重金属污染对珠江口红树林表层沉积物碳含量的影响

Effects of heavy metal pollution on the carbon content of surface sediments of mangroves in the Pearl River Estuary

湿地沉积物是红树林生态系统中重要的组成部分,其总有机碳储量的变化对红树林生态系统的固碳能力有着重要影响。现有对红树林湿地重金属的研究多集中于污染评价,鲜有涉及重金属含量对沉积物总有机碳(TOC)含量影响的研究。于2018—2019年期间4次前往珠江口典型红树林湿地,采集了0—30 cm表层土壤沉积物的样品,并测定其重金属含量和TOC含量,以探讨重金属含量变化对TOC的影响。结果表明,与广东地区的背景值相比,研究区沉积物重金属含量超标较为严重,重金属来源应是人类活动;沉积物的重金属含量能够显著影响TOC含量(P<0.01,R^(2)=0.39),间接对红树林湿地的固碳能力、甚至全球变暖产生一定影响;Cd、As、Zn含量高的沉积物环境有利于TOC的积累, Cu、Cr、Ni、Hg含量低的沉积物环境则不利于TOC的积累。沉积物的重金属对TOC的影响的机制是非常复杂的,它们可以通过影响土壤结构、土壤化学组分、土壤内微生物、上部植被群落的生长以及凋落物归还等一系列过程,导致沉积物TOC和固碳能力的变化。

Compared to most terrestrial forest ecosystems, mangrove forests have the higher carbon reserves as well as higher carbon emissions potential when they exposed to pollution. Mangroves have suffered heavy metal pollution to varying degrees in many regions and countries so far. Wetland sediments are an important part of mangrove ecosystems. The changes of total organic carbon in wetland sediments have a significant impact on the carbon sequestration capacity of mangrove ecosystem. Few studies have focused on the effects of heavy metals on the total organic carbon content(TOC) of sediments in mangrove wetlands compared to the assessment of heavy metal pollution in mangrove wetlands. The samples in this study were collected by 4 times from 0—30 cm of surface soil sediment in a typical mangrove wetland in the Pearl River Estuary during 2018—2019. The heavy metal content and TOC content in the samples were measured to explore the effect of the change in heavy metal content on TOC. The results showed that the study area has suffered heavy metal pollution, and the average value of heavy metals far exceeded the background value of soil elements in Guangdong Province. Through the principal component analysis(PCA) and related analysis, heavy metal pollution was confirmed to be mainly derived from human activities such as industrial production, mineral development, pesticide use, automobile exhaust emissions and aquaculture. The content of heavy metals in the mangrove wetlands would affect the carbon sequestration capacity of the mangrove wetlands and global warming because it could significantly affect the TOC content(P<0.01, R^(2)=0.39). The environment with high Cd, As, and Zn content was favorable for the accumulation of TOC in the sediment, while the environment with high Cu, Cr, Ni, and Hg content had the opposite performance. The mechanism of the effects of heavy metals in sediments on TOC was very complex. The heavy metals in the sediment could cause changes in the TOC and carbon sequestration capacity of the sediment through a series of processes including affecting soil structure, soil chemical composition, soil microorganisms, growth of upper vegetation communities and litter return. This study analyzed the change of heavy metal element content in mangrove sediments and explored the relationship between heavy metal content and organic carbon content in the sediments, which plays an important role in assessing the environmental risks and carbon sequestration capacity of mangrove ecosystems. It will help to guide the ecological restoration and pollution control of the Guangdong-Hong Kong-Macao Greater Bay Area, promote the formation of green and low-carbon production and lifestyle and urban construction and operation models as well.