Industrial effluents boost Nile delta fish population

January 20th, 2009 - 12:51 pm ICT by IANS  

Washington, Jan 20 (IANS) Many of the world’s fisheries may be struggling to survive, but the coastal one off the Nile Delta has expanded phenomenally since the eighties. The expansion has been attributed to the discharge of fertilisers and sewage following a collapse of the fishery after completion of the Aswan High Dam in 1965, by a University of Rhode Island (URI) researcher.

Autumn Oczkowski, a URI doctoral student, used stable isotopes of nitrogen to demonstrate that 60 to 100 percent of the current fishery production is supported by nutrients from fertiliser and sewage.

“This is really a story about how people unintentionally impact ecosystems,” Oczkowski said.

Historically, the Nile would flood the delta every autumn, irrigate nearby agricultural land, and flow out to the Mediterranean, carrying with it nutrients to support a large and productive fishery. Construction of the dam stopped the flooding, and the fishery collapsed.

“That’s when fertiliser consumption in the country skyrocketed,” said Oczkowski. “The Egyptians were fertilising the land, and then fertilising the sea with the run-off. It also corresponded with a population boom and the expansion of the public water and sewer systems.”

As a result, landings of fish in coastal and offshore waters are more than three times pre-dam levels. While increased fishing effort in recent years may have played some role in the recovery, Oczkowski’s findings indicate that anthropogenic nutrient sources have now more than replaced the fertility carried by the historical flooding.

Oczkowski and colleagues from URI, the US Environmental Protection Agency, and the University of Alexandria collected more than 600 fish in 2006 and 2007 from four regions that received run-off from the delta and two areas not affected by the Nile drainage. Stable isotopes of nitrogen in each fish were measured and compared.

She found that the isotope signatures in the fish reflected two distinct sources of nitrogen: from fertilisers and sewage in the fish caught in coastal and offshore areas of the delta, and nitrogen values consistent with the middle of the Mediterranean in fish caught in waters that were not affected by the delta drainage, said an URI release.

These results have raised questions among many scientists about the value of anthropogenic sources of nutrients to ecosystems.

“But the Egyptians don’t think it’s a bad thing. For them, it’s producing tonnes of fish and feeding millions of hungry people. It’s forcing us to reconsider whether we can say that nutrient inputs are always a bad thing.”

Her research is scheduled for publication in Wednesday’s online edition of the Proceedings of the National Academy of Sciences.

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