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Sediment chemistry of Kashmir Himalayan lakes I. Clay mineralogy
Chemical Geology, 64 (1987) 121-126 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
121
[7]
SEDIMENT CHEMISTRY OF KASHMIR HIMALAYAN LAKES I. Clay Mineralogy R.A. K A N G O 1, K.P. D U B E Y '~ and D.P. ZUTSHI 1 ICentre o[ Research for Development, University of Kashmir, Srinagar 6 (India) "Department of Chemistry, University o[ Kashmir, Srinagar-6 (India) ( Received July 25, 1985; revised and accepted February 5, 1987 )
Abstract Kango, R.A., Dubey, K.P. and Zutshi, D.P., 1987. Sediment chemistry of Kashmir Himalayan lakes, I. Clay mineralogy. Chem. Geol., 64: 121-126. Clay mineral content of six Kashmir Himalayan lakes (average elevation 1580 m a.s.1. ) have been determined using X-ray diffraction and differential thermal analysis. Illite, calcite and chlorite were the main clay minerals and their percentage contribution to the lake sediments differed significantly, with illite ranging from 16% to 84% and calcite between 22% and 72%. The ionic activity product (IAP) and equilibrium constant (K~) of calcium and carbonate ions for the ambient lake waters was used to trace the origin of calcite. IAP/Kc-values were much higher (48) in Trigam Lake in comparison to other water bodies.
1. I n t r o d u c t i o n
Clay minerals are present in all types of sediments and are common constituents of hydrothermal deposits. These may be of allogenic, endogenic, or authigenic origin. The distinction between clay minerals and their nature is of great help in the elucidation of different types of interactions between the sediment-water interface and in source identification. Until recently only a limited study had been made of clay mineral composition of the sediments accumulating in various environments (e.g., Swain, 1966; Anthony, 1977). Due to limited data available on the clay minerals for non-marine sediments, it is difficult to reach any definite conclusions about the origin and
0009-2541/87/$03.50
fate of the clay minerals in freshwater sediments. The Kashmir Himalayas in northwest India abound in freshwater lakes which are important for fisheries, agriculture and recreation. Many limnological investigations have been undertaken on these lakes in recent years (Zutshi and Vass, 1970, 1978; Zutshi et al., 1972, 1980), but very few studies have so far been undertaken on sediment chemistry. De-terra and Paterson (1937) presented data on the distribution of detritus and mineral grains in three basins of Dal Lake, Srinagar. Zutshi (1968) and Mir (1977) correlated biological productivity with the nutrient status of the sediments. The present investigations were carried out during 1982/1983 on six Kashmir Himalayan lake sediments.
© 1987 Elsevier Science Publishers B.V.
122
2. M a t e r i a l s a n d m e t h o d s
The clay fraction ( < 2 #m ) was separated by the sedimentation method ( Orr and Dallavalle, 1959 ). The individual clay minerals were identified by X-ray diffraction ( X R D ) and differential thermal analysis (DTA). X R D data were obtained with a Philips ® diffraction spectrophotometer using filtered Cu-K~ radiation. The semiquantitative percentage of each clay mineral was measured by the relative intensity of its principal diffraction peak. The apparatus used for DTA was assembled in the Analytical Chemistry Division of BARC, B o m b a y (an endothermal 457 temperature programme controller and a model A-IO, Rikadenki Kogyo ® Co., Japan, microvoltmeter (D.C.) was used for amplifying the thermal e.m.f.). The thermograms were recorded on the Y-axis of an X - Y recorder (model HR-11, H o u s t o n Omnigrafic ® Corp., U.S.A. ). Data on the supersaturation of ambient lake waters were used to describe the calcite precipitation. Calcium, alkalinity, temperature and pH of the water samples was determined according to Golterman and Clymo (1969). The product of calcium and carbonate ionic activities on multiplication yield the ionic activity product ( l A P ) , which was used as an index of supersaturation, lAP was computed from the following relationship: IAP
(Ca 2 ~ ) X ( C O ~
)=
',7(:~- [Ca '~* ] X ?'HC():~ XK2 X (alkalinity)} [H + ] where K2 is the second dissociation constant of carbonic acid. The activity coefficient was estimated from the extended Debye-Hiickel relation. The value of IAP of a lake compared to the equilibrium constant, K,., determines whether the lake water is undersaturated, saturated, or supersaturated.
BARAMULA
i JAMMU
~ ~ ~ I ~ (~ BANDIPORA
AND KASHMIR
/
f- /
*WULAR LAKE e
III
!
SOPORE
® ~ 1 ~ MANSBAL LAKE I~
® BARAMULA TRIGAM L A K E
~
@ GANDERBAL
~ z ~ - TI LWA N LAKE \. DAL
Q GULMARG
/
.J .J B E E R W A ,9 !
/
LAKE
.J SRINAGAR ,3 B A D G A M
,1
0
10 J
KM
@ CHADURA Fig. 1. Location of the lakes.
2.1. Description of the lakes Six Kashmir lakes, Dal, Wular, Mansbal, Anchar, Trigam and Tilwan, lying within geographical coordinates of 32-34 =N latitude and 74-74.9 ~E longitude have been selected for the present investigation. These water bodies lie in the floodplains of the river Jhelum at an average altitude of 1580 m above mean sea level ( Fig. 1). The lakes are of postglacial age and have probably originated as a result of the meandering of the alluvial deposits (Zutshi et al., 1980). Dal, Wular and Anchar are drainage-type lakes. Mansbal is a semi-drainage type and Trigam and Tilwan are non-drainage-type lakes with high water residence (Zutshi and Vass, 1978). The other morphometric parameters of the lakes are given in Table I. 3. R e s u l t s a n d d i s c u s s i o n The X R D analysis showed the presence of illite, calcite and chlorite in the sediment samples (Table II). Calcite was found to be the principal clay mineral in Anchar Lake, showing
9t~Z$~I,gBI~tHD 90,Z:~'"I
123 TABLE I Selected m o r p h o m e t r i c features of the lakes Feature
Dal
Wular
Mansbal
Anchar
Trigam
Tilwan
Surface area ( kin-' ) Maximum length (km) Maximum breadth (km) Maximum depth (m) L e n g t h of shoreline ( k m )
11.45 10.8 2.1 5 15.5
24 16 9.6 5.8 58
2.8 3.5 1.2 13.0
6.8 3.8 0.65 3.0 11.5
1.4 0.7 0.2 2.3 2.2
4.3 1.4 0.3 2.2 3.5
TABLE II
basal reflections at 3.33, 3.34 and 3.35 A (the diffraction diagrams are available from the authors on request). Dal and Wular lakes did not show any diffraction pattern for calcite, and Mansbal and Tilwan lakes were devoid of any chlorite. The DTA thermograms showed some welldefined endothermic peaks coupled with one or two less-pronounced exothermic ones. The endothermic effect in the region of 545-560 ° C was due to illite (the DTA thermograms are also available from the authors on request). In the case of the illite clay minerals the temperature interval of 200-700 ° C was characterised by the main endothermic effect within the 450-650 ° C range, the peak value was recorded at 550 °C,
Clay mineral content ( % ) of some Himalayan lakes as revealed by X-ray diffraction (diffraction peaks are given in parentheses) Lake
Illite
Calcite
Chlorite
Dal
72
(3.33 ,~, )
28
Wular (W:~) (WJ
84 81
(3.34 ,~ t
16 19
Mansbal
78
(3.35 ,~
Anchar
16
71
Trigam
52.1 (3.33
36.6
Tilwan
54.1 (3.33
45.9
22 (3.03 ~,)
13 11.3 (7.05 A)
a strong diffraction peak at 3.03 A. Other lakes had illite as the principal clay mineral, with
T A B L E III G e o c h e m i c a l data used for the e s t i m a t i o n of calcite saturation ranges in M a n s b a l L a k e Month
Temperature
(Ca ~ ' ) (10 4 m m o l l
1)
Alkalinity (10 4 m e q l
log K~ 1)
(~c) Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.
5.6 8.9 17.2 18.6 23.3 27.2 28.9 25.8 22.8 17.8 15.3 10.6
Ionic strength = 10 :~.
8.5 8.5 8.5 7.4 5.6 2.9 4.6 4.6 5.6 8.0 20.9 10
20,6 21.6 20,6 1,73 1,44 1.27 1.27 1.47 1.57 1.86 1.73 1.96
- 10.547 - 10.502 - 10.407 10.388 - 10.349 - 10.312 - 10.301 10.324 - 10.351 - 10.401 - 10.430 10.490
[ H + ] ion concentration (10 ~ m m o l l 15.1 12.3 7.94 3.16 0.813 1.20 1.58 2.69 6.16 15.1 18.6 20.4
log K ,
IAP/K,.
8.351 --8.356 - 8.380 8.388 - 8.408 8.424 - 8,441 8,528 --8.407 --8.383 -8.370 8.360
0.61 0.88 1.68 3.17 7.67 2.92 4.14 3.06 1.27 0.7 1.08 0.58
1)
124 TABLE IV Geochemical data used for the estimation of calcite saturation ranges in Trigam Lake Month
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.
Temperature (°C) 9 12.5 19.5 23.0 28.5 29.5 30 25.5 19 10.0 7
(Ca ~~ ) (10 '~mmoll 1)
Alkalinity (10 4meql 1)
log K~
[ H ~] ion concentration (10 9mmoll ~)
log K,.
IAP/K,,
13 11 11 10 10 10 11 11 11 11 11 12
78
-
3.16 2.09 1.58 2.09 3.16 1.58 1.77 1.99 1.58 1.99 3.16 7.94
-
8.356
15.68
8.364 8.390 8.408 8.441 8.451 8.451 8.420 8.388 8.360 8.353
32.40 29.23 20.76 48.59 48.03 41.25 43.39 30.54 14.20 6.08
70 70 69 67 64 62 61 65 67 69
10.50 10.460 10.370 10.349 10.301 10.289 10.289 10.330 10.388 10.490 10.528
-
Ionic strength = 10 :~
w h i c h c o r r e s p o n d e d to t h e loss of s t r u c t u r a l l y b o u n d w a t e r ( B l a z e k , 1973). T h e D T A c u r v e of calcite was c h a r a c t e r i s e d b y t h e e n d o t h e r m i c effect of d e c o m p o s i t i o n d e p i c t e d b y t h e p e a k in t h e region of 8 3 0 - 9 4 0 ° C. A n c h a r L a k e s h o w e d a s t r o n g e n d o t h e r m at ~ 854 ° C, in w h i c h calcite was t h e p r i n c i p a l m i n e r a l . I n t h e clay m i n erals of T r i g a m L a k e a n a d d i t i o n a l p r o m i n e n t e x o t h e r m m a y be a s s i g n e d to t h e s t r u c t u r a l c h a n g e s of c h l o r i t e m i n e r a l ( B l a z e k , 1973). A c c o r d i n g to J o n e s a n d B o w s e r (1978) t h e illite a n d t h e c h l o r i t e h a v e a n allogenic origin in f r e s h w a t e r lake s e d i m e n t s . A m o n g t h e t h r e e p r i n c i p a l m i n e r a l s d e t e r m i n e d in t h e p r e s e n t study, illite a n d c h l o r i t e are t h e p r o d u c t s of w e a t h e r i n g a n d e r o s i o n a l deposits. P o t t e r et al. (1975) r e p o r t e d t h a t illite a n d c h l o r i t e w e r e m a i n l y t h e r e s u l t of e r o s i o n of m i d d l e a n d lower Paleozoic s e d i m e n t s t h a t are rich in illite a n d c h l o r i t e c o n t e n t . M o o r e (1961) i n d i c a t e d t h a t in the s e d i m e n t s of L a k e M i c h i g a n , U.S.A., h a l f of t h e clay m i n e r a l s c o n s i s t e d of illite; t h e o t h e r half was chlorite a n d m i x e d - l a y e r m i n e r a l s . T h e results were i d e n t i c a l w i t h t h e a v e r a g e clay m i n e r a l c o m p o s i t i o n given for s i x t e e n till s a m ples w h i c h are c o n s i d e r e d p r i m a r y source material.
Calcite m i n e r a l c o n s t i t u t e d a n i m p o r t a n t f r a c t i o n in t h e H i m a l a y a n lake s e d i m e n t s . T h e c a r b o n a t e equilibria in n a t u r a l w a t e r s y s t e m s have been provided by Garrels and Christ (1965), B e r n e r (1971), S c h a f e r a n d S t a p f (1972), O t s u k i a n d W e t z e l (1972), S a n t a c h i (1975), a n d K e l t s a n d Hsfi (1978). M a n s b a l L a k e s e d i m e n t s h o w e d ~ 22% calcite. I n o r d e r to d e t e r m i n e its origin, t h e supers a t u r a t i o n of t h e lake w a t e r was c o n s i d e r e d i m p o r t a n t . T h e c h e m i c a l analysis of its a m b i e n t waters showed that: (1) t h e c o n c e n t r a t i o n v a l u e s of c a l c i u m r a n g e d f r o m 0.59 m e q 1 1 ( J u n e ) to 4.18 m e q l-1 in N o v e m b e r ; (2) t h e v a l u e of a l k a l i n i t y r a n g e d f r o m 6.58 m e q l - 1 in F e b r u a r y to 3.89 m e q 1 1 ( J u n e ) ; ( 3 ) t h e [ H + ] ion c o n c e n t r a t i o n r a n g e d f r o m 8.13-10 - l ° ( M a y ) to 1.51.10 s ( O c t o b e r a n d January) ; and (4) t h e t e m p e r a t u r e r a n g e d f r o m 5 . 6 ° C ( J a n u a r y ) to 28.9 ° C ( J u l y ) . T h e calculated saturation index IAP/Kc ( T a b l e I I I ) for t h i s lake i n d i c a t e d t h a t t h e lowest v a l u e s are o b t a i n e d d u r i n g winter. T h e i n c r e a s e f r o m 0.58 in D e c e m b e r to 7.67 in M a y s h o w e d p r o g r e s s i v e s u p e r s a t u r a t i o n . T h e val-
125 ues t h e n fall again, d e p i c t i n g few m i n o r irregularities. F r o m t h e s e c a l c u l a t i o n s it is e v i d e n t t h a t s o m e q u a n t i t y of c a l c i u m c a r b o n a t e m i g h t have been precipitated from the water column a f t e r May. T h u s , calcite in M a n s b a l L a k e m a y h a v e a n e n d o g e n i c origin b u t its allogenic origin c a n n o t be c o m p l e t e l y excluded. T h e e x a c t a m o u n t of calcite p r e c i p i t a t e d a n d t h e p e r c e n t age c o n t r i b u t i o n b y d i f f e r e n t sources h a v e n o t b e e n t a k e n into c o n s i d e r a t i o n in t h e p r e s e n t investigation. T h e I A P / K c - v a l u e s for T r i g a m L a k e are given in T a b l e IV. T h e s e v a l u e s were c o m p u t e d f r o m w a t e r c h e m i s t r y data. T h e values were e x t r e m e l y high d u r i n g a m a j o r p a r t of t h e year. T h e results i n d i c a t e t h a t large q u a n t i t i e s of calcite m i g h t be f a v o u r e d in t h i s lake a f t e r t h e o n s e t of s u m m e r . Calcite a m o u n t e d to ~ 36.5% of the t o t a l m i n e r a l c o m p o s i t i o n . T h e e x t r e m e l y high s u p e r s a t u r a t i o n w i t h o u t t h e p r e c i p i t a t i o n of C a C Q m a y be due to t h e f o r m a t i o n of s t a b l e organic c o m p l e x e s in t h e lake water. K i t a n o a n d H o o d (1965) h a v e s h o w n t h a t o r g a n i c c o m p o u n d s such as c i t r a t e s , m a l a t e s , etc., w i t h s t r o n g a f f i n i t y for c a l c i u m r e t a r d t h e r a t e of c a r b o n a t e p r e c i p i t a t i o n . B e r n e r (1971) also r e p o r t e d t h a t t h e p r e c i p i t a t i o n of c a l c i u m carb o n a t e does n o t t a k e place in s i l i c a t e - m u d p o r e w a t e r rich in s u s p e n d e d organic m a t t e r . In A n c h a r L a k e , calcite is p r o b a b l y allogenic b e c a u s e of t h e f a c t t h a t t h e f l u s h i n g r a t e in t h i s lake is e x t r e m e l y high, giving less t i m e for t h e w a t e r c o l u m n to i n t e r a c t a n d a c h i e v e t h e r m o dynamic equilibrium.
Acknowledgements T h e a u t h o r s wish to t h a n k Dr. P . N . G u p t a of t h e C h e m i s t r y D e p a r t m e n t , U n i v e r s i t y of K a s h m i r , for his help d u r i n g t h e p r e p a r a t i o n of this p a p e r .
References Anthony, R.S., 1977. Iron-rich rhythmically laminated sediments of the Clouds, northeastern Minnesota. Limnol. Oceanogr., 22: 45-54.
Berner, R.A., 1971. Principles of Chemical Sedimentology. McGraw-Hill, New York, N.Y. Blazek, A., 1973. Thermal Analysis. Van Nostrand Reinhold, London. De-terra, H. and Paterson, T.T., 1937. Studies on the ice age in India and associated human culture. Carnegie Inst. Washington Publ. Garrels, R.M. and Christ, C.J., 1965. Solutions, Minerals and Equilibria. Harper and Row, New York, N.Y. Golterman, H.L. and Clymo, P., 1969. Methods for Chemical Analysis of Fresh Water - IBP Handbook. Blackwell, London. Jones, F. and Bowser, C.J., 1978. The mineralogy and related chemistry of lake sediments. In: A. Lerman (Editor), Lakes Chemistry, Geology and Physics. Springer, New York, N.Y., pp. 179-227. Kelts, K. and Hsii, K.J., 1978. Fresh water carbonate sedimentation. In: A. Lerman (Editor), Lakes - Chemistry, Geology and Physics. Springer, New York, N.Y., pp. 295-323. Kitano, Y. and Hood, D.W., 1965. The influence of organic material on the polymorphic crystallisation of calcium carbonate. Geochim. Cosmochim. Acta, 29: 29-41. Mir, A.M., 1977. Planktons and water soils in relation to lake productivity. Ph.D. Thesis, University of Kashmir, Srinagar (unpublished). Moore, J.E., 1961. Petrography of northeastern Lake Michigan bottom sediments. J. Sediment. Petrol., 3: 402-436. Orr, Jr. C. and Dallavalle, J.M, 1959. Fine Particle Measurement - Size, Surface and Volume. Macmillan, New York, N.Y. Otsuki, A. and Wetzel, R.G., 1972. Coprecipitation of phosphate with carbonates in a marl lake. Limnol. Oceanogr., 17: 763-767. Potter, P.E., Heling, D., Shirup, N.F. and Van Wei, W., 1975. Clay mineralogy of modern alluvial muds of Mississippi river basin. Bull. Cent. Rech. Pau, 2: 353-389. Santachi, P., 1975. Chemische Prozesse in Bielersee. Ph.D. Thesis, University of Bern, Bern (unpublished). Schafer, A. and Stapf, K.R., 1972. Calcite whitings in Bodensee Untersee. Nat. Mus., 102: 8. Swain, F.M., 1966. Bottom sediments of Lake Nicaragua and Lake Managua, Western Nicaragua. J. Sediment. Petrol., 36: 522-540. Zutshi, D.P., 1968. Ecology of some lakes of Kashmir. Ph.D. Thesis, Jammu and Kashmir University, Srinagar (unpublished). Zutshi, D.P. and Vass, K.K., 1970. High altitude lakes of Kashmir. Ichthyologica, 10: 12-15. Zutshi, D.P. and Vass, K.K., 1978. Limnological studies of Dal Lake II. Chemical features. Ind. J. Ecol., 5: 90-97. Zutshi, D.P., Kaul, V. and Vass, K.K., 1972. Limnology of high altitude lakes of Kashmir. Verh. Int. Ver. Limnol., 18: 599-604.
126 Zutshi, D.P., Subla, B.A., Khan, M.A. and Wanganeo, A., 1980. Comparative limnology of nine lakes of Jammu and Kashmir Himalayas. Hydrobiologia, 72: 101-112.
121
[7]
SEDIMENT CHEMISTRY OF KASHMIR HIMALAYAN LAKES I. Clay Mineralogy R.A. K A N G O 1, K.P. D U B E Y '~ and D.P. ZUTSHI 1 ICentre o[ Research for Development, University of Kashmir, Srinagar 6 (India) "Department of Chemistry, University o[ Kashmir, Srinagar-6 (India) ( Received July 25, 1985; revised and accepted February 5, 1987 )
Abstract Kango, R.A., Dubey, K.P. and Zutshi, D.P., 1987. Sediment chemistry of Kashmir Himalayan lakes, I. Clay mineralogy. Chem. Geol., 64: 121-126. Clay mineral content of six Kashmir Himalayan lakes (average elevation 1580 m a.s.1. ) have been determined using X-ray diffraction and differential thermal analysis. Illite, calcite and chlorite were the main clay minerals and their percentage contribution to the lake sediments differed significantly, with illite ranging from 16% to 84% and calcite between 22% and 72%. The ionic activity product (IAP) and equilibrium constant (K~) of calcium and carbonate ions for the ambient lake waters was used to trace the origin of calcite. IAP/Kc-values were much higher (48) in Trigam Lake in comparison to other water bodies.
1. I n t r o d u c t i o n
Clay minerals are present in all types of sediments and are common constituents of hydrothermal deposits. These may be of allogenic, endogenic, or authigenic origin. The distinction between clay minerals and their nature is of great help in the elucidation of different types of interactions between the sediment-water interface and in source identification. Until recently only a limited study had been made of clay mineral composition of the sediments accumulating in various environments (e.g., Swain, 1966; Anthony, 1977). Due to limited data available on the clay minerals for non-marine sediments, it is difficult to reach any definite conclusions about the origin and
0009-2541/87/$03.50
fate of the clay minerals in freshwater sediments. The Kashmir Himalayas in northwest India abound in freshwater lakes which are important for fisheries, agriculture and recreation. Many limnological investigations have been undertaken on these lakes in recent years (Zutshi and Vass, 1970, 1978; Zutshi et al., 1972, 1980), but very few studies have so far been undertaken on sediment chemistry. De-terra and Paterson (1937) presented data on the distribution of detritus and mineral grains in three basins of Dal Lake, Srinagar. Zutshi (1968) and Mir (1977) correlated biological productivity with the nutrient status of the sediments. The present investigations were carried out during 1982/1983 on six Kashmir Himalayan lake sediments.
© 1987 Elsevier Science Publishers B.V.
122
2. M a t e r i a l s a n d m e t h o d s
The clay fraction ( < 2 #m ) was separated by the sedimentation method ( Orr and Dallavalle, 1959 ). The individual clay minerals were identified by X-ray diffraction ( X R D ) and differential thermal analysis (DTA). X R D data were obtained with a Philips ® diffraction spectrophotometer using filtered Cu-K~ radiation. The semiquantitative percentage of each clay mineral was measured by the relative intensity of its principal diffraction peak. The apparatus used for DTA was assembled in the Analytical Chemistry Division of BARC, B o m b a y (an endothermal 457 temperature programme controller and a model A-IO, Rikadenki Kogyo ® Co., Japan, microvoltmeter (D.C.) was used for amplifying the thermal e.m.f.). The thermograms were recorded on the Y-axis of an X - Y recorder (model HR-11, H o u s t o n Omnigrafic ® Corp., U.S.A. ). Data on the supersaturation of ambient lake waters were used to describe the calcite precipitation. Calcium, alkalinity, temperature and pH of the water samples was determined according to Golterman and Clymo (1969). The product of calcium and carbonate ionic activities on multiplication yield the ionic activity product ( l A P ) , which was used as an index of supersaturation, lAP was computed from the following relationship: IAP
(Ca 2 ~ ) X ( C O ~
)=
',7(:~- [Ca '~* ] X ?'HC():~ XK2 X (alkalinity)} [H + ] where K2 is the second dissociation constant of carbonic acid. The activity coefficient was estimated from the extended Debye-Hiickel relation. The value of IAP of a lake compared to the equilibrium constant, K,., determines whether the lake water is undersaturated, saturated, or supersaturated.
BARAMULA
i JAMMU
~ ~ ~ I ~ (~ BANDIPORA
AND KASHMIR
/
f- /
*WULAR LAKE e
III
!
SOPORE
® ~ 1 ~ MANSBAL LAKE I~
® BARAMULA TRIGAM L A K E
~
@ GANDERBAL
~ z ~ - TI LWA N LAKE \. DAL
Q GULMARG
/
.J .J B E E R W A ,9 !
/
LAKE
.J SRINAGAR ,3 B A D G A M
,1
0
10 J
KM
@ CHADURA Fig. 1. Location of the lakes.
2.1. Description of the lakes Six Kashmir lakes, Dal, Wular, Mansbal, Anchar, Trigam and Tilwan, lying within geographical coordinates of 32-34 =N latitude and 74-74.9 ~E longitude have been selected for the present investigation. These water bodies lie in the floodplains of the river Jhelum at an average altitude of 1580 m above mean sea level ( Fig. 1). The lakes are of postglacial age and have probably originated as a result of the meandering of the alluvial deposits (Zutshi et al., 1980). Dal, Wular and Anchar are drainage-type lakes. Mansbal is a semi-drainage type and Trigam and Tilwan are non-drainage-type lakes with high water residence (Zutshi and Vass, 1978). The other morphometric parameters of the lakes are given in Table I. 3. R e s u l t s a n d d i s c u s s i o n The X R D analysis showed the presence of illite, calcite and chlorite in the sediment samples (Table II). Calcite was found to be the principal clay mineral in Anchar Lake, showing
9t~Z$~I,gBI~tHD 90,Z:~'"I
123 TABLE I Selected m o r p h o m e t r i c features of the lakes Feature
Dal
Wular
Mansbal
Anchar
Trigam
Tilwan
Surface area ( kin-' ) Maximum length (km) Maximum breadth (km) Maximum depth (m) L e n g t h of shoreline ( k m )
11.45 10.8 2.1 5 15.5
24 16 9.6 5.8 58
2.8 3.5 1.2 13.0
6.8 3.8 0.65 3.0 11.5
1.4 0.7 0.2 2.3 2.2
4.3 1.4 0.3 2.2 3.5
TABLE II
basal reflections at 3.33, 3.34 and 3.35 A (the diffraction diagrams are available from the authors on request). Dal and Wular lakes did not show any diffraction pattern for calcite, and Mansbal and Tilwan lakes were devoid of any chlorite. The DTA thermograms showed some welldefined endothermic peaks coupled with one or two less-pronounced exothermic ones. The endothermic effect in the region of 545-560 ° C was due to illite (the DTA thermograms are also available from the authors on request). In the case of the illite clay minerals the temperature interval of 200-700 ° C was characterised by the main endothermic effect within the 450-650 ° C range, the peak value was recorded at 550 °C,
Clay mineral content ( % ) of some Himalayan lakes as revealed by X-ray diffraction (diffraction peaks are given in parentheses) Lake
Illite
Calcite
Chlorite
Dal
72
(3.33 ,~, )
28
Wular (W:~) (WJ
84 81
(3.34 ,~ t
16 19
Mansbal
78
(3.35 ,~
Anchar
16
71
Trigam
52.1 (3.33
36.6
Tilwan
54.1 (3.33
45.9
22 (3.03 ~,)
13 11.3 (7.05 A)
a strong diffraction peak at 3.03 A. Other lakes had illite as the principal clay mineral, with
T A B L E III G e o c h e m i c a l data used for the e s t i m a t i o n of calcite saturation ranges in M a n s b a l L a k e Month
Temperature
(Ca ~ ' ) (10 4 m m o l l
1)
Alkalinity (10 4 m e q l
log K~ 1)
(~c) Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.
5.6 8.9 17.2 18.6 23.3 27.2 28.9 25.8 22.8 17.8 15.3 10.6
Ionic strength = 10 :~.
8.5 8.5 8.5 7.4 5.6 2.9 4.6 4.6 5.6 8.0 20.9 10
20,6 21.6 20,6 1,73 1,44 1.27 1.27 1.47 1.57 1.86 1.73 1.96
- 10.547 - 10.502 - 10.407 10.388 - 10.349 - 10.312 - 10.301 10.324 - 10.351 - 10.401 - 10.430 10.490
[ H + ] ion concentration (10 ~ m m o l l 15.1 12.3 7.94 3.16 0.813 1.20 1.58 2.69 6.16 15.1 18.6 20.4
log K ,
IAP/K,.
8.351 --8.356 - 8.380 8.388 - 8.408 8.424 - 8,441 8,528 --8.407 --8.383 -8.370 8.360
0.61 0.88 1.68 3.17 7.67 2.92 4.14 3.06 1.27 0.7 1.08 0.58
1)
124 TABLE IV Geochemical data used for the estimation of calcite saturation ranges in Trigam Lake Month
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.
Temperature (°C) 9 12.5 19.5 23.0 28.5 29.5 30 25.5 19 10.0 7
(Ca ~~ ) (10 '~mmoll 1)
Alkalinity (10 4meql 1)
log K~
[ H ~] ion concentration (10 9mmoll ~)
log K,.
IAP/K,,
13 11 11 10 10 10 11 11 11 11 11 12
78
-
3.16 2.09 1.58 2.09 3.16 1.58 1.77 1.99 1.58 1.99 3.16 7.94
-
8.356
15.68
8.364 8.390 8.408 8.441 8.451 8.451 8.420 8.388 8.360 8.353
32.40 29.23 20.76 48.59 48.03 41.25 43.39 30.54 14.20 6.08
70 70 69 67 64 62 61 65 67 69
10.50 10.460 10.370 10.349 10.301 10.289 10.289 10.330 10.388 10.490 10.528
-
Ionic strength = 10 :~
w h i c h c o r r e s p o n d e d to t h e loss of s t r u c t u r a l l y b o u n d w a t e r ( B l a z e k , 1973). T h e D T A c u r v e of calcite was c h a r a c t e r i s e d b y t h e e n d o t h e r m i c effect of d e c o m p o s i t i o n d e p i c t e d b y t h e p e a k in t h e region of 8 3 0 - 9 4 0 ° C. A n c h a r L a k e s h o w e d a s t r o n g e n d o t h e r m at ~ 854 ° C, in w h i c h calcite was t h e p r i n c i p a l m i n e r a l . I n t h e clay m i n erals of T r i g a m L a k e a n a d d i t i o n a l p r o m i n e n t e x o t h e r m m a y be a s s i g n e d to t h e s t r u c t u r a l c h a n g e s of c h l o r i t e m i n e r a l ( B l a z e k , 1973). A c c o r d i n g to J o n e s a n d B o w s e r (1978) t h e illite a n d t h e c h l o r i t e h a v e a n allogenic origin in f r e s h w a t e r lake s e d i m e n t s . A m o n g t h e t h r e e p r i n c i p a l m i n e r a l s d e t e r m i n e d in t h e p r e s e n t study, illite a n d c h l o r i t e are t h e p r o d u c t s of w e a t h e r i n g a n d e r o s i o n a l deposits. P o t t e r et al. (1975) r e p o r t e d t h a t illite a n d c h l o r i t e w e r e m a i n l y t h e r e s u l t of e r o s i o n of m i d d l e a n d lower Paleozoic s e d i m e n t s t h a t are rich in illite a n d c h l o r i t e c o n t e n t . M o o r e (1961) i n d i c a t e d t h a t in the s e d i m e n t s of L a k e M i c h i g a n , U.S.A., h a l f of t h e clay m i n e r a l s c o n s i s t e d of illite; t h e o t h e r half was chlorite a n d m i x e d - l a y e r m i n e r a l s . T h e results were i d e n t i c a l w i t h t h e a v e r a g e clay m i n e r a l c o m p o s i t i o n given for s i x t e e n till s a m ples w h i c h are c o n s i d e r e d p r i m a r y source material.
Calcite m i n e r a l c o n s t i t u t e d a n i m p o r t a n t f r a c t i o n in t h e H i m a l a y a n lake s e d i m e n t s . T h e c a r b o n a t e equilibria in n a t u r a l w a t e r s y s t e m s have been provided by Garrels and Christ (1965), B e r n e r (1971), S c h a f e r a n d S t a p f (1972), O t s u k i a n d W e t z e l (1972), S a n t a c h i (1975), a n d K e l t s a n d Hsfi (1978). M a n s b a l L a k e s e d i m e n t s h o w e d ~ 22% calcite. I n o r d e r to d e t e r m i n e its origin, t h e supers a t u r a t i o n of t h e lake w a t e r was c o n s i d e r e d i m p o r t a n t . T h e c h e m i c a l analysis of its a m b i e n t waters showed that: (1) t h e c o n c e n t r a t i o n v a l u e s of c a l c i u m r a n g e d f r o m 0.59 m e q 1 1 ( J u n e ) to 4.18 m e q l-1 in N o v e m b e r ; (2) t h e v a l u e of a l k a l i n i t y r a n g e d f r o m 6.58 m e q l - 1 in F e b r u a r y to 3.89 m e q 1 1 ( J u n e ) ; ( 3 ) t h e [ H + ] ion c o n c e n t r a t i o n r a n g e d f r o m 8.13-10 - l ° ( M a y ) to 1.51.10 s ( O c t o b e r a n d January) ; and (4) t h e t e m p e r a t u r e r a n g e d f r o m 5 . 6 ° C ( J a n u a r y ) to 28.9 ° C ( J u l y ) . T h e calculated saturation index IAP/Kc ( T a b l e I I I ) for t h i s lake i n d i c a t e d t h a t t h e lowest v a l u e s are o b t a i n e d d u r i n g winter. T h e i n c r e a s e f r o m 0.58 in D e c e m b e r to 7.67 in M a y s h o w e d p r o g r e s s i v e s u p e r s a t u r a t i o n . T h e val-
125 ues t h e n fall again, d e p i c t i n g few m i n o r irregularities. F r o m t h e s e c a l c u l a t i o n s it is e v i d e n t t h a t s o m e q u a n t i t y of c a l c i u m c a r b o n a t e m i g h t have been precipitated from the water column a f t e r May. T h u s , calcite in M a n s b a l L a k e m a y h a v e a n e n d o g e n i c origin b u t its allogenic origin c a n n o t be c o m p l e t e l y excluded. T h e e x a c t a m o u n t of calcite p r e c i p i t a t e d a n d t h e p e r c e n t age c o n t r i b u t i o n b y d i f f e r e n t sources h a v e n o t b e e n t a k e n into c o n s i d e r a t i o n in t h e p r e s e n t investigation. T h e I A P / K c - v a l u e s for T r i g a m L a k e are given in T a b l e IV. T h e s e v a l u e s were c o m p u t e d f r o m w a t e r c h e m i s t r y data. T h e values were e x t r e m e l y high d u r i n g a m a j o r p a r t of t h e year. T h e results i n d i c a t e t h a t large q u a n t i t i e s of calcite m i g h t be f a v o u r e d in t h i s lake a f t e r t h e o n s e t of s u m m e r . Calcite a m o u n t e d to ~ 36.5% of the t o t a l m i n e r a l c o m p o s i t i o n . T h e e x t r e m e l y high s u p e r s a t u r a t i o n w i t h o u t t h e p r e c i p i t a t i o n of C a C Q m a y be due to t h e f o r m a t i o n of s t a b l e organic c o m p l e x e s in t h e lake water. K i t a n o a n d H o o d (1965) h a v e s h o w n t h a t o r g a n i c c o m p o u n d s such as c i t r a t e s , m a l a t e s , etc., w i t h s t r o n g a f f i n i t y for c a l c i u m r e t a r d t h e r a t e of c a r b o n a t e p r e c i p i t a t i o n . B e r n e r (1971) also r e p o r t e d t h a t t h e p r e c i p i t a t i o n of c a l c i u m carb o n a t e does n o t t a k e place in s i l i c a t e - m u d p o r e w a t e r rich in s u s p e n d e d organic m a t t e r . In A n c h a r L a k e , calcite is p r o b a b l y allogenic b e c a u s e of t h e f a c t t h a t t h e f l u s h i n g r a t e in t h i s lake is e x t r e m e l y high, giving less t i m e for t h e w a t e r c o l u m n to i n t e r a c t a n d a c h i e v e t h e r m o dynamic equilibrium.
Acknowledgements T h e a u t h o r s wish to t h a n k Dr. P . N . G u p t a of t h e C h e m i s t r y D e p a r t m e n t , U n i v e r s i t y of K a s h m i r , for his help d u r i n g t h e p r e p a r a t i o n of this p a p e r .
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