Five Centuries of Groundwater Elevations Provide Evidence of Shifting
Climate Drivers and Human Influences on Water Resources in North Central
Florida
Abstract
Groundwater depletion is a concern around the world with implications
for food security, ecological resilience, and human conflict. Long-term
perspectives provided by tree ring-based reconstructions can improve
understanding of factors driving variability in groundwater elevations,
but such reconstructions are rare to date. Here, we report a set of new
546-year tree-ring chronologies developed from living and remnant
longleaf pine (Pinus palustris) trees that, when combined with existing
bald cypress (Taxodium distichum) tree-ring chronologies, were used to
create a set of nested reconstructions of mean annual groundwater
elevation for North Central Florida that together explain 63% of the
variance in instrumental measurements and span 1498–2015. Split
calibration confirms the skill of the reconstructions, but coefficient
of efficiency metrics and significant autocorrelation in the regression
residuals indicate a weakening relationship between tree growth and
groundwater elevation over recent decades. Comparison to data from a
nearby groundwater well suggests extraction of groundwater is likely
contributing to this weakening signal. Periodicity within the
reconstruction and comparison with global sea surface temperatures
highlight the role of El Niño-Southern Oscillation (ENSO) in driving
groundwater elevations, but the strength of this role varies
substantially over time. Atlantic and Pacific sea surface temperatures
modulate ENSO influences, and comparisons to multiple proxy-based
reconstructions indicate an inconsistent and weaker influence of ENSO
prior to the 1800s. Our results highlight the dynamic influence of
ocean-atmospheric phenomena on groundwater resources in North Central
Florida and build on instrumental records to better depict the long-term
range of groundwater elevations.