Numerical Simulation of Tsunamis on the Tamil Nadu Coast of India

The State of Tamil Nadu was the most affected region in India during the tsunami of December 26, 2004, in the Indian Ocean, in terms of loss of life and damage. Numerical simulation was made for three tsunamis, the December 26, 2004, event, the Sumatra tsunami of 1833, and a hypothetical tsunami originating in the Andaman-Nicobar region. Since inundation is not included in these simulations, the tsunami amplitudes were deduced at the 10m depth contour in the ocean, off several locations on the coast of Tamil Nadu. The computed amplitudes appear reasonable as compared to known tsunami amplitudes from past events.     

Evaluation of environmental status and geochemical assessment of sediments,Manasbal Lake,Kashmir, India

The present study was conducted on the Manasbal Lake (34°14′N: 74°40′E) to assess the geochemical characteristics of the lake bottom sediments, its environmental implications and its response in the local catchment area. This study tracks the spatial distribution of grain size, geochemical analysis, C/N ratio, calcium carbonate (CaCO₃) and organic matter (OM) of the lake bottom sediments. It is observed that the clay fraction (49.79%) is predominant in the lake bottom sediments, followed by silt (35.88%) and sand (14.33%) and its spatial distribution is controlled by water depth. Geochemistry and normalized diagrams for the major oxides and trace elements reveal enrichment of CaO, K₂O, P₂O₅, S, Cl, Ni, Zn and Sr. Chemical index of alteration (CIA) reflects low to moderate weathering intensity and near compositional similarity with the bedrock exposed in the catchment area around the lake. Environmental indices (EF, Igeo) suggest that the sediments are enriched in Cu, Ni, Zn, Cr, Co, Pb followed by Mn content. Pollution load index (PLI) reveal that all the sampling sites reflect low to moderately polluted category except for few stations that are towards the southern and southeastern side of the lake. OM (16.85%), CaCO₃ (14.04%) and C/N ratio (15.5) of the lake bottom sediments is attributed to high organic activity within the lake, shell fragments, contributions from the lake flora and fauna adhering to the clayey silty sediments. The C/N ratio of 15.5 suggests a mixed source of organic matter both terrestrially and in situ formation within the lake. Sulphur and chlorine are high amongst the trace elements suggesting anthropogenic detritus input into the lake and this is due to the chemical fertilizers from the agricultural runoff and organic load into the lake. Thus, the present study suggests that in order to preserve the pristine lake ecology and the environment; continued monitoring and restoration efforts need to be undertaken.     

Impacts of sediment retention by dams on delta shoreline recession: evidences from the Krishna and Godavari deltas,India

River deltas are the major repositories of terrestrial sediment flux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea‐level rise ultimately affecting the delta environment. Analysis of multi‐date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km² area along the entire 336‐km‐long twin delta coast during the past 43 years (1965–2008) with a progressively increasing rate from 1·39 km² yr^?1 between 1965 and 1990, to 2·32 km² yr^?1 during 1990–2000 and more or less sustained at 2·25 km² yr^?1 during 2000–2008. At present the Krishna has almost become a closed basin with decreased water discharges into the delta from 61·88 km³ during 1951–1959 to 11·82 km³ by 2000–2008; and the suspended sediment loads from 9 million tons during 1966–1969 to as low as 0·4 million tons by 2000–2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three‐fold reduction in its suspended sediment loads from 150·2 million tons during 1970–1979 to 57·2 million tons by 2000–2006. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins. Copyright © 2010 John Wiley and Sons, Ltd.     

Biogeochemical cycling in the Taiwan Strait

Based on repeat observations made during 2001–2003 along two transects in the Taiwan Strait this study aims at understanding factors controlling primary productivity with an emphasis on biogeochemical cycling of nitrogen, the major bio-limiting macronutrient. The Taiwan Strait receives copious supplies of nutrients through river runoff and upwelling in its western and northeastern parts, respectively, but the phytoplankton biomass, as inferred from the Chl a concentration, does not appear to be commensurately high. It is proposed that high water turbidity results in light limitation of primary productivity, especially in the western part of the strait. The accumulation of nitrite in the surface mixed layer appears to be due to nitrate reduction during phytoplankton assimilation, whereas in the near-bottom waters nitrite is most likely produced during nitrification. The net balance between input and loss of nitrogen is inferred from the nitrogen tracer N*. The Taiwan Strait is found to be a net recipient of combined nitrogen.     

Geochemistry of Vellayani lake sediments: Indicators of weathering and provenance

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO₂, MnO, CaO, MgO, Na₂O, K₂O, and P₂O₅ content while TiO₂, Fe₂O₃ and Al₂O₃ are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO₂ is high in coarse fractions while Al₂O₃ is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area.     

Diatoms,spatial distribution and physicochemical characteristics of the Wular lake sediments,Kashmir valley,Jammu and Kashmir

Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to understand the source of organic carbon (terrestrial or in situ) in lake systems in order to monitor the health of the lake. Wular lake, located in north Kashmir, is one of the largest fresh water lake in India, situated at an average elevation of 1580m ASL. The lake is fed by a number of watersheds that bring a diverse type of sediments and organic matter and thus deposit them into the Wular lake basin. In order to understand sediment distribution pattern, content and source of organic matter, sediment provenance and the persisting environment in the Wular lake, 32 lake floor sediment samples covering the entire lake were collected and analyzed for organic element analysis, CaCO3, organic matter, sediment texture and diatom analysis. The results indicated that sediments in the lake are dominated by silt and silty clay. The organic carbon in the lake ranged from 0.83%-4.52% and nitrogen varied from 0.06%-0.5%. The Carbon to Nitrogen (C/N) ratios (9.04 to 22.03) indicate a mixed source of organic carbon but dominated by in situ lake sources from the vascular and lake biota accumulation. The diatom analysis revealed the occurrence of a diverse type of species along the sampling sites present within the lake. The wide distribution of the diatom species such as Cymbella, Cyclotella and Tabularia etc. in the lake indicate high organic pollution and alkaline fresh water environment prevailing in the lake.