INTRODUCTION:

Mysore is one of the famous tourist centres of Asia, located between latitude 11°45' to 12°40' N and longitude 75°57' to 77°15' E. The district covers an area of about 6940 sq.km and is accessible from several parts of the world (Fig.1). It has many small and medium natural and artificial lakes. The lakes are the source for drinking, washing, irrigation, entertainment, etc. The continued anthropogenic activity in and around the lakes has not only caused environmental pollution but has also contributed to their rapid degradation. There are seven taluks in Mysore District, namely, Hunsur, K.R. Nagar, Periyapatna, Heggadadevana kote, Mysore, Nanjangud and T.N. Pur. Twenty-two lakes have been considered for the present study. They are Doddakere (H.D.Kote), Erekatte, Hbbalada katte, Heggadapura kere, Bili kere, Jinahalli kere, Halebeedu kere, Dadadahalli kere, Dalavayi kere, Karanji kere, Kukkarahalli kere, Mandakalli kere, Kalale kere, Arasana kere, Chittenahalli kere, Choudanahalli kere, Doddakere, Alagudu kere, Bannuru heggere, Kaggalipura kere and Kuruburu kere. "Kere" in Kannada means 'pond or a lake' (Fig.2).

GEOLOGY:

Karnataka State is a precambrian hard rock terrain encompassing major crystalline rocks like granites, gneisses, schists, amphibolites, limestone, pyroxenites and dunites. The schists, amphibolites etc. belong to Dharwar series and occur as thin bands and lenses. This series contains economically important minerals like magnesite, chromite, graphite, garnet, corundum and soapstones. Gneissic rocks cover a major part of the Mysore District. The gneisses are weathered, fractured and jointed. The gneisses are weathered up to a depth of 3 to 10 m (Radhakrishna B.P and Vaidyanandan R., 1994).

SOIL:

The district as a whole is characterised by red loamy soil. This soil is derived from granites and gneisses. The soluble salt contents are normal and the organic matter contents are high. The percentage of phosphorous is poor and soils contain variable amounts of potassium. The thickness of the soil varies from place to place, not exceeding 0.3m in some places. The valley portions are covered with rich black silty soil. Fig.3 shows the soil types of the district.

CLIMATE AND RAINFALL:

The annual rainfall is 580mm distributed over 42 rainy days. In a normal year, good showers can be expected in the months of May, September and October. The rainfall from December to March is negligible. The average annual rainfall recorded here from 1991 to 1999 is shown in the graph. April is the hottest month of the year with a mean maximum temperature of 35°C, while January and December are the coldest months with mean minimum temperature of 15.5°C and 15.8°C respectively. Fig.4 shows the distribution of rainfall observed in several parts of the district. Mysore district experiences the following seasons:

DRAINAGE:

The drainage comprises mainly a part of the Cauvery river basin with Kabini and Lakshmana theertha as its tributaries. All of them are flowing towards east. The outlets of the lakes considered here feed most of these major rivers.

METHODS OF STUDY:

Water samples were systematically collected at 44 locations using Nansen bottle. The characteristics of the surface water may be different from that collected from the bottom. Therefore the samples have been collected at a depth between the surface and the bottom. These samples have been subjected to chemical analysis following the ISI (1964) and APHA (1976) methods. The following physico - chemical characteristics were analysed: pH, Ec, TDS, SO4, Ca, Mg, HCO3, CO3, Na, K, COD, BOD, NO3 and Cl. The results are tabulated in Table 1. The chemical quality of water has been compared with the standards of WHO (1984).

TABLE 1: CHEMISTRY OF WATER ANALYSED FROM THE LAKES OF MYSORE DISTRICT

TABLE 2: QUALITY OF WATER IN SELECTED LAKES OF MYSORE DISTRICT AS COMPARED WITH THE WORLD STANDARDS

S.No	Parameter	Max	Min	Mean	USPH Standard	ISI Standard	WHO Highest desirable	Standard Maximum Permissible
1	pH	9.44	7.52	8.46	6-8.5	6-9	7-8	6.5-9.2
2	Eh	1030	80	469.32	30	-	-	-
3	TDS	638	52	328.18	500	500	500	1500
4	SO4	44	1	11.59	250	Upto 150	200	400
5	Ca	126	22	64.45	100	-	75	200
6	Mg	194	14	91.14	30	-	30	150
7	HCO3	358	40	164.48	-	-	-	-
8	CO3	120	Traces	16.72	-	-	-	-
9	Na	206	4	76.36	-	-	-	-
10	K	15	1	6.22	-	-	-	-
11	COD	248	12	51.09	4.0	-	10	-
12	NO3	3.9	1	2.41	<10	-	45	-
13	BOD	48	2	11.27	5.0	-	6.0	-
14	Cl	110	40	63.77	250	-	200	600

RESULTS AND DISCUSSION:

It could be seen that the waters present in these lakes are fresh to moderately brackish (Trivedi R.K. and Goel P.K., 1986). The lakes have <10 ppm NO3 and also there is no variation in SO4, and Cl which does not exceed WHO standard (Ayers, R.S. and Westcot, D.W., 1985; Wilcox, L.V., 1948). NO3 concentration of <10 ppm is tolerable for all ages and >10 is bad for children. TDS is more in samples 8, 9 and 12 of Mysore, H.D. Kote, Halebeedu kere of Hunsur and Arasanakere of Nanjangud. Therefore the lake water is alkaline in this region. Ca content shows tolerable values in all the lakes but shows high in samples 8, 13 and 15. Mg content in these lakes shows higher value but it shows permissible values in the lakes in Nanjangud. BOD is more in samples 4, 7, 9, 11, 12, 13, 15, 16, 20 and 22 whereas COD exceeds permissible limit in all lakes of Mysore district.

CONCLUSION:

The lake water is mainly utilized for agriculture. The major crops around these lakes are paddy, ragi, ground nut, sugarcane etc. The lakes of Mysore district are saturated with COD. COD values in all lakes are high, may be due to excess usage of fertilizers and chemicals for increasing yield of the crop. The presence of high COD calls for an immediate action to prevent the inputs of agrochemicals into the lakes.

ACKNOWLEDGEMENT:

The first author wishes to thank the CSIR, New Delhi, for providing the financial support for carrying out this research. The authors thank the Chairman, DOS in Geology, University of Mysore, for his encouragement and for providing the facilities.

REFERENCES:

FIGURE-1: LOCATION OF MYSORE DISTRICT

FIGURE-2: LOCATION OF SELECTED LAKES IN MYSORE DISTRICT

FIGURE-3: MYSORE DISTRICT SOILS

FIGURE-4: ANNUAL RAIN OF MYSORE DISTRICT

FIGURE-5: LOCATION OF LAKE WATER SAMPLE OF MYSORE DISTRICT

Address:

1.) Department of Studies in Geology,
Manasagangotri,
Mysore - 6