Spatial and Seasonal Variation of In Situ Benthic Fluxes in the Bay of Cadiz (South-west Spain)

Spatial and seasonal variation in benthic fluxes of nutrients, oxygen and alkalinity were measured in the Bay of Cadiz, a temperate semi-confined shallow water ecosystem. Oxygen, alkalinity, ammonia, phosphate and silicate fluxes averaged (mean ± SD) 137•5 ± 48•1, 376•3 ± 177•3, 17•7 ± 7•5, 4•4 ± 2•5 and 14•8 ± 8•8 mmol m-2 day-1, respectively. These values are high in comparison to those previously reported for other coastal locations in similar latitudes. Benthic fluxes clearly changed seasonally and an exponential relationship with temperature was found. Apparent flux activation energies ranged between 10.7 kcal mol-1 for phosphate and 18•1 kcal mol-1 for silicate. Seasonal variation in the stoichiometry of nutrient, oxygen and alkalinity fluxes revealed an intensification in the anaerobic decomposition pathways of organic matter during the summer. Spatial variation, oxygen and alkalinity fluxes were found to be linearly correlated with the organic matter content of the sediment (measured as organic carbon). Also, ammonia and phosphate fluxes increased as the C/N ratio of the incorporated organic matter in the sediment decreased