Benthic fluxes of O2, N2, NH4+, NO3- and dissolved inorganic carbon (DIC) were measured to estimate total remineralization and denitrification rates in Galveston Bay (TX, USA) sediments. The denitrification rate was estimated directly from the N2 accumulation rate in the overlying water trapped in situ incubation chambers. The change of N2 concentration over time was determined using gas chromatography using argon as an internal standard. The denitrification rates (0.6 to 4.6, average = 1.8 mmole m-2d-1), sediment oxygen demand (1.8 to 19.0, average = 7 mmole m-2d-1) and DIC flux (1.2 to 40.5, average = 19 mmole m-2d-1) followed the water temperature fluctuation over a 1.5 year period. The high denitrification activity in summer appears to be the result of increased NO3- supply from nitrification when remineralization is high and oxygen is not limiting. Most of the NO3- needed for denitrification (93%) was supplied from in situ nitrification. Oxygen consumption during nitrification exceeded observed sediment oxygen demand (average = 135% of sediment oxygen demand). Oxygen production by benthic primary production seems to satisfy the O2 demand of nitrification as well as aerobic respiration and reoxidation of reduced chemicals. A three box model was used to assess the effect of benthic primary production on other benthic processes and the model results demonstrated increased aerobic respiration, nitrification and denitrification with benthic photosynthesis compared to no photosynthetic condition, which agrees with observed N2 and O2 concentration changes during in situ sediment incubations. An inverse model suggests that benthic photosynthesis supplied 92% and 52% of sediment oxygen demand for aerobic respiration and reoxidation of reduced chemicals in winter and summer, respectively. Denitrification removed 52% of the nitrogen loading in Galveston bay. This removal rate is about 4 times greater than the previous estimate obtained using an in vitro method of denitrification measurement.