Contrary to conventional wisdom, fish in the Nile delta are thriving in waters polluted with fertilizers and sewage, according to a new study. While nitrogen-rich runoff usually causes excessive growths of algae and plankton that suffocate other marine life, the Nile delta is different because it has suffered from a lack of autotrophs (that fish feed on) ever since the Aswan Dam was built in the 1960s. Researchers found that more than 60 percent of the current fishery production in the region can be attributed to human-generated runoff. “This is really a story about how people unintentionally impact ecosystems,” explained co-author Autumn Oczkowski [BBC News].
The building of the Aswan Dam on the Nile blocked off much of the fertile floodwater that drains into the Mediterranean Sea, which in turn produced a sharp fall in the number of fish being landed by Egypt’s fishermen. “But in the late 1980s, the coastal fishery began to exhibit a surprising recovery,” the researchers observed. “Today, landings are more than three times the pre-dam level” [BBC News]. The increase in fish production coincided with the rise in fertilizer use along the Mediterranean coast. To quantify the effect, researchers collected more than 600 fish from four regions contaminated by runoff and two regions that were not. In regions affected by runoff, the fish contained nitrogen isotopes that could be traced to anthropogenic sources of nitrogen, according to the study published in the Proceedings of the National Academy of Sciences.
In most bodies of water, human-generated runoff would create dead zones by upsetting the normal biological balance. However, the southeastern Mediterranean Sea is different because it is a “marine desert” in which nutrients are quickly exploited, said Autumn Oczkowski… “Add any fertilizer, and you’re going to see a big effect,” [The New York Times]. The situation in the Nile delta appears to be a case of two anthropogenic negatives–the dam and the runoff–canceling each other out.
The question now is whether the current conditions are sustainable, or whether there will be a tipping point after which the runoff will become detrimental. The same transition happened along the Gulf Coast, said Dr. Rabalais, the executive director of the Louisiana Universities Marine Consortium. “The area near the Mississippi River Delta in the 1960s was known as the ‘fertile fisheries crescent.’”… Now, she said, increased nutrients are “leading to a massive dead zone most springs and summers” [The New York Times]. But for now, at least, Oczkowski says, “The Egyptians don’t think it’s a bad thing. For them, it’s producing tonnes of fish and feeding millions of hungry people” [BBC News].
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Image: flickr / thevoyager
January 22nd, 2009 at 5:46 am
As a former Cairo resident, this news is worrying. My concern is that despite the increase in Nile fish stocks helping to provide the nation’s impoverished with an adequate source of protein in the midst of what is often a very meagre diet, the contaminants causing surplus might have adverse affects on their health. I suppose a similar argument is pivotal in the GM debate throughout the EU. But whereas in the EU there is close scrutiny and research carried out when matters of public health are in stake, that vital element is sorely lacking in the Egyptian equation. A sad fact to consider when people living in the nation’s unbearably overpopulated urban centres already have to contend with one of the world’s highest rates of pollution.
November 14th, 2010 at 3:26 pm
Scientific studies should always be monitoring these regions. Maintaining the balance is an issue that needs to be thoroughly monitored. While genetic or chemical effects on these species should be considered before the declaration that these species are fit for human consumption. These fertilizers are not natural fertilizers and should have the same effect in farming as in fisheries. If the fertilizers are natural in source then there should not much to worry about.
April 8th, 2011 at 3:35 pm
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