Dam on Danube Damaging Black Sea, New Study Finds

A dam constructed on the Danube River during the depths of the Cold War is wreaking ecological havoc more than 500 miles away, a new study has found.

Hydrologists have long known the ill effects that dams can have on a river. But the new study finds that the Iron Gates Dam also has damaged the environment in the Black Sea beyond the river’s mouth.

“Our results show that water and sediment storage in reservoirs behind the Iron Gates have altered the biogeochemistry not just of the river and adjacent coastal waters, but of the entire Black Sea basin,” German and Romanian researchers write in the current issue of the British journal Nature.

The Danube accounts for about 70% of the river inputs to the Black Sea, so any major change in the river is bound to influence the 160,000-square-mile water body, said Venugopalan Ittekkot, a marine chemist at the University of Hamburg.

And major changes have in fact occurred. Ittekkot and his colleagues found that since the dam’s construction in the early 1970s, the amount of dissolved silicon in the surface waters of the Black Sea has dropped precipitously.

That silicon is absorbed in the reservoir behind the dam, where plankton take the nutrient into their bodies and then carry it to their graves on the muddy bottom.

So by the time the Danube meets the Black Sea, its water is enriched in nitrogen and phosphorus but depleted in silicon.

That changes the nature of the diet available to the plankton at the bottom of the Black Sea’s ecological food web, allowing some species to bloom while virtually wiping out another, the diatoms.

That’s a problem, Ittekkot said, because the diatoms produce oxygen through photosynthesis. Shifting the balance to other forms of plankton aggravates the depletion of oxygen in water bodies, a process known as eutrophication.

“What makes the new paper particularly important is the possible clues it may offer to environmental problems . . . not only in estuaries and coastal areas adjacent to dammed rivers, but also in larger bodies of water, such as the Black Sea,” John D. Milliman of the Virginia Institute of Marine Science writes in a commentary that accompanies the study.

The effects may be most dramatic in the Black Sea, where most of the water comes from a single dammed river, researchers said, but the same thing almost certainly happens as the Nile flows into the eastern Mediterranean, at the mouth of the Indus River in India and the Sao Francisco River in Brazil.

“There is evidence that similar things are happening worldwide,” Ittekkot said. “But we are just beginning to assess the impact of this.”