Measurement of shipwreck-derived waterborne trace metals using DGT samplers

Figures & data

Figure 1. Map of the Bay of Plenty showing the location of the MV Rena on Otaiti (Astrolabe Reef), Mōtītī Island and Tauranga.

Figure 2. Outer reef (OR1–3) and debris field (DF1–3) sampling sites (grey ovals) on Otaiti (Astrolabe Reef) where DGTs were deployed and water samples collected. The approximate position of the bow and stern sections of the Rena are indicated in grey. A dashed line indicates the area designated in June 2013 as the main Rena debris field.

Figure 3. A, cross section of a standard open pore DGT sampler (Chelex-100 resin; 0.4 mm thick; 0.45 µm cellulose nitrate membrane filter); B, triangular polymethyl methacrylate DGT housing unit cable tied to a 10 kg vinyl plate.

Table 1. Total solution concentrations (nmol kg⁻¹) of trace metals for sites within the debris field, outer reef and Mōtītī Island sampling areas.

Area	Debris field			Outer reef			Mōtītī Island			LOD
Site	1	2	3	1	2	3	1	2	3	(nmol kg^−1)
Al	692	<482	538	<482	<482	<482	<482	<482	<482	482
Fe	1072	207	411	136	91	<75	<75	<75	109	75.0
Cu	20	<17	<17	<17	<17	<17	<17	<17	<17	17.3
Mn	25	<20	<20	<20	<20	<20	<20	<20	<20	20.0

Only the trace metals present at measurable concentrations in water samples are included in this table. Limits of detection (LOD) are presented in the right hand column. LOD for analytes not recorded in water samples are as follows: Cd 1.9 nmol kg⁻¹; Cr 21.2 nmol kg⁻¹; Co 10.7 nmol kg⁻¹; Pb 5.31 nmol kg⁻¹; Ni 107 nmol kg⁻¹; Zn 64.2 nmol kg⁻¹.

Figure 4. Two-dimensional PCO ordination of DGT data from sampling sites in the Otaiti debris field (●), Otaiti outer reef (○) and Mōtītī Island (*). Principal component axis 1 (PCO1) accounts for 43.1% and axis 2 (PCO2) 17.7% of total variance in the data.

Figure 5. DGT-available metal concentrations (C_DGT) ± SE (nmol kg⁻¹) for the three sampling areas (Figures 1 and 2); debris field (DF), outer reef (OR) and Mōtītī Island (MI).

Table 2. Pearson correlation vectors, mean ± SE and maximum trace-metal concentrations (nmol kg⁻¹) for DGTs deployed at debris field, outer reef and Mōtītī Island sampling sites.

	Pearson correlation vector		Debris field		Outer reef		Mōtītī Island
	PCO1	PCO2	Mean ± SE	Max	Mean ± SE	Max	Mean ± SE	Max
			n = 7		n = 3		n = 4
Al	0.52	−0.54	1.58 ± 1.23	8.93	0.35 ± 0.09	0.51	0.83 ± 0.20	1.34
Cd	0.09	0.89	0.054 ± 0.016	0.132	0.064 ± 0.007	0.101	0.063 ± 0.026	0.131
Cr	0.71	−0.10	0.022 ± 0.003	0.033	0.016 ± 0.003	0.022	0.019 ± 0.002	0.026
Co	0.71	−0.35	0.009 ± 0.001	0.011	0.007 ± 0.001	0.008	0.009 ± 0.000	0.009
Cu	0.93	−0.01	0.32 ± 0.03	0.43	0.25 ± 0.01	0.27	0.23 ± 0.01	0.25
Fe	0.74	0.16	3.20 ± 0.72	6.31	1.86 ± 0.93	2.89	1.65 ± 0.89	4.18
Pb	−0.53	−0.61	0.042 ± 0.002	0.050	0.064 ± 0.007	0.077	0.099 ± 0.042	0.225
Mn	0.82	0.01	0.69 ± 0.05	0.80	0.33 ± 0.02	0.36	0.37 ± 0.02	0.41
Ni	0.48	−0.25	0.25 ± 0.02	0.29	0.27 ± 0.04	0.33	0.23 ± 0.04	0.34
Zn	0.66	0.28	1.41 ± 0.29	2.85	0.98 ± 0.33	1.64	1.10 ± 0.35	1.97