Coastal blender

By Biplab Das
Published: Wednesday 15 July 2009

Tsunami left Tamil Nadu's coast turbid, marine plants sluggish

tsunami that struck India in December 2004 has affected the productivity of its coastal waters.

A research team from Chennai and Kolkata analysed the quality of coastal water at Kalpakkam in Tamil Nadu. They found the levels of the nutrients--nitrate, phosphate, silicate--and turbidity were five to 10 times the pre-tsunami levels. Other than natural sources, increased pollution such as run-off from agricultural fields could be the reason for more nutrients.

But despite higher levels of nutrients, the activity of microscopic marine plants called phytoplankton was adversely affected because of increased turbidity. The team reasoned the turbidity increased because strong currents and waves increased bottom turbulence, thus, unsettling sediments rich in organic matter.Suspended organic matter absorbs a major part of the sunlight, affecting photosynthesis in the tiny plants on which fish feed. This means low chlorophyll content and low sea productivity, said the study published in the April 29 online issue of Environmental Monitoring and Assessment.

The team also found that the level of dissolved oxygen was lower after the tsunami. The decomposition of organic matter consumes plenty of oxygen, thus lowering dissolved oxygen level in the water, it explained. Reduced photosynthesis in phytoplankton added to low oxygen levels. Decomposing organic matter added nutrients to the water.

The authors conclude these changes may affect coastal biodiversity. The study could serve as baseline data for future impact studies on coastal water.

They collected water samples between February 2006 and January 2007.

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