Determination of Nutrients, Biomass, and Bacterial Quantification in Different Mangroves Sites: A Comparative Study...

This study was conducted at eight different sites of the mangrove ecosystem in Kaozhou Yang, Huidong District, Huizhou Guangdong, South China Sea. The concentration of nutrients ( ${\mathrm{NH}}_4^{+}$ , ${\mathrm{NO}}_2^{-}$ , ${\mathrm{NO}}_3^{-}$ , ${\mathrm{PO}}_4^{3-}$ and ${\mathrm{SiO}}_3^{2-}$ ) was determined (both water and soil samples). Based on the nutrient concentration, the comparison of mangrove biomass production, total organic matter and bacterial count were also investigated. The level of nutrient values and biomass production of mangrove and bacterial count in both water and soil samples followed the same trend. The results showed that the highest concentration of ${\mathrm{NH}}_4^{+}$ (0.457 ± 0.051 mg/L), ${\mathrm{NO}}_2^{-}$ (0.223 ± 0.018 mg/L), ${\mathrm{NO}}_3^{-}$ (0.521 ± 0.038 mg/L), ${\mathrm{PO}}_4^{3-}$  = P (0.242 ± 0.049 mg/L) and ${\mathrm{SiO}}_3^{2-}$  = Si (4.094 ± 0. 095 mg/L) were found in the water samples from station S-1, while the lowest values of ${\mathrm{NH}}_4^{+}$ (0.063 ± 0.007 mg/L), ${\mathrm{NO}}_2^{-}$ (0.0124 ± 0.001 mg/L), ${\mathrm{NO}}_3^{-}$ (0.053 ± 0.003 mg/L), ${\mathrm{PO}}_4^{3-}$  = P (0.012 ± 0.002 mg/L) and ${\mathrm{SiO}}_3^{2-}$ (0.713 ± 0.009 mg/L) were recorded in station S-8. The order of nutrient values and bacterial count in the water and soil samples was same: S-1 > S-5 > S-3 > S-6 > S-4 > S-2 > S-7 > S-8. Avicennia marina was the only species found in all stations therefore; this species was considered for the assessment of the biomass of above- and belowground parts. The highest biomass (aboveground parts; 131.23 ± 2.09 Mg/ha, belowground parts; 139.86 ± 2.57 Mg/ha) was recorded at station S-1. The lowest biomass (aboveground parts; 119.72 ± 1.99 Mg/ha, belowground parts; 127.13 ± 2.01 Mg/ha) was found at station S-8. The analysis of organic matter (both water and soil samples) also showed the same trend. It was concluded that that mangrove biomass was nutrient-dependent, confirming our hypothesis that "mangrove biomass could depend on the availability of nutrients." Mangrove ecosystem plays an important role in coastal and marine food webs and is closely connected to the well-being of coastal communities. Therefore, the mangrove ecosystem is mainly included in the United Nations Sustainable Development Goals (SDGs) and the Paris Agreement (climate change mitigation) in this decade. This study is in line with SDGs 12 (Responsible consumption and production of food), 13 (Climate action), 14 (Life below water) and 17 (Partnerships with the goals). The mangrove plants convert carbon dioxide (toxic form of carbon) in its useful form (biomass), and in addition, the mangrove ecosystem serves as a food and nursery area for fish and shellfish fisheries. Therefore, this research promotes the role of the mangrove ecosystem to benefit the blue economy and mitigate climate change. It was concluded that the abundance of bacteria and the biomass of mangroves depend on the availability of nutrients. Therefore, the results of this study strengthen our hypothesis. In the future, this study could serve as a reference study for blue carbon sequestration in the mangrove ecosystem.