Benthic oxygen and nutrient fluxes in a coastal upwelling system (Ria de Vigo, NW Iberian Peninsula): seasonal trends and regulating factors

Abstract

Benthic oxygen and nutrient fluxes play a key role in the biogeochemical cycles of carbon and nutrients in coastal regions. Even so, 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 main factors that control 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 between them points to the importance of aerobic respiration in the remineralization of organic matter. The amount and quality of organic matter appears to be an influencing factor on the 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 phosphorous may account up to 41 % and 61 %, respectively, of the nutrient inputs from upwelled and continental runoff waters.

Benthic fluxes, net ecosystem metabolism and seafood harvest: Completing the organic carbon balance in the Ría de Vigo (NW Spain)

“…5) being the two variables highly correlated (r: -0.78, p < 0.01, n= 15), with no significant differences among spring, summer and autumn but significantly lower during winter. Thus, it is suggested that benthic inorganic carbon fluxes at the Ría de Vigo are also influenced by the upwelling/downwelling events and the arrival of labile organic matter to the sediment as it was previously found for the oxygen fluxes (Alonso- Pérez and Castro, 2014).…”

Relative Contributions of Biodiversity and Environment to Benthic Ecosystem Functioning

“…The fact that prokaryotic abundance remained an important variable explaining single flux variation (from multiple linear regression results) for all but silicate fluxes over a broad geographic area in our previous study (Belley et al, 2016) (i.e., Salish Sea but also sites in the open waters of the Northeast Pacific) can explain this discrepancy. We included water depth in our analysis because it often correlates well with other environmental variable known to influence benthic flux rates, such as organic flux to the seafloor (Jahnke, 1990;Berelson et al, 1996) and temperature (Hargrave, 1969;Cowan et al, 1996;Alonso-Pérez and Castro, 2014). Our model specifically accounted for differences in water depth, which explained 8.8% of the variation in benthic flux, and high fluxes of O 2 , nitrate, phosphate, and silicate (e.g., SoGE) generally characterized deeper sites.…”

“…Multiple biological and environmental factors influence benthic fluxes. Previous studies point to the importance of environmental variables such as temperature (Hargrave, 1969;Cowan et al, 1996;Alonso-Pérez and Castro, 2014), and the quality and quantity of organic matter sinking to the seafloor (Berelson et al, 1996;Jahnke, 1996). Previous studies also report a strong positive influence of biological factors such as the presence of bio-irrigators and bioturbators on benthic fluxes and organic matter remineralization (Aller, 1982(Aller, , 2014Aller and Aller, 1998), and that focus has expanded to consider the importance of functional diversity on ecosystem functioning (Snelgrove et al, 1997(Snelgrove et al, , 2014Raffaelli et al, 2003;Solan et al, 2004).…”

Toward a parameterization of global‐scale organic carbon mineralization kinetics in surface marine sediments

“…For depths >1000 m, bioirrigation is essentially zero and diffusive fluxes determined ex situ were also considered [ Glud , ]. The database was expanded with new data from the Oregon/California margin [ Berelson et al ., ], the NW African margin [ Dale et al ., ], and the NW Iberian margin [ Alonso‐Pérez and Castro , ], giving a total of 185 paired O 2 and NO 3 − flux measurements (Table S1 in the supporting information). Eighty‐two stations are on the continental shelf (0 to 200 m), 50 stations on the slope (>200 to 2000 m), and 53 lie in deeper waters (>2000 to 5100 m).…”