Suspended particulate matter in Voh lagoon (New Caledonia): Impact of ultramafic rock mining on primary production

Open-pit mines are known to exacerbate soil erosion and generate large quantities of fine particles, which are carried by watersheds to coastal waters. In New Caledonia, the exploitation of ultramafic massifs highly enriched in metals (Co, Cr, Fe and Ni) can therefore have harmful effects on tropical lagoons by increasing turbidity and releasing toxic compounds to the marine food web. In this study, we used various biogeochemical (POC, δ 13 C, PON, POP, Chl a , Pheo a ) and geochemical (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sn, Ti, V, Zn) parameters to examine the origin, transport, and fate of suspended particulate matter (SPM) in the Voh lagoon after eight years of mining activities. Maximum concentrations of SPM (1.93 mg.L -1 ), Chl a (1.23 µg.L -1 ), Cr (327 µg.g -1 ), Co (32.4 µg.g -1 ) and Ni (756 µg.g -1 ) were observed in Vavouto bay, downstream of the Koniambo ultramafic massif watershed. Approximately 34% of SPM present in surface waters originated from the Koniambo ultramafic massif. The increase in particle inputs linked to mining activity has led to the eutrophication of the lagoon. Due to transport processes, SPM are now distributed throughout the lagoon, settling at the bottom and burying the corals. In this context, the Voh lagoon presents a high ecological risk. This study provides an opportunity to refine predictive modelling techniques for contamination scenarios.