Rio runs high
High snowpack providing plenty of water for bosque ecosystem
Kim Ward goes to work wearing hip waders, and this year she needs them in areas that are normally bone dry. From April through June, the head aquarist for ABQ BioPark wades into the Rio Grande each day to gather eggs of the endangered silvery minnow. Ward and her assistant, Monika Skiba, typically collect eggs in the river’s main channel. But 2017 is not a typical year. Ward rumbled half a mile down a levee road in Los Lunas and stopped her truck where the road plunges into flowing water. “Last year, we could walk down this road all the way to the river,” Ward said, pointing toward a place 100 yards or more across flooded
bosque, thick with towering cottonwoods, Russian olives and salt cedar.
Ordinarily, this area is “dry, dry, dry,” she said. This year, “the cottonwoods are getting their feet wet.”
The U.S. Army Corps of Engineers estimates that sustained flows in the Rio Grande this spring are the highest since 2008 and are likely to continue into June or later. Many areas of the river have “overbanked” this spring, spilling into the bosque.
The corps based the forecast on reports of snowmelt from fat snowpacks in northern New Mexico and Colorado that feed the Rio Grande and its tributary, the Rio Chama.
Ward and Skiba waded into the floodplain and were instantly waist deep in coffee-colored water. They pounded fence posts into the sediment and set up wooden boxes that can trap minnow eggs floating on the current.
This day, April 28, the Rio Grande here was flowing at a rate of about 3,700 cubic feet per second, according to U.S. Geological Survey data. Last year on that date, flows hovered around 650 cubic feet per second.
Since 2000, peak flows during the spring runoff season have averaged between 1,500-2,000 cubic feet per second in this reach of the Rio Grande, between the Isleta and San Acacia diversion dams.
The silvery minnow is a 2- to 4-inch-long fish that once thrived throughout the Rio Grande and the Pecos River. By 1994, the fish survived only in the middle portion of the Rio Grande, and populations had dwindled to the point that it was placed on the endangered species list.
This year promises to yield a bumper crop of silvery minnow because slow-moving waters in overbanked areas provide an ideal habitat for the minnow hatchlings to feed and grow.
“The overbanked areas really provide a nice, shallow, warm, nutrient-rich area for nursery habitat,” Ward said.
The abundance of water in the Rio Grande benefits more than the silvery minnow, said Todd Caplan, a consultant for GeoSystems Analysis, Inc.
Caplan contracts with the U.S. Army Corps of Engineers and other agencies to create habitats that more closely resemble environments that existed in the Rio Grande before dams, reservoirs and river channelization prevented the river from flooding each year.
“The whole food-web in the floodplain relies on these sorts of inundation events,” Caplan said.
Native species of plants, animals, insects and even microorganisms in the Rio Grande basin all evolved in an environment of periodic flooding, he said.
“This basically helps the life cycle of many, many of the critters that have evolved with the floodplain,” Caplan said of this year’s high flows. “Cottonwoods, willows, all the native vegetation, and the animals that utilize these habitats, the flooding benefits all of them.”
Flooding also helps recharge the shallow aquifer, he said.
“Think of the floodplain like a sponge,” he said. “When you can fill that sponge up, it can then slowly release water later in the season when the river is at a much lower flow.”
The U.S. Fish and Wildlife Service issued a new opinion in December that gives Rio Grande water managers greater flexibility to manage flows in the river, as long as silvery minnow populations remain above certain target densities. Federal officials issued the “no jeopardy” opinion after they and water managers agreed last year that the minnow is not in jeopardy of extinction.
Ward and her ABQ BioPark colleagues drive some 800 miles a week this time of year collecting minnow eggs used for captive spawning. The collected eggs hatch in tanks at the BioPark’s Aquatic Conservation Facility and are bred with minnows collected in prior years.
The BioPark operates one of three New Mexico facilities used for spawning minnows. The others are the Southwestern Native Aquatic Resources and Recovery Center in Dexter, operated by the U.S. Fish and Wildlife Service, and the Los Lunas Silvery Minnow Refugium, operated by the state.
Most of the minnows produced are released in the late fall in stretches of the Rio Grande where they are most needed, as determined by the U.S. Fish and Wildlife Service.
“The purpose of egg collecting is to maintain the genetic diversity of the brood stock,” Ward said.