School of Environment and Energy, Shenzhen Graduate School of Peking University, Shenzhen, 518055, China.
Guangdong Neilingding Futian National Nature Reserve, Shenzhen, 518000, China.
Environ Geochem Health. 2019 Feb;41(1):159-174. doi: 10.1007/s10653-018-0130-z. Epub 2018 Jun 23.
Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/f, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.
红树林常被改造成虾塘用于水产养殖，但这种改造对沉积物中重金属的积累和行为有何影响尚不清楚。本研究旨在量化中国南方某红树林自然保护区不同生境（包括虾塘、以白骨壤（Avicennia marina）为主的红树林沼泽和光滩）沉积物中重金属的浓度和形态。结果表明，与白骨壤沼泽和光滩相比，虾塘使沉积物酸化，并降低了其电导率和总有机碳（TOC）。虾塘各深度沉积物中 Cd、Cu、Zn 和 Pb 的浓度均低于其他生境，表明虾塘降低了沉积物的肥力和重金属保持能力。根据多种评价方法，包括潜在生态风险系数、潜在生态风险指数、地积累指数、平均 PEL 比值、污染负荷指数、平均 ERM 比值和总毒性单位，虾塘沉积物的重金属污染问题也较低。重金属形态分析表明，虾塘增加了 Cd 和 Cr 的固定态向可移动态的转化。根据酸可挥发性硫化物（AVS）和同时提取的金属（SEM）分析，红树林转化为虾塘降低了 ([SEM]−[AVS])/f 值，以及 TOC 在减轻沉积物中重金属毒性方面的作用。本研究表明，将红树林沼泽转化为虾塘不仅降低了对重金属污染的生态净化能力，还增强了重金属从虾塘沉积物向附近生境的迁移。
