Marine Environment

Estuaries are semi-enclosed coastal bodies of water, located at the interface between land and ocean, where seawater is measurably diluted by the inflow of fresh water (Pritchard 1967; Attrill and Rundle 2002; Wolanski 2007). The mixing of fresh water and sea water in the estuarine systems creates strong gradients of salinity, turbidity and concentration of bioactive elements, while, at the same time, a number of biological processes also acts at different time scales. Coastal waters, including estuaries and near shore oceanic environments, are among the most highly productive areas in the world. However, several man made changes have occurred in this sensitive ecological system in recent years, which affect the general hydrographic parameters

Exploitation of marine environment for food, minerals, chemicals, recreational activities and waste disposal led to constant pollution of the aquatic environment by anthropogenic inputs. The word pollution generally refers to virtually any substance or energy released into the environment by human activities, which are detrimental to mankind or ecosystem. Human activities to improve the standard of living, have led to the introduction of many hazardous, non degradable chemicals into the aquatic ecosystem, which have attracted serious concern of the environmentalists. Similarly, deposition of harmful industrial by-products and contaminants into the surface waters poses serious problems to the environment. Organic effluents such as domestic sewages are a serious problem and the discharge of small quantities of sewages into the aquatic systems can actually increase the productivity of ecosystems, however, excessive quantities will deplete oxygen content, causing severe threat to aquatic life. As a result, the presence of organic and inorganic pollutants in aquatic system continues to be one of the most important environmental issues of the world

Rivers carry materials derived from its catchments to estuaries. Terrestrial organic carbon, whose input to coastal margin sediments is mainly controlled by riverine sources (Hedges et al. 1997; Cole et al. 2006), has been shown to represent a significant fraction of total organic carbon (TOC) in coastal and estuarine sediments (Hedges and Parker 1976; Hedges et al. 1988; Prahl et al. 1994; Raymond and Bauer 2001). During transportation, water and sediments undergo considerable changes in their physico-chemical properties depending on terrain characteristics and climate of the region through which the river flows (Gibbs 1977; Lal 1977; Subramanian 1979; Walling 1999; Somayajulu et al. 2002; Ankers et al. 2003; Turner and Rabalais 2004). River transport of particulates, nutrients and minerals plays a major role in maintaining the productivity of the coastal and the nearshore environments. Thus, rivers and their estuaries provide connectivity between terrestrial and marine environments and also act as corridors for free movement of aquatic organisms among various sub-environments. But unfortunately, extensive urbanisation and industrialisation consequent to the economic development in recent years have caused a worldwide increase in river input of geochemical constituents, especially nutrient