Variability of blue carbon storage in arid evaporitic environment of two coastal Sabkhas or mudflats

Abstract

Coastal Sabkhas are mudflats found in arid coastal regions that are located within the supratidal zone when high rates of evaporation lead to high salinity. While evaporitic minerals often accumulate underneath the surface, the microbial mats are present on the surface of Sabkhas. Coastal Sabkha, an under-studied ecosystem in Qatar, has the potential to store blue carbon. In the present study, we investigated the carbon storage capacity of two Sabkhas from contrasting geological backgrounds. The spatial and temporal variabilities of the carbon stocks were examined. The results showed that both studied Sabkhas exhibit a considerable potential for soil carbon storage with carbon stocks of 109.11 ± 7.07 Mg C ha^-1 and 67.77 ± 18.10 Mg C ha^-1 in Dohat Faishakh and Khor al Adaid Sabkha respectively. These values fall within the reported range for carbon stocks in coastal Sabkhas in the region (51-194 Mg C ha^-1). Interestingly, the carbon stocks in the sediments of the Sabkhas were higher than those in the sediments of Qatari mangroves (50.17 ± 6.27 Mg C ha^-1). These finding suggest that coastal Sabkhas can serve as blue carbon ecosystems in arid environments.

Figure 1

Sentinel-2 satellite image showing Qatar and the sampling regions (A). Dohat Faishakh Sabkha (B). Khor Al-Adaid Sabkha (C).

Figure 2

Photographic images of different microbial mats at KA Sabkha (A and B) and DF Sabkha (C and D).

Figure 3

Depth profiles for average concentrations (mg/g) of major elements and trace elements sampled from sediments of KA (red lines) and DF (Black lines).

Figure 4

PCA results showing the relationship between elements, depth, and total organic content in: (A) KA and (B) DF Sabkhas. Distinct patterns are observed between the two locations.

Figure 5

Mineralogy depth patterns semi-quantitatively calculated using XRD data of the core sediment samples collected from DF and KA Sabkha in different seasons: (A) KA1-Dec 21, (B) KA2, Feb 22, (C) KA3, Oct 22, (D) DF1, Dec 21, (E) DF2, Feb 22, and (F) DF3, Oct 22. Examples showing XRD patterns of KA3 and DF3 are illustrated in the right panel. Q: Quartz, C: Calcite, D: Dolomite, A: Aragonite, G: Gypsum, H: Halite.

Figure 6

Percentage of organic carbon and bulk density variations along with depth for each coastal Sabkha. A) DF and B) KA. Results are represented as mean ± SD.

Figure 7

Carbon stock in the two studied Sabkhas. Results are represented as mean ± SD. *P < 0.05, independent sample t-test.

Figure 8

Carbon stock in each Sabkha in different seasons. (A) KA Sabkha and (B) DF Sabkha. Results are represented as mean ± SD. *P < 0.05, **P < 0.001, one-way ANOVA.

Figure 9

Normalized Difference Salinity Index (NDSI) images of MSI of the DF Sabkha acquired on (A) December 5, 2021, (B) February 23, 2022, and (C) October 26, 2022, showing the area of saline soil (SS); Carbonate soil (CS); High Saline Water (HSW) and Low Saline Water (LSW). Normalized Difference Salinity Index (NDSI) images of MSI of the KA Sabkha acquired on (C) December 20, 2021, (D) February 18, 2022, and (F) October 26, 2022, showing the area of saline soil (SS); Carbonate soil (CS); High Saline Water (HSW) and Low Saline Water (LSW)). • locates sample site.