Flow variability effects on water chemistry in Florida's Artesian Springs

Florida's artesian springs have been conceived as hydrologically, chemically, and thermally invariant systems due to long autocorrelation lengths in discharge characteristics (e.g., > 700 days for vent fluxes in Silver Springs).  Nitrate concentrations in vent fluxes from the Floridan Aquifer have increased as much as 300-fold over background levels in the last 50 years, a change implicated in the recent nuisance proliferation of filamentous benthic algae.  While evidence for this link is weak, alternative explanations have only recently started to receive attention, in part because the prevailing conceptual model for springs presumes negligible variability in discharge chemistry.  One alternative involves changes in grazing pressure due to stress induced by declining vent dissolved oxygen concentrations.  While recent analysis revealed that vent DO levels have indeed changed dramatically since the 1970's, the magnitude of and mechanisms controlling variability in this and other chemical attributes of spring water remain poorly understood.  Here we present preliminary evidence based on analysis of archival data for strong hydrologic controls on vent chemistry driven by presumed changes in the mixing dynamics between water from shallow/rapid and deep/slow flowpaths.  We further discuss the implications of these relationships for ecosystem restoration in light of the confluence of recent drought conditions, projected future climate, and ongoing human appropriation of the Floridan Aquifer.