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Geospatial risk assessment and trace element concentration in reef associated sediments, northern part of Gulf of Mannar biosphere reserve, Southeast Coast of India
Marine Pollution Bulletin xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
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Geospatial risk assessment and trace element concentration in reef associated sediments, northern part of Gulf of Mannar biosphere reserve, Southeast Coast of India S. Krishnakumara,⁎, S. Ramasamya, T. Simon Peterb, Prince S. Godsonc, N. Chandrasekard, N.S. Mageshe a
Department of Geology, University of Madras, Guindy campus, Chennai 600025, India Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 62701, India Department of Environmental Sciences, University of Kerala, Kariavattom campus, Thiruvananthapuram 695581, India d Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 627012, India e Department of Geology, Anna University, Chennai 600025, India b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Geospatial risk assessment Sediment pollution index Trace elements Gulf of Mannar Coral reef ecosystem protection
Fifty two surface sediments were collected from the northern part of the Gulf of Mannar biosphere reserve to assess the geospatial risk of sediments. We found that distribution of organic matter and CaCO3 distributions were locally controlled by the mangrove litters and fragmented coral debris. In addition, Fe and Mn concentrations in the marine sediments were probably supplied through the riverine input and natural processes. The Geo-accumulation of elements fall under the uncontaminated category except Pb. Lead show a wide range of contamination from uncontaminated-moderately contaminated to extremely contaminated category. The sediment toxicity level of the elements revealed that the majority of the sediments fall under moderately to highly polluted sediments (23.07–28.84%). The grades of potential ecological risk suggest that predominant sediments fall under low to moderate risk category (55.7–32.7%). The accumulation level of trace elements clearly suggests that the coral reef ecosystem is under low to moderate risk.
Coral reef assemblages are affected by a wide range of environmental conditions, including wave energy (Montaggioni, 2005), physicochemical parameters (Hubbard, 1986; Kleypas, 1996), freshwater and nutrients through riverine input (Lirman and Fong, 2007), and the presence of metal and organic contaminants in the reef environment (Krishnakumar et al., 2017). Human activities and coastal developments can result in increased supply of pollutants and suspended sediments from anthropogenic and terrestrial sources to the reef environment, thus reducing light and affecting the primary productivity and coral reef growth (Telesnicki and Goldberg, 1995; Rousan et al., 2016). The supply of pollutants in the form of heavy metals is transported to the marine environment as dissolved species in water or in association with suspended sediments (Saouter et al., 1993). These discharged pollutants are subsequently deposited and accumulated in bottom sediments because of complex physical and chemical processes or mechanisms (Leivouri, 1998). The sediment incorporated with heavy metals may return to the water column through the remobilization process even after external sources have been eliminated (Schlekat et al., 1992; Jonathan et al., 2004). The sources of sediments in coastal
⁎
areas is river discharges, suspended particulate matter in the oceanic water column, particles derived from aeolian transport and biogenic matter or chemical precipitates. Such uncomfortable marine environment in the reef condition may lead to reduction in coral growth and indirectly affect coral reef associated species including reef fishes. Earlier research has been performed on multicentury climatic records through isotopic proxies to document related variations (ENSO), rainfall, sea surface temperature variations (Phinney et al., 2006) and El Nino events, ocean acidification (Kleypas et al., 1999), and so on. Moreover, more recent findings indicate that coral reefs are not only threatened by increase in temperatures, but also by ocean acidification (Gattuso et al., 1999; Kleypas et al., 1999). Recent work performed by national and international workers also focused on the effect of recent coastal developments and anthropogenic effect on coral reef ecosystem through metal accumulation in recent coral species and growth bands of Porites coral skeleton (Jayaraju et al., 2009; Krishnakumar et al., 2015). Gulf of Mannar Marine National Park (GOMMNP) consists of 21 coral islands and its 10 km buffer zone was declared as a Biosphere
Corresponding author. E-mail address: [email protected] (S. Krishnakumar).
http://dx.doi.org/10.1016/j.marpolbul.2017.08.042 Received 19 April 2017; Received in revised form 11 August 2017; Accepted 17 August 2017 0025-326X/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Krishnakumar, S., Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.08.042
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Reserve by the Government of India in 1989. GOMMNP covers an area of 10,500 km2 of ocean, islands, and the adjoining coastline. The coastal buffer zone includes seaweed communities, coral reefs and mangrove forests. This park is known to harbor over 117 hard corals and reef associated marine species. This study area experiences high temperatures from January to May and heavy rainfall due to monsoons from October to December especially during the northeast monsoon period. The Gulf of Mannar receives sediments from the east flowing rivers of Tamil Nadu state, the west coast of India through Kanyakumari and Palk Bay (Chandramohan et al., 2001; Saravanan and Chandrasekar, 2010). Almost 77.8% of this ecosystem is occupied by reef building coral (Hermatypes), and 22.2% of the reef is made of nonreef building coral (Ahermatypes). The seaward side of the coral islands consists of exposed coral/beach rock terraces and reef flats. The exposed reef flats are covered by calcareous lithic sand, and this flat is partially or fully submerged under seawater during high tides. The aim of the work was to assess the geospatial risk of reef associated sediments of the northern part of the Gulf of Mannar Biosphere Reserve, Southeast coast of India. The sampling location was fixed using a hand held GPS (Garmin eTrex GPS), and grid sampling pattern method was followed. The surface sediment was collected from 52 locations around the coral islands of the northern part of the Gulf of Mannar (Fig. 1). The surface sediments were collected using a Van Veen grab surface sediment sampler. Pre-cleaned polyethylene sampling bags were used for sample collection and properly numbered for geochemical analysis. The samples were kept in a hot air oven at 60 °C to remove the moisture content. Calcium carbonate (CaCO3) and trace element analyses were performed as suggested by Loring and Rantala (1992). Organic carbon (OC)
Table 1 Comparison of MESS 2 certified values for total trace elements. Elements
Fe Cr Mn Ni Cu Zn Cd Pb
MESS 2 Obtained value
Certified value
% Recovered
4.25 104.1 322.6 45.3 33.2 153 0.23 21.9
4.34 105 324 46.9 33.9 159 0.24 22.3
97.93 99.14 99.57 96.59 97.94 96.23 95.83 98.21
concentration was determined by exothermic heating and oxidation with potassium dichromate and concentrated H2SO4. Excess amount of dichromate was titrated with 0.5 N ferrous ammonium sulfate solution (Gaudette et al., 1974). The powdered sediment sample (< 63 μm size; 0.5 g) was completely digested in a Teflon bomb using aqua regia (2 h at 120 °C; HNO3:HClO4:HF at − 3:2:1 ratio). The final digested solution was centrifuged at 200 RPM and diluted to 50 mL (Yang et al., 2012). The dilution factor was finally multiplied by elemental concentration. The concentrations of the selected elements (Fe, Mn, Pb, Zn, Cu, Cr and Ni) were analyzed by Atomic Absorption Spectrophotometer (Model no - ELICO SL 194) at the Centre for Geo-technology, Manonmaniam Sundaranar University, Tirunelveli. The accuracy of the present analysis was checked using the MESS-2 analytical sediment standard reference material, and the recoveries of the elements were almost equal to that of the certified values (Table 1). Laboratory results showed that
Fig. 1. Sample location map of the study area.
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Fig. 2. Spatial distribution map of CaCO3 and organic matter (OM) in reef associated surface sediments of the northern part of Gulf of Mannar.
Fig. 3. Spatial distribution map of Fe, Mn, Cu and Zn in reef associated surface sediments of the northern part of Gulf of Mannar.
ArcGIS 10.2. The inverse distance weighted (IDW) algorithm was used to interpolate the geochemical data spatially and to estimate the values between measurements (Magesh et al., 2013). The spatial distribution map of OM, CaCO3, Fe, Mn, and other trace element concentrations was plotted (Figs. 2 & 3). The OM distribution was locally controlled by the mangrove litters from the coral islands.
the recovery efficiency for the studied elements ranged from 95.83% to 99.57%. The detection limit of trace elements was 0.01 μg/g for Fe, Zn, Cr, Cu and Ni, 0.02 μg/g for Mn; and 0.05 μg/g for Pb. The results were statistically analyzed using computer-aided packages such as SPSS version 22 and Microsoft EXCEL-2013. The geospatial distribution of trace element contents was analyzed by spatial analysis module in 3
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Fig. 4. Spatial distribution map of Cr, Cu and Ni in reef associated surface sediments of the northern part of Gulf of Mannar.
Fig. 5. Stock plot for the geoaccumulation index (Igeo) of reef associated surface sediments.
Fig. 6. Stock plot for the contamination factor (CF) of reef associated surface sediments.
Similarly, CaCO3 concertation was mainly controlled by the calcareous lithic fragments and fragmented coral debris/coral sand (here the coral sand is defined as particles of size ranging from 2 to 64 mm). The southern part of the study area was enriched with calcareous composition, and the northern part was abandoned by argillaceous sediments.
The accretion of calcareous clay rich sediments in the northeastern part of the coral island was probably because of the protected nature of the coral islands coast and mainland. Fe and Mn concentrations in the marine sediments are probably supplied through the riverine input and natural processes (Fig. 3a & b). The maximum Fe concentration was noticed in few samples, and it may be due to the presence of Fe rich 4
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Fig. 7. Spatial map of the Pollution Load Index (PLI) of reef associated surface sediments.
Fig. 8. Spatial map of the sediment pollution index (SPI) of reef associated surface sediments.
lithic fragments. A moderate concentration of Mn (120–160 μg/g) was noticed throughout the studied region except few locations. The Cu and Zn concentrations ranged from below detection limit (BDL) to 313 μg/g and BDL to 324 μg/g, respectively (Fig. 3c & d). An elevated concentration of these elements was observed in a few locations. However, some abnormal concentrations may be due to the enrichment from the local pollutant sources. Cr and Ni concentrations ranged from BDL to 324 and 32 to 369 μg/g (Fig. 4a & b). The maximum Cr concentration was recorded away from the coral island's coast. However, the maximum Ni concentration was reported near the Kurusadai and Pullivasal
islands. An elevated level of lead was noticed in few places around the islands (Fig. 4c). The reported Pb concentration may be because of coal incinerating power plants, commercial coal handling harbor activities in the southern part of the Gulf of Mannar and the application of leaded petrol around the coral ecosystem. Several workers have examined the enrichment factor (EF) for the assessment of contamination in various environmental conditions. Here, the EF was calculated by dividing the ratio of the normalizing element by the same ratio found in the chosen baseline as follows.
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concentration of the element “n” of crustal average (Taylor and Mclennan, 1995). Concentrations of geochemical background are multiplied every time by 1.5 to allow content fluctuations in a given substance in the environment and the effect of very small anthropogenic activities. This calculation suggests seven geo-accumulation index classes. These are as follows 0–unpolluted; 0–1 unpolluted to moderately polluted; 1–2 moderately polluted; 2–3 moderately polluted to strongly polluted; 3–4 strongly polluted; 4–5 strongly polluted to extremely polluted; and > 5 extremely polluted. According to this index, all the studied elements fall under uncontaminated category. However, lead fall under the wide contamination category, which ranges from uncontaminated–moderately contaminated to extremely contaminated category (Fig. 5). The degree of elemental pollution in the soil was measured and compared using the Pollution Load Index (PLI) calculation (Tomlinson et al., 1980). Here, this index is applied to assess the pollution level of marine sediments. This index is based on the values of the concentration factors (CF) of each element. CF was calculated as follows:
Table 2 Indices and corresponding degrees of potential ecological risk (Hakanson, 1980). Eri value
Grades of ecological risk of single metal
RI value
Grades of potential ecological risk of the environment
Eri < 40 40 ≤ Eri < 80 80 ≤ Eri < 160 160 ≤ Eri < 320 Eri ≥ 320
Low risk Moderate risk Considerable risk High risk Very high risk
RI < 150 150 ≤ RI < 300 300 ≤ RI < 600 RI ≥ 600
Low risk Moderate risk Considerable risk Very high risk
(Metal Fe )sample
(
)
Metal Fe Background
(1)
The above calculation was proposed by Taylor (1964) to represent the average composition of the surficial rocks exposed to weathering. The contamination is categorized depending on the EF: 0–1 for background concentration or no enrichment, 1–3 for minor enrichment, 3–5 for moderate enrichment, 5–10 for moderately severe enrichment, 10–25 for severe enrichment, 25–50 for very severe enrichment, and > 50 for extremely severe enrichment. Fe and Mn enrichment levels were nearly equal to the background concentration (EF: 0.089–0.89). The range of enrichment was from background concentration to very severe for Cu (EF: 0–26.9), background concentration to severe for Zn and Ni (EF: 0–15.6 and 0.5–11.3), and background concentration to severe for Cr (EF: 0–13.7), followed by background concentration to extremely severe enrichment for Pb (EF: 0–326.7). The geo-accumulation index approach was used to measure the contamination level of sediments. This calculation was proposed by Muller and Suess, 1979. To perform this calculation, the present elemental concentration was compared with the continental crust value of the respective element as follows (Eq. (2)).
Igeo = Log2
Cn 1.5 × Bn
CF =
Cmetal Cbackground
(3)
PLI = (CF1 × CF2 × CF3 × …….×CFn )1
n
(4)
where CF < 1 refers to low contamination, 1 ≤ CF < 3 implies moderate contamination, 3 ≤ CF ≤ 6 indicates considerable contamination, and CF > 6 indicates very high contamination. Cu and Ni showed low to moderate contamination, while other elements showed low contamination level, except Pb. Lead extended from low contamination level to very high contamination level (Fig. 6). PLI estimates the degree of pollution with respect to all elements considered together in a particular sample location. In this studied data set, all the sediments fall in the low contamination to moderate contamination level, except few samples in terms of Ni and Zn concentration. PLI ranged from 0.57 to 1.60. According to the PLI classification, PLI < 1 indicates no pollution and PLI > 1 indicates polluted sediment (Fig. 7). The PLI suggests that nearly 42.03% of the samples fall under unpolluted category, and 57.69% of the samples are grouped under polluted category.
(2)
In the above equation, “Cn” is the concentration of the examined element “n” in the sediments and “Bn” is the geochemical background
Fig. 9. Spatial map of the Potential Ecological Risk Index (PERI) of reef associated surface Sediments.
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Table 3 Bivariate Pearson correlations for element concentrations in reef associated surface sediments. Parameters
Fe
Mn
Cr
Cu
Pb
Zn
Ni
CaCO3
OM
Fe Mn Cr Cu Pb Zn Ni CaCO3 OM
1.000
0.145 1.000
− 0.278a 0.127 1.000
− 0.134 0.151 − 0.094 1.000
− 0.059 0.181 − 0.080 − 0.222 1.000
0.057 0.043 0.154 − 0.130 0.001 1.000
−0.066 0.134 0.566b 0.108 0.054 0.036 1.000
0.180 0.250 0.069 0.043 0.069 0.185 0.085 1.000
0.119 0.234 0.085 0.029 0.147 −0.082 0.197 0.011 1.000
a b
Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed).
SPI =
∑ (EFm × Wm) ∑ Wm
EFm = Cn Cr
(5) (6)
To calculate the SPI values, the toxicity value of elements was assigned depending on their toxicities to the environment. Toxicity weight 1 was assigned for Cr and Zn, 2 for Cu and Ni and 5 for Pb, 30 for Cd (Hakanson, 1980). In the above equation, EFm is the ratio between the measured elemental concentration (Cn), the background elemental concentration of the continental crust (Cr), and Wm is the toxicity weight. From the SPI calculation, 0–2 = natural sediment, 2–5 = low polluted sediment, 5–10 = moderately polluted sediment, 10–20 = highly polluted sediment, and > 20 = dangerous sediment. The sediment toxicity level of the studied elements revealed that 13.4% of the samples are grouped as natural sediments, 11.53% as low polluted sediments, 23.07% as moderately polluted sediments, 28.84% as highly polluted sediments, and 23.07% as dangerous sediments (Fig. 8). Ecological risk (ER) index was originally developed by Hakanson (1980), and it is widely used in ecological risk assessments of heavy metals in sediments. Before calculating the Potential Ecological Risk Index (PERI), the risk index (RI) must be calculated. The Potential Ecological Risk Index is calculated using the following equation.
Fig. 10. Principal component plot of elements in rotated matrix.
i Cfi = CD CBi
(7)
Eri = Tri × Cfi
(8)
m
RI =
∑ Eri i=1
(9)
where, RI is the sum of the potential risk of individual elements, Eri is the potential risk of individual elements, Tri is the toxic-response factor for a given element, Cfi is the contamination factor, CDi is the present concentration of the element in sediments, and CBi is the background concentration of the element in sediments. Hakanson suggested the toxic response factor for every element. The studied element toxic response factors are 2 for Cr, 5 for Cu, 1 for Zn and Mn and 5 for Pb and Ni, respectively. In this calculation, the crustal average value was used as a background value (Taylor, 1964; Li et al., 1986). Hakanson suggested five categories of ecological risk index (Eri), and four categories of RI, which are listed in Table 2. The grade of ecological risk of single metal (Eri) suggests that all the elements fall under the low risk category. However, lead falls under the low-risk category to very high-risk category (Eri − 10.8 to 428.4). The grades of potential ecological risk of the coral reef environment for the elements suggest that 55.7% of the sediments fall under the low risk category, and 32.7% of the sediments are grouped under the moderate risk category, followed by 11.53% of the sediments under considerable risk category (Fig. 9). The toxic elements, even at low concentrations, may cause problems in fertilization, larval success, and mortality, cell damage to massive coral species and damage to the reef ecosystem (Reichelt-Brushett and Harrison, 2004; Krishnakumar et al., 2015).
Fig. 11. Dendrogram plot of reef associated surface sediments.
The sediment pollution index (SPI) calculation is generally performed to assess the level of pollution in the sediments with respect to elemental concentrations and their toxicity levels. SPI was calculated to understand the pollution level in the surface sediment of the coral reef environment. Singh et al. (2002) proposed this calculation methodology and it is shown below.
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Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.P., Langdon, C., Opdyke, B.N., 1999. Geochemical consequences of increased atmospheric carbon dioxide on coral reefs. Science 284, 118–120. Krishnakumar, S., Ramasamy, S., Magesh, N.S., Chandrasekar, N., Simon Peter, T., 2015. Metal concentrations in the growth bands of Porites sp.: a baseline record on the history of marine pollution in the Gulf of Mannar, India. Mar. Pollut. Bull. 101, 409–416. Krishnakumar, S., Ramasamy, S., Chandrasekar, N., Simon Peter, T., Godson, Prince S., Gopal, V., Magesh, N.S., 2017. Spatial risk assessment and trace element concentration in reef associated sediments of Van Island, southern part of the Gulf of Mannar, India. Mar. Pollut. Bull. 115, 444–450. Leivouri, M., 1998. Heavy metal contamination in surface sediment in the Gulf of Finland and comparison with the Gulf of Bothnia. Chemosphere 36, 43–59. Li, J., Zeng, B.W., Yao, Y.Y., Zhang, L.C., Qiu, C.Q., Qian, X.Z., 1986. Studies on environmental background levels in waters of Dongting Lake system. Environ. Sci. 7, 62–68 (in Chinese). Lirman, D., Fong, P., 2007. Is proximity to land-based sources of coral stressors an appropriate measure of risk to coral reefs? An example from the Florida Reef Tract Mar. Pollut. Bull. 54, 779–791. Loring, D.H., Rantala, R.T.T., 1992. Manual for the geochemical analyses of marine sediments and suspended particulate matter. Earth Sci. Rev. 32, 235–283. Magesh, N.S., Chandrasekar, N., Krishna Kumar, S., Glory, M., 2013. Trace element contamination in the estuarine sediments along Tuticorin coast — Gulf of Mannar, southeast coast of India. Mar. Pollut. Bull. 73, 355–361. Montaggioni, T., 2005. History of Indo-Pacific coral reef systems since the last glaciation: development patterns and controlling factors. Earth-Sci. Rev. 71, 1–75. Muller, P.J., Suess, E., 1979. Productivity, sedimentation rate, and sedimentary organic matter in oceans- I organic carbon preservation. Deep-Sea Res. 26, 1347–1362. Phinney, J.T., Hoegh-Guldberg, O., Kleypas, J., Skirving, W., Strong, A., 2006. Coral reefs and climate change: science and management. In: Coastal and Estuarine Studies 61. American Geophysical Union, Washington, DC. Reichelt-Brushett, A.J., Harrison, P.L., 2004. Development of a sublethal test to determine the effects of copper and lead on scleractinian coral larvae. Arch. Environ. Contam. Toxicol. 47, 40–55. Rousan, S.A., Al-Taani, Ahmed A., Rashdan, Maen, 2016. Effects of pollution on the geochemical properties of marine sediments across the fringing reef of Aqaba, Red Sea. Mar. Pollut. Bull. 110, 546–554. Saouter, E., Campbell, P.G.C., Ribeyre, F., Boudou, A., 1993. Use of partial extractions to study mercury partitioning on natural sediment particles - a cautionary note. Int. J. Environ. Anal. Chem. 54, 57–68. Saravanan, S., Chandrasekar, N., 2010. Potential littoral sediment transport along the coast of South Eastern Coast of India. Earth Sci. Res. J. 14 (2), 153–160. Schlekat, C.E., McGee, B.L., Reinharz, E., 1992. Testing sediment toxicity in Chesapeake Bay with the amphipod Leptocheirus plumulosus: an evaluation. Environ. Toxicol. Chem. 11, 225–236. Singh, M., Müller, G., Singh, I.B., 2002. Heavy metals in freshly deposited stream sediments of rivers associated with urbanization of the Ganga Plain India. Water Air Soil Pollut. 141, 35–54. Taylor, S.R., 1964. Abundance of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta 28, 1273–1285. Taylor, S.R., Mclennan, S.M., 1995. The geochemical evolution of the continental crust. Rev. Geophys. 33, 241–265. Telesnicki, G.J., Goldberg, W.M., 1995. Effects of turbidity on the photosynthesis and respiration of two south Florida reef coral species. Bull. Mar. Sci. 57, 527–539. Tomlinson, D.C., Wilson, J.G., Harris, C.R., Jeffrey, D.W., 1980. Problems in the assessment of heavy metals in estuaries and the formation pollution index. Helgol. Mar. Res. 33, 566–575. Yang, Y., Chen, F., Zhang, L., Liu, J., Wu, S., Kang, M., 2012. Comprehensive assessment of heavy metal contamination in sediment of the Pearl River estuary and adjacent shelf. Mar. Pollut. Bull. 64, 1947–1955.
The bivariate Pearson correlation matrix for elemental concentration in reef associated surface sediments is shown in Table 3. Principal component analysis followed by Varimax and Kaiser normalization was performed to extract the elemental composition and CaCO3 and OM variables. A significant correlation of 0.01 was noticed between Cr and Ni (0.566**). No significant relationship was observed among OM, CaCO3, and other elements. However, a significant association was observed between Fe and Mn, which can be observed in the principal component plot and the Dendrogram (Figs. 10 & 11). These results indicate that these two elements were probably derived and redistributed along the study area through the riverine process. The analytical results and the statistical relationship between the studied parameters clearly show that all the elemental compositions are supplied and redistributed through sediment transport from the southern part of the Gulf of Mannar. The continuous monitoring, proactive management approach of coral reef ecosystem, and resilience assessment of coral species could help in preserving the reefs and their associated ecosystem. Acknowledgement KK is thankful to the University Grant Commission, New Delhi for providing financial support through UGC Dr. D.S·Kothari Post Doctoral Fellowship scheme (Ref No. F.4-2/2006 (BSR)/ES/13-14/0019). The authors also thank the Principal Chief Conservator of Forest and Chief Wildlife Warden, Panagal Maligai, Chennai – 600 015, for providing the permission to carry out the field work and Dr.V.Gopal, UGC Kothari Post Doctoral Fellow, Department of Geology, Anna University for his assistance during the preparation of the spatial maps. References Chandramohan, P., Jena, B.K., Kumar, V.S., 2001. Littoral drift sources and sinks along the Indian coast. Curr. Sci. 81 (3), 292–297. Gattuso, J.P., Allemand, D., Frankignoulle, M., 1999. Photosynthesis and calcification at cellular, organismal and community levels in coral reefs: a review on interactions and control by carbonate chemistry. Am. Zool. 39, 160–183. Gaudette, H.E., Flight, W.R., Toner, L., Folger, D.W., 1974. An inexpensive titration method for the determination of organic carbon in recent sediments. J. Sediment. Petrol. 44, 249–253. Hakanson, L., 1980. An ecological risk index for aquatic pollution control. A sedimentological approach. Water Res. 14, 975–1001. Hubbard, D.K., 1986. Sedimentation as a control of reef development: St. Croix, USVI. Coral Reefs 5, 117–125. Jayaraju, N., Reddy, Sundara Raja, Reddy, K.R., 2009. Heavy metal pollution in reef corals of Tuticorin coast Southeast coast of India. Soil Sediment Contam. 18, 445–454. Jonathan, M.P., Rammohan, V., Srinivasalu, S., 2004. Geochemical variations of major and trace elements in recent sediments, off the Gulf of Mannar, the southeast coast of India. Environ. Geol. 45, 466–480. Kleypas, J.A., 1996. Coral reef development under naturally turbid conditions: fringing reefs near broad sound, Australia. Coral Reefs 15, 153–167.
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Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Geospatial risk assessment and trace element concentration in reef associated sediments, northern part of Gulf of Mannar biosphere reserve, Southeast Coast of India S. Krishnakumara,⁎, S. Ramasamya, T. Simon Peterb, Prince S. Godsonc, N. Chandrasekard, N.S. Mageshe a
Department of Geology, University of Madras, Guindy campus, Chennai 600025, India Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 62701, India Department of Environmental Sciences, University of Kerala, Kariavattom campus, Thiruvananthapuram 695581, India d Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli 627012, India e Department of Geology, Anna University, Chennai 600025, India b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Geospatial risk assessment Sediment pollution index Trace elements Gulf of Mannar Coral reef ecosystem protection
Fifty two surface sediments were collected from the northern part of the Gulf of Mannar biosphere reserve to assess the geospatial risk of sediments. We found that distribution of organic matter and CaCO3 distributions were locally controlled by the mangrove litters and fragmented coral debris. In addition, Fe and Mn concentrations in the marine sediments were probably supplied through the riverine input and natural processes. The Geo-accumulation of elements fall under the uncontaminated category except Pb. Lead show a wide range of contamination from uncontaminated-moderately contaminated to extremely contaminated category. The sediment toxicity level of the elements revealed that the majority of the sediments fall under moderately to highly polluted sediments (23.07–28.84%). The grades of potential ecological risk suggest that predominant sediments fall under low to moderate risk category (55.7–32.7%). The accumulation level of trace elements clearly suggests that the coral reef ecosystem is under low to moderate risk.
Coral reef assemblages are affected by a wide range of environmental conditions, including wave energy (Montaggioni, 2005), physicochemical parameters (Hubbard, 1986; Kleypas, 1996), freshwater and nutrients through riverine input (Lirman and Fong, 2007), and the presence of metal and organic contaminants in the reef environment (Krishnakumar et al., 2017). Human activities and coastal developments can result in increased supply of pollutants and suspended sediments from anthropogenic and terrestrial sources to the reef environment, thus reducing light and affecting the primary productivity and coral reef growth (Telesnicki and Goldberg, 1995; Rousan et al., 2016). The supply of pollutants in the form of heavy metals is transported to the marine environment as dissolved species in water or in association with suspended sediments (Saouter et al., 1993). These discharged pollutants are subsequently deposited and accumulated in bottom sediments because of complex physical and chemical processes or mechanisms (Leivouri, 1998). The sediment incorporated with heavy metals may return to the water column through the remobilization process even after external sources have been eliminated (Schlekat et al., 1992; Jonathan et al., 2004). The sources of sediments in coastal
⁎
areas is river discharges, suspended particulate matter in the oceanic water column, particles derived from aeolian transport and biogenic matter or chemical precipitates. Such uncomfortable marine environment in the reef condition may lead to reduction in coral growth and indirectly affect coral reef associated species including reef fishes. Earlier research has been performed on multicentury climatic records through isotopic proxies to document related variations (ENSO), rainfall, sea surface temperature variations (Phinney et al., 2006) and El Nino events, ocean acidification (Kleypas et al., 1999), and so on. Moreover, more recent findings indicate that coral reefs are not only threatened by increase in temperatures, but also by ocean acidification (Gattuso et al., 1999; Kleypas et al., 1999). Recent work performed by national and international workers also focused on the effect of recent coastal developments and anthropogenic effect on coral reef ecosystem through metal accumulation in recent coral species and growth bands of Porites coral skeleton (Jayaraju et al., 2009; Krishnakumar et al., 2015). Gulf of Mannar Marine National Park (GOMMNP) consists of 21 coral islands and its 10 km buffer zone was declared as a Biosphere
Corresponding author. E-mail address: [email protected] (S. Krishnakumar).
http://dx.doi.org/10.1016/j.marpolbul.2017.08.042 Received 19 April 2017; Received in revised form 11 August 2017; Accepted 17 August 2017 0025-326X/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Krishnakumar, S., Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.08.042
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Reserve by the Government of India in 1989. GOMMNP covers an area of 10,500 km2 of ocean, islands, and the adjoining coastline. The coastal buffer zone includes seaweed communities, coral reefs and mangrove forests. This park is known to harbor over 117 hard corals and reef associated marine species. This study area experiences high temperatures from January to May and heavy rainfall due to monsoons from October to December especially during the northeast monsoon period. The Gulf of Mannar receives sediments from the east flowing rivers of Tamil Nadu state, the west coast of India through Kanyakumari and Palk Bay (Chandramohan et al., 2001; Saravanan and Chandrasekar, 2010). Almost 77.8% of this ecosystem is occupied by reef building coral (Hermatypes), and 22.2% of the reef is made of nonreef building coral (Ahermatypes). The seaward side of the coral islands consists of exposed coral/beach rock terraces and reef flats. The exposed reef flats are covered by calcareous lithic sand, and this flat is partially or fully submerged under seawater during high tides. The aim of the work was to assess the geospatial risk of reef associated sediments of the northern part of the Gulf of Mannar Biosphere Reserve, Southeast coast of India. The sampling location was fixed using a hand held GPS (Garmin eTrex GPS), and grid sampling pattern method was followed. The surface sediment was collected from 52 locations around the coral islands of the northern part of the Gulf of Mannar (Fig. 1). The surface sediments were collected using a Van Veen grab surface sediment sampler. Pre-cleaned polyethylene sampling bags were used for sample collection and properly numbered for geochemical analysis. The samples were kept in a hot air oven at 60 °C to remove the moisture content. Calcium carbonate (CaCO3) and trace element analyses were performed as suggested by Loring and Rantala (1992). Organic carbon (OC)
Table 1 Comparison of MESS 2 certified values for total trace elements. Elements
Fe Cr Mn Ni Cu Zn Cd Pb
MESS 2 Obtained value
Certified value
% Recovered
4.25 104.1 322.6 45.3 33.2 153 0.23 21.9
4.34 105 324 46.9 33.9 159 0.24 22.3
97.93 99.14 99.57 96.59 97.94 96.23 95.83 98.21
concentration was determined by exothermic heating and oxidation with potassium dichromate and concentrated H2SO4. Excess amount of dichromate was titrated with 0.5 N ferrous ammonium sulfate solution (Gaudette et al., 1974). The powdered sediment sample (< 63 μm size; 0.5 g) was completely digested in a Teflon bomb using aqua regia (2 h at 120 °C; HNO3:HClO4:HF at − 3:2:1 ratio). The final digested solution was centrifuged at 200 RPM and diluted to 50 mL (Yang et al., 2012). The dilution factor was finally multiplied by elemental concentration. The concentrations of the selected elements (Fe, Mn, Pb, Zn, Cu, Cr and Ni) were analyzed by Atomic Absorption Spectrophotometer (Model no - ELICO SL 194) at the Centre for Geo-technology, Manonmaniam Sundaranar University, Tirunelveli. The accuracy of the present analysis was checked using the MESS-2 analytical sediment standard reference material, and the recoveries of the elements were almost equal to that of the certified values (Table 1). Laboratory results showed that
Fig. 1. Sample location map of the study area.
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Fig. 2. Spatial distribution map of CaCO3 and organic matter (OM) in reef associated surface sediments of the northern part of Gulf of Mannar.
Fig. 3. Spatial distribution map of Fe, Mn, Cu and Zn in reef associated surface sediments of the northern part of Gulf of Mannar.
ArcGIS 10.2. The inverse distance weighted (IDW) algorithm was used to interpolate the geochemical data spatially and to estimate the values between measurements (Magesh et al., 2013). The spatial distribution map of OM, CaCO3, Fe, Mn, and other trace element concentrations was plotted (Figs. 2 & 3). The OM distribution was locally controlled by the mangrove litters from the coral islands.
the recovery efficiency for the studied elements ranged from 95.83% to 99.57%. The detection limit of trace elements was 0.01 μg/g for Fe, Zn, Cr, Cu and Ni, 0.02 μg/g for Mn; and 0.05 μg/g for Pb. The results were statistically analyzed using computer-aided packages such as SPSS version 22 and Microsoft EXCEL-2013. The geospatial distribution of trace element contents was analyzed by spatial analysis module in 3
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Fig. 4. Spatial distribution map of Cr, Cu and Ni in reef associated surface sediments of the northern part of Gulf of Mannar.
Fig. 5. Stock plot for the geoaccumulation index (Igeo) of reef associated surface sediments.
Fig. 6. Stock plot for the contamination factor (CF) of reef associated surface sediments.
Similarly, CaCO3 concertation was mainly controlled by the calcareous lithic fragments and fragmented coral debris/coral sand (here the coral sand is defined as particles of size ranging from 2 to 64 mm). The southern part of the study area was enriched with calcareous composition, and the northern part was abandoned by argillaceous sediments.
The accretion of calcareous clay rich sediments in the northeastern part of the coral island was probably because of the protected nature of the coral islands coast and mainland. Fe and Mn concentrations in the marine sediments are probably supplied through the riverine input and natural processes (Fig. 3a & b). The maximum Fe concentration was noticed in few samples, and it may be due to the presence of Fe rich 4
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Fig. 7. Spatial map of the Pollution Load Index (PLI) of reef associated surface sediments.
Fig. 8. Spatial map of the sediment pollution index (SPI) of reef associated surface sediments.
lithic fragments. A moderate concentration of Mn (120–160 μg/g) was noticed throughout the studied region except few locations. The Cu and Zn concentrations ranged from below detection limit (BDL) to 313 μg/g and BDL to 324 μg/g, respectively (Fig. 3c & d). An elevated concentration of these elements was observed in a few locations. However, some abnormal concentrations may be due to the enrichment from the local pollutant sources. Cr and Ni concentrations ranged from BDL to 324 and 32 to 369 μg/g (Fig. 4a & b). The maximum Cr concentration was recorded away from the coral island's coast. However, the maximum Ni concentration was reported near the Kurusadai and Pullivasal
islands. An elevated level of lead was noticed in few places around the islands (Fig. 4c). The reported Pb concentration may be because of coal incinerating power plants, commercial coal handling harbor activities in the southern part of the Gulf of Mannar and the application of leaded petrol around the coral ecosystem. Several workers have examined the enrichment factor (EF) for the assessment of contamination in various environmental conditions. Here, the EF was calculated by dividing the ratio of the normalizing element by the same ratio found in the chosen baseline as follows.
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concentration of the element “n” of crustal average (Taylor and Mclennan, 1995). Concentrations of geochemical background are multiplied every time by 1.5 to allow content fluctuations in a given substance in the environment and the effect of very small anthropogenic activities. This calculation suggests seven geo-accumulation index classes. These are as follows 0–unpolluted; 0–1 unpolluted to moderately polluted; 1–2 moderately polluted; 2–3 moderately polluted to strongly polluted; 3–4 strongly polluted; 4–5 strongly polluted to extremely polluted; and > 5 extremely polluted. According to this index, all the studied elements fall under uncontaminated category. However, lead fall under the wide contamination category, which ranges from uncontaminated–moderately contaminated to extremely contaminated category (Fig. 5). The degree of elemental pollution in the soil was measured and compared using the Pollution Load Index (PLI) calculation (Tomlinson et al., 1980). Here, this index is applied to assess the pollution level of marine sediments. This index is based on the values of the concentration factors (CF) of each element. CF was calculated as follows:
Table 2 Indices and corresponding degrees of potential ecological risk (Hakanson, 1980). Eri value
Grades of ecological risk of single metal
RI value
Grades of potential ecological risk of the environment
Eri < 40 40 ≤ Eri < 80 80 ≤ Eri < 160 160 ≤ Eri < 320 Eri ≥ 320
Low risk Moderate risk Considerable risk High risk Very high risk
RI < 150 150 ≤ RI < 300 300 ≤ RI < 600 RI ≥ 600
Low risk Moderate risk Considerable risk Very high risk
(Metal Fe )sample
(
)
Metal Fe Background
(1)
The above calculation was proposed by Taylor (1964) to represent the average composition of the surficial rocks exposed to weathering. The contamination is categorized depending on the EF: 0–1 for background concentration or no enrichment, 1–3 for minor enrichment, 3–5 for moderate enrichment, 5–10 for moderately severe enrichment, 10–25 for severe enrichment, 25–50 for very severe enrichment, and > 50 for extremely severe enrichment. Fe and Mn enrichment levels were nearly equal to the background concentration (EF: 0.089–0.89). The range of enrichment was from background concentration to very severe for Cu (EF: 0–26.9), background concentration to severe for Zn and Ni (EF: 0–15.6 and 0.5–11.3), and background concentration to severe for Cr (EF: 0–13.7), followed by background concentration to extremely severe enrichment for Pb (EF: 0–326.7). The geo-accumulation index approach was used to measure the contamination level of sediments. This calculation was proposed by Muller and Suess, 1979. To perform this calculation, the present elemental concentration was compared with the continental crust value of the respective element as follows (Eq. (2)).
Igeo = Log2
Cn 1.5 × Bn
CF =
Cmetal Cbackground
(3)
PLI = (CF1 × CF2 × CF3 × …….×CFn )1
n
(4)
where CF < 1 refers to low contamination, 1 ≤ CF < 3 implies moderate contamination, 3 ≤ CF ≤ 6 indicates considerable contamination, and CF > 6 indicates very high contamination. Cu and Ni showed low to moderate contamination, while other elements showed low contamination level, except Pb. Lead extended from low contamination level to very high contamination level (Fig. 6). PLI estimates the degree of pollution with respect to all elements considered together in a particular sample location. In this studied data set, all the sediments fall in the low contamination to moderate contamination level, except few samples in terms of Ni and Zn concentration. PLI ranged from 0.57 to 1.60. According to the PLI classification, PLI < 1 indicates no pollution and PLI > 1 indicates polluted sediment (Fig. 7). The PLI suggests that nearly 42.03% of the samples fall under unpolluted category, and 57.69% of the samples are grouped under polluted category.
(2)
In the above equation, “Cn” is the concentration of the examined element “n” in the sediments and “Bn” is the geochemical background
Fig. 9. Spatial map of the Potential Ecological Risk Index (PERI) of reef associated surface Sediments.
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Table 3 Bivariate Pearson correlations for element concentrations in reef associated surface sediments. Parameters
Fe
Mn
Cr
Cu
Pb
Zn
Ni
CaCO3
OM
Fe Mn Cr Cu Pb Zn Ni CaCO3 OM
1.000
0.145 1.000
− 0.278a 0.127 1.000
− 0.134 0.151 − 0.094 1.000
− 0.059 0.181 − 0.080 − 0.222 1.000
0.057 0.043 0.154 − 0.130 0.001 1.000
−0.066 0.134 0.566b 0.108 0.054 0.036 1.000
0.180 0.250 0.069 0.043 0.069 0.185 0.085 1.000
0.119 0.234 0.085 0.029 0.147 −0.082 0.197 0.011 1.000
a b
Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed).
SPI =
∑ (EFm × Wm) ∑ Wm
EFm = Cn Cr
(5) (6)
To calculate the SPI values, the toxicity value of elements was assigned depending on their toxicities to the environment. Toxicity weight 1 was assigned for Cr and Zn, 2 for Cu and Ni and 5 for Pb, 30 for Cd (Hakanson, 1980). In the above equation, EFm is the ratio between the measured elemental concentration (Cn), the background elemental concentration of the continental crust (Cr), and Wm is the toxicity weight. From the SPI calculation, 0–2 = natural sediment, 2–5 = low polluted sediment, 5–10 = moderately polluted sediment, 10–20 = highly polluted sediment, and > 20 = dangerous sediment. The sediment toxicity level of the studied elements revealed that 13.4% of the samples are grouped as natural sediments, 11.53% as low polluted sediments, 23.07% as moderately polluted sediments, 28.84% as highly polluted sediments, and 23.07% as dangerous sediments (Fig. 8). Ecological risk (ER) index was originally developed by Hakanson (1980), and it is widely used in ecological risk assessments of heavy metals in sediments. Before calculating the Potential Ecological Risk Index (PERI), the risk index (RI) must be calculated. The Potential Ecological Risk Index is calculated using the following equation.
Fig. 10. Principal component plot of elements in rotated matrix.
i Cfi = CD CBi
(7)
Eri = Tri × Cfi
(8)
m
RI =
∑ Eri i=1
(9)
where, RI is the sum of the potential risk of individual elements, Eri is the potential risk of individual elements, Tri is the toxic-response factor for a given element, Cfi is the contamination factor, CDi is the present concentration of the element in sediments, and CBi is the background concentration of the element in sediments. Hakanson suggested the toxic response factor for every element. The studied element toxic response factors are 2 for Cr, 5 for Cu, 1 for Zn and Mn and 5 for Pb and Ni, respectively. In this calculation, the crustal average value was used as a background value (Taylor, 1964; Li et al., 1986). Hakanson suggested five categories of ecological risk index (Eri), and four categories of RI, which are listed in Table 2. The grade of ecological risk of single metal (Eri) suggests that all the elements fall under the low risk category. However, lead falls under the low-risk category to very high-risk category (Eri − 10.8 to 428.4). The grades of potential ecological risk of the coral reef environment for the elements suggest that 55.7% of the sediments fall under the low risk category, and 32.7% of the sediments are grouped under the moderate risk category, followed by 11.53% of the sediments under considerable risk category (Fig. 9). The toxic elements, even at low concentrations, may cause problems in fertilization, larval success, and mortality, cell damage to massive coral species and damage to the reef ecosystem (Reichelt-Brushett and Harrison, 2004; Krishnakumar et al., 2015).
Fig. 11. Dendrogram plot of reef associated surface sediments.
The sediment pollution index (SPI) calculation is generally performed to assess the level of pollution in the sediments with respect to elemental concentrations and their toxicity levels. SPI was calculated to understand the pollution level in the surface sediment of the coral reef environment. Singh et al. (2002) proposed this calculation methodology and it is shown below.
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Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.P., Langdon, C., Opdyke, B.N., 1999. Geochemical consequences of increased atmospheric carbon dioxide on coral reefs. Science 284, 118–120. Krishnakumar, S., Ramasamy, S., Magesh, N.S., Chandrasekar, N., Simon Peter, T., 2015. Metal concentrations in the growth bands of Porites sp.: a baseline record on the history of marine pollution in the Gulf of Mannar, India. Mar. Pollut. Bull. 101, 409–416. Krishnakumar, S., Ramasamy, S., Chandrasekar, N., Simon Peter, T., Godson, Prince S., Gopal, V., Magesh, N.S., 2017. Spatial risk assessment and trace element concentration in reef associated sediments of Van Island, southern part of the Gulf of Mannar, India. Mar. Pollut. Bull. 115, 444–450. Leivouri, M., 1998. Heavy metal contamination in surface sediment in the Gulf of Finland and comparison with the Gulf of Bothnia. Chemosphere 36, 43–59. Li, J., Zeng, B.W., Yao, Y.Y., Zhang, L.C., Qiu, C.Q., Qian, X.Z., 1986. Studies on environmental background levels in waters of Dongting Lake system. Environ. Sci. 7, 62–68 (in Chinese). Lirman, D., Fong, P., 2007. Is proximity to land-based sources of coral stressors an appropriate measure of risk to coral reefs? An example from the Florida Reef Tract Mar. Pollut. Bull. 54, 779–791. Loring, D.H., Rantala, R.T.T., 1992. Manual for the geochemical analyses of marine sediments and suspended particulate matter. Earth Sci. Rev. 32, 235–283. Magesh, N.S., Chandrasekar, N., Krishna Kumar, S., Glory, M., 2013. Trace element contamination in the estuarine sediments along Tuticorin coast — Gulf of Mannar, southeast coast of India. Mar. Pollut. Bull. 73, 355–361. Montaggioni, T., 2005. History of Indo-Pacific coral reef systems since the last glaciation: development patterns and controlling factors. Earth-Sci. Rev. 71, 1–75. Muller, P.J., Suess, E., 1979. Productivity, sedimentation rate, and sedimentary organic matter in oceans- I organic carbon preservation. Deep-Sea Res. 26, 1347–1362. Phinney, J.T., Hoegh-Guldberg, O., Kleypas, J., Skirving, W., Strong, A., 2006. Coral reefs and climate change: science and management. In: Coastal and Estuarine Studies 61. American Geophysical Union, Washington, DC. Reichelt-Brushett, A.J., Harrison, P.L., 2004. Development of a sublethal test to determine the effects of copper and lead on scleractinian coral larvae. Arch. Environ. Contam. Toxicol. 47, 40–55. Rousan, S.A., Al-Taani, Ahmed A., Rashdan, Maen, 2016. Effects of pollution on the geochemical properties of marine sediments across the fringing reef of Aqaba, Red Sea. Mar. Pollut. Bull. 110, 546–554. Saouter, E., Campbell, P.G.C., Ribeyre, F., Boudou, A., 1993. Use of partial extractions to study mercury partitioning on natural sediment particles - a cautionary note. Int. J. Environ. Anal. Chem. 54, 57–68. Saravanan, S., Chandrasekar, N., 2010. Potential littoral sediment transport along the coast of South Eastern Coast of India. Earth Sci. Res. J. 14 (2), 153–160. Schlekat, C.E., McGee, B.L., Reinharz, E., 1992. Testing sediment toxicity in Chesapeake Bay with the amphipod Leptocheirus plumulosus: an evaluation. Environ. Toxicol. Chem. 11, 225–236. Singh, M., Müller, G., Singh, I.B., 2002. Heavy metals in freshly deposited stream sediments of rivers associated with urbanization of the Ganga Plain India. Water Air Soil Pollut. 141, 35–54. Taylor, S.R., 1964. Abundance of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta 28, 1273–1285. Taylor, S.R., Mclennan, S.M., 1995. The geochemical evolution of the continental crust. Rev. Geophys. 33, 241–265. Telesnicki, G.J., Goldberg, W.M., 1995. Effects of turbidity on the photosynthesis and respiration of two south Florida reef coral species. Bull. Mar. Sci. 57, 527–539. Tomlinson, D.C., Wilson, J.G., Harris, C.R., Jeffrey, D.W., 1980. Problems in the assessment of heavy metals in estuaries and the formation pollution index. Helgol. Mar. Res. 33, 566–575. Yang, Y., Chen, F., Zhang, L., Liu, J., Wu, S., Kang, M., 2012. Comprehensive assessment of heavy metal contamination in sediment of the Pearl River estuary and adjacent shelf. Mar. Pollut. Bull. 64, 1947–1955.
The bivariate Pearson correlation matrix for elemental concentration in reef associated surface sediments is shown in Table 3. Principal component analysis followed by Varimax and Kaiser normalization was performed to extract the elemental composition and CaCO3 and OM variables. A significant correlation of 0.01 was noticed between Cr and Ni (0.566**). No significant relationship was observed among OM, CaCO3, and other elements. However, a significant association was observed between Fe and Mn, which can be observed in the principal component plot and the Dendrogram (Figs. 10 & 11). These results indicate that these two elements were probably derived and redistributed along the study area through the riverine process. The analytical results and the statistical relationship between the studied parameters clearly show that all the elemental compositions are supplied and redistributed through sediment transport from the southern part of the Gulf of Mannar. The continuous monitoring, proactive management approach of coral reef ecosystem, and resilience assessment of coral species could help in preserving the reefs and their associated ecosystem. Acknowledgement KK is thankful to the University Grant Commission, New Delhi for providing financial support through UGC Dr. D.S·Kothari Post Doctoral Fellowship scheme (Ref No. F.4-2/2006 (BSR)/ES/13-14/0019). The authors also thank the Principal Chief Conservator of Forest and Chief Wildlife Warden, Panagal Maligai, Chennai – 600 015, for providing the permission to carry out the field work and Dr.V.Gopal, UGC Kothari Post Doctoral Fellow, Department of Geology, Anna University for his assistance during the preparation of the spatial maps. References Chandramohan, P., Jena, B.K., Kumar, V.S., 2001. Littoral drift sources and sinks along the Indian coast. Curr. Sci. 81 (3), 292–297. Gattuso, J.P., Allemand, D., Frankignoulle, M., 1999. Photosynthesis and calcification at cellular, organismal and community levels in coral reefs: a review on interactions and control by carbonate chemistry. Am. Zool. 39, 160–183. Gaudette, H.E., Flight, W.R., Toner, L., Folger, D.W., 1974. An inexpensive titration method for the determination of organic carbon in recent sediments. J. Sediment. Petrol. 44, 249–253. Hakanson, L., 1980. An ecological risk index for aquatic pollution control. A sedimentological approach. Water Res. 14, 975–1001. Hubbard, D.K., 1986. Sedimentation as a control of reef development: St. Croix, USVI. Coral Reefs 5, 117–125. Jayaraju, N., Reddy, Sundara Raja, Reddy, K.R., 2009. Heavy metal pollution in reef corals of Tuticorin coast Southeast coast of India. Soil Sediment Contam. 18, 445–454. Jonathan, M.P., Rammohan, V., Srinivasalu, S., 2004. Geochemical variations of major and trace elements in recent sediments, off the Gulf of Mannar, the southeast coast of India. Environ. Geol. 45, 466–480. Kleypas, J.A., 1996. Coral reef development under naturally turbid conditions: fringing reefs near broad sound, Australia. Coral Reefs 15, 153–167.
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