Determining spatial and temporal inputs of freshwater, including submarine groundwater discharge, to a subtropical estuary using geochemical tracers, Biscayne Bay, South Florida

Jeremy C. Stalker, René M. Price, Peter K. Swart

Research output: Contribution to journalArticle

26 Scopus citations

Abstract

Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr 2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ 18O=-2.66‰, δD -7.60‰) similar to rainfall (δ 18O=-2.86‰, δD=-4.78‰). Canal water had a heavy isotopic signature (δ 18O=-0.46‰, δD=-2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1-2% of the total fresh and saline water input.

Original languageEnglish (US)
Pages (from-to)694-708
Number of pages15
JournalEstuaries and Coasts
Volume32
Issue number4
DOIs
StatePublished - Jul 1 2009

Keywords

  • Florida
  • Geochemistry
  • Groundwater
  • Isotopes
  • Submarine groundwater discharge
  • Trace metals

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Ecology

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