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Heavy metal distribution in sediments of Muthupettai mangroves, south east coast of India

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Page 1: Heavy metal distribution in sediments of Muthupettai mangroves, south east coast of India

J. Ocean Univ. China (Oceanic and Coastal Sea Research) DOI 10.1007/s11802-011-1807-4 ISSN 1672-5182, 2011 10 (4): 385-390 http://www.ouc.edu.cn/xbywb/ E-mail:[email protected]

Heavy Metal Distribution in Sediments of Muthupettai Mangroves, South East Coast of India

B. Thilagavathi, K. Raja, Bandana Das, A. Saravanakumar, S. Vijayalakshmi, and T. Balasubramanian

CAS in Marine Biology, Faculty of Marine Sciences, Annamalai University, Tamilnadu, India

(Received November 18, 2010; revised April 5, 2011; accepted June 21, 2011) © Ocean University of China, Science Press and Springer-Verlag Berlin Heidelberg 2011

Abstract Core sediments from the Muthupettai mangroves on the southeast coast of India were analyzed for soil texture, total nitrogen, organic carbon, phosphorus and heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Zn and Cd). The distinct seasonal variation in the distribution of metals in the sediments was observed. The minimum concentration was recorded in river mouth and the maximum was in lagoon. High metal concentration in sediment was observed during monsoon and low concentration in summer. The total nu-trient in lagoon and river mouth was recorded in the range of 4.528 to 8.526 mg g-1 for organic carbon, 2.213 to 10.5 mg g-1 for nitro-gen and 0.824 to 7.22 mg g-1.

Key words mangroves; heavy metals; core sediment; soil texture; sediment nutrients

1 Introduction Mangrove wetlands found along the coastal zone act as

a barrier against cyclones, protect coastal erosion and provide good nursery ground for a number of commer-cially important aquatic organisms (Kathiresan and Bingham, 2001). Mangroves are woody plants growing in the inter-tidal zones of tropical and subtropical coastal rivers, estuaries and bays (Yim and Tam, 1999). Pollut-ants like oil, solid wastes and industrial wastes reaching mangrove environments can cause damage to mangrove roots that may affect the respiratory and osmoregulatory capabilities of the plant leading to death (Getter et al., 1981) and/or exert acute and chronic effects on aquatic organisms. Among pollutants, heavy metals have been of interest because of their toxicity, persistence, and preva-lence in the environment (Cosma et al., 1979). The sedi-ments in such areas have a large capacity to retain heavy metals from tidal waters, fresh water of rivers and storm water runoff. (Harbison, 1986; Lacerda et al., 1993; Tam and Wong, 1993, 1995, 2000). Mangrove sediments are anaerobic, rich in sulfide and organic matter content, fa-voring the retention of water borne heavy metal (Lacerda and Abrao, 1984). Enrichment of heavy metals in bottom sediments represents a critical measure on the health of any mangrove ecosystem. Studies on Muthupettai man-groves have been related to mangrove seedling, manage-ment, mature mangrove species, and documentation of

* Corresponding author. E-mail: [email protected]

degradation (Selvam, 2003). But little is known about how mangroves and the infaunal communities are af-fected by the distribution of heavy metals. General dis-tribution pattern as well as the cycling of heavy metal in the coastal waters is largely controlled by both abiotic and biotic parameters. Hence investigation of heavy metals in the sediment is essential to assess the extent of pollution. Moreover, sediment has aptly been called as a heavy metal trap (Chester and Stoner, 1974) as it eventually receives almost all the heavy metals which enter the aquatic environment (Greig and McGrath, 1977). The scavenging by suspending particles results in large con-centration of pollutants being retained in estuarine sedi-ments (Juracle and Prohic, 1986). Sediment samples have also been widely used to monitor heavy metal pollution in coastal areas (Shiber, 1980; Holmes, 1986; Langston, 1986; Kouadio and Trefry, 1987; Lynby and Brix, 1987; and Prohic and Kniewald, 1987). However, comprehen-sive information is lacking on the concentration of heavy metals such as iron, magnesium, manganese, lead, mer-cury, cadmium, copper and zinc in an estuary which re-ceives them from anthropogenic inputs. Hence as part of a wider investigation, the present study focuses on pre-senting initial baseline data on the level of heavy metal and whether current management practices are resulting in improved sediment quality for the restoration of Mu- thupettai lagoon mangroves in the southeast coast of India.

2 Materials and Methods Muthupettai mangroves (Lat 10˚25′N: Long 79˚39′E)

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are situated at the southernmost end of the Cauvery delta connected to Palk strait which opens to Bay of Bengal (Plate 1). The present study was carried out on the transi-tion zone between the two different environmental re-gions of dead mangrove forest and tidal mudflats where geochemical gradients and potential metal mobility changes are likely to be more significant, especially at the mouth of the creek, where it is connected with the open ocean. Core samples were collected with the help of a fiber boat across the mangrove region during January 2008 to December 2008, and two core sampling sites were selected for the present study. Lagoons were pre-ferred as the adjoining areas and draining sites for minor rivers, which flood during monsoon periods. A river mouth was selected as another sampling site to decipher the influence of tides and input from the coastal environ-ments. A PVC coring tube (6.3 cm diameter and 2.5 m length, pre-cleaned with acid), was used for the collection of core samples in lagoon and river mouth.

The percentage composition of sand, silt and clay in the sediment samples were determined by the combined sieving and pipette method of Krumbein and Pettijohn (1938). Sediment samples were transferred from the corer to clean polyethylene cover using cleaned plastic spatula. The triplicate sediment samples were collected and stored in frozen conditions for further analysis. The preserved sediment sub-samples were dried at 110oC to constant weight for estimation of metals. For extraction of Iron, magnesium, manganese, lead, mercury, cadmium, copper and zinc from the sediments, an improved acid digestion

procedure was adopted (Watling and Walting, 1981). The residue formed was then dissolved in 10 ml of 10% nitric acid solution and the same was aspirated into the AAS and the concentration quantified is expressed in µg/g. Textural studies for sand, silt, and clay were conducted by following the procedure of Ingram (1970). Determination of total organic carbon was done by the procedure of (Gaudette et al., 1974). Total nitrogen and total phospho-rus were analyzed by standard method (Chhatwal et al., 1974).

Plate 1. Study area map.

3 Results The heavy metals of Iron, Zinc, Magnesium, Manga

Fig.1 Heavy metals (Fe, Mg, Zn) distribution (µg g-1) in Lagoon and River mouth.

Fig.2 Heavy metals (Cd, Cr, Pb) distribution (µg g-1) in Lagoon and River mouth.

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Fig.3 Heavy metals (Mn, Ni, Hg) distribution in (µg g-1) Lagoon and River mouth.

Fig.4 The total nutrients (nitrogen, phosphorus and organic carbon) of (mg g-1) Lagoon and river mouth sediment.

nese, Cadmium, Chromium, Lead, Nickel, Mercury were found in the ranges of 628 to 4248μg g-1, 628 to 4248 μg g-1, 54.10 to 495.68μg g-1, 0.59 to 4.95 μg g-1, 10.74 to 48.53μg g-1, 16.64 to 76.25 μg g-1, 5.99 to 16.59 μg g-1, 11.6 to 62.54 μg g-1 and 11.6 to 62.54 μg g-1

respectively (Figs.1 to 3). The minimum concentration was recorded in river mouth and the maximum was recorded in lagoon sediments.

The nutrients at both stations were varied, from 4.528 to 8.526 mg g-1 (organic carbon), 2.213 to 10.5 mg g-1 (nitrogen) and 0.824 to 7.22 mg g-1 (phosphorus) (Fig.4). The minimum was recorded in river mouth and maximum was recorded in lagoon.

Percentage composition of sediment texture in lagoon and river mouth were varied from 88.73 to 99.58 % for

Fig.5 Percentage composition of sediment textural (sand, silt and clay) of Lagoon.

Fig.6 Percentage composition of sediment textural (sand, silt and clay) of River mouth.

clay 0.30 to 11.01 % for silt and 0.16 to 1.07 for sand (Figs.5-6), with clay and silt dominating in lagoon com-pared with the river mouth, but sand was dominating in river mouth. Among all the metals studied, Fe (r=0.859, P<0.01 and r =0.621), Cu (r=0.556, P<0.05 and r = 0.525, P<0.05) and Ni (r = 0.442, P<0.05, r = 0.478, P<0.05) showed significant positive correlation with silt and clay.

4 Discussion Textural data in both lagoon and river mouth regions

are presented as mud which combines silt and clay. Ob-servations reveal that there has been a pulsating supply of

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fine sediments into the mangrove-dominating lagoon be-cause the high-energy coastal environment of Palk bay promotes early flocculation of clay particles into the creek (Vasudevan and Seetaramaswamy, 1983). This can be confirmed by the domination of mud (90%) in the core sampling of the present study. The lack of substantial river input and the elongated shape of the creek are also responsible for the high mud content (Ergin and York, 1990). As the study area lies along the east-west trending coastline on the southeast coast of India, the marine input of mud is due to northerly current prevailing in Palk bay (Selvaraj et al., 2005). In the present study, nearly 99% of mud in lagoon was collected in the river mouth, which is selectively trapped by mangrove roots (Furukawa et al., 1997). The high mud content also indicates the prevalent hydrodynamics and presence of mangrove roots, which are well developed and retain the finer fraction with the dense grid of vertical pneumatophores and aeraial roots. This structure traps floating detritus and reduces flow, eventually creating conditions wherein suspended clay and silt particles settle in the creek itself (Jimenez and paez-osuna, 2001).

Nutrients are considered as one of the most important parameters in the mangrove environment in influencing growth, reproduction and metabolic activities of biotic components. Distribution of nutrients depends on season, tidal condition and freshwater inflow from land. Organic carbon can serve as an important tool in determining the status of food available to benthic fauna and indicates the extent to which the bottom is fertile for sustenance of microbes (Sahoo et al., 2008). In the present study total nutrients in both stations of lagoon and river mouth was recorded in the range of 4.528 to 8.526 mg g-1 for organic carbon, 2.213 to 10.5 mg g-1 for nitrogen and 0.824 to 7.22 mg g-1 for phosphorus. Our study agrees with the organic carbon content in the sediment samples of Bhi-tarkanika mangrove, i.e. 1.7mg g-1, 10.16mg g-1 and 19.20 mg g-1 in Thakurdia, Baraipur and Khola regions respec-tively (Sahoo et al., 2008), In Gulf of Kachchh –Gujarat mangroves area the organic carbon varied from 0.29% to 2.56% and the total inorganic phosphorus ranged between 0.12 mg g-1 and 1.97 mg g-1. Total nitrogen varied from 0.02 mg g-1 to 1.95 mg g-1 (Saravanakumar et al., 2008).

The nutrients and organic matter in the study area are derived more from autochanthnous sources and less from allochanthnous sources. The organic carbon is maximum in monsoon and minimum in summer. The peak values in monsoon could be attributed to the decomposition of mangrove detritus, litter and decomposition of dead or-ganisms. Evidently lower pH in the Bhagoda creek is mainly due to decomposition of organic material such as mangrove detritus and dead organisms (Badarudeen et al., 1996; and shriadah, 1999).

Earlier reports suggest that naturally occurruing ele-ments such as Cu, Mn, Fe, and Zn are essential micronu-trients for plants, but can become toxic at concentrations higher than the amount required for normal growth (Nies, 1999). In the present study, higher concentration of Mg and Cr might be due to the land drainage, irrigation

through channels and municipal wastes. The increase in concentration during monsoon and Premonsoon could be attributed to the peak agricultural activities due to the release of fresh water from the reservoirs. These drainage waters have high concentrations of heavy metals that en-ter the river and mix up with seawater. The concentration of zinc and magnesium in all the stations was found to increase during monsoon superseded by pre monsoon and to decrease in summer seasons. Zinc and magnesium al-ways have a tendency to couple with organic carbon de-composition of the mangrove vegetative remains which are found to release the accumulated heavy metals back to sediments and this process might be responsible for the strong association of zinc and magnesium with organic carbon (Badarudeen et al., 1996). Heavy metal cycling is a serious problem addressed in mangrove environment (Marchand et al., 2006; Pekey, 2006). In the present study high values of Mn, Fe and Ni in lagoon area could be ascribed to the high silt and clay contents that can adsorb metals by fine-grained particles. In comparison with the present study the higher concentrations of Al, Cu, and Ni in mangrove environement could the reason that high silt and clay contents can adsorb metals by fine grained parti-cles (Shriadah, 1999; Ranjan et al., 2008) In Muthupettai lagoon hundreds of vessels are used for fishing; this may be another reason for the higher concentration in the study area. The paints used for boats contain zinc, while antifouling paints contain Cu at appreciable levels (Goldberg, 1976). The present study compare with the Abu Dhabi mangroves, especially in metals and organic carbon, the levels and distributions of eight heavy metals in the sediments of four mangrove areas, namely Abu Dhabi, Umm al-Quwain, Ras al-Khaimah, and Khor Khuwair along the shoreline of the United Arab Emirates. The concentrations of the metals (µg g−1) as well as or-ganic carbon percentages scattered in the ranges: 3.12–6.94 for cadmium, 5.70–14.0 for cobalt, 8.28–18.9 for chromium, 5.31–29.4 for copper (mean 7.21), 28.8–169 for manganese, 14.8–109 for nickel, 13.2–49.8 for lead, 4.59–22.4 for zinc and ND–2.13 for organic carbon (Shriadah 1999). Among the heavy metals (Mn, Cu, Zn, Ni, Pb, Fe, Cr, Cd) in mangrove sediments of Punta Mala Bay, Fe, Zn and Pb were in higher concentra-tions, which cause moderate to serious contamination within the bay, and thus pose a serious threat to the re-generation and growth of the mangrove (Defew et al., 2005). In Sabah mangrove sediment of Borneo Island, all the heavy metals have relatively higher concentration at high tide compared to low tide; tides control the wa-ter-flows, carrying the sediments into the mangrove forest (Praveena et al., 2010). Fe(r=0.859, P<0.01 and r =0.621, Cu (r=0.556, P<0.05 and r = 0.525, P<0.05) and Ni (r = 0.442, P<0.05, r = 0.478, P<0.05) showed significant positive correlation with silt and clay showed significant value with silt and clay this value comparable to man-grove and seagrass soils metals Al, Cu and Ni parameters positive correlation with silt and clay. This Indicates that these metals better bind with the finer particles than with the larger sand particles. Incidentally, the mangrove sta-

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tions with more silt and clay have higher concentrations of these metals (Nobi et al., 2010). In the present studies the lagoon coastal ecosystem of the Muthupettai is still in its pristine stage. As there are not enough studies for this part of the study area for comparing the sediment quality, the information collected through the present study can be used as baseline data for future monitoring of the pristine nature of the lagoon.

5 Conclusions The present study shows the interspecific variations in

heavy metal concentrations in river mouth and lagoon sediments and their sensitivity to season and water quality changes and environmental contamination of the lagoon environment. These baseline data can be used for regular ecological monitoring, considering the anthropogenic pollutants into the lagoon environment.

Acknowledgements The authors would like to thank Director and Dean,

Center of Advanced study in Marine Biology, and Faculty of Marine sciences for their providing facilities, fellow-ship and encouragement for our studies and we are also very grateful to Annamalai University authorities for giv-ing us this opportunities.

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(Edited by Ji Dechun)