Spatial and Temporal distribution of metals in sediments of a tropical lagoon, SW coast of India: Environmental Indicators ABSTRACT

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1 Spatial and Temporal distribution of metals in sediments of a tropical lagoon, SW coast of India: Environmental Indicators C.P. Priju 1 and A.C. Narayana 2 * 1 Department of Marine Geology & Geophysics Cochin University of Science & Technology, Cochin , India 2 Centre for Earth & Space Sciences University of Hyderabad, Hyderabad , India * of corresponding author: acnes@uohyd.ernet.in ABSTRACT In this paper, the spatial and temporal accumulation patterns and pollution load index of heavy metals in sediments of Vembanad Lake (VL) of Kerala coast, India, are discussed. Sediment cores were analyzed for texture, organic carbon, major and trace metal concentrations. In total, 164 samples (about 20 well-powdered sub-samples from each core) were analysed for metal concentrations. The mean concentrations and ranges of major (Fe, Mn & Al) and trace metals (Cu, Pb, Zn, Ni, Co, Cd & Cr) are discussed. The major and trace element data obtained were subjected to statistical analyses. Pollution load index (PLI) for the sediment samples was calculated from the concentration factor (CF) of each metal. Introduction In the last few decades, distribution and variations of heavy metals in space and time in aquatic environments have been extensively used as indicators of pollution and other environmental hazards. The gross chemical attributes of modern sediments provide potential information on various aspects such as sources, level of contamination, environmental hazards etc. Heavy metals are considered serious inorganic pollutants because of their toxic effects on biota (Alloway and Ayres, 1997; Plant et al., 2000). The processes of generation and contribution of pollutants in estuaries are a subject of environmental interest and extensively studied in the last decades (Apte et al., 1990; Birch et al., 1996; Owen and Sandhu, 2000; De Carlo and Anthony, 2002; Zachmann et al., 2009; Jernstrom et al., 2010). The present study is aimed at understanding the spatial and temporal distribution of major and traces metals in the sediment cores recovered from the Vembanad Lake, a lagoonal system, on the south-west coast of India (Fig.1), and to assess the environmental impact of industrial effluents discharged in to the watershed. 339

2 The core samples were analyzed for major and trace metal concentrations. In total, 164 sub-samples were digested as per the procedure given in Shapiro and Brannock (1962) and elemental contents were determined using Atomic Absorption Spectrophotometer (Model PERKIN ELMER 3110). Samples at 1 cm interval for the top 10 cm length of the core, and samples at every 5 cm interval for the remaining portion of the core were subjected to major and trace elemental analysis. Tomlinson s pollution load index (PLI) (Tomlinson et al., 1980) was calculated for the heavy metal data Results and Discussion Total Organic Carbon (TOC) content ranges from 0-56 g kg -1. The central and southern sectors of the lagoon recorded high TOC content (3-56 g kg -1 ) compared to that of the northern sector (< 27 g kg -1 ). The top portions of cores exhibit higher TOC content compared to that of bottom portions. Fe and Mn contents in the cores vary from % and from µg g - 1 respectively. High Mn content is found in the top portions (0-10 cm) of all cores, and most of the cores show decreasing trend towards down core. Copper content ranges between µg g -1. Cores from the northern sector of the lake exhibit low Cu content (5-21 µg g -1 ) compared to the cores from central and southern sectors. Nickel content ranges from µg g -1. Generally, Ni content is higher in the cores from the central and southern sectors of the lagoon. Cobalt content in the cores ranges from 0-52 µg g -1. In general, Co content varies in down core. Cores (VC-23 & 24) from the northern sector of the lagoon exhibit less Co content compared to other cores. Zinc content ranges from µg g -1. Significant down core variations are observed in cores. Overall Pb content ranges between µg g -1 and is mostly recorded from the top portions of the cores (0-15 cm). Cr ranges from µg g -1. In general, less Cr content is recorded in core sediments of the northern sector compared to that of central and southern sectors. Cadmium content is low (0-16 µg g -1 ) in all the cores, but slightly enriched in the surface portions of the cores. Spatially, Cd content is higher in the cores adjacent to Cochin inlet compared to other areas of the lake

3 Fig.1 Study area showing the locations of core samples. The distribution pattern of major and trace metals in the core sediments of the Vembanad Lake revealed significant spatial and vertical variations. It is found that the 341 3

4 deposition rate of heavy metals in the lake increases with time. Spatially the metals are more concentrated in the sediments of central and southern sectors of the lake, which can be attributed to anthropogenic activities. The grain size analysis reveals that the metals are accumulated in the fine-grained sediments along with higher organic carbon content. This suggests that lithogenic nature also plays an important role in enrichment of metals. The proximity to the major heavy metal sources and the higher organic sewage with finer size particles can be attributed for the metal enrichment in the central sector of the Lake. The metals Zn, Pb and Cd are mainly enriched in the southern part of the northern sector, which is proximal to the industrial establishments. A gradual increase in the concentration of Fe & Mn towards the southern parts of the lagoon is conspicuous. The downcore distribution of metals in the lake sediments suggests metal enrichment in the top 5-10 cm of the sediment column. Towards the bottom portions, the metal contents show a decreasing trend. Sediment cores located near the industrial segments show distinctly higher metal content throughout the core length. The organic matter content is higher in the lake sediments proximal to the river mouths in the northern and southern sectors of the lagoon. The correlation coefficients and scatter diagram of the metals, TOC and Mz show a strong interrelationship between Fe, Cu, Ni & Mz as well as Zn & Cd. The factor and cluster analysis show similar grouping of metals (Table 1). The pollution load index (PLI) of the core sediments revealed that three segments of the lake, that are enriched in pollutants - one is near the mouth of southern arm of Periyar River, second in the central sector, south of Ernakulam, and the third, the southern part of the lake. The PLI values range from < 1, in the northern most area of the lake, to 2-4 in the central area, and in the southern sector. High PLI value (4) is recorded for the lake sediments along the mouth of southern arm of Periyar River, on which various chemical industries are lcoated. Summary and Conclusion The distribution patterns of major and trace metals in core sediments of the Vembanad Lake reveal significant spatial and temporal variations. Spatially the metals are mainly concentrated in the sediments of central and southern sectors of the lake, and can be attributed 342 4

5 to anthropogenic input. The down core metal distribution in the lake sediments exhibits enrichment of metals in the top 5-10 cm of the cores, whereas towards the bottom of the cores the metal contents show a decreasing trend. This suggests that the recent increasing trends in anthropogenic activities are responsible for the enrichment in the upper portions of the cores. The pollution load index reveals that the pollutants are enriched near the mouth of southern arm of Periyar River, central sector and southern sector of the lake. References Alloway, B.J., Ayres, D.C., 1997, Chemical principles of environmental pollution: 2nd. Ed., Blackie Academic and Professional, Chapman and Hall, London, 395pp. Plant, J., Smith, D., Smith, B., Williams, L., 2000, Environmental geochemistry at the global scale: Journal of Geological Society of London, 157, Apte, S.C., Gardner, M.J., Gunn, A.M., Ravenscroft, J.E., Vale, J., 1990, Trace metals in the Severn estuary: A reappraisal: Marine Pollution Bulletin, 21, Birch, G.F., Evenden, D., Teutsch, M.E., 1996, Dominance of point source in heavy metal distributions in sediments of a major Sydney estuary (Australia): Environmental Geology, 28(4), Owen, R.B., Sandhu, N., 2000, Heavy metal accumulation and anthropogenic impacts on Tolo Harbour, Hongkong: Marine Pollution Bulletin, 40(2), De Carlo, E.H., Anthony, S.S., 2002, Spatial and temporal variability of trace element concentrations in a sub-tropical water shed, Honolulu, Hawaii: Applied Geochemistry, 17, Zachmann, D.W., Mohanti, M., Treutler, H.C., Scharf, B., 2009, Assessment of element distribution and heavy metal contamination in Chilika Lake Sediments (India): Lakes & Reservoirs: Research and Management, 14, Jernstrom, J., Lehto, J., Dauvalter, V.A., Hatakka, A., Leskinen, A., Paatero, J., 2010, Heavy metals in bottom sediments of Lake Umboxero in Murmansk Region, Russia: Environmental Monitoring and Assessment, 161, Shapiro, L., Brannock, W. W., 1962, Rapid chemical analysis of silicate, carbonate and phosphate rocks: U.S. Geological Survey Bulletin, 1144A, 56. Tomlinson, D. L., Wilson, J. G., Harris, C. R., Jeffney, D. W., 1980, Problems in the assessment of heavy metals levels in estuaries and the formation of pollution index: Helgol. Wiss. Meeresunters, 33,

6 Table 1. Correlation matrix of heavy and trace metals, TOC and mean size of the core samples (n=159) Fe Al Mn Cu Ni Co Zn Pb Cr Cd Mz TOC Fe 1.00 Al Mn Cu Ni Co Zn Pb Cr Cd Mz TOC

7 Fig.2. Scatter diagram showing interrelationship of metals, Mz and TOC 345 7