Trace Metal Pollution Risk Assessment in Urban Mangrove Patches: Potential Linkage with the Spectral Characteristics of Chromophoric Dissolved Organic Matter

Mangroves are inter-tidal ecosystems with important global ecological roles. Today, mangroves around the world are at risk of fragmentation, especially in areas with rapid urbanization. Mangroves experiencing habitat fragmentation may be more intensely affected by human activities and a scenario that might have been ignored by previous studies on trace metal (TM) environmental geochemistry. Here, we investigated the typically fragmented habitats in a subtropical mangrove estuary (the Danshuei Basin in Taiwan Strait) to evaluate how human activities affect the geochemical behaviors of TMs. Ni, Sb, Zn, Cr, Cu, and Cd were the primary contaminants found in the mangrove patches. Metal sequestration from the riverine (Ni, Cr) and in-patch activity (Sb, Zn, Cu, Cd) are primary sources of TM's risk. Using the synthesized pollution risk assessment, we showed that most of the mangrove patches are under moderate pollution risk. A significant relationship between the TMs pollution indicators and the absorption coefficient at 254 nm (a), implying that the a could be a potential convenient parameter in the TMs risk assessment, which might be partly explained by the bio-remediation of sulfate-reduction microorganism. This study demonstrates the ecological risks posed by TM pollution on urban mangrove patches and emphasizes the importance of a more comprehensive survey for estuarine mangrove patch environments to achieve Sustainable Development Goals.