Booming coalbed methane development in Wyoming's Powder River Basin is aiding the spread of West Nile virus, the mosquito-borne disease that is particularly lethal to birds, including the imperiled sage grouse, according to new research.
The problem, according to researchers at the Colorado Division of Wildlife and the University of Montana, is linked to the millions of gallons of groundwater pumped by coalbed methane (CBM) drillers into holding ponds and dry creek beds every day. The water creates breeding grounds for mosquitoes that carry the disease.
West Nile is "an important new source of mortality" because it "can simultaneously reduce juvenile, yearling, and adult survival -- three vital rates important for population growth in this species," according to the study, included in a U.S. Geological Survey collection of research entitled "Ecology and Conservation of Greater Sage-Grouse: A Landscape Species and its Habitats."
Experts say West Nile virus has killed potentially thousands of sage grouse in Wyoming as well as nine other Western states and parts of Canada, adding yet another layer of complexity to the Fish and Wildlife Service's ongoing status review for the grouse, which could be added to the endangered species list as soon as February.
"When you have a disease that's causing 100 percent mortality across the range, it's definitely a concern," said Pat Deibert, FWS's lead biologist for sage grouse in Cheyenne, Wyo. Deibert added that threats from disease are one of five major criteria the FWS is required to consider in its listing decision.
The West Nile virus findings are based mainly on studies done after 2003, when the outbreak near Spotted Horse, Wyo., in the heart of the Powder River Basin, resulted in the loss of an entire breeding population of grouse, according to researchers.
Within a year of the disease outbreak, male grouse in five breeding grounds, called "leks," declined by 75 percent, while female birds dropped from 36 individuals to one bird over the course of a year. By the spring of 2005, the leks were deserted, researchers say.
While large-scale bird mortalities due to West Nile virus are not unique to the Powder River Basin, researchers say the 2003 outbreak is troubling because it was "associated with coal-bed natural gas ponds." The ponds are common with CBM drilling operations because water must be pumped out of deep coal seams to coax methane gas to the surface where it can be collected.
According to the research, West Nile infection rates for Powder River Basin grouse were relatively low in undeveloped sagebrush habitats "due, in part, to lack of available surface water in late summer." But, the researchers found, infection rates "were higher in areas with surface water provided by coal-bed natural gas ponds."
The discoveries about CBM drilling, West Nile virus and sage grouse mortality come amid one of the largest sustained natural gas booms in recent history in the Powder River Basin, where nearly 30,000 wells dot the coal-rich region.
CBM operators withdrew 174 billion gallons of groundwater from the Powder River Basin between 1987 and 2006, according to a recent study by the Bureau of Land Management and the Wyoming State Engineers Office (Land Letter, Aug. 20).
Some of the water is pumped into rivers and dry creek beds where it flows downstream. But the majority is pumped into holding ponds that allow the water to slowly percolate back into the ground.
But that standing water, and particularly the shallow areas along the edges of the ponds, make a perfect habitat for mosquito larvae to mature and hatch. Moreover, experts say, the holding ponds "support abundant" populations of the mosquito species Culex tarsalis, known to carry the virus.
Sage grouse are particularly susceptible to infection because during the hot, dry summer months, grouse gather around standing water where mosquitos are most abundant, exposing themselves to disease-transmitting bites.
Duane Spencer, field manager for the BLM's Buffalo, Wyo., office, said that since 2004 the agency has required CBM operators on Wyoming federal lands to design and build holding ponds that prevent larval growth along their edges. They are also required to spray ponds with a larvae-killing pesticide if mosquitoes are detected.
But Spencer noted that many water impoundments are on private or state land. And the state of Wyoming has no similar design requirements pertaining to mosquito control at holding ponds, said John Barnes, surface water administrator for the Wyoming State Engineers Office.
Instead, Wyoming officials have asked CBM operators to voluntarily spray their ponds to help prevent mosquitoes, said Tom Christiansen, sage grouse program coordinator for the Wyoming Game and Fish Department.
"There's been a good bit of work by the companies in northeast Wyoming to treat their produced waters," Christiansen said.
But some are skeptical whether such measures are working.
FWS's Deibert noted that West Nile virus has been detected in sage grouse populations in the Powder River Basin every year since the disease first turned up in Wyoming in 2002, and no other range in the state has shown the same infection rates. "It's telling me that the presence of that water on the landscape is facilitating that vector" of West Nile exposure, she said. "There's definitely cause for concern."
Meanwhile, the number of CBM holding ponds in the Powder River Basin have exploded over the past decade, according to researchers at the University of Wyoming and the Agriculture Department's Arthropod-Borne Animal Disease Research Laboratory in Laramie, Wyo.
In a 2006 peer-reviewed study, researchers used satellite data and aerial photography to map holding ponds and other standing water in the basin that could provide habitat for mosquitoes. Their findings revealed that "potential larval habitats" grew by 75 percent between 1999 and 2004.
The increase, according to the study, was "primarily because of the large increase in small coalbed methane water discharge ponds."
Because the satellite and aerial data could only measure water sources roughly 1 acre in size or larger, "we probably missed a bunch" of areas where standing water was a potential habitat for mosquitoes, said Scott Miller, a University of Wyoming hydrologist and one of the study's lead authors.
What is certain is that "CBM development is the primary source of new standing water bodies in this region" and that the "observed increase in aquatic habitat with the potential to support larval mosquito populations is directly linked to growth in the CBM production."
Yet even without the water ponds, West Nile virus would remain a primary threat to sage grouse across the bird's range, along with habitat fragmentation, wildfire and natural predators.
"With sage grouse, it's a problem of death by a thousand cuts, and this is just another cut," said Brett Walker, an avian researcher with the Colorado Division of Wildlife and the West Nile virus study's lead author.
David Naugle, an ecologist at the University of Montana and the co-author of the West Nile study with Walker, said the virus is helping to create a "perfect storm" of sage grouse threats. "You've already got energy development and habitat fragmentation, and now you've added all this shallow water which produces more [mosquitoes] to move the disease around," Naugle said.
And sage grouse have shown little ability to survive once infected with the virus. "We have a susceptible critter to this new emerging disease," Naugle said.
Some fear the virus could undermine government efforts to protect sage grouse, especially in Wyoming, which last year took the unprecedented step of mapping out core sage-grouse habitat areas and steering energy and other development projects away from these "core areas."
FWS officials say that preserving Wyoming's sage grouse is key to avoiding an Endangered Species Act listing because the state is home to an estimated 54 percent of the world's remaining grouse.
Walker, the Colorado Division of Wildlife expert, said treating the water storage ponds would go a long way to eliminating the West Nile virus threat. Such treatments could include chemical sprays like those being used by some CBM operators, design and structural fixes to make ponds less suitable for larvae, or stocking ponds with larvae-eating fish.
But other factors contributing to the virus's spread cannot be controlled. For example, a warming climate will mean more mosquitoes survive the Mountain West's traditionally harsh winters, allowing the virus to move to higher elevations.
"I think it's going to be a persistent and variable source of [sage grouse] mortality," Walker said. "West Nile virus is here to stay."
Scott Streater writes from Colorado Springs, Colo.
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