D. Padmalal

Vegetation Response and Landscape Dynamics of Indian Summer Monsoon Variations during Holocene: An Eco-Geomorphological Appraisal of Tropical Evergreen Forest Subfossil Logs

The high rainfall and low sea level during Early Holocene had a significant impact on the development and sustenance of dense forest and swamp-marsh cover along the southwest coast of India. This heavy rainfall flooded the coastal plains, forest flourishing in the abandoned river channels and other low-lying areas in midland.The coastline and other areas in lowland of southwestern India supply sufficient evidence of tree trunks of wet evergreen forests getting buried during the Holocene period under varying thickness of clay, silty-clay and even in sand sequences. This preserved subfossil log assemblage forms an excellent proxy for eco-geomorphological and palaeoclimate appraisal reported hitherto from Indian subcontinent, and complements the available palynological data. The bulk of the subfossil logs and partially carbonized wood remains have yielded age prior to the Holocene transgression of 6.5 k yrs BP, suggesting therein that flooding due to heavy rainfall drowned the forest cover, even extending to parts of the present shelf. These preserved logs represent a unique palaeoenvironmental database as they contain observable cellular structure. Some of them can even be compared to modern analogues. As these woods belong to the Late Pleistocene and Holocene, they form a valuable source of climate data that alleviates the lack of contemporaneous meteorological records. These palaeoforests along with pollen proxies depict the warmer environment in this region, which is consistent with a Mid Holocene Thermal Maximum often referred to as Holocene Climate Optimum. Thus, the subfossil logs of tropical evergreen forests constitute new indices of Asian palaeomonsoon, while their occurrence and preservation are attributed to eco-geomorphology and hydrological regimes associated with the intensified Asian Summer Monsoon, as recorded elsewhere.

Mangrove Responses to Climate Change along the Southwestern Coast of India during Holocene: Evidence from Palynology and Geochronology

Mangrove vegetation is an important component of the coastal ecosystem and is associated with near-shore marine habitat in the tropics and subtropics of the world. Indian mangrove vegetation covers about 6749 km2 along the 7516 km long coast line, including Island territories (Mandal and Naskar, 2008). The distribution of mangrove areas along the Indian coast is influenced by physical forces such as geomorphology, climate, tidal amplitude and duration and quantity of freshwater inflow (Selvam, 2003). In fact, the geomorphic setting of the mangroves of east coast of India is different from that of the west coast (Ahmed, 1972). The coastal strip of west coast is narrow, and steep in slope as compared to the gentle slope of east coast. Though there are large number of small rivers bringing enormous quantity of sediment to the Arabian Sea along the west coast, deltas are not developed, possibly due to the high-energy conditions of the coast. This topographic set up gives a contrasting pattern of mangrove vegetation in India. Accordingly, the mangrove wetlands of west coast are small, less diverse and less complicated in tidal creek network, while the east coast has larger mangrove wetlands with high species diversity. Besides, beach morphological changes along the west coast are controlled by the southwest monsoon. Therefore it is interesting to ascertain the consequences of mangroves in response to climate changes along the Kerala coast, southwestern India using the sedimentary archives of the coastal plains.

Delineation of Groundwater Potential Zones in River Basins Using Geospatial Tools—an Example from Southern Western Ghats, Kerala, India

The remote sensing and geospatial tools have wide applications in water resource assessment studies. Satellite images are increasingly being used in groundwater exploration because of their utility in identifying various geomorphic features. The present study has been carried out in two important river basins—the Ithikkara and the Kallada river basins, of Southern Western Ghats, Kerala, India. The groundwater potential zones are delineated from 14 thematic layers such as drainage density, geomorphology, slope, lithology, soil, land use/land cover, lineament density, topographic wetness index, rainfall distribution, roughness, curvature, dissection index, depth to water level and topographic position index using multi-criteria evaluation method. Integration of the factors has been performed in GIS platform using weighted overlay analysis. Different classes of thematic maps have been assigned weights based on influence on groundwater hydrology (through discussions with the experts in the field), and finally, factor ranks are assigned. The final map indicates the potentiality values of groundwater occurrence in the study area, which was classified into three categories—high, moderate and low. A total of 37.2% of the study area fall in low groundwater potential zone, 42.3% in moderate potential zone and 20.5% of the area in high potential zone. The groundwater potential zones delineated using the method are validated with data of springs and dug wells from field investigations, and it was found that the overlay method using GIS and remote sensing gives 95% accuracy.

Climate and Sea Level Changes in a Holocene Bay Head Delta, Kerala, Southwest Coast of India

The Holocene epoch, all over the world, has witnessed exceptional climate and sea level changes. Although the south-west coast of India has a fairly thick deposit of Holocene sediments of 50-60 m in the South Kerala Sedimentary Basin (SKSB) and its adjoining coastal lowlands (see inset in Fig. 13.1), not much focus has been given to unfold its palaeo-climatic and palaeo-environmental potential till the beginning of the present century (Joseph and Thrivikramji, 2002; Nair and Padmalal, 2003; Nair et al., 2006; Kumaran et al., 2005; Limaye et al., 2007). South-west coast of India was affected significantly by sea level and climate changes which in turn had a strong bearing on human settlements/migration in the area. Recent advances in archaeological investigations in the Pattanam-Kodungallur stretch in Central Kerala (Shajan et al., 2004; Abraham, 2006) gave indications of shifts in human settlements in accordance with changing climates and/or sea level positions.

Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene

Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic—rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub—coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon—lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0–3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of land modification and development is destabilizing these carbon pools resulting in large scale carbon emissions to the atmosphere and loss of low-latitude peat palaeorecords. Therefore, these palaeorecords are to be conserved and addressed for better understanding and utilizing the carbon pool for effective climate change adaptation. This communication is the first attempt of addressing the peat formation and peatland development during the Holocene from the tropical region of Peninsular India.

Dissolved nutrients (NO3-N and PO4-P) and Fe in the interstitial and overlying waters of two tropical freshwater lakes in Southern Kerala, India

Studies on the geochemical reactions between sediments and overlying waters of freshwater systems have received considerable attention in the past few decades as these reactions impart significant changes in the quality of overlying waters. Although many studies are available in the global scientific scenario, not much effort has been made in India and practically very little information is available about Kerala, a state endowed with numerous lakes and backwaters. Here we report the level variabilities of dissolved nutrients such as NO3-N and PO4-P, and Fe in the surface, bottom and interstitial waters of the Sasthamkotta and Vellayani lakes– two important perennial freshwater sources in southern Kerala. Further the Lake Sasthamkotta, the largest fresh water lake of Kerala, is declared as a Ramsar site of international importance. NO3-N, PO4-P and Fe exhibit marked increase in the interstitial water compared to overlying waters. Among these two lake systems, the content of NO3-N is higher in the Vellayani lake than the Sasthamkotta lake, whereas the concentrations of PO4-P and Fe are marginally higher in the overlying waters of the Sasthamkotta lake. However the interstitial water samples of Vellayani lake record higher PO4-P and Fe values. Although fertilizer intensive agricultural activities around the lake systems are one of the major causative factors for the enhanced concentrations of nutrients in the overlying waters, early diagenetic release of nutrients and Fe also plays a pivotal role in enriching these hydrochemical signals in the lake systems.

Geomorphic response to sea level and climate changes during Late Quaternary in a humid tropical coastline: Terrain evolution model from Southwest India

The coastal lands of southern Kerala, SW India in the vicinity of Achankovil and Thenmala Shear Zones reveal a unique set of geomorphic features like beach ridges, runnels, chain of wetlands, lakes, estuaries, etc. The chain of wetlands and water bodies that are seen in the eastern periphery of the coastal lands indicates the remnants of the upper drainage channels of the previously existed coastal plain rivers of Late Pleistocene age that are later broadened due to coastal erosion under the transgressive phase. The terrain evolutionary model developed from the results of the study shows that the Late Pleistocene transgressive events might have carved out a major portion of the land areas drained by the coastal plain rivers and as a result the coastal cliff has been retreated several kilometers landwards. The NNE—SSW trending beach ridges located close to the inland wetlands indicate the extent of shoreline shift towards eastwards during Late Pleistocene period. The present beach parallel ridges in the younger coastal plain indicate the limit of the Mid Holocene shoreline as the transgression was not so severe compared to Late Pleistocene event. The zone of convergence of the two sets of beach ridges coincides with the areas of economically viable heavy mineral placers that resulted from the size and density based sorting under the repeated transgressive events to which the coast had subjected to. The chain of wetlands in the eastern side of the study area has been evolved from a mega lagoon existed during Late Pleistocene. The Pallikkal River that links discrete eastern wetland bodies has been evolved into its present form during Early Holocene.

Workshop on Western Ghats: Evolution and Environmental Issues

Older than the Himalaya, the mountain chain of Western Ghats adjacent to the west coast of India represents a major geomorphic feature of extreme geo-environmental significance. This ~1600 km long mountain ranges extend from the Satpura Range in the north to Kanyakumari in the south and passes through different lithologies. It fringes the west coast in the form of a Great Escarpment overlooking the western coastal lowlands. Geological observations attribute the genesis of Western Ghats to the breakup of supercontinent, Gondwana and subsequent modification in the north due to Reunion hotspot-related volcanism. Being a dominant orographic feature, the Western Ghats is a major climate regulator in the Indian sub-continent. The high mountain forest ecosystems of Western Ghats are treasure troves of biological diversity in the world and have an exceptionally high level of endemism and biological richness. Considering its extreme ecologic and environmental importance, this unique life sustaining system of Peninsular India has recently been declared as a World Heritage Site for preservations by the UNESCO. The Ministry of Earth Sciences has taken many important initiatives for deep crustal studies in the Western Ghats region using multi-parametric investigations including geological, geophysical and deep drilling methods. But more need to be done from the point of view of its evolution and environmental aspects for evolving a sustainable development frame work for this most ecologically sensitive region in the world. In this context, a twoday National workshop on “Western Ghats; Evolution and environmental issues” had been conducted by the National Centre