模拟酸雨对红树林底泥中营养元素及Cu、Zn分布的影响

Influence of simulated acid rain on the spatial distribution of nutrients,Cu,and Zn in mangrove sediments

采用柱状试验,研究不同pH值酸雨对红树林底泥中营养元素(N、P及有机碳)和重金属(Cu、Zn)空间分布的影响。结果表明,不同pH值的酸雨对底泥化学性状指标Eh、pH及盐度影响不显著(P>0.05),对底泥不同层次TN、TOC及Cu的分布具有极显著影响(P<0.01)。酸雨对底泥上层的氮及有机碳的淋溶具有显著促进作用(P<0.05)。在酸雨作用下,营养元素及Cu、Zn含量分布具有随底泥深度增加而减小的趋势。TN、TOC与Cu、Zn的分布均呈极显著正相关关系(P<0.01),TP与Cu、Zn的分布均呈正相关关系(P<0.05),表明营养元素N、P和有机碳对重金属的淋溶、沉积具有显著促进作用。底泥中的TN是影响营养元素及重金属特别是Cu分布最重要因子。

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.