Sunday, April 12, 2009
By Sue Major Holmes
It's one of those unintended consequences: People who came to the arid Southwest didn't mean to destroy wetlands, but that's what happened as they drained swamps for farmland and dammed rivers for flood control, water storage and recreation.
"Water is such a scarce resource in New Mexico that whatever use one makes of it affects the other uses," said Steve Cary, natural resource planner for New Mexico State Parks.
Federal government scientists estimate New Mexico and Arizona have lost about a third of their wetlands since colonial times. In recent decades, with growing recognition that wetlands have lost ground, private groups and public agencies have stepped in to fund restoration work.
"In the last five years, there's been a nice little explosion in riverside or riparian restoration projects," Cary said.
Wetlands are threatened by agricultural conversion, water diversion, urbanization, invasive nonnative plants and animals, mining and oil and gas development.
In New Mexico, 80 percent of vertebrate species depend on riverside, or riparian, areas for some part of their life cycle although only about 2 percent of the state's land is riparian, said Jill Wick, aquatic habitat specialist with the New Mexico Department of Game and Fish. More than 70 percent of New Mexico's threatened and endangered species use riparian areas.
A few strips of riverside area and few acres of marshland "actually support most of our biological diversity," Cary said.
Wetlands also recharge groundwater and act as nature's filter, removing sediment, pesticides, heavy metals, even disease-causing bacteria.
The Southwest's wetland cycle is characterized by wet and dry periods. Snowmelt flows from the mountains in spring, clearing soil of compacted vegetation. Plants germinate as the river goes down, then summer monsoons bring a second inundation.
"A healthy and functioning watershed will increase water quality, reduce the threat of flooding, increase the amount of available water, provide fish and wildlife habitat, provide recreational opportunities, increase the quality of living and preserve historical land uses in New Mexico," Wick said.
But 85 percent to 90 percent of New Mexico's riparian habitat has been destroyed or degraded, and the state has lost about 36 percent of its wetlands, she said. More than 90 percent of Arizona's riparian areas have been lost or modified, said Jim Rorabaugh, a biologist with the U.S. Fish and Wildlife Service in Tucson.
"Streams, ponds, cienegas, springs even cattle tanks that's where a lot of our threatened and endangered species are found," Rorabaugh said. "Most native fish in the Southwest are imperiled, as are a number of native frogs, garter snakes, riparian-dependent birds."
Now even sewage effluent is being used to create wetlands.
Tres Rios wetlands in Phoenix is an example. Output from a large sewage treatment plant on the Salt River near the confluence of the Gila River goes into the river "and creates some really dramatically beautiful" woodlands and cattail marshes. Ponds there are popular with birdwatchers and others who like outdoor recreation, Rorabaugh said.
Even without natural fluctuations in precipitation, humans worldwide have taken land that's too wet to plow or too dry to drink and converted it to farmland, Cary said. Since wetlands also tend to flood, dams are built. Some wetlands are filled in for development.
And changes affect how people view and value wetlands.
For example, urban encroachment jeopardizes fishing and hunting opportunities.
Native fish are threatened by nonnative, often sport fish. River diversions disrupt natural river cycles, and reduced flows also can raise water temperature, harming many native fish.
"As you lose those opportunities for people, you lose people's value in the wetlands," said John Vradenburg, supervisory biologist for the Bosque del Apache National Wildlife Refuge in central New Mexico.
Without dramatic natural spring floods, salt cedar takes over it's the dominant tree in the lower Colorado's riparian system instead of cottonwoods and willows.
Cary said responsibility for managing water is divided among different agencies, adding to the complexity.
"We need to figure out a way to work together," he said. "It's hard to do sometimes for government agencies. Sometimes we recognize the boundaries between us more than we recognize the shared missions."
In the Rio Grande Valley through the heart of New Mexico alone, the Fish and Wildlife Service, the Bureau of Reclamation, the Interstate Stream Commission, the Corps of Engineers and the Middle Rio Grande Conservation District must balance agricultural, urban and habitat interests as well as those of endangered species such as the silvery minnow and Southwestern willow flycatcher.
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