HYDROBIOLOGICAL STUDIES ON THE RIVER KALLAYI IN KERALA* VARKEY JOHN St. Thomas College, Kozhencheri, Kerala. ABSTRACT Hydrobiological studies were conducted on Kallayi river In northern Kerala, during 1965-66. The data on water temperature showed a correlation to the sea­ sonal cycle of variations of atmospheric air. pH varied within narrow ranges. Considerable amount of nutrients which are released from land during monsoons enhanced the production of planktonic organisms during October to December and January to May. Salinity distribution in the river was influenced by tidal currents especially during January to June, November and Deosmber. Peak values of sali­ nity were observed during April-May and the salinity was considerably decreased in monsoon periods due to the influx of rainwater from uplands. Dissolved oxygen varied considerably during the seasoiis. The decomposing organic materials from the coconut husks and timber barks were the causative factors for the decline in the oxygen. However, the oxygen content increased during the monsoon periods. There was a definite inverse correlation between salinity and dissolved-oxygen content. The phytoplankton was abundant especially during the pre- and post- monsoon seasons. Diatoms were the dominating group among the phytoplankton. The zooplankton distribution was influenced by hydrological factors especially tide and salinity. Most of the zooplankters were brackishwater types and they were numerically more during periods of high salinity (January to May). However, these forms dwindled off during monsoons commencing in June, only to increase again from October. The poor fish catch of Kallayi river could be attributed to the low oxygen content. INTRODUCTION Kallayi river originates from Kunnamangalam as a small stream and flows down 30 km through Kunnathupalam, Mankavu and Kallayi towns and ends in the Arabian Sea (Fig. 1). Perennial in nature, it is connected to Beypore river by a channel at Mankavu. Considerable amount of coconut husks are deposited in this river by the coir cottage-industry units for retting. These husks settle onto the bottom and due to the decay of these, a black silt is formed on the substratum mixed with sand. Further, a large number of logs are kept in the river for conditioning all through the year which also foul the water. During the rainy season the water level rises 2 to 4 metres. In fact, the torrential flow of rainwater from uplands cleanses the river seasonally. The tidal currents enter * From the thesis approved for the Ph.D. degree of the University of Kerala in 1971. HYDROBIOLOGICAL STUDIES ON KALLAYI RIVER 73 upstream into the river up to about 18 to 20 km and hence the water is saline during most of the months of the year. Mankavu has been choosen as the station for this study because, being 4.8 km above the outfall, it is in the tidal zone of the river. Depth of this station ranges from 2 to 3 metres. •U« RAYON PULP FACTORY R'^TATION KOZHIKODE KALLAYI RIVER 4, \ /^>CROKe STATION BEYPORE RIVER KAOALUNDI iKONDOTTI ^ N SCALE 1 . 4 MILES FIG. 1. Map of Kallayi river showing the collection stations. MATERIALS AND METHODS Hydrobiological conditions of Kallayi river were studied at Mankavu during 1965 and 1966. Water and plankton samples were collected once every fortnight during high tide. The data presented in the tables and figures are the average of the samples. The surface water samples were collected from a few inches below the surface. Samples of water from the bottom were collected with the help of a casella bottle. Temperature was recorded in the field. pH values 74 VARKEY JOHN were measured using an AE>CO pH meter. Dissolved-oxygen content was mea­ sured according to the modified Winkler method of Alsterberg (1926). The results of oxygen analyses were calculated as percentage saturation values from Fox's table (1907). Salinity was estimated employing the method suggested by Harvey (1945). Plankton samples were collected by a net made of fine silk having 77 threads per cm, which was towed for 10 minutes from a canoe. The speed of the canoe was kept as constant as possible during the hauls. Surface samples were taken from just below the surface of water and bottom samples were col­ lected by keeping the net at the desired depth just above the bottom by a weight attached to the rim of the net. The fresh plankton were strained and made to a fixed volume — usually 20 ml or multiples of 20 ml when the sample was large — by adding 4% formaldehyde. Duplicate samples, one for zooplankton and the other for phytoplankton, were taken which were qualitatively and quantitatively examined employing methods as suggested by Ganapathi (1962) and Chakravarthy et al (1959). All animals in 1 ml of subsample were counted. Phytoplankton in 0.2 ml were counted and then calculated for 1 ml. Seasonal indices of important zooplankton were estimated from three years' data during 1964-66, employing Moving Average Method (Croxton and Cowden 1956). The data for 1964 had already been reported (John and Alexander 1969). ENVIRONMENTAL DATA The data for the two years are given in Table 1. The maximum tempe­ rature was recorded during April and the minimum in January. There was a wide variation in the rainfall, the peaks being in June-July. During January to April there were a few showers. Generally a year could be divided as follows: March, April and May forming hot weather; June, July, August and September constituting the southwest monsoon season; October and November forming northeast monsoon season and December, January and February forming cold season. Monthly average rainfall was 169.9 mm and 223.7 mm for 1965 and 1966, respectively. The variations in temperature, pH, salinity and dissolved-oxygen content of the water samples are given in Figs 2 and 3. Temperature The water temperature was always higher than the air temperature ex­ cept during September 1966. The highest temperature in 1965 (30.5°C) and in 1966 (32.0°C) were recorded during the months May and April respectively, whereas, the lowest temperature was recorded in January, July, September and December 1965 (27.5°C) and during September in 1966 (26.0°C). The air- water temperature difference was comparatively higher during the summer months than in the monsoons. HYDROBIOLOGICAL STUDIES ON KALLAYI RIVER 75 TABLE 1. Meteorological data of Calicut for 1965 and 1966. Temperature Relative humidity at Monthly t otal rainfall monthly monthly 08301ST 17301ST (mm ) mean mean % /o maximum minimum oC oC 1965 1966 1965 1966 1965 1966 1965 1966 1965 1966 January 31.3 31.9 21.1 22.7 73.0 74.0 60.0 64.0 0.0 0.0 February 31.7 32.5 22.5 24.0 77.0 76.0 65.0 68.0 0.0 0.0 March 32.5 33.1 24.4 25.3 74.0 74.0 69.0 73.0 0.0 2.6 April 32.8 33.2 25.6 26.1 72.0 73.0 69.0 71.0 20.8 49.4 May 31.9 32.4 25.5 26.2 80.0 79.0 76.0 80.0 226.7 105.6 June 29.3 29.6 23.7 24.3 91.0 93.0 84.0 87.0 893.5 669.5 July 28.7 28.1 23.4 23.6 91.0 95.0 84.0 91.0 520.2 791.5 August 28.9 29.3 23.7 24.0 90.0 93.0 84.0 90.0 279.7 151.6 September 29.7 29.9 24.3 24.5 87.0 89.0 82.0 87.0 67.5 277.7 October 31.6 30.6 25.0 23.6 82.0 88.0 75.0 78.0 154.1 476.1 November 31.9 30.4 24.4 23.7 77.0 85.0 70.0 77.0 62.7 176.9 D3cember 30.8 31.5 23.3 22.6 81.0 81.0 72.0 70.0 138.1 82.0 Tidal effect Tidal effects were very marked in Mankavu station on Kallayi river which was well-indicated by the salinity. Owing to the relative shallowness of the river during summer months, the tidal currents could easily enter the river and the effects of tides were observed far upstream (18 to 20 km from the river mouth). However, during the monsoons, the torrential flow of water from uplands pre­ vent the tidal flow from coming upstream. pH The pH varied from 6.8 to 7.5 and 7.0 to 8.6 during 1965 and 1966, respectively. Salinity The highest salinity at Mankavu in 1965 (32.0 %,) and in 1966 (33.23%'o) were recorded during April and March respectively, and the lowest salinity (1.44% to 6.83%'o in 1965 and 0.65% to 5.08%'o in 1966) was recorded during June to August. In both years there was a sudden decline in 16 VARKEY JOHN salinity June onwards, to increase again after the monsoon, in September. A gradient in salinity between surface and bottom waters was noted. From Sep­ tember to December and January 1965 and in January, September and Novem­ ber-December 1966, the bottom water had relatively high salinity. During February to May, the surface-bottom variation in salinity was narrow. MANK*vu • SUDFACE 45 • WATEI) a AIR D BOT»">M 40 I ^? • ts' FMAMJJASON JFMAMJJASOND 1969 1965 • SUITACt D BOTTOM JFMAMJJASOND 1965 MANKAVU Si g • SURFACE • SuBTACt 0 aorroM < 0 BOTTOM z y it JFMAMJOASONi luOi 1965 FIG. 2. The chemical environmental features of Kallayi river during 1965. HYDROBIOLOGICAL STUDIES ON KALLAYI RIVER 77 Dissolved-oxygen content The dissolved oxygen exhibited very low values, ranging from 0.0 to 3.11 cc|l in 1965 and from 0.0 to 3.4 cc|l in 1966.