THE effect of dams on surrounding ecosystems could be traced even to the seas which receive the waters of dammed rivers. According to researchers from the University of Hamburg and the Baltic Research Institute in Rostock, both in Germany, the Iron Gates dam on the Danube river has transformed the distribution of different types of algae that live in the Black Sea - leading to a sudden spurt in toxic blooms that can kill other marine life.

The Iron Gates dam stands on the Danube between Serbia and Romania. It deposits suspended sediments carrying dissolved silicates in the huge lake behind the dam which would otherwise have been deposited into the seawater, Silicates provide essential nutrients for diatoms - single-celled algae that grow in large numbers on the surface of the sea and that support the marine ecosystem by providing a source of food. Researchers have found that due to decreased silicate deposits in the Black Sea - by more than 60 per cent blooms of non-diatoms, some of which are toxic, have increased faster than diatoms.