White Is a New Shade of Blue Carbon: A Case Study of a Traditional Salt Production Pond That is a Net Carbon Sink

Abstract To address for the first time the carbon budget of traditional salterns, we measured the diel, seasonal, and spatial variability of water‐air CO 2 ‐eq fluxes (CH 4 and CO 2 ) and the Organic Carbon (OC) stock and burial rate in the sediment. Temperature, salinity, dissolved oxygen, pH and wind were assessed as potential environmental drivers of the fluxes. The saltern emitted CH 4 to the atmosphere throughout the year, with no significant differences among sites or seasons. On the contrary, the saltern were a sink of CO 2 in summer, autumn and winter, and a source of CO 2 in spring. Water temperature was the main positively related predictor variable of CH 4 fluxes, explaining 29% of their variance, whereas CO 2 fluxes were significantly negatively related to the concentration of O 2 and pH in the seawater and positively related to wind, which explained 66% of fluxes variance. The sedimentary and OC stocks and burial rates were not significantly different among the sampled ponds and averaged 11.9 ± 2.2 Mg OC ha −1 and 0.011 ± 0.004 Mg OC ha −1 yr −1 , respectively. The carbon budget of the saltern was −35.0 g CO 2 ‐eq m −2 yr −1 , corresponding to −1.49 Mg CO 2 ‐eq yr −1 for the total saltern area. This suggests that the‐salt industry may function as a carbon sink as opposed to other coastal industries such as fish and shrimp aquaculture. Future studies with additional measurements across a wider range of salterns are needed to evaluate the relevance of “white carbon.”