Sodium is one of the poorly documented elements in the marine and estuarine sediments of the Indian coast. Sodium concentration in surface sediments collected during the pre monsoon varies from 2.43-5.39%, the average being 3.41%. Monsoon records an average of 3.53% with the concentration varying from 2.465.33% and post monsoon show an average of 3.82% with the variation from 2.65-5.44%. Seasonal variation for Na concentration ranges from 3.41 to 3.82 % with maximum during post monsoon. Potassium is a common rock-forming mineral and is associated with non-carbonate minerals in the coastal sediments. The more specific common mineral association of K is with the mica minerals and potash feldspars. Pre monsoon samples in the study area record an average of 1.00%, 1.05%, 1.53%, with the variation from 0.39 – 1.64%, 0.68 –1.41%, and 0.36-2.56% in pre monsoon, monsoon, and post monsoon respectively. The concentration of K in S7 and S8 is below 1 % and is the highest at S6 during post monsoon.Ca is normally present in silicate minerals at very low levels of 1%; hence, its contribution to sediment composition from detrital silicate minerals is relatively minor. The minor source of CaO in the sediments is from calcium rich shell material contributed by marine life. The larger shell fragments of more than 2 mm size were removed by sieving before analysis; hence, the contribution of Ca by shell fragments is substantially minimized. However, whole of the samples were used for CaCO₃ determination and so the total CaCO₃ content of the sample is much higher than the Ca content in the sample. Estimated concentration of Ca in pre monsoon shows an average of 4.27% with a variation of 2.62-6.20%; in monsoon it varies from 2.18-5.15% with an average of 3.91%; and in post monsoon, Ca records an average of 3.85% and ranges from 2.75-7.32%. The highest Ca concentration is recorded at S6 during post monsoon and pre monsoon seasons. During monsoon a maximum of 5.15% is recorded at S8. The concentration of Ca in the surface sediments is mostly of biogenic origin and mainly attributed to the abundance of skeletal components, which are dominated by mollusks, bryozoans, and foraminifers and, to a certain extent, to the inflow of seasonal rivers that enrich the Ca content.

Mg is present in silicate minerals at less than 1% concentration to as high as few tens of percent. In detrital silicate sediments, the Mg content is usually associated with certain phyllosilicates such as chlorites. Analytical results state an average value of 0.11% in pre monsoon, 0.13% in monsoon, and 0.10% in post monsoon. Mg in the samples varies from 0.04-0.22%, 0.07-0.23%, and 0.06-0.19% in pre monsoon, monsoon and post monsoon. The concentration is below 0.25%. Compared to other seasons, the Mg is found very much less during post monsoon season. Fe can be combined with a variety of anions to form complexes and minerals. The common mineral forms are present as silicates, oxides, sulphides and phosphates. Under a variety of natural environmental conditions, Fe also changes its oxidation state steadily with changes in the amount of oxygen and variations in pH conditions in the aqueous phases. Hence, this element provides useful information on the present and past depositional and environmental conditions (Buckley and Hargrave, 1989). Analytical results pertaining to the different seasons in the present study record an average of 1.56%, 1.54%, and 1.46% of Fe in pre monsoon, monsoon and post monsoon respectively. It varies from 1.42 to 1.61% in pre monsoon, 1.46 to 1.62% in monsoon and 0.96 to 1.64% in post monsoon.The iron concentration in the sediments shows a low value below 2% in all the seasons at all stations except at S6 (0.96%). The higher concentrations of Fe in the sediments are attributable to the contribution from detrital mineral grains supplied through adjacent rivers, in addition to precipitation of its dissolved species. The removal of dissolved riverborne iron by coagulation in estuaries is more common (Coonley et al., 1971; Holiday and Liss, 1976; Sholkovitz, 1976 and Boyle et al., 1977).The surface sediments clearly show that the concentration of P is the maximum at S1 in all the three seasons. In pre monsoon, P concentration varies from 0.10-0.49% with an average of 0.32%. In monsoon, it ranges from 0.38-0.77% with an average of 0.60% during post monsoon the average concentration of P is 0.65% and it varies from 0.43-0.83%.

Element/Al ratios of Pre monsoon, Monsoon and Post monsoon are presented in Table 6.

Estimated average values of Si/Al are 3.56%, 3.44%, and 3.50% for pre monsoon, monsoon and post monsoon respectively.There is not much variation between the stations during all the seasons. The mean values of Si/Al during the seasons are observed to be slightly lower than the upper crustal value of 3.83 (Taylor and McLennan, 1985). These values are produced due to different quartz and K-feldspar (Si/Al=3.1) contents relative to illite (Si/Al=1.7), the variations being induced by variable texture and amount of opaline silica (Calvert et al., 1993). In the study area, the samples with high Si/Al ratios are generally coarse grained and are manifested by a higher ratio of quartz and feldspar, as that of clays. A higher proportion of turbidite sands in these samples are, probably, the cause for higher ratios. Estimated Na/Al average in the sample indicates 0.41, 0.42, and 0.46 in pre monsoon and post monsoon respectively and the ratios show a variation of 0.30-0.89, 0.24-0.70, and 0.28-0.73 during different seasons. The Na/Al ratios are slightly higher than the CCV during all the seasons. Estimated K/Al ratios in the seasonal samples indicate average values of 0.12, 0.12 and 0.18 in pre monsoon, monsoon, and post monsoon respectively.Estimated ratios for Ca/Al in pre monsoon vary from 0.29-0.90 with 0.52 averages; in monsoon it varies from 0.25-0.72 with an average of (0.47) and in post monsoon it varies from 0.30-0.99 .The relatively higher Ca/Al ratio in the pre monsoon is mainly due to the higher CaCO₃ content and calcium-rich shell fragments. According to Zeller and Wray (1956), the high Ca/Al ratio could also be due to the precipitation and extraction of CaCO₃ separated by organisms in warm water in tropical regions. This is well supported by the high Ca/Al ratios in surface sediments of the present study. Estimated ratios of Mg/Al in the samples indicate average for pre monsoon and post monsoon as 0.01 while monsoon records 0.02.

Estimated average values of Fe/Al are 0.19, 0.18, and 0.17 for pre monsoon, monsoon and post monsoon respectively. In sediments free from authigenic Fe-bearing minerals, the Fe₂O₃/Al₂O₃ ratio is known to be reasonably constant at average of 0.18, as Fe is held in structural position with alumino-silicates (Calvert, 1976). Any iron exceeding the represented average Fe₂O₃/Al₂O₃ ratio may, therefore, be used as an approximate measure of authigenic minerals of iron and iron oxide coatings (on settling particles). Estimated P/Al ratios in pre monsoon vary from 0.01-0.06 with an overall average of 0.04 in monsoon, P/Al ratio varies from 0.04-0.10 with an average of 0.07. Post monsoon records an average of 0.08 and it ranges from 0.05-0.11. The relatively low P/Al ratios and the lack of relationship between P/Al and organic carbon suggest that organic contribution of P in these samples is of minor importance and that detrital phases mainly control the P content. These observations correlate well with earlier studies made on the slope regions off Mangalore to Ratnagiri on the west coast of India by Rao and Murty (1990), and on the east coast by Purnachandra Rao et al. (1998).If S1, S11 and S12 are excluded, a moderate increase of P/Al with increasing organic carbon concentration is observed in the samples. This suggests that P is at least partly controlled by organic supply. Hence, an additional P fraction must be present, which is likely to occur in estuarine samples because of the supply of detrital phosphorite from the neighbouring land or shelf.The major element concentrations can be summarized in the decreasing order as Si > Al > Ca > Na > K > Fe > P > Mg. There is not any change in the order with respect to different seasons.

The concentration of trace elements in the sediments is shown in Table 7. Mn is mostly found in trace elements in the lattice structures of most rock forming silicates or it occurs as major element in carbonates and oxides. Mn is precipitated as hydroxides in the estuarine and near shore areas as the less saline river water rich in Mn mixes with high saline low Mn seawater. However, the deposited Mn in sediments are re-dissolved in the pure water below the surface sediments due to the biogeochemical processes and it can also diffuse up to the oxidized sediment interface and can be precipitated as oxide or oxy-hydroxide (Buckley and Cranston, 1991). During monsoon season, Mn records a high concentration of 870 mg/kg at S4, located near the mouth of Serthalaikadu creek and a low concentration of 451.5 mg/kg at S7 (located between Serthalaikadu creek and Muthupet lagoon). In post monsoon, the high and low concentrations are observed at S8 (583.7 mg/kg) and at S6 (280.6 mg/kg) respectively. The pre monsoon concentration of Mn is more than that of monsoon and post monsoon. Generally, the concentration of Mn is high in the study area.

The geochemical reactions, which occur in near shore sediments, are mostly controlled by the physico-chemical conditions in the sediment water complex, in particular the redox potential. Hence, the low value of Mn at the riverine side and high value near the lagoonal side are due to the physicochemical characters of the adjacent rivers and wave action. The low input of river flow, stagnant nature of the water column might control the distribution of Mn in the Creek. Further, the relationship between sediment texture and Mn also indicates the same. The Mn content at the sediment water interface is found to be highly variable in the near shore region. Manganese is very sensitive to variations in redox conditions around +340 mV and is frequently exchanged between the solid and dissolved phase if the environment fluctuates between oxic and anoxic conditions (Blazer, 1982).The total Cr concentration in pre monsoon ranges from 6.00-13.20 mg/kg with an average of 8.19 mg/kg. Monsoon records an average, slightly lower (7.33mg/kg) than pre monsoon. S11, located near the mouth of Muthupet lagoon records a high value of 13.2 mg/kg and S2, close to Vedaranyam records a minimum value of 6 mg/kg during pre monsoon. During post monsoon a maximum and minimum of 84 mg/kg and 3.5 mg/ kg are recorded at S4 and S8 respectively. Samples collected during all seasons revealed the same kind of distribution pattern. In general, the concentration of Cr is high near the mouth of the estuary but less at the riverine end (Akkarapallivasal). Generally, these near shore sediments show very minimal concentration of manganese. Globally, the average concentration of Cr in river-borne solids transported in estuaries is relatively higher than that of near shore sediments (Aston and Chester, 1976).

Cu usually occurs in silicates at trace levels, but may precipitate as a major element in some specific sulphides, oxides and it also complexes readily with various organic components. Cu reveals an average of 34.52 mg/kgin premonsoon, 28.03 mg/kgin monsoon and 24.98 mg/kg in post monsoon respectively. Cu concentration varies from 28.90-41.90 mg/kg in pre monsoon, 20.80- 33.70 mg/kg in monsoon and 12.30-34.70 mg/kg in post monsoon. High and low concentrations of 41.9 mg/kg at S7 and 28.9 mg/kg at S2 are observed in pre monsoon where as a high concentration of 33.77 mg/kg at S6 and a low of 20.8 mg/kg at S10 are recorded in monsoon. Post monsoon shows a high of 34.7 mg/kg and a low of 12.3 mg/kg of Cu at S12 and S4 respectively. On an average, pre monsoon records the highest and post monsoon records the lowest. In general, Cu concentration is lesser than the continental crustal averages. Globally, the average concentration of Cu in river-borne solids transported in estuaries is relatively higher (2500 mg/kg) than that of near shore sediments (48 mg/ kg) (Aston and Chester 1976). The geochemical reactions, which occur in the near shore sediments, are mostly controlled by the physico-chemical conditions in the sediment water complex, in particular the redox potential.

The average concentration of Ni is 2000 mg/ kg in ultramafic rocks, 130 mg/kg in mafic rocks, 4.5 mg/kg in granitic rocks, 17 mg/kg in soils, 18 mg/kg in plant ash, and 1.5 ppb in fresh waters. Its siderophile associations are with Mg and Co in mafic and ultramafic rocks, and Co, Cu and Pb in sulphide deposits. It is present in mafic minerals. Its weathering products are Fe-oxides and nickeliferous silicates. Its aqueous species are Ni^2+. Nickel is relatively immobile, limited to co-precipitation with limonite and hydrolysis where pH > 6.5. The distribution of Ni in igneous rocks is, as for other metals, generally closely related to the distribution of Mg and Fe (Rankama and Sahama, 1950). Ni concentrations in the study area record an average value of 33.81 mg/kg in pre monsoon, 32.85 mg/kg in monsoon and 36.55 mg/kg in post monsoon. Ni concentration of 57.5 mg/kg is recorded during pre monsoon at S5 with the lowest concentration of 12.06 mg/kg at S6. Ni concentration is the highest at S5 during all the seasons with the lowest at S11.Only during monsoon, S6 shows the lowest concentration of Ni.

Cobalt is relatively scarce in the earth’s crust. The average concentration of Co in ultramafic rocks is 110 mg/kg, in mafic rocks 48 mg/kg, in granitic rocks 1 mg/kg, in soils 10 mg/kg, in plant ash 5 mg/kg, and in fresh water it is 0.1 ppb. Its chalcophile associations are Mg and Ni in mafic and particularly in ultramafic rocks. It is present in mafic minerals. Its weathering products are carbonates and hydroxides, adsorbed and coprecipitated Mn oxides or, to a less extent, Fe oxides. Its aqueous species are Co2+ and organic complexes. Cobalt is one of the more important trace elements in animal nutrition. Mobility of Co is intermediate, controlled mainly by adsorption and co-precipitation with Fe and Mn oxides. During pre monsoon Co concentration ranges from 7.5 mg/kg to 22.35 mg/kg at S5 the average being 14.45 mg/kg. Monsoon shows a range of 5.55 mg/kg at S6 to 23.55 mg/kg at S5 with an average of 13.78 mg/kg. During post monsoon the high and low concentration of 25.05 mg/kg at S6 and 5.25mg/kg at S4 occurs with an average of 16 mg/kg. There is not much variation in average Co concentration (13.78 to 16 mg/kg) during different seasons.Cobalt levels in surface sediments collected during three seasons and the corresponding average values are listed in Table 7. When compared with the average value of shale (19 mg/kg), Bulk Continental Crustal value (29 mg/kg) (Taylor and McLennan, 1985), and upper continental crustal value (17 mg/kg) (McLennan 2001), cobalt concentration is less in the sediments. The concentrations of cobalt in granites (1 mg/ kg), basalts (35 mg/kg), soil (8 mg/kg), limestone (0.1 mg/kg) and sandstone (0.3 mg/kg) (Bowen, 1979), which are the main lithogenic sources for metals in marine and marginal marine sediments, are compared with the results of the study area. The comparison shows that Co concentrations in the samples of the study area are lower than the values of the geological source materials for the marine sediments. This indicates that the concentration of Co present in the sediments of the study area is associated with lithogenic origin with little contribution from external sources. The concentration does not vary much. However, maximum values are observed at the S5. A slight increase is observed during post monsoon.

Pb occurs in the nature as Pb sulphide and it is extremely insoluble, especially under reducing conditions it is readily adsorbed by organic matter. Lead is generally toxic to vegetation and animal life when present in its ionic form. Mobility of Pb is relatively low, restricted by tendency for adsorption on to Mn-and Fe-oxides and insoluble organic matter, but assisted by formation of soluble organic complexes and anion complexes. Its chalcophile associations are Ag in precious metal deposits and Fe, Zn and Cu in many other sulphide deposits and F in rock forming silicates. It is present in mica and potash feldspar. Its weathering products are cerussite, anglesite, and pyromorphite, plumbojarosite over sulphide ores, and Mn- and Fe-oxides and pyromorphite in soils. Its aqueous species are Pb²⁺, PbCO₃, Pb (OH)⁺, Pb (OH) ₂, soluble organic matter and complex with Cl^- and HCO₃^-. The average Pb concentration in the study area in 45.54 mg/kg in pre monsoon, 47.29 mg/kg in monsoon, and 44.45 mg/kg in post monsoon. Pb concentration does not vary much during different seasons. During pre monsoon, the high concentration is recorded at S9 (52.62 mg/kg) located in between serthalaikadu and Muthupet lagoon. The lowest concentration (37.52 mg/kg) is shown at S6, serthalaikadu mouth. The high concentration is at S8 (54.54 mg/kg) and the low concentration (35.85mg/kg) is at S6. Post monsoon records a high value at S9 and a low value at S4. When compared with the average value of shale (20 mg/kg) and Bulk Continental Crustal value (8 mg/kg) (Taylor and McLennan, 1985), the lead concentration is higher in the sediments. The concentrations of lead in granites (24 mg/kg), basalts (3 mg/kg), limestone (8 mg/kg), soil (35 mg/kg) and sandstone (10 mg/kg) (Bowen, 1979) were compared with the sediments of the study area. It indicates that the lead concentrations of the samples of the study area are slightly higher than the values of geological source materials mentioned above.

Zinc is an essential trace metal and is an important component for plants and human. Its chalcophile associations are Cu, Pb, Ag, Au, Sb, As and Se in base metals and precious metal deposits, and Mg in some silicates. It is present in mafic minerals. Its weathering products are zinc sulphates, carbonates, hydrated silicates and zinc clay minerals over zinc sulphide ores, Fe^- and Mnoxides and organic matter in normal soils. Its aqueous species are variable partition between Zn²⁺, Zn (OH)₂, soluble organic complexes and floating live organisms. The mobility of Zn is moderately high, limited by its tendency to be adsorbed by MnO₂and by insoluble organic matter (Krauskopf, 1979). The spatial distribution patterns for the 3 periods indicate that there is much variation in the seasonal samples. Zinc concentration in the study area reveals an average of 90.65 mg/kg in pre monsoon, 72mg/kg in monsoon and 58.87 mg/kg in post monsoon. It ranges from 68.7 to 193.90 mg/kg during pre monsoon. During monsoon it ranges from 61.8 to 99.20 mg/kg and during post monsoon from 43.70 to 84.20 mg/kg. The concentration is the lowest during post monsoon season and the highest during pre monsoon season. The concentration is high at S3 except during post monsoon where S8 dominates.Trace element analysis of surface sediments during the three seasons of sampling shows the following trend: Pre monsoon Mn > Zn > Pb > Cu > Ni > Co >Cr ; Monsoon & Postmonsoon Mn >Zn > Pb >Ni >Cu > Co > Cr . It is seen that the pattern remains the same for monsoon and postmonsoon seasons.Normalization of trace elements with Al values was done for all samples.The metal/Al ratios and enrichment factors for pre monsoon, monsoon and post monsoon are presented in Tables 8, 9 and 10. The EF close to 1 point out the crustal origin, while those with factor >10 are considered to be of non-crustal source.

Mn/Al ratios in the study area range from 45.19 to 106.44 x 10^–4 (Average= 73.16 x 10^-4) during pre monsoon with the highest at S4. It ranges from 45.09 to 122.91 x 10^-4 (Average= 68.9 x 10^-4) in monsoon with the highest at S4. During post monsoon it ranges from 37.71 to 79.99 x10^-4 with an average of 54.58 x 10^-4 (highest at S8). The Mn/Al value is slightly higher during pre monsoon than in succeeding seasons. The ratio is higher than the average continental crustal value and average shale. The enrichment factor for pre monsoon, monsoon and post monsoon ranges from 0.47 to 1.11, 0.47 to 1.28 and 0.39 to 0.83 respectively. Cr/ Al ratios vary from 0.62 to 1.26 x10^-4 with respect to different stations during pre monsoon season with an average of 0.96 x 10^-4. It ranges from 0.61 to 1.07 x10^-4 during monsoon and 0.47 to 11.68 x 10^-4 during post monsoon with an average of 0.61 x 10^-4 & 1.66x10^-4 respectively. Cr/Al records monsoonal minimum and is high during post monsoon. High values are observed at S4 except during monsoon. Enrichment factor for Cr gives an average of 0.09 during pre monsoon, 0.08 in monsoon, and 0.16 in post monsoon.The calculated Cu/Al ratios in the study area record an average of 4.11x10^-4 (3.15 to 4.86x10^-4), 3.29x10^-4 (1.96 to 4.52x10^-4) and 2.90x10^-4 (1.71 to 4.22x10^-4) for pre monsoon, monsoon and post monsoon respectively. The enrichment factors range from 0.62 to 0.95 in pre monsoon, 0.38 to 0.89 in monsoon and 0.34 to 0.83 in post monsoon the mean Cu/Al values of surface sediments collected during the three seasons are lower than the values of upper continental crust confirming the lower enrichment of Cu in the present study. Ni/Al ratios vary from 1.24 to 6.14x10^-4, 1.34 to 5.83x10^-4, and 1.69 to 6.26x10^-4 with an average of 4.04x10^-4, 3.85x10^-4, and 4.31x10^-4 for pre monsoon, monsoon, and post monsoon respectively. Enrichment factors vary from 0.16 to 0.83, 0.17 to 0.76, and 0.22 to 0.81 in pre monsoon, monsoon and post monsoon respectively. Estimated Co/Al values for different seasons range from 0.90 to 2.57x10^-4, 0.59 to 2.29x10^-4, and 0.73 to 3.37x10^-4 for pre monsoon, monsoon and post monsoon respectively. Higher values are observed at S3 (2.57x 10^-4), S7 (2.27 x 10^-4) and at S6 (3.37 x10^-4) during pre monsoon, monsoon and post monsoon with an average of 1.71x10^-4, 1.60x10^-4, and 0.98x10^-4 respectively. Enrichment factor ranges from 0.47 to 1.35 in pre monsoon, 0.31 to 1.20 in monsoon and 0.38 to 1.77 in post monsoon.

An estimate of Pb/Al ratios for various seasons shows a variation of 3.84 to 6.99x10^-4, 3.80 to 7.59x10^-4, and 3.95 to 5.93x10^-4 respectively for pre monsoon, monsoon and post monsoon the average being 5.44x10^-4, 5.53x10^-4, and 5.21x10^-4 . Enrichment factors in the study area record an average of 2.72, 2.77, and 2.61 in pre monsoon, monsoon and post monsoon respectively. Zn/Al ratio in the seasonal samples ranges from 6.99 to 25.01x10^-4, 6.66 to 12.56x10^-4, and 5.37 to11.54x10⁴ with an average of 11.01x10^-4, 8.46x10^-4 and 6.86x10^-4 in pre monsoon, monsoon, and post monsoon respectively. Enrichment factor shows an overall average of 1.02, 0.78, and 0.64 with a variation of 0.65 to 2.33, 0.62 to 1.16, and 0.5 to 1.07 in pre monsoon, monsoon, and post monsoon respectively. The Zn/Al ratios show positive correlation with Mn/Al and Fe/Al indicating coprecipitation of Zn along with Fe^-, Mn and oxyhydroxides. The mean Zn/Al values of surface sediments collected during sampling periods are higher compared to the values of upper continental crust and average shale, confirming the enrichment of Zn in the study area. Comparison with the enrichment factor of average shale (Calvert and Pedersen, 1993) shows enrichment of Zn in the study area and the range from 1 to 4 indicates anthropogenic input of the element.It is interesting to note that enrichment factor values over the crust in the study area decreases in the following order for trace elements in different seasons:

Pre monsoon Pb > Zn> Co > Cu > Mn > Ni >Cr
Monsoon Pb > Co >Zn >Mn > Cu > Ni >Cr
Post monsoon Pb > Co >Zn > Cu > Mn > Ni >Cr

Manganese concentration, however, does not show any relationship with coarse fraction, fine fraction, organic matter and CaCO₃.The lithophile associations of Mn are Mg and Fe in silicates, under mafic minerals. In the present study, Mn does not show any relationship with Fe and Mg. Hence, the lithogenic contribution of Mn cannot be estimated because of its modification due to contamination from point and nonpoint sources. However, when compared with the average value of shale (850 mg/ kg) and Bulk Continental Crustal value (1400 mg/ kg) (Taylor and McLennan 1985), which are considered to be the main baseline for near shore sediments, the manganese concentration is less in the study area. The results of trace metals analysis are compared with those in other coastal regions around the world (Table 11).The major oxide data for surface sediments are plotted (Fig. 2). inAl₂O₃– CaO* 1 Na₂O–K₂O (A–CN–K) compositional space (molecular proportions). In the entire sediments plot on a trend parallel to the Al₂O₃– CaO*+Na₂O join, suggesting that the sediments represent the products from granite and charnockite sources (Fedo et al., 1996) (Fig. 3). Paleo-weathering conditions can also be determined with the help of a K₂O–Fe₂O3–Al₂O₃ ternary diagram (Wronkiewicz and Condie, 1989).The present study in comparison to the CIA of granite, typical illite, montmorillonite, average shale and kaolinite (ranges from Nesbitt and Young, 1982). Note that CIA for kaolinite is 100. CIA values for the sediments of the present study vary between 21 to 45 for pre monsoon, post monsoon and monsoon samples (Fig. 4).