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B. R. Manjunatha ¹, R. Shankar ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri - 574 199, IN

Abstract

Physico-chemical properties of water (pH, dissolved oxygen, salinity and suspended matter concentrations) and geochemistry (Cu, Pb, Zn, Ni, Co, Mn, Fe, Al, Ca and loss-on-ignition) of suspended particulates have been measured for the first time in the Netravati-Gurpur estuary and the adjacent coastal environment, southwestern India. The main objective was to understand the influence of physico-chemical properties of estuarine and coastal waters on the behaviour, association and dispersal patterns of particulate metals.

Suspended particulate matter (SPM) from the estuarine and coastal environments have higher Cu, Pb and Zn (by factors of 1.5-2.7) than the Netravati-Gurpur riverine SPM, indicating enrichment of these metals with increasing salinity. In contrast, Al, Fe, Mn, Co and Ni contents and the corresponding metaltal ratios are marginally lower (by factors of 1.1 - 1.5) than those for riverine SPM, suggesting not only a decrease of terrigenous influx seaward, but also removal of trace metals from the particulate phase. R-mode factor analysis of the data has shown that detrital particles (with Fe oxide coating), clays and Mn-oxide are the major factors that control particulate metal association. Factor score distribution patterns suggest that detrital particles coated with Fe oxide are deposited in the estuary and nearshore region, whereas clays and Mn-oxide seem to be transported further into the coastal sea. Copper, Pb and Zn show an anomalous behaviour and are negatively loaded on all the three major factors.

Keywords

Estuarine Geochemistry, Particulate Metal Association, Elemental Dispersal Patterns, Netravati-Gurpur Estuary, West Coast, India.

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B. R. Manjunatha ¹, R. Shankar ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri-574199, IN

Abstract

Magnetic susceptibility and sedimentological studies have been carried out on Netravati and Gurpur river-bed sediments along the west coast of India to throw light on the distribution and movement of magnetic minerals in the riverine environment. The sediments studied are coarse to fine sands, platy to leptokurtic and poorly to well sorted. Granule to medium size sands dominate in the upstream segment. whereas very fine sand and silt+clay are either absent or of negligible importance. Netravati river-bed sediments have a two-fold higher bulk susceptibility than Gurpur sediments because the Netravati drainage basin has magnetite quartzites, amphibolites and garnetiferous biotite gneisses in contrast to granitoids found in the Gurpur drainage basin. This trend of susceptibility is seen for the 13 particle size fractions studied.

Magnetic minerals are concentrated in poorly sorted, fine grained sediments of Netravati river and in leptokurtic sediments ofGurpurriver. They are particularly enriched in the size range of 0.063-0.125 mm and to a lesser extent in the >4 mm fraction. Downstream decrease in susceptibility of both bulk samples and particle size fractions reflects on the vicinity or otherwise of sampling sites to the source of magnetic minerals in the drainage basin.

On the basis of bulk susceptibility data, it is.estimated that about 87% of sediment in the Netravati main river is derived from Kumaradhari river and 13% from Netravati (upstream) tributary. However. about 78% of particles >0.35 mm in size in Netravati main river are contributed by Kumaradhari river and 22% by Netravati (upstream) tributary. The bulk susceptibility of Ourpur river sediments shows that the Venoor hole is the dominant sediment contributor (83%) to the main river when compared to Hosangadi hole (17%). In contrast, Hosangadi hole contributes ca. 63% of the fine particles (0.55-1.0 mm) to the Gurpur main channel. This discrepancy could be attributed to the higher susceptibility of coarse fraction (> 1 mm) of Gurpur (main) river when compared to its tributaries.

Magnetite is the most important mineral that accounts for nearly a half of the susceptibility. Magnetite weight percentage and susceptibility are significantly correlated (r=O.50). About 21 % of the suspectibility is explained by ilmentite and garnets. Amphiboles, pyroxenes and other weakly magnetic minerals account for ca. 27% of the susceptibility. The residual fraction, censtituting ca. 60% of sample weight, explains only 8% of the susceptibility of samples.

Keywords

Sedimentology, Magnetic Susceptibility, River Sediments, Netravati and Gurpur Rivers, Karnataka.

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R. Shankar ¹, B. R. Manjunatha ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangothri-574 199, IN

Abstract

Radiocarbon measurements of a core from the Laccadive Trough, SE Arabian Sea have yielded ages which show that sediments from the Pleistocene, Holocene and a transition zone can be recognized by virtue of colour variation. The mean sedimentation rate decreases from 4.11 to 3.15 cm/10³yr for Pleistocene and Holocene respectively, witha peak of 6.36 cmcm/10³yr determined for the transitional zone. A sediment slump or turbidite emplacement resulting from higher terrigenous influx during the transition period has been inferred. This is in contrast to the bioclastic turbidite of the central continental margin-pelagic region (off Bombay-Ratnagiri sector of western India). The decrease in sedimentation rate from Pleistocene to Holocene can be most likely ascribed to entrapment of riverine sediments in estuaries and continental shelf, as a result of Holocene sea level rise.

The mean sedimentation rate in the Laccadive Trough (3.84 cm/10³yr) is lower than that on the northwestern continental margin of India (4.6-9.8 cm/10³yr) because of relatively low terrigenous influx from the small west-flowing rivers of Peninsular India. The Holocene sediment thickness in the Laccadive Trough is 35 cm as against 50 cm in the northeastern Arabian Sea. The onset of environmental conditions representative of Holocene is estimated at ca. 9300 yr B.P. which corroborates the date proposed for the northern Indian Ocean.

Keywords

Sedimentation, Quaternary, Laccadive Trough, Arabian Sea.

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R. Shankar ¹, B. R. Manjunatha ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri- 574 199, IN

Abstract

Physico-chemical parameters of water (pH, dissolved oxygen, salinity and suspended Particulate concentration) and geochemistry (Cu, Pb, Zn, Ni, Co, Mn, Fe, Al, Ca and organic matter) and magnetic susceptibility of suspended particulates have been measured, incidentally for the first rime. in two west-flowing rivers - Netravati and Gurpur - of southwestern India in order to understand weathering processes, to determine gross particulate metal fluxes to the coastal Arabian Sea and to decipher anthropogenic influences, if any. Physico-chemical parameters do not show significant variations because of the heavy fresh water discharge during southwest monsoon. The composition of Netravati and Gurpur rivers SPM (suspended particulate matter) are similar and characterized by enrichment of Al, Fe, Ni and Co but strong depletion of Ca in comparison with temperate and major rivers of the world. This is an imprint of the intense chemical weathering in the study area. Copper, Pb, Zn and Mn contents in Netravati and Gurpur R. SPM are lower than world river SPM, implying that there may not be significant anthropogenic input of these metals.

The gross particulate metal fluxes from the Netravati R. are considerably higher than those in Gurpur R, because of the former's high sediment discharge. However, the fluxes are significantly lower than those of Narbada and Tapti rivers.

Magnetic susceptibility of Netravati and Gurpur SPM is nearly the same, but substantially low (by a factor of three) when compared to the silt+clay fraction of river-bed sediments, indicating that dense magnetic minerals are not transported in suspension but as bed-load.

Keywords

Geochemistry, Marine Geology, West Coast, Arabian Sea.

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K. Balakrishna ¹, B. R. Manjunatha ², R. Shankar ¹

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri 574 199, IN
2 Marine Chemistry Division, Bedford Institute of Oceanography, Dartmouth, NS-B2Y 4A2, CA

Abstract

River water-sea water mixing experiments were carried out to study the time dependence of flocculation process, the flocculation behaviour of dissolved Cu, Pb, Zn, Ni, Co, Mn, Cr and Fe in the Kali estuary. Flocculation appears to be maximum at high salinities (>25‰) and is rapid, about 7 to 60% of the dissolved metal content flocculating within half an hour of mixing. This brings out the role of sea water as a powerful flocculating agent for the dissolved load of river water.

Keywords

Marine Geology, Pollution, West Coast, Kali River, Karnataka.

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A. R. Karbassi ¹, R. Shankar ², B. R. Manjunatha ²

Affiliations
1 Institute of Environmental Studies, Tehran University, P.O. Box 14155-6135, Tehran, IR
2 Department of Marine Geology, Mangalore University, Mangalagangotri - 574 199, IN

Abstract

A sediment core collected from the shelf (50 m water depth) off the Mulki-Pavanje river mouth has been studied for down-core variations of base metals, magnetic susceptibility (x_m) and partitioning of metals in various accumulative phases of sediment, to understand the impact of late Quaternary sea level fluctuations on shelf sedimentation processes.

The 192 cm-long core may be demarcated into two zones: the lower (140 to 192 cm) dark green to greenish black clayey silt with abundant plant debris; and the upper (0 to 140 cm) light green to dark green silty sand. Sediments of the lower zone are characterised by higher Cu, Zn, Pb, Co, Mn, Fe, Al, x_m and organic matter contents and higher metal/Al ratios, but lower Ca, and Pb/Al and Mn/Al ratios when compared to the upper zone indicating textural control on the geochemistry of sediments. Although Mn is high in the lower zone, the low Mn/Al ratios suggest that a part of Mn has been remobilised under anoxic-sulphidic conditions. Higher Pb/Al ratios in the upper zone may not imply mobilisation of Pb, but may be suggestive of anthropogenic input of this element from the use of leaded petrol in modern times.

Geochemical and textural variations of these sediments suggest changes in the depositional environments: Sediments of the lower zone were deposited in a marshy environment when the core site was close to the shore during the late Pleistocene low stand of sea level. The late Quaternary sea level rise led to a shift in the depositional environment - from marsh to a still stand beach environment- when silty sands were deposited. Although the core site has been in the shelf since the beginning of Holocene, there has not been much sedimentation not only because of the negligible quantity of sediment supplied by the small west-flowing rivers but also due to the rapid rise in sea level during early Holocene. The reconstructed depositional history of the core is in consonance with the recently proposed sea level curve for the western continental margin of India.

Keywords

Geochemistry, Late Quaternary, Sea level Fluctuations, western Continental Shelf, Mulki, Karnataka.

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Minal Gune ¹, K. Balakrishna ¹, H. N. Udayashankar ¹, B. R. Manjunatha ²

Affiliations
1 Department of Civil Engineering, Manipal Institute of Technology, Manipal University, Manipal-576104, IN
2 Department of Marine Geology, Mangalore University, Mangalagangothri-574199, IN

Abstract

This study focuses on the seasonal variations in ground water, river water chemistry and estimation of ground water budgeting using chloride mass balance method around Mulki River basin. Chloride ion is used as a tracer due to its conservative nature, thus making it easier for estimation of ground water budgeting as well as to assess the sources in river and ground water of Mulki River basin. The seasonal variability of major ions, Na/Cl ratio in ground water and river water revealed that, the dissolution of Ca-bearing silicate rocks and atmospheric inputs are the major sources vis-a-vis anthropogenic sources. The annual ground water recharge estimation reveals that the mean ground water recharge (272 mm/year) is lower than the mean river water discharge (58 m³/s) and annual rainfall (3763 mm). This decrease in the ground water recharge may be due to the impact of evapotranspiration (1466 mm/year), high discharge in to the river due to steep slope and the presence of granitic terrain that possess less porosity and are of impermeable nature. This method is found to be suitable for ground water budgeting in places where there are less number of rain gauge stations on river basins in India. This baseline study would be very helpful for ground water modelling and water resource management. This work could be the first report on the seasonal variability of major ions, their source determination using chloride ion as a tracer in ground water, river water and also water budgeting using chloride mass balance technique in Mulki River basin Southwest coast of India.

Keywords

Major Ion Concentration, Seasonal Variations, Principal Component Analysis, Chloride Mass Balance, Thematic Mapping.

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