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Mangroves have high ecological service value and play an important role in achieving carbon neutrality. However, the ecological services provided by mangroves are gradually declining due to the threat of various pollutants, especially heavy metal (HM) pollution. Researching the status and history of heavy metals (HMs) in mangrove sediments improves understanding of how mangroves can be protected. We studied the Zhanjiang Bay mangroves, which is an important part of the Zhanjiang Mangrove National Nature Reserve, and is greatly affected by human activities, as an example. We analyzed the pollution levels and deposition process of HMs and their influencing factors. In the mangrove surface sediments of Zhanjiang Bay, Pb, Cr, and Co were slightly to moderate enriched and Cu was moderate-heavy enriched. Zn and Hg showed moderate-heavy enrichment and heavy enrichment, respectively. Cu, Zn, Hg, and Co were 1.5, 1.88, 2.66, and 1.27 times the local background, respectively. Cu, Zn, and Hg mainly originated from anthropogenic sources, and Co may have derived from natural sources. The HM data of mangrove sedimentary cores in Zhanjiang Bay were obtained for the first time; high HM content appeared in the deep layer of the cores but not in the mangrove surface sediments. Both cores were well documented for the effects of natural and anthropogenic factors on the deposition process of HMs. Among them, the high enrichment of Hg in 1909–1921 may be closely related to human activities rather than natural formation. Before 1954, dense mangroves favored the accumulation and gradual increase of HMs. The intense human activity in 1945–1963 during the period of economic construction and reclamation of the Nansan Island Engineering led to significant increases in Cu, Zn, Pb, Cr, and Co, which reached their highest values in more than one hundred years. After 1963, anthropic factors such as deforestation and conversion to aquaculture sharply reduced mangrove area. Reclamation engineering enhanced tidal erosion. Natural factors such as precipitation, storm surge, sea-level rise, and high tides have accelerated the erosion and dilution of mangrove sediments in Zhanjiang Bay. These factors have led to the gradual reduction of HM content in sedimentary cores.

Earthquakes can be destructive, killing many people and causing great financial loss. Costs from earthquakes are increasing rapidly, and thus seismic research is an important tool for reducing loss. Traditional studies of earthquakes have mainly been based on geophysics (seismic waves, geomagnetism, and geoelectricity), hydrogeology, and geogas. However, earthquakes can also release numerous particulates, which can be carried by ascending gas to reach the surface. These particulates provide us with abundant and direct information about earthquake activity and can serve as a new medium for studying earthquakes. In this study, we first find, using a transmission electron microscope (TEM), that ascending gas in the soil of the 2013 Ya'an earthquake region carries many particulates. These particulates are usually 20–600 nm and are composed of amorphous crystal, monocrystalline, and polycrystalline structures. In addition, these particulates contain O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Cr, Fe, Zn, Ba, Hg, Ti, Mn, Ni, Cu, Cd, Sn, Sb, Cs, Pt, and Pb. Compared to the background areas (Yuhe and Hongzi Village and the Fengguanshan inactive fault), particulates carried by ascending gas in the Ya'an earthquake region have many abnormal elements (element associations), including Ti, Mn, Ni, Cd, Sn, Sb, Pt, and Pb. This finding confirms our hypothesis that earthquakes can release particulates carried by ascending gas that reach the surface. In addition, the elements occurring in these particulates indicate that earthquakes can trigger element activation and migration in the form of particulates. As particulates carried by ascending gas in the earthquake region are significantly different from those in the background areas, they can be used to predict earthquakes. The particulates in our study are significantly different from particulates carried by ascending gas from ruptures caused by the Wenchuan earthquake; therefore, we first propose that particulates in ascending gas from earthquake regions may exhibit a close relationship with the magnitudes and hypocentre depths of earthquakes and can be used to predict earthquakes with larger magnitudes and deeper hypocentre depths.