Aqueous copper bioavailability linked to shipwreck-contaminated reef sediments

Abstract

Pollution from the grounding or sinking of ships can have long lasting effects on the recovery and dynamics of coastal ecosystems. Research on the impact of copper (Cu) pollution from the 2011 MV Rena shipwreck at the Astrolabe Reef (Otaiti), New Zealand, 5 years after the grounding, followed a multi-method and multi-disciplinary approach. Three independent measures of aqueous Cu using trace-element-clean-techniques substantiate the presence of high total, total dissolved (<2 µm) and elevated bioavailable Cu in the water column immediately above the aft section of the wreck where the highest sedimentary load of Cu was located. Intermittently elevated concentrations of strong Cu-binding ligands occurred in this location, and their binding strength was consistent with ligands actively produced by organisms in response to Cu induced stress. The recruitment of benthic invertebrates was modified at the high-Cu location. Taxonomic groups usually considered robust to pollution were restricted to this site (e.g. barnacles) or were the most abundant taxa present (e.g. foraminifera). Our results demonstrate that Cu-contaminated sediments can impose a persistent point source of Cu pollution in high-energy reef environments, with the potential to modify the composition and recovery of biological communities.

Figure 1

Map of the Bay of Plenty showing the location of the MV Rena on Otaiti (Astrolabe Reef),Okarapu (Control site), Motiti Island and Tauranga.

Figure 2

Chart of Otaiti showing the locations of water sampling and DGT deployments (discs) and settlement plate deployments (squares) along the 25 m depth contour. The Cu concentration measured in reef sediments is shown by the coloured cylinders (data from Ross, et al.). Elongate remnants of the wreck lie on the central reef (south of settlement plate A), overlap with the northeast corner of the reef and lie parallel to its northeastern edge.

Figure 3

Conceptual figure of the three complementary analytical techniques used to analyse the concentration, speciation, and bioavailability of Cu in the study area of the MV Rena at Otaiti (Astrolabe Reef). Depicted AdCSV measurements reflect the Cu speciation analysis, not the _dCu_T evaluation.

Figure 4

Averaged [Cu_T] determined by HR-SF-ICP-MS, [_dCu_T] determined by AdCSV in water samples collected in June 2016, and [Cu_DGT] determined from multi-day DGT deployments at Otaiti and Okarapu Reef (control site) in June 2016. Error bars represent the ±1 σ values for measurements carried out on two separate days (i.e. the inter-sample variability rather than analytical errors). [Cu_DGT] values are calculated from the average of four DGT Chelex-100 probes deployed between three and four days (n = 4). Dashed lines show the Australian and New Zealand Environment and Conservation Council water quality guidelines for total dissolved Cu concentrations ([_dCu_T]) to protect 99–80% of species.

Figure 5

Results of AdCSV measurements detailing total dissolved Cu concentrations ([_dCu_T]) and the properties of natural organic Cu-binding ligands in samples from Otaiti and Okarapu Reef (control site) collected on 16^th June 2016 (orange columns) and 20^th June 2016 (green columns) including ligand concentrations ([L]), conditional stability constants of ligand-Cu (CuL) complexes (logK), and the calculated bioavailable Cu concentration ([Cu’]). Error bars are ±1σ.

Figure 6

Exploration of AdCSV data: (a) Ratio of [Cu’] to [Cu_T] in water samples collected from Otaiti and Okarapu Reef (control) on the 16^th June 2016 (orange columns) and the 20^th June 2016 (green columns); and (b) relationship between Cu-binding ligand concentration and [Cu’].

Figure 7

Panel A shows a schematic of settlement plate deployment unit including (a) polystyrene net float, (b) PVC pipe, (c) settlement plates and (d) 15 kg plastic coated weight. Three of these units were deployed at each settlement plate sampling station (Sites A, B and C). Panel B shows an example of a 15 × 15 cm terracotta settlement plate deployed at Otaiti to a depth of 25 m for 3 months.