Proc. lndian Acad. ScL, Vol. 87 A (E & P sciences-z), No.7, July 1978,pp. 77-88, @ printed in India Input by Indian rivers into the world oceans V SUBRAMANIAN School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067 MS received 16 March 1978; revised 31 May 1978 Abstract. The chemical, sediment and total load carried by the major river basins in India-Ganges, Brahmaputra, Indus (Jhelum), Godavari, Krishna, Narmada, Tapti, Mahanadi and Cauvery have been calculated, based partly on new set of data and partly on existing data. There is a significant amount of chemical load transported by all the Indian rivers, and for global mass transfer calculation, these cannot and should not be ignored. The chemical mass transfer during the monsoon is not surpri­ singly small, as would be expected for excess discharge and dilution controlled run­ off. The sediment mass transfer from non-Hirnalyan rivers, all within the same range of magnitude, accounts for less than a tenth of that of the Ganges but during the monsoon, except for Cauvery, all the Indian rivers carry a sediment load of greater than 1000 ppm. The total mass transfer from the Indian subcontinent accounts for 6'5 per cent of the global transfer. Except for the Ganges and the Brahmaputra, the erosion rates are similar for all Indian basins, independent of their size and these rates are agreeable with the conti­ nental earth average. The Ganges-Brahmaputra basin erosion rates are highest on the continental earth. Based on the average rate of denudation of the Indian sub­ continent, the mean elevation of this landmass will be that of the present day mean sea level in 5 million years from now. The average denudation rate of 2'1 cmjl00 years is different from the calculated average sedimentation rate of 6'7 cmjl00 years in the Bay of Bengal suggesting that an accurate erosion rate in the continent is needed to determine sedimentation rate in the oceans. The chemical and sediment mass transfer rates appear to have a logarithmic linear relationship on a global scale, as against the reported negative logarithmic trend for North America alone. Keywords. Mass transfer: Indian rivers; chemical load; sediment load; total load; erosion rate; basin changes. 1. Introduction Continental mass transfer into the oceans in the present day environment need to be understood well for a variety ofreasons: the principal one among them is the possible fluctuation in the mass transfer in the geological past with implications on the evolu­ tion of the oceans, on one hand, and the sedimentary rocks, on the other. The pre­ sently accepted proposition on the constancy of chemical composition of the sea water for the last 600 million years implies similar invariance of the mass transfer over the same period. The sedimentary recycling model, propounded by Garrels and Mackenzie (1971a) depends very much on the uniform rate of continental input into world oceans since Cambrian time; however, Gregor (1970) calculated an erosion rate for the paleozoic period to be nearly four times that for the present day environ­ ment; on the other hand, Garrels and Mackenzie (1971b) calculated a depositional rate which is less than one fourth of paleozoic erosion rate of Gregor. Everi though 77 78 V.Suaramanian sedimentary rocks constitute a very insignificant portion of the total rock mass in the crustal earth, more than 90 per cent of rocks on the surface, the part of the earth intimately associated with weathering, erosion and mass transfer, represent some type of sediments. Hence mass transfer can be thought to involve, recycling of all the recent and ancient sedimentary rocks, whose mass is estimated to be 32 x 10~o kg. Based on the chemical analysis of a number ofmajor rivers in the world, compiled by Livingstone (1963) and data on the suspended sediment transport, compiled by Holeman (1968), Gibbs (1972a) has tabulated chemical and sediment mass transfer for these rivers. There are several limitations to the data compiled by various wor­ kers: First, there is no common agreement among the various set of data probably because of different sources of data; there is no agreement on the average mass trans­ port which is being continuously revised; but the principal deficiency of the existing numbers is the lack of accurate information on a number of Asian drainage basins and the total neglect of basins in Asia which are big enough to be quantitatively significant but whose discharge may not qualify it to be among the -largest basins of the world. To this category belongs basins such as Godavari. As pointed out by Mebeck (1976), middle-size homogenous basins are ideal for the mass transfer studies since in these basins several environmental factors can be well defined. In India, except [or the Ganges and Brahmaputra, all other important basins, namely, Goda­ vari, Mahanadi, Narmada, Tapti, Krishna and Cauvery are middle-size of the order of (1-3)105 km2 basin area and together they add up to half the basin size of Ganges and Brahmaputra. Hence, any mass transfer studies ignoring these second order basins will be quantitatively not reliable; with this limitation in mind, an attempt has been made in this paper to understand the net mass transfer from the entire Indian subcontinent into the world oceans. %. Sampling and source of additional data For the eight major basins in India, water samples were collected at a number of stations. For each basin, one station in the watershed and other in the mouth (for example, Hoshingabad and Broach for Narmada) were chosen. Two litres water samples were collected in polyethylene bottles, pH and alkalinity measured immedi­ ately (pH with Phillips portable pH meter and carbonate alkalinity by micropipette titration techniques), sealed tight and with wax outside and sent to the laboratory. The samples were filtered through millipore 0·45 micron membrane filters to collect the suspended matter and the filtered water was used for elemental analysis. Water samples were collected once during May 1-15 and again during July 15-Aug.. 15, 1977. Chlorinity was measured by AgNOa titration, Na and K by emission mode and Ca and Mg by absorption mode of AAS-l spectrophotometer. S04-2, P04- 3 and silicates were analysed by standard complexation techniques for fresh waters (Golterman 1970) using ECIl spectrophotometer; conductivity was measured with II syntronic direct reading conductivity meter, standardised with 0·1 N KCl solution. In dilute waters such as fresh waters, the conductivity values can be converted to total dissolved salts, by certain multiplication factors or.can be numerically equated to TDS (Davis and Dewiest, 1967). Such conversions were checked with the actual chemical analysis and were used only where the numbers matched; otherwise, the actual chemical.analyses were summed to get TDS. Input by Indian rivers into the world oceans 19 Data for the winter season were taken from the file of Central Soil and Material Research Station, New Delhi. The average values for 1972 to 1976 were taken for calculations. The discharge values and basin areas for the rivers were taken either from Rao (1975) or the Newsletters of the Indian National Committee for IHD (1972-77). Pooling of data from such diverse sources puts some limitationson the interpretation but in this paper a beginning has been made by pooling such data with the ones generated by the author; this is still not satisfactory and interpretations presented here are bound by these limitations. It is further realised here that monthly, preferably daily, sampling will better reflect the natural process but sampling costs and logistics dictate optimisation of fieldwork. It is hoped to refine the data presented here with continued observations during the next few years. As such, interpretations presented in this paper do not represent the last word in the mass transfer studies. 3. Chemical mass transfer Table I indicates the annual chemical and suspended load, total denudation and various rates calculations from the f3,W data (CSMRS, 1973 ar.d Subramanian, present manuscript) for the eight Indian river basins under investigation. For com­ parison, data for the major river basins, such as Amazon, Mississippi, _Congo, Mekong, etc. are computed in table 2. Continent-wise mass transfer are presented ill table 3. Based on their limited sampling, Carbonnel and Meybeck (197STcalcu1ated the chemical mass transfer from the Mekong basin to be a very significant portion ofthe total chemical load input into the world oceans; but a look into the respective values in tables I, 2 and 3 suggest that the entire Asian continent contributes a maximum 40 %of the chemical load and out of this, the Mekong's contribution is a mere 4 % and on the total input, Mekong accounts for less than 2% of the chemical load. All the Indian rivers together contribute about 6 %of the chemical load. Since the land mass ofIndia accounts for a mere 2 %of the continental earth, she contributes the chemical load much in excess of her size. In other words, compared to the chemi­ cal denudation rate of 2·3 x 104 kgjkm2 /yr for the continental earth, the chemical Table 1. Denudation rates for major Indian rivers Chemical Sediment Total Chemical Sediment Total Basinload loadrate rate denuda- lOt kg/yr load io- kg/km2/yr tion rate Cauvery 7-60 0·71 8'31 8·70 0·87 9'57 Krishna 15·01 8'50 23-51 6·11 HI 9-42 Godavari 22'02 16·20 38'22 7-32 5-30 12-60 Narmada 11-03 6'20 17-23 12·11 7·00 i9·10 Tapti 5-31 2·70 8'01 8'75 4'30 13'00 Mahanadi 8-41 7-10 15·51 6'43 5-40 11·80 Ganges 71'04 460'10 531-14 7-32 47-21 54'51 Brahmaputra 81-03 711'20 792>23 12·26 110'11 122-31 India Total 221'45 1212·71 1434'16 8'61 46'81 55-42 80 V Subramanian Table 1.