Indian Journal of Marine Sciences Vol. 30, June 2001, pp. 75-80

Sediment characteristics of Poonthura estuary (southwest coast of ) in relation to pollution

K S Anila Kumary School of Applied Life Sciences, Mahatma Gandhi University Regional Centre, Pathanamthitta 689 645, , India and P K Abdul Azis & P Natarajan Department of Aquatic Biology & Fisheries, University of Kerala, Beach P.O., 695 007, Kerala, India Received 17 August 2000, revised 27 January 2001

Texture, redox potential and organic carbon of sediments in Poonthura estuary, Thiruvananthapuram, presently exposed to sewage pollution were evaluated over a period of one year. Textural study revealed the presence of highest percentage of finer particles at the sheltered upstream stations. Oxidation-reduction potential varied between −211 and +156. Strong negative potentials recorded from the most polluted stations while freshwater and oceanic stations always recorded positive values. Organic carbon widely varied between 2.4 to 83.3 mg/g, and showed enrichment always at the polluted zone. Organic carbon content was more than the prescribed limit for unpolluted estuaries at some stations and reflects the level of pollution in the estuary. Significant variation in organic carbon and redox potential during the monsoon season shows that better dilution can diminish the high organic load to a great extent.

Sediments are indicators of the quality of overlying of untreated sewage from the disposing area leaches water and its study is a useful tool in the assessment into the estuary through the canal. The seriousness of of the status of environmental pollution. The level of this waste disposal problem has been realized lately organic carbon in sediments is reported to be a but no steps have been taken to study the effect of reliable index of nutrient regeneration and the productivity of a water body. Redox potential is a readily obtained description of organic matter within the sediment and of its oxidizing or reducing power. Oxidation-reduction activities at the sediment-water interface bear marked influence upon the estuarine chemistry and upon the type of organisms present in the sediment. Although the components and composition of sediments have received much attention, most of the work in India relates to the texture and organic contents of marine sediments1-5 and not much information is available on the estuarine material6-8. Poonthura estuary and the lower reaches of (8° 25’-8° 30’ N latitude and 76° 55’- 77° 00’ E longitude) on the south-west coast of India (Fig. 1) near to Thiruvananthapuram city, is facing enormous load of untreated domestic wastes emanating from the fastly growing Thiruvananthapuram city over the last few years. The city sewage farm is located at Muttathara on the bank Fig. 1—Map of the Poonthura estuary, with study sites (St. I - of Parvathy-Puthanar canal which joins the estuary Karimbuvila, II - Moonnattumukku, III - Edayar, IV - Panathura, about 2.4 km down to Muttathara and a huge quantity V - Poonthura) 76 INDIAN J. MAR. SCI., VOL. 30, JUNE 2001

pollution except for the fragmentary work of Anila corer (5.5 cm internal diameter and 45 cm long). Kumary & Abdul Azis9. The present paper deals with These samples were transferred separately to clean, the sediment characteristics such as texture, redox dry polythene containers, homogenized well and were potential and organic carbon of the sediments in brought to the laboratory for analysis. Readings of Poonthura estuary and discusses the extent of redox potential were taken as soon as the samples pollution in the estuary. were brought to the laboratory using inert platinum electrode connected top pH-Eh meter (Pearson & Materials and Methods Stanley)10. A portion of each of these samples was Five stations, almost equidistant from one another dried at 60-70°C and pulverised to estimate the which representing different ecological conditions, organic carbon11. The oven-dried samples were were selected in the estuary for regular monitoring subjected to textural study by sieving and pipette (Fig. 1). Station I (Krimbuvila) representing a riverine method following Krumbein & Pettijohn12. station is comparatively free from sewage pollution and is exposed to freshwater influx. Station II Results and Discussion (Moonnattumukku) is located in the western segment The textural study revealed that, silt and clay were of the estuary where the sewage drains open directly the predominant fractions at stations I and II, whereas into the estuary and is heavily polluted. Station III the sand fraction was predominant at stations III, IV (Karimbuvila) represents the interior segment of the and V (Table 1). The percentage of fine fraction was estuary where the sewage is comparatively diluted. maximum (65%) at station II. Further, the sand Station IV (Panathura) lies in the estuary near the fraction shows an increasing trend and the fine estuary mouth into the Arabian Sea and station V is fraction shows decreasing trend from stations III to V. a typical beach station located outside the estuary In estuaries generally fine mud get deposited near the mouth. The depth of these stations varied head and other sheltered regions, while along the from 0.5 to 3.5 m. main channel and at the mouth coarser sediments are Sediment samples (triplicate) were collected from deposited. Weak tidal currents in the upstream and the all these stations at monthly intervals for a period of heavy land drainage could be the reason for the one year (February 1992-January 1993) using a metal dominance of silt at station I. However, the mixing up

Table 1—Monthly variation in percentage eight of sediments grain size composition at different stations St no. Sediment Feb Mar Apr May June July Aug Sept Oct Nov Dec Jan type

I Sand 29.25 32.50 41.21 27.85 51.55 42.35 22.30 31.65 28.73 36.78 52.25 46.85 Silt 65.46 61.35 56.85 64.75 39.28 46.83 76.52 62.25 55.25 60.95 44.72 45.85 Clay 5.29 6.15 1.94 7.40 9.17 10.82 1.18 6.10 16.02 2.27 3.03 7.30

II Sand 22.10 38.65 26.38 32.40 41.25 36.12 38.15 37.85 35.28 39.85 38.13 33.58 Silt 70.67 42.88 38.31 29.55 52.35 58.75 55.29 40.55 52.25 50.95 48.64 50.38 Clay 7.23 18.47 35.31 38.05 6.40 5.13 6.56 21.60 12.47 9.20 13.23 16.04

III Sand 48.50 56.78 42.15 57.54 49.88 79.37 58.45 60.15 52.83 48.15 59.35 44.18 Silt 41.95 40.65 34.83 31.87 47.74 18.55 38.15 27.43 44.54 44.94 39.18 46.30 Clay 9.55 2.57 23.02 10.59 2.38 2.08 3.40 12.42 2.63 6.91 1.47 9.52

IV Sand 63.35 55.95 59.29 74.75 93.25 100 81.58 80.15 62.75 76.52 53.43 41.75 Silt 30.63 40.35 34.24 24.25 6.75 0.00 10.20 17.45 36.85 23.20 40.58 53.25 Clay 6.02 3.70 6.47 1.00 0.00 0.00 8.22 2.40 0.40 0.28 5.99 5.00

V Sand 72.00 84.15 59.90 95.00 100 100 95.00 90.80 100 96.00 100 90.50 Silt 10.80 12.35 28.50 5.00 0.00 0.00 3.50 7.55 0.00 2.80 0.00 2.50 Clay 17.20 3.50 11.60 0.00 0.00 0.00 1.50 1.65 0.00 1.20 0.00 7.00

ANILA KUMARY et al.: SEDIMENT CHARACTERISTICS OF POONTHURA ESTUARY 77

of great amount of sewage and the low energy Redox potential on one hand is related with the condition allowing the settling of fine particles distribution of oxygen and on the other hand, with the favored the enrichment of silt at station II. cycles of most of the important elements occurring in Oxidation-reduction potential (Eh) of sediments is water. Hence the redox state in a given place is a convenient index as to whether or not the sediment influenced to a great extent by hydrodynamical and is reducing in reaction. A positive Eh reading result sedimentological conditions13. Riverine zone was from a state tending towards oxidation, and a negative characterised by strong water flow and high Eh indicates a system causing reduction. The concentration of dissolved oxygen in the overlying predominance of positive values at stations I, IV and water, which could lead to the strongly oxygenated V, and negative values at stations II and III (Fig. 2), conditions. The oxygenated conditions at the marine suggests that the marine and riverine sediments are zone can be attributed to the highly porous medium of less reduced than interior estuarine sediments. The coarse sediment, which made a high oxygen diffusion monthly values varied between −211 (station II) and rate possible. The rearrangement of sediment by +156 mv (station V). Table 2 also shows that most strong hydrodynamic action could also be reduced sediments were present at station II and most contributing to healthier sediment at the marine oxidised conditions at station V. Variations between zone14. stations were significant at 1% level (ANOVA: A distinct seasonal influence was discernible on the DF = 4, F = 26.6201). variation in the oxidation-reduction potential. All the

Fig. 2—Monthly variations of redox potential at the 5 stations 78 INDIAN J. MAR. SCI., VOL. 30, JUNE 2001

stations showed least values of the potential during The presence of large quantities of hydrogen sulphide the premonsoon period (February-May) and the as well as the observed Eh value gives indirect highest values during the monsoon period (June- evidence of sulphide reduction and consequently of September) at stations I, II and III and during the bacterial process occurring within the sediment13. postmonsoon period (October-January) at stations IV Aiyer & Rajendran15 also have reported very low and V (Table 2). Statistical analysis also proves this values of Eh when high concentration of hydrogen by showing significant variation between seasons sulphide would be produced with total depletion of (ANOVA: DF = 2, F = 9.5159) and period within oxygen. seasons (ANOVA: DF = 11, F = 3.9417). Stations II The organic carbon values of the sediments were and III were characterised by reduced sediments, higher at station II compared to other stations (Fig. 3). especially during the premonsoon period. Degradation At station I, it varied from 8.4 to 26.8 mg/g in of the natural environment due to discharge of sewage December to March; at station II from 13.4 to 84.3 waste is the noticeable aspect at these stations. During mg/g in December to February; at station III, from 6.7 summer the fresh water influx was at its minimum to 37.5 mg/g in November to February; at station IV, and hence the chances of dilution of wastes in the from 7.8 to 30.8 mg/g in November to August and at water column was also less. The most surprising station V, from 2.5 to 15.4 mg/g in January to April. situation was observed at station II which being Variations in organic carbon between stations were located near the entrance of sewage fed water. significant at 1% level (ANOVA: DF = 4, F= Anaerobic condition with high hydrogen sulphide in 19.8005). Annual mean values were minimum at the overlying water was reported from this station9. stations I and V and maximum at the polluted

Table 2—Seasonal (n=4) and annual (n=12)mean valus of sediment Eh at different stations Station I Station II Station III Station IV Station V

Premonsoon 62.50± 6.96 -136.75± 23.07 -80.25± 11.04 73.25 15.42 110.00± 17.42 Monsoon 73.75± 7.89 20.50± 20.12 -22.25± 20.41 78.25± 8.38 130.25± 11.25 Postmonsoon 69.75± 13.76 -66.25± 57.80 -49.75± 50.49 84.25± 34.34 116.00± 28.01 Annual 68.67± 5.18 -60.83± 26.48 -50.75± 17.44 78.58± 11.21 118.75± 10.36

Fig. 3—Monthly variation of organic carbon at the 5 stations ANILA KUMARY et al.: SEDIMENT CHARACTERISTICS OF POONTHURA ESTUARY 79

Table 3—Seasonal (n=4) and annual (n=12) mean values of sediment organic carbon(mg/g) at different stations Station I Station II Station III Station IV Station V

Premonsoon 18.60± 3.3 62.40± 8.8 28.6± 4.8 24.1± 2.1 7.30± 2.8 Monsoon 12.90± 1.7 35.80± 3.2 16.3± 2.6 17.5± 4.6 7.3± 1.5 Postmonsoon 12.80± 2.5 20.10± 3.3 9.5± 1.2 9.6± 0.9 5.60± 1.3 Annual 14.80± 1.5 39.40± 5.8 18.1± 2.8 17.1± 2.3 6.1± 1.0 estuarine stations (Table 3). The upstream fresh water sediment is < 5% whereas in areas where organic station is mainly characterised by weak tidal currents pollutants are high16, organic carbon level often and high oxygen. These factors are detrimental to the exceeds 5%. Organic carbon in sediments in the ample supply and accumulation of organic carbon in present study exceeded this proposed limit during sediments16. The low organic carbon content in the summer months at station II with strong negative Eh beach (station V) can be ascribed to the sandy nature values. The accumulation of organic compound in the of the substratum and strong tidal currents, which form of sewage contributed to the high percentage of continually drain out available suspended organic organic carbon at station II where the sewage drains matter to the sea. Association of organic matter with open into the estuary whereas the dilution of sewage fine-grained sediment is well established4,8,17-19. Finer in the downstream stations of the estuary is particles may provide increased surface area per unit responsible for the gradual decrease in organic carbon weight for absorption of organic matter. The effect of content at stations III and IV. land drainage and the possible organic supply from The organic matter in the Poonthura estuary is tributaries in the upstream region accounts for the higher than the reported values from some other comparatively higher percentage at the upstream estuaries and coastal waters of Kerala6,7,17. Apart from region when compared to the beach station. The high the autonomous contribution sewage drain into the values of stations II, III and IV can be ascribed to the estuary contributes to the greater enhancement of heavy sewage discharges and the absorption of organic matter. The low level of tidal mixing and organic matter by the increased finer fractions of the seasonal monsoon dilution at the polluted stations are sediment. Similar input of wastes and enrichment of not adequate to enable self-purifying mechanisms to organic matter was earlier recorded from the Mandovi operate successfully. However, the horizontal gradient estuary16 and from the Cochin harbour20. in organic load noted indicates that better dilution can Changes in organic carbon content of sediment reduce the high organic load to a considerable extent. with respect to seasons were observed in all the five Acknowledgement stations (Table 3). Organic carbon was highest during The first author is grateful to University of Kerala the premonsoon period at all the stations whereas the for the award of a Research Fellowship during the seasonal minimum at all the stations was during the period of work. postmonsoon period. Variations in the organic carbon between seasons were statistically significant at 1% References level (ANOVA: DF=2, F=23.7213). The 1 Kalesha M, Distribution of organic matter in shelf sediments postmonsoon period followed by monsoon was also of Kakinada, east coast of India, Indian J Mar Sc, 8 (1979) marked with heavy rain and river discharge and the 58-59. 2 Paropkari A L, Distribution of organic carbon in sediments estuary was heavily flooded and the conditions were of the northwestern continental shelf of India, Indian J Mar not favorable for the accumulation of organic matter. Sci, 8 (1979) 127-129. The low rainfall, reduced river discharge and the 3 Chauhan O S, Sediment dynamics of Puri and Konark closure of the mouth of the estuary during the beaches along the northeast coast of India, Indian J Mar Sci, premonsoon resulted in the development of a stagnant 21 (1992) 201-206. 4 Chavadi V C & Bannur C R, Beach profile study along condition in the estuary leading to a sharp rise in the Ramangundi beach of north Karnataka coast (Westcoast of organic carbon content at all stations. India), Indian J Mar Sci, 21 (1992) 107-110. Mixing of sewage is one of the principal sources of 5 Sathyanarayanan D, Panigrahy P K & Sahu S D, Texture, mineralogy, carbon, nitrogen and phosphorus of organic pollution in estuaries. In most unpolluted Visakhapatnam shelf sediments, east coast of India, Indian J estuaries organic carbon content of the bottom Mar Sci, 22 (1993) 235-240. 80 INDIAN J. MAR. SCI., VOL. 30, JUNE 2001

6 Sankaranarayanan V N & Panampunnayil S V, Studies on 14 Fichez R, Absence of redox potential discontinuity in dark organic carbon, nitrogen and phosphorus in sediments of submarine cave sediments as evidence of oligotrophic Cochin backwater, Indian J Mar Sci, 8 (1979) 27-30. condition, Estuar Coast Shelf Sci, 31 (1990) 875-881. 7 Remani K N, Venugopal P, Sarala Devi K, Lalitha S & 15 Aiyer R S & Rajendran P, Physico-chemical aspects of Unnithan R V, Sediments of Cochin backwater in relation to estuarine and lake bed sediments, in Proc National Seminar pollution, Indian J Mar Sci, 9 (1980) 111-113. on Estuarine Management, (Kerala State Committee on 8 Bijoy Nandan S & Abdul Azsis P K, Organic matter of Science, Technology & Environment, Trivandrum) 1987, sediments from the retting and nonretting areas of pp. 117-122. Kadinamkulam estuary, southwest coast of India, Indian J 16 Alagarsamy R, Organic carbon in the sediments of Mandovi Mar Sci, 25 (1996) 25-28. estuary, Goa, Indian J Mar Sci, 20 (1991) 221-222.

9 Anila Kumary K S & Abdul Azis P K, Water quality of the 17 Sajan K & Damodaran K T, Studies on the distribution of Poonthura estuary, Thiruvananthapuram, Mahasagar, 25 organic matter content in sediments of Ashtamudy lake, (1992) 1-9. Kerala, Bull Dept Mar Sci Univ Cochin, 12 (1981) 22-26. 10 Person T H & Stanley S O, Comparative measurement of the redox potential of marine sediments as a rapid means of 18 Nair C K, Balchand A N & Jacob Chacko, Sediment assessing the effect of organic pollution, Mar Biol, 53 (1979) characteristics in relation to changing hydrography of Cochin 371-379. estuary, Indian J Mar Sci, 22 (1993) 33-36. 11 El Wakeel S K & Riley J P, The determination of organic 19 Sarala Devi K, Venugopal P & Sankaranarayanan V N, carbon in marine mud, J Cons Perm Inst Explor Mer, 22 Organic matter and sediment characteristics of some (1956) 180-183. estuaries of north Kerala, in Proc Seventh Kerala Science 12 Krumbein W C & Pettijohn F J, Manual of sedimentary Congress, (Kerala State Committee on Science, petrography (Appleton Century Crofts, inc N Y), 1938, pp 549. Technology & Environment, Trivandrum) 1995, pp. 113- 13 Plante R, Aleolado P M, Martinez-Iglesias J C & Diana- 114. Ibarzabal, redox potential in water and sediments of the 20 Seralathan P, Meenakshikutty N R, Asaref K V & Padmalal Gulf of Batabano, Cuba, Estuar Coast Shelf Sci, 28 (1989) D, Sediment and organic carbon distribution in the Cochin 173-184. harbor area, Indian J Mar Sci, 22, (1993) 252-255.