Nickel Mining Transformed Microbial Life in New Caledonia Lagoon

Intensive nickel mining has significantly altered the microbial biodiversity of the Thio Lagoon in New Caledonia. A study published in *Communications Earth & Environment* details how mining operations, particularly since the 1950s, led to increased sediment and nickel concentrations in the lagoon.

Researchers from Ifremer, IRD, the universities of Western Brittany (UBO) and Bordeaux, CNRS, and the University of Tartu conducted the study. They analyzed a 2.26-meter sediment core from the lagoon, representing nearly 1,000 years of environmental history. This natural archive allowed them to track physical, chemical, and microbiological changes over time.

The study found that the mechanization of mining in the 1950s caused a sharp increase in soil erosion. Rivers carried these nickel-rich sediments into the lagoon. Between 1950 and 1975, approximately 27 million tons of mining waste entered the Thio watershed. This period saw a fivefold increase in sedimentation rates and nickel concentrations, along with a sharp decline in microbial biodiversity.

Before the 1950s, marine microbial communities remained stable for centuries. After mechanization, some foraminifera, sensitive to environmental disturbances, disappeared completely. More tolerant microalgae, such as Desmodesmus, became dominant. Environmental regulations implemented since 1975 reduced mining-related sediment inputs. However, the sedimentation rate remains high, averaging 0.9 centimeters per year, compared to 0.1 centimeters per year before mining.

While some microbial communities have recolonized the environment, their composition has not returned to its original state. Scientists continue to investigate the causes of the persistently high sedimentation rates, including the impact of recurring wildfires. The study highlights the interconnectedness of terrestrial and marine environments and calls for integrated management of the "land-sea continuum."