Mercury, carbon and nitrogen accumulation in mangrove and seagrass sediments of an impacted tropical estuary

Mangrove forests and seagrass meadows play a crucial role in retaining carbon, nutrients and pollutants within their sediments. However, environmental degradation and coastal deforestation as a result of urban expansion can impact their ability to provide these important ecological services. Here we use 210 Pb dating to present ∼120-year records of carbon, nitrogen and mercury accumulation in mangrove and seagrass sediments from a tropical estuary, highly impacted by anthropogenic activities. Our results show that the organic carbon, total nitrogen and mercury accumulation in the mangrove and seagrass sites were 87 ± 33.4; 8.7 ± 2.7 g m -2 yr -1 ; 72 ± 11.1; 7.1 ± 2.5 g m -2 yr -1 and 8.9 ± 8.1; 9.9 ± 5.0 mg m -2 yr -1 respectively. Mercury enrichment factors (EF) in both mangrove and seagrass sites increased 7-fold, indicating anthropogenic impact since the 1940’s and peaking in the late 1970’s and early 1980’s, likely from industrial waste discharged in rivers adjacent to the estuary during this period. This study highlights the crucial role of blue carbon systems in mitigating natural and human-derived pollutant impacts. However, the long-term consequences of blue carbon ecosystem degradation in developing regions remain a concern. Accurately measuring historical pollution retention, particularly in rapidly developing coastal regions, is critical for effective environmental monitoring and mitigation purposes.