厦门同安湾红树林及临近光滩沉积物孔隙水中溶解活性磷和亚铁分布特征的对比分析

为了解红树林与光滩磷、铁地球化学行为的差异,借助薄膜扩散梯度技术(ZrO-Chelex DGT),对厦门同安湾红树林及临近光滩孔隙水中溶解活性磷(DRP)、Fe~(2+)浓度进行了原位测量,并采集了相应沉积物柱状样进行测定分析。结果表明:(1)Fe~(2+)与DRP呈现较好的线性正相关,说明磷的吸附/解吸与铁氧化还原循环有关;(2)在不同深度,光滩孔隙水中DRP浓度均高于对应深度红树林。在浅层,由于溪水的补给造成光滩的磷富集;在深层,红树植物根部吸收导致磷浓度下降,光滩有机质含量较多,矿化释放DRP使其浓度较高;(3)孔隙水中的Fe~(2+)浓度分布表明,红树林区域随着深度的增加,逐渐由好氧环境进入厌氧环境;而光滩沉积物氧化还原环境可能受到红树林的影响,孔隙水Fe~(2+)在垂向上波动分布。

Difference in dissolved reactive phosphorus and ferrous iron distribution between the porewater of mangrove wetlands and bare mudflats in Tongan Bay

To better understand the geochemical behavior of phosphorus and iron in mangrove wetlands and bare mudflats, we conducted an in situ measurement of phosphorus and iron in the porewater in Tongan Bay, Xiamen, using the technique of diffusive gradients in thin films (DGT). For measuring the total organic carbon (TOC) content, salinity, total iron, and particle size, we sampled the sediment using a DGT device. The result demonstrates the following:(1) the concentrations of dissolved reactive phosphorus (DRP) and ferrous iron (Fe²⁺) exhibited a positive correlation, verifying the key role of iron-redox cycling in controlling DRP variation. (2) The concentration of DRP in bare mudflats is higher than that in mangrove wetlands, which can be attributed to river contamination, mangrove plant adsorption, and the decomposition of organic matter (OM). (3) The distribution of the Fe²⁺ concentration in the mangrove porewater indicates that with increasing depth, the oxic condition in shallow wetlands gradually becomes anoxic; the variation of Fe²⁺ implies that the OM flushed from the mangrove affected the redox environment in the nearby bare mudflats and thus influenced iron-redox cycling.