Responses of depth-dependence of C:N:P stoichiometry to check dam in mangrove wetlands

Carbon (C) sequestration and nitrogen (N) and phosphorus (P) deposition in mangrove wetlands are significant for global climate regulation and the removal of marine nutrient pollutant. To protect and restore mangroves, numerous check dams have been implemented within mangrove wetlands; however, the influence of these check dams on C, N, and P content, stoichiometry, and their depth-dependence remains largely unexplored. To establish a causal relationship between the check dams and C and nutrient variations, we first determined soil deposition depth post-check dam construction in both a natural mangrove and a neighboring check dam-affected mangrove. We then analyzed the C, N, and P content, stoichiometry, and their depth-dependence in soil systems-including bulk soil, microbial biomass, and extracellular enzymes-at depths of 0-100 cm across three vegetation types. Our results indicated that check dam significantly increased the contents of C, N, and P within the soil-microorganism-enzyme system by15.42%-851.15%, and enhanced the stoichiometry of soil C:P and N:P by 79.81%-94.48%. Check dams also enhanced the depth-dependence of soil C, with C varying more slowly than N and P in the natural mangrove but faster in the check dam-affected mangrove. These findings demonstrate that check dams can significantly promote C accumulation in mangroves. Structural equation models revealed that check dam-induced hydrological processes primarily affected C, N, and P content by regulating soil physical properties, while influenced C:N:P stoichiometry through basic chemical properties. Overall, our research emphasizes the implications of costal management for C accumulation and nutrient pollution deposition in mangrove wetlands.