Interferences between natural and anthropic hazards in marine-coastal environments: Assessing transport from land to the offshore systems in the Crotone basin (Ionian Sea)

This paper is focused on the field-evidence of environmental hazard associated with flood events in highly contaminated marine coastal areas. The Crotone site (Ionian Sea), in the 1900s hosted a large industrial settlement (with the largest plant in Europe of zinc production, phosphorus manufacture, etc.) which left a severe legacy of environmental pollution. Here, we report the results of an investigation related to the distribution of heavy metals (Zn, Pb, Cd, Cu) in 230 sediment cores that allowed a detailed reconstruction of the contamination due to the discharge at sea of industrial wastes deriving from the Zn-sulphides leaching processes. High concentrations of heavy metals (e.g., Zn > 5000 mg kg-1) accumulated in sediments of the seabed along coastline, exposed to the fluvial and coastal dynamics, act as a potential long-term source of pollution for the marine ecosystem. Fingerprints of historically flash flood events evidenced in two 210Pb dated sediment cores suggest that these catastrophic events played a crucial role in the land-to-sea transferring (and sequent dispersing effects) of highly polluted sediments. Anomalous depositions of heavy metals-rich sediments in the offshore system (4-6 km from the coastline) testify secondary contamination due to mobilization and redistribution of old contaminated sediment due to flood events. These interactions between natural and anthropic hazards trigger cumulative mechanisms of multiple-pollution and transfer of contamination from polluted nearshore to offshore nearly pristine areas trough main canyon axes.

Automated summary

This paper focuses on providing field evidence of the environmental hazards associated with flood events in highly contaminated marine coastal areas. Using sediment cores from the Crotone site in the Ionian Sea, the study examines the distribution of heavy metals and their potential as long-term sources of pollution for the marine ecosystem. The results show that historically flash flood events played a crucial role in transferring highly polluted sediments from land to sea, leading to secondary contamination in offshore areas. This study highlights the cumulative mechanisms of multiple pollution and transfer of contamination in coastal and offshore environments.