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Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India
MPB-07225; No of Pages 8 Marine Pollution Bulletin xxx (2015) xxx–xxx
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India S. Krishnakumar a,⁎, S. Ramasamy a, N.S. Magesh b, N. Chandrasekar b, T. Simon Peter b a b
Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai 600025, India Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 627012, India
a r t i c l e
i n f o
Article history: Received 5 August 2015 Received in revised form 5 October 2015 Accepted 8 October 2015 Available online xxxx Keywords: Marine pollution Metal accumulation Growth bands Metal selectivity index Pollution Load Index Gulf of Mannar
a b s t r a c t The present study was carried out on the Porites coral growth bands (1979 to 2014) to measure the metal accumulation for assessing the environmental pollution status. The concentrations of studied metals are compared with similar global studies, which indicate that the metals are probably derived from natural sources. The identical peaks of Fe and Mn are perfectly matched with Cu, Cr and Ni concentrations. However, the metal profile trend is slightly depressed from a regular trend in Zn, Cd and Pb peaks. The metal accumulation affinity of the reef skeleton is ranked in the following order Cr N Cd N Pb N Fe N Mn N Cu N Ni N Zn. The distribution of metal constituents in coral growth bands is primarily controlled by Fe and Mn in the reef skeleton. Other reef associated metals such as Pb and Cd are derived from other sources like coastal developments and anthropogenic sources. © 2015 Elsevier Ltd. All rights reserved.
Corals are important primary producers co-occurring in tropical shallow water reefs (Crossland et al., 1991; Hatcher, 1997). One third of all reef-building coral species are at risk of being extinct as a result of climate change and local ecosystem impacts including impacts of overfishing and pollution (Wilkinson, 2004; Hughes et al., 2007). The skeletal growth bands of massive scleractinian corals have been recognized to be useful in time series studies for tracing the variations in seawater properties, nutrient levels, and even pollutants entering the marine environment. A valuable attribute of using corals as proxy indicators of these parameters lies in its capacity for sub-annual dating resolution. A wide range of metals have been determined in the skeletal growth bands of reef-corals. Moreover, Pb and Cd are well known indicators of anthropogenic activity (Shen et al., 1987; Magesh et al., 2011; Magesh et al., 2013) that are brought into reef environment by coastal construction, land reclamation, beach nourishment, port construction, sewage effluents and effluent transportation by waves and currents. Pollution studies in recent years have examined trace metal concentrations in corals, usually being able to link this to a local or even global anthropogenic source of contaminants (Esslemont, 1999; Bastidas and Garcia, 1999; Fallon et al., 2002; Jayaraju et al., 2009; Krishnakumar et al., 2010). Under these circumstances, no systematic study has been carried ⁎ Corresponding author. E-mail addresses: [email protected] (S. Krishnakumar), [email protected] (S. Ramasamy), [email protected] (N.S. Magesh), [email protected] (N. Chandrasekar), [email protected] (T. Simon Peter).
out to address the reef skeletal accumulated metal pollutants in the present study region. So, the aim of the present study is to assess the growth band accumulated metal contaminants and to trace their pollutant sources. Coral core samples were collected in the Gulf of Mannar region (Fig. 1) using an assembled electric diamond drill corer (10 cm in diameter and 1 m long) at a water depth of 2 m. The collected samples were rinsed in de-ionized water and dried at 60 °C. Each sample was then sectioned into 1 cm-thick slabs perpendicular to the perceived growth direction using water lubricated diamond bit masonry saw. X-ray images of each slab were taken to gray scale image to reveal density banding. The images were then scanned and converted to a gray-scale positive image. Slabs were sub-sampled for metal analysis by alternately washing with double distilled water and weak acid (0.2 N HNO3) and H2O2 in an ultrasonic bath to remove surface contamination and soft tissues. The sub-sampling was done by employing a dentist driller to obtain the sample weight of 15 to 25 mg. The total length of the sampling profile is represented by 36 subsampling spots. Samples were then dissolved in acid (5% HCl–5% HNO3 solution) and filtered and centrifuged prior to metal analysis. All the samples were run with duplicates from the nearby sampling locations and the documented values are the composites of two samples. The blank and quality control standard analysis (carbonate reference-MACS-1) is repeated for every 15 samples to obtain the accuracy and precision. Metal analyses were performed using an inductively-coupled plasma atomic emission spectrometer (ICP-AES-Model No. IRIS INTREPID II XSP-Thermo Electron
http://dx.doi.org/10.1016/j.marpolbul.2015.10.009 0025-326X/© 2015 Elsevier Ltd. All rights reserved.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 1. Study area map.
Corporation). The detection limit of studied metals was 0.01 ppm for Fe, Cd, Ni, Cu, Cr, Zn, and Mn, and 0.05 ppm for Pb. The mineralogical composition of the residues was identified using a XRD instrument (Xpert PRO X-ray Diffractometer) at the Centre for Earth Science Studies, Thiruvananthapuram. The geochemical compositions of the insoluble residues were identified by EP-SEM and EDAX facilities at the Centre for Nanotechnology, University of Madras, Chennai. The accumulated metal concentration and Pollution Load Index (PLI) in the coral skeleton are given in Table 1. The vertical variations of metal concentrations are shown in Fig. 2. The positive images of the Xradiographs were used to mark separate annual growth bands along the cores. The annual extension rates of corals were directly measured along the major growth axes from the positive prints. Each couple of high and low density bands represents an annual growth increment. The upper growth band of the recent coral was aligned to the date of collection (2014). According to Brachert et al. (2006), the high density
bands indicate the cool SSTs with winter and the low density bands with warm SSTs reflecting summer climate. The average thickness of the growth band layers is about ≤2 mm wide and occurs rhythmically and perpendicular to the growth direction of the coral. XRD peaks of the insoluble residue show a mineralogical composition of quartz together with a mixture of the clay minerals (Fig. 3). In addition, EPSEM images and EDAX analysis suggest that the rhythmic layers of insoluble residue represent seasonal in-vivo incorporation of detrital particles (Fig. 4). The incorporation of detrital materials with coral skeleton under in-vitro condition was reported by Erez and Braun (2007) and the natural accumulation of such materials was also documented in literatures (Pingitore et al., 2002; Wyndham et al., 2004; Mertz-Kraus et al., 2009). Neil et al. (1994) and Naqvi (1994) suggested that the variations in geochemical composition and the amount of sediment particles trapped in coral skeletons provide valuable information about the provenance and temporal differences in sediment
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Table 1 Descriptive statistics, metal concentration, Metal Selective Index (MSI), Pollution Load Index in the growth bands of Porites sp. Year
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Max Min Mean
Fe
Mn
Cu
Cd
Cr
NI
Pb
Zn
PLI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
2.2 2.07 3.48 4.28 1.69 0.61 3.66 2.05 3.04 0.52 1.01 1.67 1.08 0.81 1.28 1.9 0.93 0.73 0.9 0.65 2.09 1.35 1.9 4.81 0.83 1.03 0.76 0.92 0.96 0.81 1.16 0.11 1.45 1.69 3.25 1.5 4.81 0.11 1.64
11.59 13.56 9.89 17.21 12.98 5.35 11.71 8.16 15.82 7.49 12.52 11.38 14.48 12.35 12.81 9.28 13.12 10.55 13.31 10.27 18.81 12.83 13.94 13.02 10.94 10.84 9.87 8.65 12.00 10.90 11.81 0.75 13.65 11.99 11.60 10.18 18.81 0.75 11.54
3.51 2.06 4.6 3.44 1.96 2.02 4.78 3.22 2.59 1 0.9 2.21 1.2 1.04 2.12 2.61 1.04 1.22 1.01 0.87 1.63 2.32 2.83 6.21 1.76 0.98 1.56 1.04 0.86 0.8 1.02 0.12 1.13 1.53 3.71 1.65 6.21 0.12 2.02
18.48 13.49 13.07 13.83 15.05 17.70 15.29 12.81 13.48 14.41 11.15 15.06 16.09 15.85 21.22 12.75 14.67 17.63 14.94 13.74 14.67 22.05 20.76 16.82 23.19 10.32 20.26 9.78 10.75 10.77 10.39 0.82 10.64 10.85 13.24 11.19 23.19 0.82 14.37
4 3 12.5 3.5 1 1.5 8 6 4 BDL BDL 2.5 BDL BDL 0.5 3.5 BDL BDL BDL BDL BDL 0.1 0.5 9 BDL BDL BDL BDL BDL BDL 1 0.1 BDL 1 6.5 1 12.5 0.1 3.46
21.06 19.65 35.51 14.07 7.68 13.15 25.59 23.88 20.81 NA NA 17.04 NA NA 5.01 17.10 NA NA NA NA NA NA 3.67 24.37 NA NA NA NA NA NA 10.18 0.68 NA 7.09 23.20 6.78 35.51 0.68 15.61
0.34 0.37 0.43 0.98 0.58 0.33 0.52 0.57 0.45 0.35 0.45 0.46 0.41 0.4 0.48 0.38 0.42 0.43 0.41 0.4 0.5 0.38 0.4 0.34 0.48 0.47 0.25 0.42 0.45 0.43 0.46 0.5 0.4 0.51 0.53 0.52 0.98 0.25 0.45
1.79 2.42 1.22 3.94 4.45 2.89 1.66 2.27 2.34 5.04 5.58 3.14 5.50 6.10 4.80 1.86 5.92 6.21 6.07 6.32 4.50 3.61 2.93 0.92 6.32 4.95 3.25 3.95 5.63 5.79 4.68 3.40 3.77 3.62 1.89 3.53 6.32 0.92 3.95
0.04 0.03 0.29 0.11 BDL BDL 0.55 0.25 0.4 BDL 0.11 0.18 BDL BDL BDL 0.41 BDL 0.02 0.02 BDL 0.38 0.23 0.32 1.12 BDL 0.04 BDL BDL BDL BDL 0.09 BDL 0.08 BDL 0.48 BDL 1.12 0.02 0.26
0.21 0.20 0.82 0.44 NA NA 1.76 0.99 2.08 NA 1.36 1.23 NA NA NA 2.00 NA 0.29 0.30 NA 3.42 2.19 2.35 3.03 NA 0.42 NA NA NA NA 0.92 NA 0.75 NA 1.71 NA 3.42 0.20 1.32
0.97 0.9 4.72 1.85 1.01 0.76 6.73 4.81 4.34 0.66 1.45 4.29 0.87 0.84 1 5.18 0.91 0.73 0.96 0.75 2.69 2.77 3.92 11.75 0.93 1.77 1.53 0.9 1.31 1.05 2.11 1.85 2.22 2.03 7.4 1.36 11.75 0.66 2.48
5.11 5.89 13.41 7.44 7.76 6.66 21.53 19.14 22.58 9.51 17.97 29.24 11.66 12.80 10.01 25.31 12.83 10.55 14.20 11.85 24.21 26.33 28.76 31.82 12.25 18.63 19.87 8.47 16.38 14.13 21.49 12.58 20.90 14.40 26.41 9.23 31.82 5.11 16.15
0.89 0.82 0.83 2.05 1.24 0.83 1.31 1.26 0.87 0.84 0.87 0.82 0.95 0.79 0.94 1.11 0.92 0.92 0.96 0.89 1.02 0.73 0.98 1.14 0.96 1.14 0.95 1.03 1.1 1.06 0.99 1.47 1.29 1.42 1.41 1.54 2.05 0.73 1.07
4.69 5.37 2.36 8.24 9.52 7.27 4.19 5.01 4.53 12.10 10.78 5.59 12.73 12.04 9.41 5.42 12.98 13.29 14.20 14.06 9.18 6.94 7.19 3.09 12.65 12.00 12.34 9.69 13.75 14.27 10.08 9.99 12.15 10.07 5.03 10.45 14.27 2.36 9.24
7.04 6.02 8.35 8.66 5.54 5.36 5.71 6.97 3.53 3.57 3.28 2.54 2.95 2.68 3.67 5.38 2.87 2.87 2.5 2.77 2.8 2.64 2.78 2.56 2.63 4.07 2.65 6.32 3.32 3.28 2.99 10.56 4.05 5.92 4.74 7.17 10.56 2.5 4.47
37.07 39.42 23.72 34.82 42.55 46.98 18.27 27.74 18.37 51.44 40.64 17.31 39.54 40.85 36.74 26.28 40.48 41.47 36.98 43.76 25.20 25.10 20.40 6.93 34.65 42.84 34.42 59.45 41.50 44.15 30.45 71.79 38.14 41.99 16.92 48.64 71.79 6.93 35.75
2.55 0.94 2.31 1.92 1.38 1.09 2.59 1.98 1.72 0.88 0.81 1.27 1.03 0.94 1.11 1.74 1.00 0.59 0.60 0.90 1.22 0.79 1.18 2.77 1.06 0.79 1.02 1.11 1.07 1.00 0.86 0.61 0.94 1.48 2.37 1.45 2.78 0.59 1.31
NA—not available, BDL—below detection limit, Con—concentration, Min—minimum, Max — maximum, PLI—Pollution Load Index, MSI—Metal Selective Index
availability, runoff in the specific period and variations in environmental conditions. The maximum amount of insoluble residue was obtained from 1979 to 1983 and 2000 to 2003 growth bands. The composition of insoluble residues clearly shows that this sediment is chiefly derived from siliciclastic riverine inputs. The accumulated Fe and Mn in the coral growth bands act as an indicator of detrital inputs. The concentration of Fe and Mn ranges from 0.11 to 4.81 μg g−1 and 0.12 to 6.21 μg g−1 respectively. The elevated concentration of Fe and Mn was noticed in 1981, 1982, 1985 and 2002 growth bands. The maximum concentration of Fe, Mn and Cu in the topmost bands may be due to the incorporation of terrigenous matter inputs and burrowing algal remains (David, 2003). The concentration of metals in coral reef growth bands ranges from 0.1 to 12.5 μg g−1 for Cu, from 0.25 to 0.98 μg g−1 for Cd, from 0.02 to 1.12 μg g−1 for Cr, from 0.66 to 11.75 μg g−1 for Ni, from 0.73 to 2.05 μg g−1 for Pb, and from 2.5 to 10.56 μg g− 1 for Zn (Table 1). Zinc dominates the metal concentration in coral growth band followed by Fe and Mn. Zinc is an essential element for growth, protein synthesis, repairing of cells and enzyme circulation in organisms (Brown and Howard, 1985; Krishnakumar et al., 2010). The concentration of Cd, Cr, Ni and Pb is less than the Cu and Zn concentrations. The concentrations of the studied metals show the following order Cr N Cd N Pb N Fe N Ni N Cu N Zn N Mn. Even very low concentration of these metals typically affects the coral growth related process including fertilization, larval success, and larval mortality (Reichelt-Brushett and Harrison, 2004; Krishnakumar et al., 2010).
The coral skeletal structures are showing undulated spikes of metal concentrations from 1979 to 2014. Some narrow maximum spikes were observed in all the metals from 1979 to 1986 and from 1999 to 2004, respectively. The concentrations of studied metals are compared with similar global studies which indicate that the metals are probably derived from natural sources. However, the elevated concentration of metals in the Tuticorin coast is probably due to the vicinity of industries and confluence of industrial effluents along the coast through riverine input (Jayaraju et al., 2009; Table 2). The identical peaks of Fe and Mn are perfectly matched with Cu, Cr and Ni concentrations. It clearly suggests that these metals are typically controlled by skeletal accumulated organic phase. However, the metal profile trend is slightly depressed from a regular trend in Zn, Cd and Pb peaks. The concentration of Pb is probably derived from the application of alkyl lead gasoline in motor vehicles and mechanized boats and also from the fly ash from a thermal power plant. The variation in the metal accumulation also depends on the incorporation capability of reef skeletal composition via calcium substitution of metals or association of organic particulate matters with skeletal pores. The concentration of metals in the growth bands of coral reef is expressed as the Metal Selectivity Index (MSI)
MSI ¼
Absolute concentration of a metal ðskeletonÞ 100: Total concentration of all metals ðskeletonÞ
ð1Þ
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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Fig. 2. Vertical distribution of metals in the coral core sample.
Fig. 3. XRD peaks of the reef skeletal accumulated insoluble residues.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 4. EPSEM & EDAX of the reef skeletal accumulated insoluble residues.
and bio-fouling of the membrane surface (Nair et al., 2006). Bioaccumulation of metals will always be affected by site-specific differences in bioavailability. The metal affinity of the reef skeleton is ranked based on MSI in the following order Cr N Cd N Cu N Pb N Fe N Mn N Ni N Zn. The Pollution Load Index (PLI) was proposed by Tomlinson et al. (1980) for detecting metal pollutants and used to compare the pollution levels between different sites at different times. The PLI was calculated
Here, MSI is defined as the relative metal-accumulating capacity of a coral reef skeleton for a particular metal. The concentration of MSI value is presented in Table 1. The mean Metal Selectivity Index (MSI) value of each band is 11.54 for Fe, 14.37 for Mn, 15.61 for Cu, 3.95 for Cd, 1.32 for Cr, 16.15 for Ni, 9.24 for Pb, and 35.75 for Ni. The uptake and accumulation of metals depend not only on their chemical and physical properties but also on the temperature, turbulence, flow rate, water column,
Table 2 Heavy metal concentrations in the Gulf of Mannar and comparative worldwide studies of Porites sp. Station name
Porites species
Fe
Mn
Cu
Cd
Cr
Ni
Pb
Zn
Present study-Gulf of Mannar (avg) Gulf of Aquba (Al-Rousan et al., 2007) Daya Bay, Northern South China Sea (Chen et al., 2010) Tuticorin coast (Jayaraju et al., 2009) Nha Trang Bay, Vietnam (Nguyen et al., 2013) Pioneer Bay (Esslemont, 2000) Nelly Bay (Esslemont, 2000) Lakshadweep Archipelago (Anu et al., 2007)
Porites sp. Porites sp. Porites sp. P. andrewsi Porites sp. P. damicornis P. damicornis P. andrewsi P. contigua P. lutea Poritidae
1.64 14.49 78.54 48.25 36.77 NA NA 5.15 19.33 NA NA
2.02 0.35 1.77 8.53 2.9 NA NA 2.24 11.16 4.27 NA
3.46 3.88 NA 10.65 5.53 1.6 5.5 0.49 36.88 11.7 0.28
0.45 4.19 NA 7.21 0.01 0.09 0.09 2.13 11.16 0.097 0.054
0.26 NA NA 5.23 NA 44 21 4.33 15.6 1.08 NA
2.48 NA NA 72.2 NA 31 10 11.10 18.01 9.5 0.17
1.07 38.17 NA 28.3 0.24 0.24 0.19 24.18 3.33 1.02 0.27
4.47 7.32 3.57 2.51 NA 23 37 2.62 38.71 16.9 2.4
Dafangji Island, China (Peng et al., 2006) Heron and Wistari Reef–Great Barrier Reef, (St. John 1974)
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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Table 3 Bivariate Pearson correlations for metal concentration in Porites sp. in the study area. Parameters
Fe
Fe Mn Cu Cd Cr NI Pb Zn
1 .902⁎⁎ .825⁎⁎ .396⁎ .780⁎⁎ .769⁎⁎ .388⁎ .255
Mn 1 .888⁎⁎ .142 .803⁎⁎ .812⁎⁎ .174 .211
Cu
Cd
Cr
NI
Pb
Zn
1 .130 .693⁎⁎ .760⁎⁎ .152 .391⁎
1 −.015 .023 .778⁎⁎ .449⁎⁎
1
.958⁎⁎ .101 −.075
1 .190 .023
1
.580⁎⁎
1
⁎⁎ Correlation is significant at the 0.01 level (2-tailed). ⁎ Correlation is significant at the 0.05 level (2-tailed).
as a concentration factor of each metal with respect to the background level of the crust. The natural available metal concentrations are chiefly derived from natural sources, including river input and weathering of source rock types. According to Angulo (1996), PLI will able to give an estimate of metal contamination status for further assessment. The equation for calculating the PLI is shown below
PLI ¼ ðCF1 CF2 CF3 ……: CFn Þ1=n
ð2Þ
where Cfn is the concentration of metal n in the sample. The PLI values of the studied metals are presented in Table 1. The Pollution Load Index of the studied coral growth bands ranges from 0.59 to 2.77 with a mean value of 1.33. Low pollution index value was noticed in the year 1996 and 1997. The Pearson correlation matrix of the studied metals is shown in Table 3 and extracted factor (Principal Component Analysis) was used to decipher the metal association in the reef skeleton (Fig. 5). Moreover, the Principal Component Analysis (PCA) was useful for data reduction, and to determine the sources of variation between parameters (Güler et al., 2002). The PCA data sets of metals in the reef skeleton reveal that Fe, Mn, Ni, Cr and Cu are categorized under a single group (component 1) which are scored nearly 62.5% of the variance. This clearly
indicates that the above said metals are derived from the same source and moving together in the marine environment. Similarly 25% of variance (Pb and Cd) was observed under component 2 which shows that they are derived from metal leaching from anthropogenic sources. Pb and Cd are the primary indicators of human induced metal pollution in the marine environment (Krishnakumar et al., 2010). This is also supported for the above conclusion with maximum PCA score at component 2. Further Zn is categorized under component 3 with 12.5% of variance, which indicates that this element is derived from reef growth and their related process. Dendrogram plot was prepared using an average relationship linkage between the groups (Fig. 6). Fe, Mn, Ni, Cu, Cr and Zn are following the same trend and it is justified from PCA plot and correlation analysis. Moreover, the distribution of metal constituents is primarily controlled by Fe and Mn in the reef skeleton. Other reef associated metals such as Pb and Cd are derived from other sources like coastal developments and anthropogenic sources. Acknowledgement KK is thankful to the University Grant Commission, New Delhi and D.S Kothari Post Doctoral Cell, University of Pune. The present work is supported by UGC Dr. D.S.Kothari Post Doctoral Fellowship scheme (Ref No. F.4-2/2006 (BSR)/ES/13-14/0019). Authors are thankful to
Fig. 5. Principal component plot of metals in rotated space.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 6. Dendrogram of the reef skeletal accumulated studied metals.
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Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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Baseline
Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India S. Krishnakumar a,⁎, S. Ramasamy a, N.S. Magesh b, N. Chandrasekar b, T. Simon Peter b a b
Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai 600025, India Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 627012, India
a r t i c l e
i n f o
Article history: Received 5 August 2015 Received in revised form 5 October 2015 Accepted 8 October 2015 Available online xxxx Keywords: Marine pollution Metal accumulation Growth bands Metal selectivity index Pollution Load Index Gulf of Mannar
a b s t r a c t The present study was carried out on the Porites coral growth bands (1979 to 2014) to measure the metal accumulation for assessing the environmental pollution status. The concentrations of studied metals are compared with similar global studies, which indicate that the metals are probably derived from natural sources. The identical peaks of Fe and Mn are perfectly matched with Cu, Cr and Ni concentrations. However, the metal profile trend is slightly depressed from a regular trend in Zn, Cd and Pb peaks. The metal accumulation affinity of the reef skeleton is ranked in the following order Cr N Cd N Pb N Fe N Mn N Cu N Ni N Zn. The distribution of metal constituents in coral growth bands is primarily controlled by Fe and Mn in the reef skeleton. Other reef associated metals such as Pb and Cd are derived from other sources like coastal developments and anthropogenic sources. © 2015 Elsevier Ltd. All rights reserved.
Corals are important primary producers co-occurring in tropical shallow water reefs (Crossland et al., 1991; Hatcher, 1997). One third of all reef-building coral species are at risk of being extinct as a result of climate change and local ecosystem impacts including impacts of overfishing and pollution (Wilkinson, 2004; Hughes et al., 2007). The skeletal growth bands of massive scleractinian corals have been recognized to be useful in time series studies for tracing the variations in seawater properties, nutrient levels, and even pollutants entering the marine environment. A valuable attribute of using corals as proxy indicators of these parameters lies in its capacity for sub-annual dating resolution. A wide range of metals have been determined in the skeletal growth bands of reef-corals. Moreover, Pb and Cd are well known indicators of anthropogenic activity (Shen et al., 1987; Magesh et al., 2011; Magesh et al., 2013) that are brought into reef environment by coastal construction, land reclamation, beach nourishment, port construction, sewage effluents and effluent transportation by waves and currents. Pollution studies in recent years have examined trace metal concentrations in corals, usually being able to link this to a local or even global anthropogenic source of contaminants (Esslemont, 1999; Bastidas and Garcia, 1999; Fallon et al., 2002; Jayaraju et al., 2009; Krishnakumar et al., 2010). Under these circumstances, no systematic study has been carried ⁎ Corresponding author. E-mail addresses: [email protected] (S. Krishnakumar), [email protected] (S. Ramasamy), [email protected] (N.S. Magesh), [email protected] (N. Chandrasekar), [email protected] (T. Simon Peter).
out to address the reef skeletal accumulated metal pollutants in the present study region. So, the aim of the present study is to assess the growth band accumulated metal contaminants and to trace their pollutant sources. Coral core samples were collected in the Gulf of Mannar region (Fig. 1) using an assembled electric diamond drill corer (10 cm in diameter and 1 m long) at a water depth of 2 m. The collected samples were rinsed in de-ionized water and dried at 60 °C. Each sample was then sectioned into 1 cm-thick slabs perpendicular to the perceived growth direction using water lubricated diamond bit masonry saw. X-ray images of each slab were taken to gray scale image to reveal density banding. The images were then scanned and converted to a gray-scale positive image. Slabs were sub-sampled for metal analysis by alternately washing with double distilled water and weak acid (0.2 N HNO3) and H2O2 in an ultrasonic bath to remove surface contamination and soft tissues. The sub-sampling was done by employing a dentist driller to obtain the sample weight of 15 to 25 mg. The total length of the sampling profile is represented by 36 subsampling spots. Samples were then dissolved in acid (5% HCl–5% HNO3 solution) and filtered and centrifuged prior to metal analysis. All the samples were run with duplicates from the nearby sampling locations and the documented values are the composites of two samples. The blank and quality control standard analysis (carbonate reference-MACS-1) is repeated for every 15 samples to obtain the accuracy and precision. Metal analyses were performed using an inductively-coupled plasma atomic emission spectrometer (ICP-AES-Model No. IRIS INTREPID II XSP-Thermo Electron
http://dx.doi.org/10.1016/j.marpolbul.2015.10.009 0025-326X/© 2015 Elsevier Ltd. All rights reserved.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 1. Study area map.
Corporation). The detection limit of studied metals was 0.01 ppm for Fe, Cd, Ni, Cu, Cr, Zn, and Mn, and 0.05 ppm for Pb. The mineralogical composition of the residues was identified using a XRD instrument (Xpert PRO X-ray Diffractometer) at the Centre for Earth Science Studies, Thiruvananthapuram. The geochemical compositions of the insoluble residues were identified by EP-SEM and EDAX facilities at the Centre for Nanotechnology, University of Madras, Chennai. The accumulated metal concentration and Pollution Load Index (PLI) in the coral skeleton are given in Table 1. The vertical variations of metal concentrations are shown in Fig. 2. The positive images of the Xradiographs were used to mark separate annual growth bands along the cores. The annual extension rates of corals were directly measured along the major growth axes from the positive prints. Each couple of high and low density bands represents an annual growth increment. The upper growth band of the recent coral was aligned to the date of collection (2014). According to Brachert et al. (2006), the high density
bands indicate the cool SSTs with winter and the low density bands with warm SSTs reflecting summer climate. The average thickness of the growth band layers is about ≤2 mm wide and occurs rhythmically and perpendicular to the growth direction of the coral. XRD peaks of the insoluble residue show a mineralogical composition of quartz together with a mixture of the clay minerals (Fig. 3). In addition, EPSEM images and EDAX analysis suggest that the rhythmic layers of insoluble residue represent seasonal in-vivo incorporation of detrital particles (Fig. 4). The incorporation of detrital materials with coral skeleton under in-vitro condition was reported by Erez and Braun (2007) and the natural accumulation of such materials was also documented in literatures (Pingitore et al., 2002; Wyndham et al., 2004; Mertz-Kraus et al., 2009). Neil et al. (1994) and Naqvi (1994) suggested that the variations in geochemical composition and the amount of sediment particles trapped in coral skeletons provide valuable information about the provenance and temporal differences in sediment
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Table 1 Descriptive statistics, metal concentration, Metal Selective Index (MSI), Pollution Load Index in the growth bands of Porites sp. Year
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Max Min Mean
Fe
Mn
Cu
Cd
Cr
NI
Pb
Zn
PLI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
Con
MSI
2.2 2.07 3.48 4.28 1.69 0.61 3.66 2.05 3.04 0.52 1.01 1.67 1.08 0.81 1.28 1.9 0.93 0.73 0.9 0.65 2.09 1.35 1.9 4.81 0.83 1.03 0.76 0.92 0.96 0.81 1.16 0.11 1.45 1.69 3.25 1.5 4.81 0.11 1.64
11.59 13.56 9.89 17.21 12.98 5.35 11.71 8.16 15.82 7.49 12.52 11.38 14.48 12.35 12.81 9.28 13.12 10.55 13.31 10.27 18.81 12.83 13.94 13.02 10.94 10.84 9.87 8.65 12.00 10.90 11.81 0.75 13.65 11.99 11.60 10.18 18.81 0.75 11.54
3.51 2.06 4.6 3.44 1.96 2.02 4.78 3.22 2.59 1 0.9 2.21 1.2 1.04 2.12 2.61 1.04 1.22 1.01 0.87 1.63 2.32 2.83 6.21 1.76 0.98 1.56 1.04 0.86 0.8 1.02 0.12 1.13 1.53 3.71 1.65 6.21 0.12 2.02
18.48 13.49 13.07 13.83 15.05 17.70 15.29 12.81 13.48 14.41 11.15 15.06 16.09 15.85 21.22 12.75 14.67 17.63 14.94 13.74 14.67 22.05 20.76 16.82 23.19 10.32 20.26 9.78 10.75 10.77 10.39 0.82 10.64 10.85 13.24 11.19 23.19 0.82 14.37
4 3 12.5 3.5 1 1.5 8 6 4 BDL BDL 2.5 BDL BDL 0.5 3.5 BDL BDL BDL BDL BDL 0.1 0.5 9 BDL BDL BDL BDL BDL BDL 1 0.1 BDL 1 6.5 1 12.5 0.1 3.46
21.06 19.65 35.51 14.07 7.68 13.15 25.59 23.88 20.81 NA NA 17.04 NA NA 5.01 17.10 NA NA NA NA NA NA 3.67 24.37 NA NA NA NA NA NA 10.18 0.68 NA 7.09 23.20 6.78 35.51 0.68 15.61
0.34 0.37 0.43 0.98 0.58 0.33 0.52 0.57 0.45 0.35 0.45 0.46 0.41 0.4 0.48 0.38 0.42 0.43 0.41 0.4 0.5 0.38 0.4 0.34 0.48 0.47 0.25 0.42 0.45 0.43 0.46 0.5 0.4 0.51 0.53 0.52 0.98 0.25 0.45
1.79 2.42 1.22 3.94 4.45 2.89 1.66 2.27 2.34 5.04 5.58 3.14 5.50 6.10 4.80 1.86 5.92 6.21 6.07 6.32 4.50 3.61 2.93 0.92 6.32 4.95 3.25 3.95 5.63 5.79 4.68 3.40 3.77 3.62 1.89 3.53 6.32 0.92 3.95
0.04 0.03 0.29 0.11 BDL BDL 0.55 0.25 0.4 BDL 0.11 0.18 BDL BDL BDL 0.41 BDL 0.02 0.02 BDL 0.38 0.23 0.32 1.12 BDL 0.04 BDL BDL BDL BDL 0.09 BDL 0.08 BDL 0.48 BDL 1.12 0.02 0.26
0.21 0.20 0.82 0.44 NA NA 1.76 0.99 2.08 NA 1.36 1.23 NA NA NA 2.00 NA 0.29 0.30 NA 3.42 2.19 2.35 3.03 NA 0.42 NA NA NA NA 0.92 NA 0.75 NA 1.71 NA 3.42 0.20 1.32
0.97 0.9 4.72 1.85 1.01 0.76 6.73 4.81 4.34 0.66 1.45 4.29 0.87 0.84 1 5.18 0.91 0.73 0.96 0.75 2.69 2.77 3.92 11.75 0.93 1.77 1.53 0.9 1.31 1.05 2.11 1.85 2.22 2.03 7.4 1.36 11.75 0.66 2.48
5.11 5.89 13.41 7.44 7.76 6.66 21.53 19.14 22.58 9.51 17.97 29.24 11.66 12.80 10.01 25.31 12.83 10.55 14.20 11.85 24.21 26.33 28.76 31.82 12.25 18.63 19.87 8.47 16.38 14.13 21.49 12.58 20.90 14.40 26.41 9.23 31.82 5.11 16.15
0.89 0.82 0.83 2.05 1.24 0.83 1.31 1.26 0.87 0.84 0.87 0.82 0.95 0.79 0.94 1.11 0.92 0.92 0.96 0.89 1.02 0.73 0.98 1.14 0.96 1.14 0.95 1.03 1.1 1.06 0.99 1.47 1.29 1.42 1.41 1.54 2.05 0.73 1.07
4.69 5.37 2.36 8.24 9.52 7.27 4.19 5.01 4.53 12.10 10.78 5.59 12.73 12.04 9.41 5.42 12.98 13.29 14.20 14.06 9.18 6.94 7.19 3.09 12.65 12.00 12.34 9.69 13.75 14.27 10.08 9.99 12.15 10.07 5.03 10.45 14.27 2.36 9.24
7.04 6.02 8.35 8.66 5.54 5.36 5.71 6.97 3.53 3.57 3.28 2.54 2.95 2.68 3.67 5.38 2.87 2.87 2.5 2.77 2.8 2.64 2.78 2.56 2.63 4.07 2.65 6.32 3.32 3.28 2.99 10.56 4.05 5.92 4.74 7.17 10.56 2.5 4.47
37.07 39.42 23.72 34.82 42.55 46.98 18.27 27.74 18.37 51.44 40.64 17.31 39.54 40.85 36.74 26.28 40.48 41.47 36.98 43.76 25.20 25.10 20.40 6.93 34.65 42.84 34.42 59.45 41.50 44.15 30.45 71.79 38.14 41.99 16.92 48.64 71.79 6.93 35.75
2.55 0.94 2.31 1.92 1.38 1.09 2.59 1.98 1.72 0.88 0.81 1.27 1.03 0.94 1.11 1.74 1.00 0.59 0.60 0.90 1.22 0.79 1.18 2.77 1.06 0.79 1.02 1.11 1.07 1.00 0.86 0.61 0.94 1.48 2.37 1.45 2.78 0.59 1.31
NA—not available, BDL—below detection limit, Con—concentration, Min—minimum, Max — maximum, PLI—Pollution Load Index, MSI—Metal Selective Index
availability, runoff in the specific period and variations in environmental conditions. The maximum amount of insoluble residue was obtained from 1979 to 1983 and 2000 to 2003 growth bands. The composition of insoluble residues clearly shows that this sediment is chiefly derived from siliciclastic riverine inputs. The accumulated Fe and Mn in the coral growth bands act as an indicator of detrital inputs. The concentration of Fe and Mn ranges from 0.11 to 4.81 μg g−1 and 0.12 to 6.21 μg g−1 respectively. The elevated concentration of Fe and Mn was noticed in 1981, 1982, 1985 and 2002 growth bands. The maximum concentration of Fe, Mn and Cu in the topmost bands may be due to the incorporation of terrigenous matter inputs and burrowing algal remains (David, 2003). The concentration of metals in coral reef growth bands ranges from 0.1 to 12.5 μg g−1 for Cu, from 0.25 to 0.98 μg g−1 for Cd, from 0.02 to 1.12 μg g−1 for Cr, from 0.66 to 11.75 μg g−1 for Ni, from 0.73 to 2.05 μg g−1 for Pb, and from 2.5 to 10.56 μg g− 1 for Zn (Table 1). Zinc dominates the metal concentration in coral growth band followed by Fe and Mn. Zinc is an essential element for growth, protein synthesis, repairing of cells and enzyme circulation in organisms (Brown and Howard, 1985; Krishnakumar et al., 2010). The concentration of Cd, Cr, Ni and Pb is less than the Cu and Zn concentrations. The concentrations of the studied metals show the following order Cr N Cd N Pb N Fe N Ni N Cu N Zn N Mn. Even very low concentration of these metals typically affects the coral growth related process including fertilization, larval success, and larval mortality (Reichelt-Brushett and Harrison, 2004; Krishnakumar et al., 2010).
The coral skeletal structures are showing undulated spikes of metal concentrations from 1979 to 2014. Some narrow maximum spikes were observed in all the metals from 1979 to 1986 and from 1999 to 2004, respectively. The concentrations of studied metals are compared with similar global studies which indicate that the metals are probably derived from natural sources. However, the elevated concentration of metals in the Tuticorin coast is probably due to the vicinity of industries and confluence of industrial effluents along the coast through riverine input (Jayaraju et al., 2009; Table 2). The identical peaks of Fe and Mn are perfectly matched with Cu, Cr and Ni concentrations. It clearly suggests that these metals are typically controlled by skeletal accumulated organic phase. However, the metal profile trend is slightly depressed from a regular trend in Zn, Cd and Pb peaks. The concentration of Pb is probably derived from the application of alkyl lead gasoline in motor vehicles and mechanized boats and also from the fly ash from a thermal power plant. The variation in the metal accumulation also depends on the incorporation capability of reef skeletal composition via calcium substitution of metals or association of organic particulate matters with skeletal pores. The concentration of metals in the growth bands of coral reef is expressed as the Metal Selectivity Index (MSI)
MSI ¼
Absolute concentration of a metal ðskeletonÞ 100: Total concentration of all metals ðskeletonÞ
ð1Þ
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 2. Vertical distribution of metals in the coral core sample.
Fig. 3. XRD peaks of the reef skeletal accumulated insoluble residues.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
S. Krishnakumar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 4. EPSEM & EDAX of the reef skeletal accumulated insoluble residues.
and bio-fouling of the membrane surface (Nair et al., 2006). Bioaccumulation of metals will always be affected by site-specific differences in bioavailability. The metal affinity of the reef skeleton is ranked based on MSI in the following order Cr N Cd N Cu N Pb N Fe N Mn N Ni N Zn. The Pollution Load Index (PLI) was proposed by Tomlinson et al. (1980) for detecting metal pollutants and used to compare the pollution levels between different sites at different times. The PLI was calculated
Here, MSI is defined as the relative metal-accumulating capacity of a coral reef skeleton for a particular metal. The concentration of MSI value is presented in Table 1. The mean Metal Selectivity Index (MSI) value of each band is 11.54 for Fe, 14.37 for Mn, 15.61 for Cu, 3.95 for Cd, 1.32 for Cr, 16.15 for Ni, 9.24 for Pb, and 35.75 for Ni. The uptake and accumulation of metals depend not only on their chemical and physical properties but also on the temperature, turbulence, flow rate, water column,
Table 2 Heavy metal concentrations in the Gulf of Mannar and comparative worldwide studies of Porites sp. Station name
Porites species
Fe
Mn
Cu
Cd
Cr
Ni
Pb
Zn
Present study-Gulf of Mannar (avg) Gulf of Aquba (Al-Rousan et al., 2007) Daya Bay, Northern South China Sea (Chen et al., 2010) Tuticorin coast (Jayaraju et al., 2009) Nha Trang Bay, Vietnam (Nguyen et al., 2013) Pioneer Bay (Esslemont, 2000) Nelly Bay (Esslemont, 2000) Lakshadweep Archipelago (Anu et al., 2007)
Porites sp. Porites sp. Porites sp. P. andrewsi Porites sp. P. damicornis P. damicornis P. andrewsi P. contigua P. lutea Poritidae
1.64 14.49 78.54 48.25 36.77 NA NA 5.15 19.33 NA NA
2.02 0.35 1.77 8.53 2.9 NA NA 2.24 11.16 4.27 NA
3.46 3.88 NA 10.65 5.53 1.6 5.5 0.49 36.88 11.7 0.28
0.45 4.19 NA 7.21 0.01 0.09 0.09 2.13 11.16 0.097 0.054
0.26 NA NA 5.23 NA 44 21 4.33 15.6 1.08 NA
2.48 NA NA 72.2 NA 31 10 11.10 18.01 9.5 0.17
1.07 38.17 NA 28.3 0.24 0.24 0.19 24.18 3.33 1.02 0.27
4.47 7.32 3.57 2.51 NA 23 37 2.62 38.71 16.9 2.4
Dafangji Island, China (Peng et al., 2006) Heron and Wistari Reef–Great Barrier Reef, (St. John 1974)
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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Table 3 Bivariate Pearson correlations for metal concentration in Porites sp. in the study area. Parameters
Fe
Fe Mn Cu Cd Cr NI Pb Zn
1 .902⁎⁎ .825⁎⁎ .396⁎ .780⁎⁎ .769⁎⁎ .388⁎ .255
Mn 1 .888⁎⁎ .142 .803⁎⁎ .812⁎⁎ .174 .211
Cu
Cd
Cr
NI
Pb
Zn
1 .130 .693⁎⁎ .760⁎⁎ .152 .391⁎
1 −.015 .023 .778⁎⁎ .449⁎⁎
1
.958⁎⁎ .101 −.075
1 .190 .023
1
.580⁎⁎
1
⁎⁎ Correlation is significant at the 0.01 level (2-tailed). ⁎ Correlation is significant at the 0.05 level (2-tailed).
as a concentration factor of each metal with respect to the background level of the crust. The natural available metal concentrations are chiefly derived from natural sources, including river input and weathering of source rock types. According to Angulo (1996), PLI will able to give an estimate of metal contamination status for further assessment. The equation for calculating the PLI is shown below
PLI ¼ ðCF1 CF2 CF3 ……: CFn Þ1=n
ð2Þ
where Cfn is the concentration of metal n in the sample. The PLI values of the studied metals are presented in Table 1. The Pollution Load Index of the studied coral growth bands ranges from 0.59 to 2.77 with a mean value of 1.33. Low pollution index value was noticed in the year 1996 and 1997. The Pearson correlation matrix of the studied metals is shown in Table 3 and extracted factor (Principal Component Analysis) was used to decipher the metal association in the reef skeleton (Fig. 5). Moreover, the Principal Component Analysis (PCA) was useful for data reduction, and to determine the sources of variation between parameters (Güler et al., 2002). The PCA data sets of metals in the reef skeleton reveal that Fe, Mn, Ni, Cr and Cu are categorized under a single group (component 1) which are scored nearly 62.5% of the variance. This clearly
indicates that the above said metals are derived from the same source and moving together in the marine environment. Similarly 25% of variance (Pb and Cd) was observed under component 2 which shows that they are derived from metal leaching from anthropogenic sources. Pb and Cd are the primary indicators of human induced metal pollution in the marine environment (Krishnakumar et al., 2010). This is also supported for the above conclusion with maximum PCA score at component 2. Further Zn is categorized under component 3 with 12.5% of variance, which indicates that this element is derived from reef growth and their related process. Dendrogram plot was prepared using an average relationship linkage between the groups (Fig. 6). Fe, Mn, Ni, Cu, Cr and Zn are following the same trend and it is justified from PCA plot and correlation analysis. Moreover, the distribution of metal constituents is primarily controlled by Fe and Mn in the reef skeleton. Other reef associated metals such as Pb and Cd are derived from other sources like coastal developments and anthropogenic sources. Acknowledgement KK is thankful to the University Grant Commission, New Delhi and D.S Kothari Post Doctoral Cell, University of Pune. The present work is supported by UGC Dr. D.S.Kothari Post Doctoral Fellowship scheme (Ref No. F.4-2/2006 (BSR)/ES/13-14/0019). Authors are thankful to
Fig. 5. Principal component plot of metals in rotated space.
Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009
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Fig. 6. Dendrogram of the reef skeletal accumulated studied metals.
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Please cite this article as: Krishnakumar, S., et al., Metal concentrations in the growth bands of Porites sp.: A baseline record on the history of marine pollution in the Gulf of Mannar, India, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.10.009