The Northern San Jorge Gulf (NSJG) was declared Coastal Marine Park in 2008 with the goal of preserving its biodiversity. In situ benthic fluxes experiments were performed using an opaque chamber in Sara Creek (SC) and Malaspina Creek (MC). Moreover, ex situ nitrate reduction activity was assessed using a continuous flow-through system. Benthic fluxes in MC, showed a consumption of oxygen (794 ± 196 mg m−2 h−1) and nitrate (103 ± 68 µmol m−2 h−1) by sediment and release of ammonium (175 ± 60 µmol m−2 h−1), phosphate (66 ± 10 µmol m−2 h−1) and silicate (116 ± 66 µmol m−2 h−1) towards the water column. In SC, the same pattern was observed and the fluxes values were 375 ± 132, 128 ± 1, 76 ± 12, 39 ± 24 and 133 ± 81, respectively. Only, ammonium and oxygen fluxes showed significant differences between sites, due to the highest organic matter content and the particular hydrodynamic conditions in MC. These are the first benthic flux measurements made within the protected area. Nitrate uptake rate, based on Michaelis–Menten kinetic, was Km: 155.3 µM and Vmax: 0.053 µM g−1 h−1 in SC and Km: 131.2 µM and Vmax: 0.039 µM g−1 h−1 in MC. Considering the nitrate dynamic we concluded that the sediments both SC and MC act as a sink of nitrate. This ion could be principally used as a terminal electron acceptor during the oxidation process of organic compounds in sediments of NSJG.Fil: Torres, Américo Iadran. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Faleschini, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Esteves, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentin
