More powerful storms push harmful matter into drinking water -- study
Christa Marshall, E&E reporter
Published: Tuesday, October 2, 2012
Last year's Hurricane Irene sent excessive levels of harmful organic matter into waterways feeding New York City's drinking supply, a condition that could worsen with climate change, a new study warns.
The storm increased by fourfold the concentration of dissolved organic carbon and dissolved organic nitrogen in Esopus Creek, which feeds the Ashokan Reservoir supplying the city, says the study published recently in Geophysical Research Letters. The dissolved matter came from leaf litter and soil churned up by Irene, which caused more than $15 billion in damage nationwide.
"No one has measured dissolved organic matter during a precipitation event this large. It's uncharted territory," said Peter Raymond, a professor of ecosystem ecology at Yale University and co-author of the study.
He said that Irene did not cause an immediate health crisis for New York's water supply, but the insertion of the dissolved mix into the watershed raises questions about a warming world that may have more intense storms and rainfall. The larger the storm, the more matter flows into a waterway, he said.
One problem with organic matter is that it absorbs light that freshwater plants need to thrive, Raymond said. It further blocks ultraviolet rays that otherwise would kill bacteria and pathogens in water harmful to humans, he said.
Additionally, large amounts of organic matter can flow downstream to drinking water treatment plants and react with chlorine used as a disinfecting agent, he said. That in turn can create carcinogenic byproducts, Raymond said.
The regulation of disinfection byproducts is a relatively new area, and the link between heavy rainfall and carcinogens in waterways needs more research, he said.
Irene brewed a potent 'tea' of pollutants
He compared the storm dynamic to the brown residue created after making tea -- large weather events essentially "increase the landscape's ability to make tea," he said.
Cost could be a future concern for water managers, if drinking water treatment plants have to upgrade their systems to address the problem, he said. While the immediate study examined Esopus Creek near the Catskill Mountains, the surge in organic matter likely occurred in multiple areas of the New York watershed, he said.
The water-sampling equipment used by the researchers -- which happened to be in place because of a graduate student project -- reported a 330-fold increase in the amount of water discharging from the creek to the reservoir. The resulting release of dissolved organic carbon and nitrogen reached more than 30 percent of their annual flux in five days, the study says.
Existing research models that do not use on-the-ground sampling may be severely underestimating the impact of extreme events, the study says. With the Esopus, existing models would have lowered the projections of organic matter from the actual recorded amounts by 18 to 62 percent.
An official in the New York City Department of Environmental Protection said there was an increase in organic matter that entered area reservoirs after Hurricane Irene and Tropical Storm Lee in 2011. But he said that "all measurements of organic matter returned to normal levels within a few months."
"The storm did not impact [the department's] ability to provide proper disinfection," the official said. Water delivered in the wake of the storm "met all drinking water standards," he added.
By the end of the 21st century, man-made warming could increase the average intensity of hurricanes by 10 percent, according to a fact sheet from the National Oceanic and Atmospheric Administration.