MEPS 511:17-32 (2014)  -  DOI: https://doi.org/10.3354/meps10915

ABSTRACT: Benthic oxygen and nutrient fluxes play a key role in the biogeochemical cycles of carbon and nutrients in coastal regions. However, there are no previous studies focused on benthic fluxes in the NW Iberian coastal upwelling system on an annual basis. The present work analyses the seasonal trends of benthic oxygen and nutrient fluxes as well as the main factors controlling them in the Ría de Vigo. Between April 2004 and January 2005, 16 oceanographic cruises were carried out to measure water column properties, vertical fluxes of particulate organic matter by means of sediment traps, and oxygen and nutrient fluxes using a benthic chamber. Rates of sediment oxygen consumption (18 to 50 mmol m^-2 d^-1), phosphate (0.08 to 0.34 mmol m^-2 d^-1), silicate (1.7 to 10 mmol m^-2 d^-1), ammonium (1.1 to 4.9 mmol m^-2 d^-1) and nitrate (-0.95 to 0.78 mmol m^-2 d^-1) ranged near the upper limit of benthic fluxes found in similar coastal areas. Nitrogen fluxes were dominated by ammonium fluxes (83%). Benthic fluxes of oxygen, ammonium, phosphate and dissolved silicate were significantly lower during winter but did not show differences during spring, summer or autumn. The strong mutual correlations among fluxes points to the importance of aerobic respiration in the remineralization of organic matter. The amount and quality of organic matter appears to be a factor influencing benthic fluxes, but it seems that changes in temperature, modulated by upwelling/downwelling pulses, trigger and control the benthic fluxes on the short time scale. The study assesses the importance of benthic fluxes to the potential primary production of the system, as remineralized benthic nitrogen and phosphorus may account for up to 41 and 60%, respectively, of the nutrient inputs from the sum of upwelled and continental runoff waters.

KEY WORDS: Benthic fluxes · Galician Rías · Upwelling · Vertical fluxes · Remineralization · Nutrients · Oxygen