Current Research - Himalayan Lake Study

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Reconstruction of the Holocene climatic history
and recent anthropogenic changes
in the southwestern Himalayas (Panjab and Kumaun Lakes)

1. Aim of the study
Sedimentation in lakes is much more affected by regional tectonic and climatic processes than the sedimentation in the oceans. However, many lake studies have shown that regional climatic oscillations can be related to global climatic processes. In this project we investigate lake sediments from the southwestern Himalayas.
The marine monsoon record from the northern Indian Ocean has been extensively studied during the last few years. Data from the continent are, however, very scarce. The aims of this investigation are (i) a reconstruction of the Holocene climatic history in the southwestern Himalayas based on sediment cores from the Mansar Lake as well as (ii) the investigation of the impact of anthropogenic activity on lake chemistry and sedimentation during the last 200-300 years in the Panjab and Kumaun Himalaya. Samples provided by our project partner at the Panjab University, Chandigarh, India, consist of subsamples from a long core from the Mansar Lake spanning almost the complete Holocene record. Furthermore, samples from six short sediment cores from Himalayan lakes with different levels of anthropogenic pollution have been supplied (Renuka, Rewalsar, Nainital, Bhimtal, Naukuchiyatal and Sattal Lakes).
Inorganic geochemical as well as biogeochemical investigations on these samples will provide information on the changes in the sources of clastic material, the weathering intensity, primary productivity and the organic matter source. The combination of these results will add to a reconstruction of the climatic history of the western Himalayas and will be compared to the information from the marine record of the northern Indian Ocean, the ice core record, and results from other lake studies.

2. Study Area
a ) The Mansar Lake is situated 60 km east of Jammu at an altitude of 666 m at 75°23`E und 32°48`N. It is the largest fresh water lake of Jammu and Kashmir state with an area of 0.53 km2 and a circumference of 3020 m. The lake does not freeze in winter and is considered as oligotrophic. It has no natural tributaries and is fed primarily by ground water through springs. It is a tectonic lake situated at the WNW-NW and ESE-SE striking Surin-Mastarh anticline. The lithology in the catchments consists of the sedimentary sequence of the Lower Siwaliks which has been deposited between the mid Miocene and the mid Pleistocene. The lower Siwaliks consist of sand stones interlayered with silt- and claystone bands of 1-2 m thickness., purple shales, nodular conglomeratic shales and breccia.
The Mansar Lake water is of alkaline-earth-bicarbonate type. Total dissolved solids reach 140 mg/L. Chemical weathering of silicate rocks is the primary source of solutes in the lake. Pollution in the catchment area is low. The Mansar lake is oligotrophic having very low phosphate concentrations, partly below detection limit (Das and Kakkar, 2000). The organic carbon concentration in surface sediments is 2-3 %. The anthropogenic pollution of the lake is less as the area is sparcely populated.

b) The Rewalsar Lake is situated at an altitude of 1400 m, 16 km from the city of Mandi in the state Himachal Pradesh. Its maximum depth is 6,5 m. The catchment area is situated to the north and west of the lake. Surface water flow into the lake is low except during the monsoons which is characterized by moderate to high precipitation in the areas. The lithology is mid Siwaliks consisting of fine-grained, light coloured sand stones with silt- and clay interlayering. Flakes of mica are observable in siltstones. A thin clay rich soil has been formed on the Siwaliks. Similar to the Mansar the Rewalsar lake is oligotrophic. As it is a religious centre the environment has been kept largely in its pristine condition so that the anthropogenic imprint is even less than on the Mansar lake (Das et al., unpublished). The trace metal concentration in surface sediments are lower than the reference values of the PAAS (Post Archaean Australian Shale), NASC (North American Shale Composite) or UCC (Upper Continental Crust) so that they are considered to be derived from a crustal source.

c) The Renuka Lake is situated at an altitude of 620 m, 35 km and 125 km away from the cities Nahan and, respectively, Chandigarh in the state Himachal Pradesh. The oval lake has a length of 1050 m, a width of 204 m and a maximal depth of 13 m. Together with the Parashram Tal it is an abandoned course of the Giri River. The lake is fed by rain water, ground water and a few small watersheds. The Proterozoic rocks of the catchment are strongly disrupted by Krol-Giri thrust. The rocks of the Infra-Krol formation consist of iron and pyrite rich black limestones, black carbonaceous shales and slatey quartzites. On top of the Krol formation there are red and green shists, dolomitic and cherty limestones and well bedded light coloured limestones and cherts. Due to the presence of organic rich shales including black shales in the catchment area the nutrient concentrations and thus the productivity are much higher than in the Rewalsar und Mansar Lakes although the level of pollution is not much higher than in the catchment areas of the latter two lakes. The higher productivity is reflected in organic carbon contents of about 8 % in surface sediments and in amounts of total dissolved solids twice as high as in the oligotrophic lakes (TDS=360-420 mg/L). Phosphate concentrations are between 1 and 15 ?g/l. The weathering of black shales leads to high sulfate concentrations. The major anions carbonate and sulfate as well the major kations calcium and magnesium make up about 45 % of total an- and kations each (Das and Kaur, 2001). The Renuka Lake is supersaturated with dolomite and calcite. There is a wetland to the west of the lake.

d) The lakes of the Kumaun-Himalaya are all close to the intensively utilized tourist resort of Nainital. Investigations of Das (2001) have shown an increasing level of pollution due to changes in land use and sewage discharge form the Sattal, Naukuchiyatal, Bhimtal to the Nainital Lake. All these lakes are of tectonic origin and have been formed in the Holocene. The rocks in the catchment area belong primarily to the Krol-formation. The Nainital Lake is a tourist centre. Its surrounding area is densely populated and largely deforested and sealed. The erosion rate and the resulting input of suspension are, consequently, very high. The Krol-formation in the catchment area consists of dolomites, carbonaceous shales, iron rich shales, greywacks and gypsum. Consequently, the contents of bicarbonate ions (75 %) and sulfate (25 %) are high. Kations are dominated by magnesium from the dolomites. Eutrophication is reflected in phosphate contents 124 to 174 ?g/L being more than tenfold than in the Renuka Lake.
The Bhimtal and Naukuchiyatal Lakes have metabasites, quartzites, konglomerates, phyllites and green schists on their banks which are not very densely populated. The chemical composition of the lake reflects the lower grade of pollution. Phosphate concentrations in the Bhimtal Lake are 28.8 and 6.6 ?g/l which is higher than in the Renuka Lake. Phosphate concentrations in the Naukuchiyatal and Sattal Lakes are in the same range as in the Renuka Lake. Heavy metal concentrations have been measured in lake suspension and sediments of the Nainital Lake. Whereas suspended matter shows manyfold enrichment compared to the rock standard of Turekian und Wedepohl (1961) sediments show high concentrations only for a few metals typical of anthropogenic pollution such as Cr, Zn and Pb (Das et al., 1995). This is probably due to the strong dilution by the enormous amounts of silt and sand transported into the lake during the rainy season from the deforested catchment area (Das et al., 1995).

Little is known about the seasonality of primary productivity and sedimentation in the lakes. The productivity in the more pristine lakes depends on the lithology in the catchment area. Investigations in the Kumaun Lakes have shown low nutrient concentrations in surface waters compared to 5 m water depth implying that the water column is stratified, especially during the hot pre-monsoon season. The major input of nutrients, probably, occurs during the monsoon season due to erosion. The denser cloud cover and the high suspended matter concentrations would lead to light limitation during part of this season. We would expect that the productivity maximum occurs after the monsoons when the suspension has settled out so that abundant light is available and the large amounts of nutrients can be utilised. In winter when light is, probably, not limiting temperature induced convection could also lead to higher productivity compared to the strongly stratified pre-monsoon. We would also expect that the overall seasonality is stronger in the oligotrophic lakes with an intense post monsoon bloom.

Lake	Altitude [m]	Size	Maximum depth [m]	Rate of sedimentation [mm a-1]	Precipitation [mm a-1]	Anthropogenic activity
Mansar	666	1.1 km, 0.6 km, 0.53 km2	40	4.5 – 8.5	80-100	Low, oligotrophic
Rewalsar	1400	1.0 km, 0.5 km	6.5	3.0	100-200	Very Low, oligotrophic
Renuka	620	1,05 km, 0,204 km; 670 ha	13	3.3	150-200	Moderate, mesotrophic
Sattal	1286	1.3 km, 0.2 km	20	3.0	200	Low, mesotrophic
Naukuchiyatal	1219	0.95 km, 0.69 km	40,2	3.7	200	Low, mesotrophic
Bhimtal	~1200	1.8 km, 0.45 km	26.5	4.7	200	Moderate, mesotrophic
Nainital	1938	1.5 km, 0.36 km	27	11.5	249	High eutrophic (Anoxia observed)

Das, B.K. and Dhiman, S.C., 2003. Chemical characteristics of waters in Higher Himalayan Lakes in Spiti Valley, Himachal Pradesh, India "ARPAN" Kurukshetra, Vol.2, Nos. 1-2, 1-21.

Das, B.K. and Dhiman . S.C., 2003.Water and sediment chemistry of Higher Himalayan Lakes in the Spiti Valley: control on weathering, provenance and tectonic setting of the basin. Jour Env. Geol., vol. 44, No.6, 717-730.

AL-Mikhlafi, Das. B.K., Kaur, P., 2003. Water chemistry of Mansar Lake (India)- an indication of source area weathering and seasonal variability. Jour. Env. Geol. Vol.44, No.6, 645-653.

Das, B.K., 2002. Biogeochemistry as indicator of organic matter sources, paleolimnological and paleoenvironmental changes in lacustrine sediments- a study of Himalayan lakes. Jour. Env. Geosciences, Vol. 9, No.3, 115-126.

Das, B.K.. 2002. Environmental pollution of surface water- a case study of Kumaun Himalayan Lakes. Jourrnal "ARPAN" Kurukshetra University, Haryana. Das, B.K., 2002. Ecohydrologyand biogeochemistry of the Himalayan lakes: a case study. Proceedings of Symposium "Ecohydrology", Jawaharlal Nehru University, New Delhi, November 2001, V.Subramanian and AL Ramanathan(eds.).

Das, B.K., Kaur, Parkash., 2001. Major ion chemistry and weathering processes of the Mansar Lake and weathering processes, Sirmur District, Himachal Pradesh, India. Env. Geology, 40, 908-917.

Das, B.K. and Kakkar, R.K., 2000. Major ion chemistry and weathering processes of the Mansar Lake, sub-Himalaya, Jammu, India. Jour. Pun. Academy Sciences, 2 (1), 241-247.

Das, B. K, Schafer. P., Jennerjahn. T.C., l999. Biogeochemical Studies in Lesser Himalayan Lakes of Jammu District, India. Mitt. Geol.-Palaont. Inst. Univ. Hamburg. 82, 245-253.

Das, B.K.Singh, M., Van Grieken, R, l995. The elemental chemistry of sediments in the Nainital Lake, Kumaun Himalaya, India. The Scie. of Total Environment, 168, 85-90.

Scientist in Charge
Dr. B. Gaye, Dr. M. G. Wiesner

Duration of Project:
2005-2006 (DFG Grant No. Ga 755/3-1)