Carbon Dioxide and Methane Dynamics in Three Coastal Systems of Cadiz Bay (SW Spain)

The partial pressure of CO2 (pCO(2)) and concentration of dissolved CH4 in surface waters have been studied in three coastal systems connected to Cadiz Bay (southwestern coast of Spain) over different time scales. The concentration of CH4 varied from 1 to 4200 nmol kg(-1) (192.1 +/- 463.6 nmol kg(-1)) and the saturation percent from 19 to 159,577% (6645 +/- 16,921%), and pCO(2) from 315 to 3240 mu atm (841.9 +/- 466.3 mu atm), with saturation percent values varying between 72 and 981% (220 +/- 133%). The seasonal variation of pCO(2) mainly depends on the temperature. On the contrary, the annual distribution of dissolved CH4 is associated with the precipitation regime. In addition, pCO(2) and dissolved CH4 showed spatial variation. pCO(2) increased toward the inner part of the systems, with the proximity to the discharge points from human activities. Dissolved CH4 is influenced by both anthropogenic inputs and natural processes such as benthic supply and exchange with the adjacent salt marshes. pCO(2) and dissolved CH4 also varied with the tides: The highest concentrations were measured during the ebb, which suggests that the systems export CO2 and CH4 to the Bay and adjacent Atlantic Ocean.