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A Subsoil Inspection in a Mangrove Habitat Using Electrical Resistivity Tomography59Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0005 The global distribution of coastal blue carbon ecosystems is different. Mangroves are mainly distributed in tropical and subtropical areas, whereas salt marshes are mainly distributed in temperate regions. Seagrass beds have the widest distribution among the three coastal blue carbon ecosystems, spanning over tropical andtemperate regions (Davidson et al., 2019). Mangroves refer to the habitats of trees and shrubs growing in the upper intertidal zone. Salt marshes often inhabit in the intertidal zone regularly inundated by tides. This area is densely populated with salt-tolerant emergent herbaceous plants. Seagrass beds are composed of submerged flowering plants that can grow in completely halophytic and wholly underwater environments (Howard et al., 2014). Among Taiwan's coastal blue carbon ecosystems, mangroves are the most widely distributed (Lin et al.,2023). They are mainly distributed along the western coast of Taiwan, extending from the estuary of the Tamsui River in northern Taiwan to Donggang, Pingtung County in southern Taiwan (Lin et al., 2023). Taking Da'an in Taichung City as the dividing line, Avicennia marina is dominant in southern Taiwan, andKandelia obovata is dominant in northern Taiwan. Two mangrove species, Lumnitzera racemosa and Rhizophora stylosa are scattered sporadically in the southern coast of Chiayi County. The area of mangroves in Taiwan increased from 178 hectares to 586 hectares from 1976 to 2011 (Wang et al., 2015). Lin et al. (2023) reported that the total area is 681 hectares. However, the increase in the mangroves in Taiwan is partly caused by artificial planting and subsequent expansion (Wester & Lee, 1992). Overly dense growth of mangroves may cause mosquito breeding and river flooding (Shih et al., 2015), and may even lead to a reduction in carbon sequestration capacity (Ho et al., 2018) and biodiversity (Pan et al., 2021). Therefore, mangroves in Taiwan are often affected by expansion or deforestation. Mangroves are comprised of true mangroves, which are salt-tolerant woody plants growing in the intertidal zones, and mangrove associates, which are salt-tolerant herbs, vines, and shrubs growing in the border areas of mangroves (Rivera-Monroy et al., 2017). True mangroves can be further subdivided into minor mangroves and major mangroves. The former ones cannot form pure forests in the intertidal zone. The later ones generally have specialized salt secretion mechanisms. Their viviparous seedlings and roots can fully adapt to the soil conditions of tidal flooding (Polidoro et al., 2010). Due to the anaerobic soil conditions and their ability to form pure forests, major mangroves are generally the focus of blue carbon assessments (Howard et al., 2014). The carbon sequestration capacity of the two most dominant mangrove species (Kandelia obovata andAvicennia marina) in Taiwan has been determined by constructing mangrove carbon budgets (Li et al., 2018). Lin et al. (2020) and Lin et al. (2021) further determined methane emissions from the two most dominant mangrove species in Taiwan. They concluded that methane emissions from mangroves cannot be ignored when calculating the carbon sequestration capacity.2.2 Mangroves in Taiwan