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Mangroves represent highly dynamic and fragile ecosystem, which occupy a large fraction of the tropical and subtropical coastline, dominating the intertidal zone of diverse environmental settings. The potential role of mangrove ecosystems as sinks for anthropogenic contaminants in tropical and subtropical areas has been widely recognized. Sediments are important carriers of trace metals in the hydrological cycle and because metals are partitioned with the surrounding waters, they reflect the quality of an aquatic system (Szefer et al., 1995). Heavy metals are natural constituents of the marine environment and some of them, such as Cu, Fe, Zn, and Mn, are biologically essential for normal growth and development (Astorga Espana et al., 2004). Metals such as Cd and Hg have no known use in physiological processes (Darmono and Denton, 1990), but when present in excess have ecological significance due to their toxicity and cumulative behaviour and constitute a potential hazard for environment.

Bengal Delta region is currently confronted with largest groundwater arsenic calamity in history of human kind (BGS-DPHE, 2001; Mukherjee and Bhattacharya, 2001; Bhattacharya et al., 2002a; McArthur et al., 2001; Smedley and Kinniburgh, 2002; Mukherjee et al., 2006; Nath et al., 2005, 2007, 2008). Concentrations of arsenic in drinking water wells in the region often exceed the WHO drinking water guideline value (10 μg L−1) and the national safe limit of both India and Bangladesh for arsenic in drinking water (Smedley and Kinniburgh, 2002; RGNDWM, 2002; CGWB, 1999; Bhattacharya et al., 2002a). About one third (35 million) population inhabiting in this region (West Bengal and Bangladesh), currently at risk of long-term arsenic exposure (Bhattacharya et al., 2001; RGNDWM, 2002; Chakraborti et al., 2004; Kapaj et al., 2006), are being diagnosed with a wide spectrum of adverse health impacts including skin disorders such as hyper/hypo-pigmentation, keratosis and melanosis and are also in hot-spot areas of BDP which is reflected in a rise in the number of cancer cases (Guha Mazumdar et al., 1988). The distribution pattern of arsenic occurrence in BDP is patchy and there are numerous hotspots of arsenic contamination in the semi-confined shallow Holocene aquifer (Bhattacharya et al., 1997; Smedley and Kinniburgh, 2002). The scale of the problem is serious both in terms of hotspots and geographic area coverage (173 × 103 km2, eastern part of Hoogly-Bhagirathi/Western part of Ganga-Padma-lower Meghna flood plains).

Mangrove forests function as a link between marine and terrestrial ecosystems; are important for the stability and maintenance of various adjoining ecosystems such as seagrass, coral reef, and other marine ecosystems; and provide habitats for juvenile crustaceans and fish. Mangroves also contribute significant quantities of organic matter (OM) via litter fall that can be transported offshore (Odum and Heald, 1972; Alongi, 1990). Depending upon the geomorphology of the basin and tidal amplitudes, mangrove stands receive nutrients and OM from terrestrial runoff, estuarine outflows (Boto and Bunt, 1981; Alongi, 1990), marine inputs and water column production by phyto-plankton and -benthos (Bouillon et al., 2004). As a result, mangrove ecosystems are considered sites of intensive biogeochemical processes with a potentially impacting global element cycles (Dittmar et al., 2006; Bouillon et al., 2008).

Coastal areas face increasing pressures from land use change, developmental activities, shoreline erosion, biodiversity losses and natural calamities. This volume addresses these issues facilitating the integrated analysis of the sustainability of coastal zones. The contributors have tried to focus their respective works on the problems that need urgent attention relevant to present day issues. Coastal Zone Management and its sustainability strategy should safeguard ecological security of the coastal areas, avoid pollution as well as exploitation of living and non living aquatic resources, protecting also the agrarian community and avian population and other floral and faunal breeding grounds. Articles have been selected on the basis of sound scientific findings hoping that it will help in developing meaningful regulations for future sustainable coastal management zone.

In majority of the arid and dry regions of the world and in monsoon-dependent countries in Asia, groundwater is a major freshwater resource for drinking and other uses. The coastal regions, which support maximum density of population, mainly depend on the ground water. Due to the population growth and the fact that about 50% of the world population now already live in coastal regions, the groundwater issues in the coastal areas are increasingly becoming crucial (UNWWDR, 2009). Over-exploitation of groundwater in these areas can potentially lead to saltwater intrusion, land subsidence, permanent damage to the ability of an aquifer to store and transmit water, and reduced discharges to rivers, streams, and critical aquatic habitat areas (Fig. 1). Further, coastal groundwater plays an important role in nutrient flux to the ocean. The influence of submarine groundwater discharge (SGD) on the coastal water quality, their biogeochemical process and their ecology are very significant in most of the coastal regions. Investigations of interactions between groundwater and coastal seawater have been restricted mainly to the case of water movement from sea to the land, i.e. saltwater intrusion (Segol and Pinder, 1976; Reilly and Goodman, 1987) while submarine groundwater discharge (SGD) considers the water output from a basin-scale hydrological cycle, representing an input into the ocean (Fig. 2). Open image in new window Figure 1: A compilation of processes affecting coastal groundwater. Open image in new window Figure 2: Schematic depiction of processes associated with SGD (modified after Taniguchi et al., 2002). Arrows indicate fluid movement.

Groundwater bodies which were recharged by precipitation represent a potential source of information on past climate conditions. The isotopic and elemental compositions of groundwater influenced by climate conditions at the time of recharge may serve as indicators of climate change. The relationship between climate and mean annual stable isotope contents of precipitation (Dansgaard, 1964; Rozanski et al., 1992) provides significant insights into paleoclimatic conditions. Therefore, selected confined aquifers can be used as continental paleoclimatic archives (Fontes et al., 1993). It is essential to appropriate aquifers to avoid the various processes and to have a good sampling strategy to make climatic interpretation. Such studies have been carried out, for example, in Africa (Dray et al., 1983; Andrews et al., 1994), Europe (Rozanski, 1985; Stute and Deak 1989), North America (Claassen, 1986; Phillips et al., 1986; Stute et al., 1992; Plummer, 1993; Dutton, 1995) and Australia (Davidson and Airey, 1982; Jacobson et al., 1989). (1999) discussed the hydrochemical trends, paleorecharge and groundwater ages in the fissured chalk aquifer of the London and Berkshire basins, UK. Isotope stratigraphy of the major ice caps has been examined by various groups to reconstruct the Holocene and late Pleistocene climate (Koerner, 1989). In Asia, (1998), obtained the isotopic signature of paleoclimate for the past 30 ka in ground waters of southern India.