Benthic Nutrient Flux in a Small Estuary in Northwestern Florida (USA)

Abstract

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.