Benthic nutrient flux in a small estuary in northwest Florida (USA)

DiDonato, Guy T. (author)
Lores, Emile M. (author)
Murrell, Michael C. (author)
Smith, Lisa M. (author)
Caffrey, Jane M. (author)

Gulf and Caribbean Research

1528-0470

18

1

15

25

2006

Benthic nutrient fluxes of ammonium (NH₄⁺), nitrite/nitrate (NO₂⁻ + NO₃⁻), phosphate (PO₄⁻³), and dissolved silica (DSi) were measured in Escambia Bay, an estuary within the larger Pensacola Bay system of northwestern Florida (USA). Our study occurred during a severe drought which reduced riverine inputs to Escambia Bay. Laboratory incubations of field-collected cores were conducted on 8 dates between June and October 2000 to estimate nutrient flux, and cores were collected from locations exhibiting a range of sediment organic matter content. NH₄⁺ flux ranged from – 48.1 to 110.4 μmol m⁻² h⁻¹, but the mean flux was 14.6 μmol m⁻² h⁻¹. Dissolved silica (DSi) fluxes were also variable (– 109. 3 to 145.3 μmol m⁻² h⁻¹), but the mean net flux (9.3 μmol m⁻² h⁻¹) was from the sediment to the water column. Bay sediment fluxes for NO₂⁻ + NO₃⁻ and PO₄⁻³ were less variable during this period (– 7.93 to 28.73 and – 1.74 to 3.29 μmol m⁻² h⁻¹ for NO₂⁻ + NO₃⁻ and PO₄⁻³, respectively). Low NH₄⁺ fluxes were similar to published estimates from lagoonal Gulf of Mexico (GOM) estuaries, possibly due to the reduced freshwater input. Diminished regeneration of phosphate relative to inorganic nitrogen observed during the study period was consistent with previous research in Pensacola Bay suggesting phytoplankton phosphorus limitation. Finally, the estimated residence time of Escambia Bay and the mean turnover times for NH₄⁺ and NO₂⁻ + NO₃⁻ suggested that benthic flux significantly influenced nitrogen concentrations in overlying water.

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