Abstract
Coral reef lagoons of New Caledonia form the second longest barrier reef in the world. The island of New Caledonia is also one of the main producers of nickel (Ni) worldwide. Therefore, understanding the fate of metals in its lagoon waters generated from mining production is essential to improving the management of the mining activities and to preserve the ecosystems. In this paper, the vertical fluxes of suspended particulate matter (SPM) and metals were quantified in three bays during a dry season. The vertical particulate flux (on average 37.70 ± 14.60 g·m2·d−1) showed fractions rich in fine particles. In Boulari Bay (moderately impacted by the mining activities), fluxes were mostly influenced by winds and SPM loads. In the highly impacted bay of St Vincent and in the weakly impacted bay of Dumbéa, tide cycles clearly constrained the SPM and metal dynamics. Metals were associated with clay and iron minerals transported by rivers and lagoonal minerals, such as carbonates, and possibly neoformed clay as suggested by an unusually Ni-rich serpentine. Particle aggregation phenomena led to a reduction in the metal concentrations in the SPM, as identified by the decline in the metal distribution constants (Kd).
Highlights
Numerous studies of the south-western lagoon of New Caledonia have been conducted investigating hydrodynamics, sediment transport, sedimentation dynamics, metal fluxes, accumulation zones, and particle sources [23,27,31,32,33,34,35,36,37]. In complement to these works, this paper aims at characterizing the suspended sediment mineralogy and geochemistry in three bays; analysing the relationships between their composition and the mining activities; determining how hydrodynamics forced by wind regimes affect the transportation of particulate metals bounded to the lateritic Suspended Particulate Matter (SPM) into the lagoon
Geochemistry and hydrodynamics allowed us to determine how driving factors are affecting the dynamics of particulate matter in lagoonal ecosystems influenced by the mining industry (Table 12)
The spring and neap tides do not appear to play a major role in the conditions observed during the study period, except in St Vincent Bay
Summary
The mining industry in New Caledonia is one of the most important environmental concerns for the tropical island lagoonal ecosystem [1,2,3,4,5,6,7,8,9].With about 85% endemism among terrestrial plants, 24 different species of mangroves among the 70 listed throughout the world, about 2800 species of molluscs and the second longest barrier reef inWater 2017, 9, 338; doi:10.3390/w9050338 www.mdpi.com/journal/waterWater 2017, 9, 338 the world [10,11,12,13,14,15], New Caledonia’s ecosystems and biodiversity are highly sensitive to anthropogenic activities (e.g., [16,17,18,19,20,21,22,23] for its lagoons). The mining industry in New Caledonia is one of the most important environmental concerns for the tropical island lagoonal ecosystem [1,2,3,4,5,6,7,8,9]. Since the beginning of mining in New Caledonia, more than 160 × 106 tonnes of ore have been extracted. This has led to the mobilization and transport of approximately 300 million m3 of soil material (laterites). Environmental studies are required in order to mitigate the effects of 400–500 km of deforestation related to the mining industry in
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