Indian Journal of Marine Sciences Vol. 12. September 1983. pp. 154-159

Ecology of Indian Estuaries: Part Ill-Physico-Chemical Features of -- Backwater Systems, SW Coast of

N BALAKRISHNAN NAIR. K KRISHNA KUMAR, P K ABDUL AZIS, K DHARMARAJ, M ARUNACHALAM & N K BALASUBRAMANIAN Department of Aquatic Biology & Fisheries, University of , Trivandrum 695007 • Received 15 February 1983; revised received 24 May 1983

As a part of an ecological survey conducted during March 1981 (premonsoon period) at the Akathumuri-Anchuthengu• Kadinamkulam backwaters (Iat.8'35'-8'44'N and long. 76'44'-76D51'E), the physico-chemical conditions were studied at 28 stations. Maximum bottom water temperature was recorded at the river zone (zone A). Comparatively low light penetration and dissolved oxygen content observed at the Anchuthengu backwater (zone C) can be attributed to retting. Salinity distribution was of mixohaline nature and maximum bottom water salinity was recorded at zone A. A distinct stratification in salinity distribution-a surface layer of mixo-oligohaline water and a bottom layer of mixo-mesohaline water-was noticed at zone A. Uniform temperature and salinity distribution observed in the surface and bottom waters at the Akathumuri r- backwater (zone B) is an indication of its well mixed condition. Nutrient distribution showed comparatively higher concentration at the Kadinamkulam backwater (zone D).

Abundance and diversity of biotic community in each parameter and student's t test was applied to find backwaters are influenced by the interaction ofa series out the significance of variations at each zone. of physico-chemical factors. Though extensive studies Results and Discussion on the hydrographic conditions of the Kerala Different physico-chemical parameters estimated backwaters have been madel -11, no attempt has are given in Table 2. hitherto been made to elucidate the hydrographic conditions of the Akathumuri-Anchuthengu-Kadi• namkulam backwaters. This paper reports physico• chemical features of these backwater systems during March 1981 (premonsoon period).

Study Area The area of study and stations investigated are shown in Fig. I and the details ofthe stations are given in Table I. The Akathumuri-Anchuthengu-Kadinam• kulam backwater system-an interconnected, shallow brackish water tract with depth not more than 5 m-is situated in the southern part of Kerala. The backwater I system has no permanent connection with the Arabian i sea, but seasonally it gets connected with the sea I through the opening of the sandy bar at Perumathura I (05, Table I). During the present investigation the bar N was closed. Generally, the backwater system is free I from industrial pollution. t J Materials and Methods A total of 28 stations were selected for the investigation. Surface and bottom water samples from corresponding depths as shown in Table I were collected for the estimation 12. 13 of dissolved oxygen, 76°44' 76°51' salinity, pH, phosphate, nitrate, nitrite and silicate. Fig.I-AkaIhumuri-Anchuthengu-Kadinamkulam backwater sys• Light penetration was measured using a Secchi disc. tems and the river (station details are given in Zonal variations were elucidated by taking the mean of Tablel)

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Table1-Study Sites and Their Features in Akathumuri-Anchu.thengu-Kadinamkulam Backwater Systems St. Station Depth Features St. Station Depth. Features No. (cm) No. (em) . banks; C3CIC2C4C6C5C7 clam bed yards;backwaterunits;tensiveVarkalabottombidthoroughlyttingitster);common; water) bottom (black bottom bottom land clayeyclayey; in.tensive bottom polluted turbid reclamation clayey mUl;idy;in~. muddy; extensive clayey water); retting; by re- bottom clayey onriver;SiteKavahiyoorNarrowBottomRettingThazhampallyRetting;CoirAkatllumuripilnuPuthenBathingThuruthyV.anThalamukkuShinkaraKayalAnchuthenguKulamuttomPerumathuraKavalayoorExtensiveShavamuttyKollampuzhaKarankunnuSandPanayilKaikkaraShoresVarnanapuramPulimootuPoothuraMurukumpuzhaBanksMananakkuPerunguzhiEranguPoovamparaMannayathMud·reclamationMeeranManakandathilIntensiveRettingonbanks;shorethebottombottomjoinsbottom of kadavu processingcanal collection;kayal bankprotected barmouth;for protected kadavuand kadavugroundsandcoir(blacksandyhard waterghat;kadavubottomnarrowcoir thoppuretting retting kadavu405B7 kadavuthOOujoinscoir kadavukadavu304processingproCessingkadavu bridgelaterite churchbanksa tract; turbid river ~llyardscentresunits coirregion;clayey; withand(blackprocessing 232405435254415260201208295210230231217processingwith370355235219207grounds205195196190165186189 regionveryZoneA pro,joins pro-coir oncanalwa-la- onla- tur-onD3ya-DID6D5 re-un" of (Lower reaches ofC8 the VamanapuramntresmuddystoneprotectionParvathiputhenarlection;barmaximumstructedsandy;backwater; gets river) wall intensive oyster opened; tidalwhich bottom beds effect sand bottom is joins con-muddy on coL-when the the B5 B2 walls . Intensive retting; coir prp-D2D4 Zone D (Kadinamkulamcentres; bottomcessingbeds; backwater) clayey; bottom unitZone ba-onC muddy banks;(Anchuthengu clam backwater) 1I BIB6B4 Zonenksterite protected BAl stone(Akathumuri walls;with lateriteterite bottomstonetectedclayey;rdsbackwater)withclayeyactive on laterite stone walls banks; banks with landmuddy; walls; stone reclamation; late,rite protected bottom banks bottom walls stone pro- B3 muddy andclayey;backwater; coir clam processing banks beds noticedprotected units; A7A6A4A3A5A2 kadavu tected with laterite stonejoinsbanks;leftcessingrightwithbottommuddy;processingsandywalls;hard bank;lateritebank; thelaterite bottom bottom yards sandyclayeybanks river; bottom units; Valia stone on hardprotectedmuddy bottom banks;bottom ela sandy wallswalls; laterite thodu from nearby paddy fields

Depth-Depth of the backwater system showed that the pith of the -a waste product after variation fro.m one station to the other (Table 1).The the separation of the coir fibre-is dumped into the river zone (zone A) was comparatively deeper and backwater system. Successive years of dumping of this recorded maximum depth at st A4 (435cm). Heavy waste material results in a drastic decrease in the der;th flow of the river and intense sand collection make this giving way to easy reclamation of that part and Y1.' •• , ultimately in the reduction of the total area of the t zone deeper. Zone C recorded the lowest mean depth with the minimum at st C2 (165 cm). It was observed backwater system. Comparatively low values of depth' ~55 INDIAN J. MAR. SCI., VOL. 12, SEPTEMBER 1983

""N •.••00 •...N recorded at zone C is possibly due to the deposition of "" co '

'" •... "'~ between 28 and 32.8°C. The range of surface and '

0.. N •.•• '

156 NAIR el al.: ECOLOGY OF INDIAN ESTUARIES-PART III oxygen content of the surface and bottom waters suddenly closed. This results in a total stagnation and showed a homogeneous distribution, It exhibited no external factors are at work to alter the salinity significant regional variations. A comparison showed distribution at the bottom. Besidcrs this, during that the variations between zones A and C, and Band premonsoon season the river discharge is meagre. All C, were significant at 1% level in both the surface and these have contributed to the. comparatively high· bottom waters while the variations between zones C salinity values for the bottom water at these zones. ' and D were significant at 5% level in the bottom water. pH-pH fluctuatedbetween 7 and 7.8 at the surface All these variations were predominantly due to low and 7.4 and 7.8 at the bottom. No vertical pH gradient values recorded at zone C. There is great depletion of was observed at zones A and C. However, zones Band oxygen at zone C owing to the intense retting of D showed marked variation with high pH values at the coconut husk. Oxygen depletion and consequent bottom. pH variation between zones A and D, Band anoxic conditions have been reported from the retting D, and C and D in the surface waters were significant zones of -Nadayara backwater during Feb. to at 1% level. Though it showed considerable variation late July1. in the surface water, it remained almost uniform at all Salinity-According to the Venice system of zones in the bottom. Comparatively low values were classification 14, the salinity distribution in the recorded in the surface water at zone D. backwater system is of mixohaline nature. Bottom Inorganic phosphate-The values varied between 3 salinity values were higher than the surface at zones A, and 10.4 /1g-at'I-1 for surface and 3.8 and 11.6 Jlg• C and D. Surface and bottom salinity showed marked at-I -1 for bottom water with a wide range of variation in zones A and D at 1% leveland in zone C at fluctuation between the stations. Though surface and 5% level and followed homogeneous distribution at bottom values showed no significant variation, the zone B. Comparison of the surface salinity indicated bottom mean values were slightly higher than those of that the variation between zones A and B, A and C, A the surface. The variations at surface and bottom and D, and Band D were significant at I% level and between zones Band D, and C and D were significant between C and D at 5% level, and was due to the low at I% leveland between zones A and B, A and C, and A values recorded at zones A and D. Bottom water and D at 5% level. Regional distribution of phosphate salinity variations between Band C were significant at showed significant variations but presented a relatively 1% level and A and B, and Band D at 5% level. homogeneous nature at zones Band C. As the bar mouth remained closed during the Comparatively low values were reported during present investigation, the salinity distribution in the premonsoon season at Cochin backwater3 and at the backwater system was mainly influenced by the Mandovi and Zuari river system 15in contrast to the freshwater discharge through the . higher values recorded during the present in• The vertical homogeneity observed in salinity and vestigation. As the bar remained closed during. the temperature distribution at zone B is an apparent survey normal flushing of nutrients from the indication of the well mixed nature of that zone. As backwater to the sea does not take.place. Coupled with zone B is comparatively broader, mixing by means of this, retting causing the death and decay of organisms wind is more effective than at the other zones. Besides, due to oxygen depletion may also contribute to the it is less affected by the freshwater discharge as it is replenishment of phosphate. The higher values at away from the river mouth. Salinity distribution zone D is believed to be associated with the influx of showed a distinct stratification at zone A-a surface water from the Veli lake and from the Vamanapuram layer of mixo-oligohaline water (4.30 x 10-3) and a river. Comparatively higher bottom values observed at bottom layerofmixo-mesohalinewater(17.15 x 10-3). all zones is indicative of an autochthonous source of The low saline nature of the surface water at this river phosphate. This may either be by regeneration from zone is due to the dilution resulting from the the bottom sediment or through decomposition of freshwater flow. Among the backwater zones (zones B, organic matter. Similar trend of higher bottom water C and D), zone D recorded the low surface salinity and phosphate has been reported at the Bay16 is due to the freshwater influx from the river zone and and Ashtamudi backwaterl1. Subramanian and the water flow from the adjacent Veli lake through the Venugopalan17 discussed that the higher particulate Parvathi Puthenar canal. Bottom water salinity was organic phosphorus of the bottom water at Veqar the maximum at zoneA. However, zonesA and C estuary might be due to higherconcentratioIl· of exhibited close similarity in bottom salinity particulate matter and relatively high concentration of distribution. These zones being narrow reduces the phosphorus in the suspended sediments. chance of mixing by wind. The tongue of high saline Inorganic nitrate-Surfllce water nitrate fluctuated bottom water which penetrated into these zones during between 1.1 and 6.4 Jlg-at-l -1 and that of bottom its exposure to the sea gets trapped when the bar is between 1.38 and 6 Itg-at-l -1 with wide fluctuations

157. INDIAN 1. MAR. sel., VOL. 12, SEPTEMBER 1983 between the zones. Like phosphate, surface and replenishment. Since it is an unstable form, rapid bottom values showed no significant variation. Zones oxidation into nitrate can be considered as the main A and B had uniform distribution at both surface and reason for the observed low nitrite content. At the bottom. Regional surface water values exhibited Cochin backwater the values of nitrite-N were much significant variation between zones A and D, Band D, lower than those of nitrate-N and the conversion of and C and D at I % level and between Band C at 5% nitrite-N into nitrate-N, explail1S reason for the low level, while bottom values showed variation between nitrite content3. zones A and C, A and D, and Band D at 5% level. Inorganic silicate-It varied in surface water Inorganic nitrogen is present in an aquatic biotope between 25 and 82 pg-at'l -) and that of the bottom as oxidised nitrite and nitrate, and as reduced water between 23 and 54 pg-at'l -] and exhibited a ammonia. Though no distinct vertical gradient could wide range of fluctuations between the zones. A be observed, nitrate distribution showed wide regional notable feature observed was its invariably higher fluctuation during the present investigation. Similar to concentration in the surface water at all zones. Vertical phosphate, nitrate concentration was also higher at variation was more pronounced in zone D where it was zone D. Values at zone D are likely to be influenced by significant at I% level and in zone B it was at 5% level. the influx of water from the Veli lake and by the Surface and bottom concentrations between zones A freshwater discharge from the Vamanapuram river. and C, and Band C were somewhat similar. Regional However, the higher bottom nitrate mean values at surface silicate comparison showed variation at 1% zones A, Band C indicate the possibility of a local level between zones A and B, A and D, Band D, and C nitrate enrichment by means of regeneration from the and D, while that of bottom showed variation at 1% bottom sediment or through decomposition of organic level between A and B, and Band D and at 5% level matter. Higher bottom nitrate values at the Ashtamudi between C and D. Similar to the other nutrients silicate backwater and the possibility of nitrate regeneration concentration was also higher at zone D. from the sediment are reported]]. At the Cochin Comparatively higher values observed at zone D might backwater nitrate was very low during premonsoon be due to the freshwater influence from the riverine season when the conditions are predominantly marine zone and the water flow from the Veli lake lying and explained that the contribution from sea was very adjacent to this ecosystem. Low values at zone B can be little 3. attributed to its highly secluded position in the Inorganic nitrite--Nitrite concentration was very backwater system, free from any land drainage and low throughout the backwater system and ranged water flow. Rao and George8 recorded a range of20 to between 0 and 0.38 J.1g-at·1 -] in the surface and 0 and 220 /lg-at·1 -I of silicate in the river mouth at the 0.33 J.1g-at·1 -] in the bottom water. Surface and estuary and attributed this to the laterite of bottom values showed variation only in zone D at 5% the drainage area. level, where as the surface water values were higher than the bottom, while all other zones experienced a Acknowledgement vertical homogeneity. It showed uniformity in the This work was carried out under a project entitled surface and bottom waters at zones A and C. Surface "Studies on the coastal ecosystem of Kerala in relation values showed variation between zones A and D, Band to Fisheries", sponsored by the UGC, New Delhi C, Band D, and C and D at I% level and between A [No. F. 22-9j7 (SR-II)] and the financial support and B at 5% level. Bottom values exhibited regional provided is gratefully acknowledged. variation between zones A and B, Band C, and Band D at I %, level. References A notable feature was its low concentration ) Abdul Azis P K & Balakrishnan Nair N, Aqua Bioi, 3 (1978) 41. compared to other nutrients throughout the backwater 2 Ramamirtham C P & Jayaraman R, J Mar BioI Ass India, 5 (1963) 170. system. Like phosphate and nitrate, nitrite also 3 Sankaranarayanan V N & Qasim S Z, Mar Bioi, 2 (1969) 236. showed higher values at zone D. This interesting co• 4 Wellershaus S, On the hydro1!,raphy of the Cochin backwater (a incidence was another noticeable feature of the nitrite South Indian estuary), paper presented at the Symposium on distribution. The nitrite concentration remained very Indian Ocean and adjacent seas-their origin, science and low at zone B and recorded zero values in both the resources, Cochin (1971). surface and bottom waters at st B3 and B4. The lower 5 Joseph P S, Indian J Mar Sci, 3 (1974) 28. surface water nitrite values observed at the river zone 6 Manikoth S & Salih K Y M, Indian J Mar Sci. 3 (1974) 125. (zone A) and the higher values at the backwater zones 7 Sarala Devi K, Venugopal p, Remani K N, LalithaS&Unnithan R V, Indian J Mar Sci, 8 (1979) 141. (zone C and 0) clearly suggest that nitrite input does 8 Suryanarayana Rao S V & George P Co J Mar BioI Ass India, I not entirely depend on the freshwater discharge during (1959) 212. premonsoon and indicates pO$sibilities of local 9 Nair G S, Bull Dept Mar Bioi Oceanogr Univ Cochin, 5 (1971) 87.

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10 Mary John C Bull Cent Res Inst, (Series C, 14 Venice System, Symposium on the classification of brackish Natural Science) 6 (1958) 97. waters; Arch Oceanog Limnol, 2 (1959) Suppl 1-248. II Dharmaraj K & Balakrishnan Nair N, The nature of distribution 15 De Sousa S N, Sen Gupta R, Sanzgiri S & Rajagopal M D, Indian of maior inorganic nutriems in the Ashtamudi backwaters in J Mar Sci, 10 (1981) 314. relation to enl'ironmentalfaclOrs, paper presented at the All India seminar on the status of environmental studies in 16 Dharmaraj K, Balakrishnan Nair N & Padmanabham K G, India. Trivandrum (1981) Abst27. Studies on the hydrographical features of Vizhinjam Bay, 12 Martin D F. Marine chemistry. Voll (Marcel Dekker, Inc, New paper presented at the Symposium on Coastal Aquaculture, York) 1968. Cochin (1980) Abst No 30. 13 Strickland J D H & Parsons T R, A practical handbook of sea 17 Subramanian B R & Venugopalan V K, Indian J Mar Sci, 9 lrater analysis. (J Fish Res Bd Canada, Bull 167) 1972, 311p. (1980) 246..

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