of groundwater. In this study,
we demonstrate that groundwater development, even without overdraft, can
transform a fresh, open basin into an evaporation dominated,
closed-basin system, such that most of the groundwater, rather than
exiting via stream baseflow and lateral subsurface flow, exits
predominantly by evapotranspiration from irrigated lands. In these newly
closed hydrologic basins, just as in other closed basins, groundwater
salinization is inevitable because dissolved solids cannot escape, and
the basin is effectively converted into a salt sink. We first provide a
conceptual model of this process, called “nthropogenic asin losure and
groundwater inization” (ABCSAL). We then examine the temporal dynamics
of ABCSAL using the Tulare Lake Basin, California, as a case study for a
large irrigated agricultural region with Mediterranean climate,
overlying an unconsolidated sedimentary aquifer system. Even with modern
water management practices that arrest historic overdraft, results
indicate that shallow aquifers (36 m deep) exceed maximum contaminant
levels for total dissolved solids on decadal timescales. Intermediate
(132 m) and deep aquifers (187 m), essential for drinking water and
irrigated crops, are impacted within two to three centuries. Hence,
ABCSAL resulting from groundwater development in agricultural regions
worldwide constitutes a largely unrecognized constraint on groundwater
sustainable yield on similar timescales to aquifer depletion, and poses
a serious challenge to global groundwater quality sustainability, even
where water levels are stable.