Multiparametric study to understand the coastal blue carbon in the Canary Islands

Coastal systems host a large amount of biodiversity, play a fundamental role in socio-economic development, and are highly affected by human activities.  Canary Islands are a natural laboratory that allow the study of CO₂ system in coastal sites with different characteristics, natural and human-pressure. Then, it will help to identify the potential amount of blue carbon as well the relationship with other parameters such as Fe concentration, dissolved organic carbon (DOC), nutrients, etc. However, there are lack of information about these multidisciplinary processes and the implications on blue carbon. In this present work, we present the  data related with the CO₂ system and the fixed carbon in the biomass.

During one year, two coastal sites in the Canary islands (El Pajar, Gran Canaria island; and Abades, Tenerife island) and three habitats were monitored: seagrass beds, algal covers, and sandy zones. This work provides an overview of project activities and preliminary findings, encompassing monthly measurements of key parameters including sea surface temperature (SST), sea surface salinity (SSS), partial pressure of CO₂ (pCO₂), pH, and dissolved oxygen (DO). Each parameter was measured for 1 h. Samples to measure total alkalinity (A_T) and total inorganic carbon (C_T) were collected and measured in the laboratory. Additionally, analyses extend to include the percentage of carbon, hydrogen, and nitrogen (CHN) content.

According to the results, the temperature controls the partial pressure of CO₂ (pCO₂) in these coastal sites. pCO₂ was ranged from 363.1 to 660 ppm in El Pajar, and 343.4 to 541.2 ppm in Abades. The maximum pCO₂ level coincided with the higher temperature 25.3 and 25.1ºC, respectively, and resulted in the lower pH value (7.9 in both sites), in September. The minimum values were measured in winter period (February). Measuring the carbon content of the biomass in the area, the sequestered carbon was computed as 2.1± 0.6 gCO₂/gbiomass, and the DOC in the two locations and three habitats were practically constant during the whole year, ranked for both sites between 0.70 and 1.24 mg L^-1.

The results of this investigation are helping to quantify the amount of carbon transfer from the atmosphere to the seawater and the fixed by the biomass in these two sites. Since the seagrass has been decreasing in the Canary Islands by more than 90% in the last 10 years, the capacity to act as a sink of CO₂ is also drastically decreasing and the role of the temperature has to be estimated. The results of this project will be a decision-making tool for regional and national agencies to conserve those ecosystems where there is greater CO₂ capture.

 

Keywords: CO₂ observations, coastal waters, blue carbon, Canary Islands

 

Acknowledgements: Multi-COast Project (TED2021-130892B-I00) has been funded by MCIN/AEI/10.13039/501100011033 and the Europe Union “NextGenerationEU”/PRTR».