Land-use conversion in tropical coastal wetlands profoundly alters sediment geotechnics and biogeochemistry, yet their complex interactions remain poorly integrated. This study evaluated the relationships among sediment pore geometry, soil organic carbon (SOC), and salinity (EC) across five distinct natural and anthropogenic land-cover types in southern Denpasar, Bali. This study integrates geotechnical pore geometry analysis with biogeochemical indicators across five contrasting coastal land-use types to evaluate how anthropogenic land-use conversion modifies sediment structure and ecosystem functioning. To ensure internally consistent estimates of pore geometry, established soil mechanics equations, including the theoretical mixture equation and conventional soil phase relationships, were applied within a reproducible analytical workflow. Data were evaluated using Kruskal-Wallis tests, Spearman correlations, and Inverse Distance Weighting (IDW) spatial interpolation. Results demonstrated that pore geometry positively correlates with SOC (rs = 0.757, p = 0.001). Anthropogenic land-use conversion, particularly to commercial aquaculture ponds, was consistently associated with reduced pore geometry and lower soil organic carbon (SOC), reflecting substantial deterioration of sediment structural condition across the investigated coastal wetland sites. This structural degradation significantly heightens land subsidence vulnerability and severely undermines the ecosystem's blue carbon sink capacity. Conversely, EC lacked correlation with pore geometry. IDW mapping visually confirmed that salinity is dictated by external hydrological forcing, evidenced by irrigation-driven salt leaching in paddy fields and toxic salinity anomalies in natural mangroves adjacent to a landfill. Sustainable coastal management necessitates an integrated spatial strategy to mitigate mechanical disturbances, protect blue carbon stores, and halt subsurface pollution.