Tell me where

The underground discharge of water and minerals to oceans is now known to be much more significant. This considerably reduces the weightage given to the contribution of rivers and streams to oceanic content

Published: Thursday 31 October 1996

where do oceans derive their water and salts from? The textbook answer would say 'from the rivers'. Although the answer is correct, there are several other sources which can account for nature's water and mineral cycles. The weathering of ocean floors which yields minerals, the atmospheric deposition of dust and trace elements directly on the ocean surface and the direct flow of water into the sea through porous rocks known as sgwd (sub-marine groundwater discharge) are some of the other sources through which oceans get their water and minerals.

sgwd has become the focus of recent attention because of the measurement of trace elements, that are known to be naturally enriched in groundwater, for quantifying the extent of water discharge into the oceans from groundwater. Willard S Moore of the department of geological sciences, University of South Carolina in the us has now estimated that levels of 226radium in the coastal waters of south-eastern us far exceed what might be feeding into the ocean from rivers.

As a result, Moore estimates that the extent of direct discharge of underground water into the ocean is about 40 per cent of what the oceans get through run off from rivers and streams. Prior to these measurements, groundwater discharge was thought to be no more than one to 10 per cent of the discharge from rivers. These findings have altered our understanding of oceanic chemical balance. They also have serious implications for the conservation of potable groundwater in the coastal region because Moore's measurements have also suggested that salt water from the sea has of late seeped into underground freshwater reserves. Such intrusion is likely to continue and intensify as the sea level rises and the demand for fresh water increases.

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