Economic damages from nutrient pollution create a “toxic debt”

Nutrient-rich, oxygen-starved dead zones in coastal areas have been steadily growing in the past few decades. But the problem is not restricted to coastal waters. As a new study published in ES&T (DOI 10.1021/es801217q) shows, freshwater bodies throughout the U.S. are also polluted with excess nitrogen and phosphorus. Such pollution is costing the country a significant amount of money: at least $4 billion is lost annually as a result of the degradation of freshwater sources, the authors conclude.

To understand the true extent of nutrient pollution in freshwater bodies, ecologist Walter Dodds and his colleagues at Kansas State University examined the data on nitrogen and phosphorus levels in water bodies throughout the country collected by the U.S. EPA. Ecologists have broadly divided the U.S. by ecoregions on the basis of geography, geology, vegetation, and human impacts. The authors found that 90% of rivers in 12 out of the 14 regions contained excessive nitrogen and phosphorus, compared with reference nutrient levels calculated in several previous studies. The average total nitrogen was 5.5 times greater and the total phosphorus 3 times higher than median reference levels, Dodds found.

The environmental impacts of nutrient pollution are widely acknowledged by scientists and regulators. EPA has developed water-quality criteria for nitrogen and phosphorus pollution, and states are working on plans to tackle the problem. But given that the major contributors to this pollution are nonpoint sources, individual states and EPA have had less success in regulating these sources than they have had with point sources of pollution. Nutrient pollution remains a persistent problem throughout most of the country, but its economic impacts are less studied.

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