KREMMLING — In the gray light of dawn, hundreds of swallows darted over a pool of standing water in an irrigated field along the Colorado River. The birds were attracted to the early-morning mosquitos swarming the saturated landscape. Bill Vetter, a wildlife biologist with Wyoming-based Precision Wildlife Resources, methodically counted the birds. For six minutes, he marked down every bird he saw or heard at eight locations across the ranch, 250 meters apart.
Vetter is part of an avian-monitoring program, headed up by Audubon Rockies, which aims to learn more about how birds use irrigated agricultural lands. In 2020, the fields near Kremmling where Vetter counted purposely did not irrigate as part of a state-grant-funded study on water use in high-elevation pastures. This year, irrigators are back to watering their usual amount and Vetter is tracking the trends in bird species and numbers.
This year, Vetter counted four or five additional species, including the yellow-headed blackbird, white-faced ibis and sora.
“I can say that for sure we got additional species this year that we didn’t have last year, and those species are largely associated with water habitat,” he said.
Across the Western Slope, birds and other wildlife have come to depend on these artificially created wetlands, a result of flood irrigation. But as the state of Colorado grapples with whether to implement a demand-management program, which would pay irrigators to temporarily dry up fields in an effort to send more water downstream, there could be unintended consequences for the animals that use irrigated agriculture for their habitat.
Learning more about how birds use these landscapes is a key first step, according to Abby Burk, Western rivers regional program manager with Audubon Rockies.
“Wetlands are the unsung hero for all the ecological services and functions they provide for wildlife,” she said. “Those low-field wetlands are good habitat for birds, for breeding, for migratory stopovers.”
In 2020, the bird count turned up 1,285 birds, comprising 39 different species, including great blue herons, meadowlarks, red-winged blackbirds, an osprey, a peregrine falcon, and several types of swallows, warblers and sparrows. The numbers are not yet tallied for this year, but the general expectation is that more water means more birds.
“Birds have adapted to how we have created these different habitat types,” Burk said. “We’ve really got to look at the larger effects of how we use water can impact birds and other wildlife. Where there’s water, birds also do thrive.”
The seven ranches where the avian monitoring is taking place are part of a larger water study that is evaluating conserved consumptive use in the upper Colorado River basin. Consumptive use is a measure of how much water is consumed by thirsty plants. Conserved consumptive use is the amount by which consumptive use is reduced as a result of changing irrigation practices.
Researchers from Colorado State University are studying the impacts of using less water on the high-elevation fields in Grand County and how long it takes them to recover once water returns. Researchers hope to fill in a data gap about the impacts of reducing irrigation water on high-elevation pastures.
In 2020, some participating landowners did not irrigate at all and some could only irrigate until June 15. This year, landowners reverted to their historical irrigation practices. Remote sensors and ground-based instruments are monitoring the difference in plant and soil conditions, and will continue to do so through 2023. Early results found that the plants used about 45% less water in 2020 compared with the previous four years.
The first phase of the project received a $500,000 grant from the Colorado Water Conservation Board (CWCB) under its Alternative Agriculture Water Transfer Method program, which aims to find alternatives to “buy and dry” water transfers. The CWCB in September will consider another $60,000 grant request for Trout Unlimited to continue to do monitoring.
Although the project is not directly related to the state’s demand-management feasibility investigation, the results could have implications for any potential program that the state eventually comes up with.
“We are hoping all this information and research is going to be used down the road if a program does develop,” said Mely Whiting, Colorado water project legal counsel with Trout Unlimited. Trout Unlimited is helping to fund and implement the research project.
At the heart of a demand-management program is paying irrigators on a voluntary and temporary basis to not irrigate and to leave more water in the river in an effort to bolster levels in Lake Powell and help Colorado meet its downstream obligations.
Under the Colorado River Compact, the Upper Basin (Colorado, Wyoming, Utah and New Mexico) must send 7.5 million acre-feet each year to the Lower Basin (California, Arizona and Nevada). Failure to meet this obligation could trigger a “compact call” where junior water users in the Upper Basin would have their water cut off. (An acre-foot is enough water to cover one acre of land one foot deep.)
As rising temperatures due to climate change continue to rob the Colorado River and its tributaries of flows and increase the risk of a compact call, finding solutions to water shortages is becoming more urgent. Lake Powell, the river’s biggest reservoir, is just under 34% full and projected to decline further. Demand management would let the Upper Basin set aside up to 500,000 acre-feet in a special pool in Powell to help avoid a compact call.
Some still-unanswered questions remain: How much of the conserved consumptive water from high-elevation pastures would actually make it downstream to Lake Powell? And how much would local streams benefit from the added flows?
“One critical part of what we’re doing is looking at the stream and saying: Do we see any changes from one year to the next? How much water would actually make it to the stream?” Whiting said. “We are measuring to see if there’s any distinction between the year the conservation practices were applied and the following year.”
The unintended consequences of different irrigation patterns under a demand-management program could be many and far-reaching. In 2018, the CWCB formed nine workgroups to examine some of these issues, including one that looked at environmental considerations.
In notes submitted to the CWCB last July, the environmental workgroup acknowledged there could be trade-offs, sometimes among species. For example, reducing irrigation and leaving more water in rivers would benefit fish and riparian habitats, but might negatively impact birds or other species that use wetlands created by flood irrigation. And with full irrigation, birds may thrive, but to the detriment of river ecosystems.
David Graf, water-resource specialist with Colorado Parks and Wildlife, participated in the environmental-considerations workgroup. He said irrigated agriculture provides a lot of diversity in forbes, grasses and insects — good sources of…