Patterns of groundwater discharge into Florida Bay

Abstract

Natural chemical tracers of groundwater discharge (222Rn and CH4) were surveyed to evaluate possible patterns of groundwater interactions with surface water in Florida Bay. Radon and methane concentrations in water samples collected from wells, solution holes, canals, and Florida Bay showed a significant correlation, despite the fact that these two trace gases have independent sources. Groundwater flux was also measured directly via seepage meters in several Florida Bay locations. Natural abundance of nitrogen isotopes measured on attached algae and seagrass showed the greatest 15N enrichment near the Keys. Collectively, our results suggested greater groundwater flow along the bay side of the Florida Keys. Nutrient flux estimates, based on interstitial nutrient concentrations and groundwater flux measurements, suggested that groundwater in the eastern part of Florida Bay may provide as much nitrogen (110 ± 60 mmol N m−2 yr−1) and phosphate (0.21 ± 0.11 mmol PO43− m−2 yr−1) as surface freshwater sources from the Everglades (i.e., Taylor Slough and C‐111). However, the inputs are clearly not uniform, and areas near solution holes or tidal springs may have a substantially greater nutrient flux into surface waters then these estimates.