With cooperation from U.S. and Mexico, regular “pulse flows” could restore an ecological corridor
Vermillion Flycatcher. Photo: Camilla Cerea/Audubon
COLORADO RIVER DELTA, Mexico -(ENEWSPF)–October 20, 2016. In 2014, 34 billion gallons of the Colorado River reached the sea, connecting the river through its ancient delta for the first time in nearly two decades. The flow was the first time the United States and Mexico deliberately sent water down the Colorado River into the delta for the benefit of nature. This release was a major part of a bilateral agreement between the United States and Mexico known as “Minute 319.” Today, after two years of analyzing the flow’s environmental impact, the International Boundary and Water Commission (IBWC) published a study suggesting native flora and fauna could return to the long dried-out river channel.
“It’s very straightforward: More water means more vegetation, which offers a better chance for birds and other wildlife to return,” said Jennifer Pitt, Colorado River project director for the National Audubon Society. “For a region with a scarcity of good news about water, the US and Mexican governments pretty much nailed it. If just one pulse flow can have this impact, imagine what a longer-term commitment to more flows can bring back to this ecosystem. We encourage the US and Mexico to commit to more sustained flows and more resources for restoration.”
The clearest impact of the pulse flow was in the region’s hydrology. The Colorado River flowed over its banks onto terraces where native trees can create important habitat. Groundwater levels increased temporarily up to nine meters in some places. Water on riparian terraces and higher groundwater levels increase the chances that native trees like cottonwood, willow and mesquite return to the riparian corridor. Historically, the Colorado River delta would flood during the spring due to melting snowpack, and these floods would regularly clear the adjacent plains of vegetation, allowing for new growth of these native species.
Since the delta has dried out, invasive tamarisk trees have taken over the former river bed. Areas where the tamarisks were cleared prior to the pulse flow saw more of the desirable native species than in areas where tamarisks had grown too dense for the flood to clear them out naturally. This finding suggests that any future pulse flow should be paired with advance restoration efforts for maximum ecological impact.
Experts also observed an increase in bird diversity and abundance following the pulse flow, however it is too early to say if these trends will persist. Historically, the Colorado River delta was home to nearly 400 species of birds and is considered a Globally Significant Important Bird Area by BirdLife International. Restoring healthy riparian forests of native cottonwoods and willow trees will also benefit species like the eye-catching Vermilion Flycatcher, the endangered southwestern Willow Flycatcher and threatened western Yellow-billed Cuckoo.
Minute 319 was negotiated between the US and Mexico in 2012, and the bilateral agreement will expire in 2017. Currently, negotiations are underway to renew the agreement and continue binational water management and delta restoration. By including flexible water management solutions, reduced water use and benefits for both people and wildlife, the US and Mexico can serve as a model for continued water negotiations throughout the entire Colorado River basin.
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