Dataset (PDF Available) · June 2013with434 Reads
  • [Show abstract] [Hide abstract] ABSTRACT: The Hindu Kush–Himalayan Mountains extend 3500 km, cover 3.5 million km2, and include parts of 8 countries. They are home to many spectacular lakes and wetlands, a major source of water and regulators of water storage. Eighty-four peaks above 7300 m and innumerable others over 6000 m are interspersed with thousands of lakes and wetlands, some of which are rich in biodiversity and are home to rare species. Whereas the mountains have attracted attention, there is very little documentation on water bodies in the region. Some lakes are above 5000 m. Conservation of these fragile ecosystems is important, particularly in an era of international tourism, climate change, and megaprojects in the region.
    Article · Jan 2009
  • [Show abstract] [Hide abstract] ABSTRACT: The geochemical study of the Dankar, Thinam and Gete lakes of the Spiti Valley has revealed that these lakes are characterized by varying contents of major ions, i.e. Ca, Mg, HCO3, Na, K, Cl, SO4, SiO2 and Sr as trace element. The concentration of these elements is significant, as they indicate the nature of the lithology and the type of weathering at the source. The sediment chemistry data have also been employed to quantify weathering intensity and to elucidate the provenance and basin tectonic setting where terrigenous sediment is deposited. Dankar Lake is located on the limestone-dolomite-rich Lilang Group of rocks (Triassic), and dissolution of carbonate is the prime source of ionic concentration in this lake. The high (Ca+Mg):HCO3 equivalent ratio of 6.94 indicates carbonate weathering, and the very low (Na+K):TZ+ ratio of 0.07, which is used as an indicator of silicate weathering, shows insignificant silica dissolution in this lake. On the other hand, in Lake Thinam a relatively low (Ca+Mg):HCO3 equivalent ratio of 2.09, a (Na+K):TZ+ ratio of 0.12 and other parameters indicate that carbonate is derived from calcareous nodules and thin intercalations of limestone in the Spiti shales (Jurassic), and also some contribution from silicate lithology is evident. Mixing of groundwater cannot be ruled out, as springs are observed in this lake. In Lake Gete, the (Ca+Mg):HCO3 equivalent ratio is again high at 5.04, and the (Na+K):TZ+ ratio is 0.15, indicating dissolution of both carbonate and silicate rocks in the basin. This is consistent with the corresponding lithology in the lakes, and their denudation. Very high Sr contents of 2,331 µg/l in Dankar Lake, 715 µg/l in Gete Lake and 160 µg/l in Thinam Lake are significant and support dissolution of carbonate rocks, as the silicate rocks contribute less Sr although its isotopic ratio is high. It is also reflected that mechanical erosion and chemical weathering are perhaps the effective processes in this region. The former exposes fresh mineral surface for dissolution. The chemical index of alteration (CIA), with an average value of 78.79 in Dankar and 81.06 in Gete, indicates high weathering conditions. The K2O–Fe2O3–Al2O3 triangular plots of the samples demonstrate residual clay formation, indicating intense weathering at the source. The clay mineralogical data corroborate the above observation. The sediment chemistry data document depletion in SiO2 and Al2O3, as they are enriched in carbonates and depleted in Na2O, K2O, MnO, and TiO2, as compared to PAAS and UCC which are related to strong weathering at the source. The positive linear correlation between K and Rb suggests that they are contained in the illitic phase, and high positive correlation of Zr and Y with SiO2 indicates their association with coarser-grain, quartz-rich sandstone. The high phyllosilicates and low feldspar and major element chemistry indicate recycling and mineral maturity of sediments deposited in the Tethyan basin in a passive margin setting. This also indicates older sedimentary-metasedimentary rocks which are ideally exposed in the Spiti Valley. The tectonic discriminant plots portray a passive margin tectonic setting of the detritus in these lakes.
    Article · Jan 2003
  • [Show abstract] [Hide abstract] ABSTRACT: The magnetic compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, "Cluster N", show high neuronal activity when night-migratory songbirds perform magnetic compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference compass direction of the geomagnetic field and that migratory birds "see" the reference compass direction provided by the geomagnetic field.
    Full-text · Article · Feb 2007
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