Abstract:Mangrove ecosystems are important for providing habitat, primary productivity, and protection against coastal erosion. The Futian mangrove wetland (22°32'N, 114°03'E) is located in a Nature Reserve of the Shenzhen Special Economic Zone, Guangdong Province, China. Acid rain emerged in the late 1970s as an important environmental problem in China. The average pH of precipitation in Shenzhen City and nearby suburban areas is less than 5.0, and the frequency of acid rain events has reached 82%. Acid deposition has had a wide range of harmful effects on mangroves. Sediments and plants in the Futian mangrove ecosystem are moderately contaminated by heavy metals (primarily Cu and Zn). Acid rain leads to a reduction in sediment pH and an increase in metal cation leaching intensity, and these effects are closely related to sediment properties. Although acid rain could eventually lead to the loss of mangrove forests, the effects of acid rain on heavy metal and nutrient transport in mangrove sediments are largely unknown. In this study, a field column experiment was conducted to analyze the effects of simulated acid rain on the spatial distribution of heavy metals (Cu and Zn) and nutrients (N, P, and organic C) in mangrove sediments at different depths. The pH treatments were as follows:S1 (pH 4.0), S2 (pH 3.0), and S3 (pH 2.0); deionized water (pH 6.7) was applied in the control (CK) treatment. Sediment depths were H1 (0-10 cm), H2 (10-20 cm), H3 (20-30 cm), H4 (30-40 cm), and H5 (40-50 cm). Acid rain had no significant (P>0.05) effect on overall of Eh, pH, or salinity, but it significantly (P<0.01) influenced the distribution of Eh and pH among the sediment depths. Total nitrogen in H2 differed significantly (P<0.05) among the simulated acid rain (SAR) treatments. The CK, S1, and S3 treatments significantly (P<0.01) affected the distribution of TN among sediment depths, and CK (P<0.05) and S1 (P<0.01) significantly affected the distribution of TP. The CK (P<0.05), S1 (P<0.01), and S3 (P<0.05) treatments significantly affected TOC content in the sediments, and CK (P<0.05) and S1 (P<0.05) significantly affected Cu concentrations. In addition, the CK treatment (P<0.05) significantly affected the distribution of Zn. Acid rain significantly (P<0.05) accelerated the leaching of N and organic C to upper sediment layers, and nutrient and heavy metal concentrations decreased with depth. The distribution patterns of N, P, and organic C were significantly (P<0.05) positively related to patterns of Cu and Zn, implying that nutrients can influence the accumulation or leaching of heavy metals in mangrove sediments. Soil N concentration was the most significant factor affecting the distribution of the other nutrients and heavy metals, indicating that soil N level may be an effective indicator of the effects of acid deposition on sediment nutrients and heavy metals.