Tidal and seasonal carbon and nutrient dynamics of the Guadalquivir estuary and the Bay of Cádiz (SW Iberian Peninsula)

Abstract

To study the effects of the physical environment on carbon and nutrient cycle dynamics on the north-eastern shelf of the Gulf of Cádiz, changes in currents, tides, salinity, temperature, carbon system parameters (fugacity of CO₂ (<i>f</i>CO₂), dissolved organic carbon, dissolved inorganic carbon (DIC) and pH) and other related parameters(dissolved oxygen, total dissolved nitrogen (TDN), nutrients and suspended particulate matter) were measured in transects across the Guadalquivir estuary and Bay of Cádiz mouths. The main objective of this study is to investigate the influence of these inner ecosystems on the carbon and nutrient distributions on the adjacent continental shelf. Three cruises were undertaken in June 2006, November 2006 and February 2007. During the whole study period, Guadalquivir estuary exported components at a rate of 3 Gmol of SiO₂, 4 Gmol of DIN, 3 Gmol of TDN, 31 Gmol of DOC and 604 Gmol of DIC per year. On the other hand, Bay of Cádiz imported 3 Gmol of SiO₂, 1 Gmol of DIN, 2 Gmol of TDN, 33 Gmol of DOC and 562 Gmol of DIC per year. Diurnal variability of <i>f</i>CO₂ could have a potentially important implication on the estimate of air–sea CO₂ fluxes. Tides influence velocity and transport of carbon and nutrients: we found statistically significant differences (<i>p</i> < 0.0001, <i>n</i> = 220) between the flood tide (the mean velocity was 4.85 cm s^&ndash;1) and the ebb tide (the mean velocity was −5.67 cm s^&ndash;1). Biological activity and diurnal changes have also an important role on the carbon and nutrient dynamics. Seasonal carbon and nutrient variations were found. During June, both systems were exporting components to the adjacent continental shelf of the Gulf of Cádiz, whereas in February both systems were importing. Monthly studies should be undertaken to completely understand this dynamic system

Local Variability of CO2 Partial Pressure in a Mid-Latitude Mesotidal Estuarine System (Tagus Estuary, Portugal)

“…The results strongly illustrate the need for higher temporal resolution data for the assessment of coastal carbon fluxes for this estuary, supporting previous similar claims by other researchers referring to other ecosystems [14,46,[56][57][58]. Therefore, the combination of seasonal point and transect evaluations with periodic diurnal measurements of system parameters will improve annual carbon budget calculations and may provide better numeric modelling of water quality.…”

“…Studies on the inorganic carbon systems in coastal areas have reported high pCO 2 associated with upwelled waters, suggesting that upwelling is a source of both nutrient-rich and high CO 2 levels [45,46]. This occurrence, however, is not evident in the results, probably due to the strong influence of inner estuarine waters, frequently characterized by the same combination of nutrients and high pCO 2 .…”

Decadal acidification in Atlantic and Mediterranean water masses exchanging at the Strait of Gibraltar

“…Therefore, regional inputs of organic matter are likely to occur, which could well lead to an intensification in the ecosystem respiration and inorganic carbon accumulation with time. In addition, a considerable discharge of inorganic carbon from the Guadalquivir river estuary to the continental shelf of the GC has been measured 51,52 , which could be accounted as an extra DIC source for the NACW. These external inputs would contribute to the natural component affecting the decadal pH change in this water mass, which represented 40% of the total pH reduction.…”

Effects of Wind-Driven Lateral Upwelling on Estuarine Carbonate Chemistry

“…Turbulent mixing generated by tides and winds may mix acidic bottom water upward, leading to large changes in the airsea CO 2 flux (Cai et al, 2017;Paerl et al, 2018). Advection by tidal and wind driven currents across the horizontal gradient may cause large short-term pH fluctuations at fixed locations, which may add further stress to organisms for coping with extreme low pH events (Ribas-Ribas et al, 2013;Saderne et al, 2013;Pacellaa et al, 2018). There is an increasing recognition for the large temporal pH variability and extreme pH values in estuarine and coastal environments (Hofmann et al, 2011;Baumann et al, 2015;Baumann and Smith, 2018;Carstensen and Duarte, 2019), but most research has focused on metabolically driven pH fluctuations such as the diel photosynthesis/respiration cycle (Saderne et al, 2013;Baumann and Smith, 2018;Pacellaa et al, 2018).…”