Spatial and temporal variations in thesediment fluxes and metal contaminationin nickel mining-impacted catchments
Item statusRestricted Access
Embargo end date07/06/2023
Domingo, Justine Perry Tomines
Understanding of the entire sediment routing system and the links between sources and storage at the catchment scale remains limited in nickel mining-affected regions. This research aims to address the knowledge gap by examining the spatial and temporal variability in the sediment delivery and the extent of siltation and metal contamination in nickel mining-impacted catchments in the Philippines. Discharge and suspended sediment concentrations and fluxes were monitored across 13 sub-catchments with contrasting degrees of mining influence from June 2018 to July 2019 in the Santa Cruz and Pamalabawan catchments. The findings highlight the importance of the size of the area that has been physically disturbed within the sub-catchments (i.e., 10-22% of relative disturbance area generating fourfold to eightfold increase in the sediment yield) and the strong control of floodplain sediment recycling on sediment delivery at both reach and catchment scales (i.e., the relative contribution of floodplain sources to the sediment budget progressively increased over the wet season). Two-dimensional unsteady flow modelling of flood inundation during storms identified the extent of intermediate sediment stores and the zone of preferential silt deposition. Integrating the hydraulic models with the sediment budgets provided additional insight on how erosional and depositional processes vary in between events. Composite geochemical fingerprinting of overbank deposits pointed to mine effluents as the dominant sediment source (77.0 ± 8.7 %), with lower contribution from natural (16.9 ± 5.4 %) and agricultural sources (5.4 ± 1.1 %). Minimal contamination was assessed with respect to background sources due to inherently elevated background metal concentrations in the catchment that are orders of magnitude higher than the threshold values set by international sediment quality guidelines. Element partitioning data indicate that metals are dominantly associated with and transported to the floodplain and coastal areas via suspended particulate matter. Overall, this study underscores the importance of the entire sediment routing system in controlling sediment transport, and that focussing on managing sediment from mining structures and intermediate stores in the catchment is the key to minimising siltation and potential ecological impacts downstream of mining areas. The novel dataset and interpretations provided by this study could optimise environmental management in this ecologically important yet data-scarce region that is threatened by enhanced erosion from mining.