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Chapter 4: River of Change
This chapter is devoted to creating a cloth and paper model of the river valley that can be used for many lessons. The basic activity, "Changing River," provides a setting for the subsequent activities that explore the roles of animals, plants, cottonwood trees, agriculture, and change in the river of the past, the present, and the future. The River of Change model, which is designed for classroom use, is unique to this program and provides a hands-on approach to understanding river ecology.
- A Model of the Rio Grande Valley
- Bulldozers in the Bosque
- Threatened and Endangered Animals
- Introduced and Non-Native Species
- Resources and Activities
A Model of the Middle Rio Grande Valley Rio Bravo, Rio Manso, Rio Nuevo—A Tale of Three RiversIntroduction
It is the nature of rivers to change. As described in Chapter 2, Bosque Background, until the past century most of the dramatic changes along the Middle Rio Grande occurred through a natural flooding cycle. The river valley was a changing mosaic of habitats: over the years marshes would form, silt in, and dry out; river banks would develop and then shift locations; cottonwood trees would sprout and then some would be washed away while other stands would grow to maturity. Although these changes were sometimes dramatic, they were generally cyclical. If a single stand of trees was washed away, somewhere in the valley other stands were getting established. When a marsh dried out and became grassland, other marshes were being formed elsewhere which provided that wet habitat.
Human activity has disrupted this annual flooding cycle, particularly in the past century. To control flooding and dry out waterlogged soils in the valley, people built dams, reservoirs, levees, and drains. In addition, people have intentionally and accidentally introduced many exotic plants and animals to the area. Major compo- nents of the bosque, such as water table levels and plant and animal communities, are rapidly changing. Instead of occurring in a circular pattern, with all habitats occurring in the valley, this kind of change follows a linear pattern. As a response to differences in available water, new communities of plants and animals are replacing some habitats that had existed in this valley for hundreds of thousands of years.
Humans also impact the bosque in many positive ways. Particularly since 1993, many projects in the bosque have been focused on restoring the ecological sustainability of this ecosystem. In order to treat our river wisely, we must understand the role of change in the river ecosystem. We need to be able to recognize what kinds of changes are healthy for our bosque, and what kinds of changes may permanently affect our bosque and the plants and animals that live there.
The hands-on activities in this chapter help students learn about some of the changes, both natural and human-influenced, that our river has faced and will continue to face. The core of these activities is a model consisting of a large cloth (blanket-sized), paper cutouts, and material strips. Models are tools that help up simplify complex systems so we can understand various components of those systems more clearly. This model illustrates the Rio Grande in three different stages depending on the kind of changes the river is experiencing.
We are calling these stages Rio Bravo (the wild river), Rio Manso (the tame river), and Rio Nuevo (the new river). By constructing the images of these rivers students will grasp some of the differences between the historical and the present-day systems and understand some of the challenges we face in managing our new river.
Rio Bravo is the old river, the prehistoric river that was not strongly influenced by human activity. This river experienced an annual flooding cycle, although the intensity of these floods varied from year to year. We can speculate about many features of Rio Bravo, but this river no longer exists. It is important to understand what it was like in order to preserve some of its features in managing today’s river.
Modern communities along the Rio Grande had trouble living harmoniously with the wild river. Homes, farms and businesses were regularly flooded. Farmers needed water to be available throughout the growing season, not just in one major flood early in the summer. Many projects were developed to harness the Rio Grande to fit human needs. Dams were built so that spring runoff could be stored in reservoirs and made available to farmers throughout the summer. Levees and jetty jacks were constructed to prevent the river from meandering and flooding communities. Rather than allow the river to move around on the valley floor, human settlement dictated that the river stay in a designated location. In the Middle Rio Grande Valley, a large cottonwood-dominated forest developed between the levees and the river. On the model, we call this river Rio Manso. Like a horse that has been tamed for riding, this river now serves the people who live within the valley.
The changes that created this tame river, that allow our communities to live and thrive in the Middle Rio Grande Valley, do not always provide the optimum conditions for the native plants and animals that evolved in the valley under the conditions of the old river. Some species that lived in and around the old river are now extinct, and several more species are endangered. To manage the river for all creatures — human needs and the needs of plant and animal species — we must find a way to incorporate the features of both Rio Bravo and Rio Manso into a river system that supports a diversity of life. In this model we call that Rio Nuevo, or the new river. This is the river of our future, and with each thoughtful action we come closer to meeting these goals.
“Changing River,” the core activity, is simply the process of laying out the model and making the transitions between Rio Bravo, Rio Manso, and Rio Nuevo. Although this may be a time-consuming activity the first time, students quickly acclimate to this task and will soon be able to set up each of these scenarios in a matter of minutes.
The rest of the activities are based on the “Changing River” activity. Recognizing that the time constraints of each class will vary, there is flexibility in these modeling exercises. Not every class will be able to participate in every activity, and there is no specific order for introducing the remaining activities. In practice we have found that these remaining activities work well alone in separate sessions or combined together. These two approaches for using this chapter are outlined on the next two pages.
“Cottonwood Creation” helps students understand how cottonwoods are established and why cottonwood trees in the valley are declining. This two-step activity includes a germination step, where students toss cotton balls and determine which locations are likely to allow seeds to germinate, and the “Root Race” when the young seedlings are trying to survive their first season by reaching their roots to the ground water table.
“Who Lives Where?” builds the students’ understanding of the animal life in the bosque and river. Students read about an animal’s characteristics and place a picture of the animal on the model in the appropriate habitat. In this edition of the guide, there are two sets of animal cards for different levels of readers. Some cards have also been added for classes focusing on upper watersheds north of Cochiti Lake.
“Who Grows Where?” is similar to the animal game, but with plant cards instead.
“Working Water” takes an in-depth look at the agricultural systems of water management and how these support agriculture as well as wildlife.
“Bosque Chaos” is a game that uses dice to help students see the role of change and chaos in annual flooding patterns in Rio Bravo, then compare the linear types of changes in Rio Manso and a combination of cyclical and linear changes in Rio Nuevo.
The model is presented here in a simple format of using a large blanket or cloth, cutouts prepared from this guide or as a kit provided at workshops, or in a trunk checked out from various support agencies. In addition, the same concepts can be explored using natural elements outdoors such as sticks, a large sand pit, a garden hose, etc. To avoid confusion, we have written the following activities using one set of materials (in this case paper model pieces), but we encourage classes to adapt these ideas to other media as well. For example, you may want to create the model indoors first, and then set up an outdoor demonstration with the hose and sand.
The most important concept is for students to create a visual picture of the differences between Rio Bravo, Rio Manso, and Rio Nuevo. Students should be able to contrast the river of the past with the river of today, and then to also contrast today’s river when it is managed for human development with today’s river when it is managed for the whole ecosystem. By creating models of these three stages of the Rio Grande, the powerful teaching technique of contrast is used to clarify the role humans have played and can play in this river ecosystem.
Hey, they’re bulldozing the bosque! How can that be restoration?
In recent years resource managers have been using these big machines with a new goal in mind. Instead of bulldozing the forest to clear it for human use, dozers are now being used to help restore the forest. In what managers and scientists like to call “bulldozer ecology,” heavy equipment is being used to clear out exotic vegetation and alter the river bank to allow flooding. One successful example of this is the Albuquerque Overbank Project.
The Albuquerque Overbank Project (AOP) is a collaborative effort with participants from the U.S. Bureau of Reclamation, University of New Mexico Department of Biology, City of Albuquerque Open Space Division, Middle Rio Grande Conservancy District, New Mexico Natural Heritage Program, U.S. Fish and Wildlife Service, State of New Mexico Environment Department, and U.S. Army Corps of Engineers. The AOP site is located on the southern end of an elevated, attached river bar on the west side of the Rio Grande, north of Rio Bravo. Because of riverbed degradation, it had received little if any overbank flooding in recent decades. This project was designed to evaluate the effectiveness of bank clearing and lowering to reestablish native woody vegetation (cottonwoods and willows) on such a site in the Albuquerque Reach of the Middle Rio Grande bosque.
Site preparation, using bulldozers and other heavy equipment, began in March 1998. It involved clearing and root plowing 4 acres (1.6 ha) of the bar’s dense Russian olive cover, then lowering over half of the cleared area by 2 feet (0.6 m) to allow for flooding during spring runoff events and summer wet periods. Trees that were cleared were removed and chipped. Material from the bank was spread over a connected (lower) sand bar south of the cleared site. Shallow channels and topographic undulations were created on the cleared bar to facilitate floodwater distribution to promote the establishment of native tree seedlings.
A number of physical and biological parameters have been monitored throughout the project. Shallow ground water wells (piezometers) were set up at various distances from the bank to see how ground water is affected by river flow, distance to the river bank and distance to the old, established bosque. Vegetation was sampled throughout the lowered bar area to monitor which herbaceous and woody species came onto the cleared site. Soil salinity was measured and soil textural types identified. A fenced weather station was erected at the site’s north end. Surface-active arthropods, bird populations, and beaver activity were monitored on the new bar as well as in the adjacent cottonwood bosque and in an uncleared Russian olive thicket north of the site.
The site flooded in May and June of 1998. Flooding occurred at flows over approximately 2,500 cubic feet per second (cfs). In 1999, there were three overbank inundations: in late May–early June, late June, and early August. Relatively elevated parts of the site did not flood, even at flows approaching 5,000 cfs. Ground water levels correlated well with Rio Grande stage heights and discharge rates measured at the Albuquerque Central Avenue Bridge USGS gages. Ground water response was most rapid and had the greatest amplitude in wells nearest the bank.
Changes in river channel morphology (shape) were quite notable. Prior to restoration activities, the river channel adjacent to the site maintained uniform depth, velocity and width for variable river discharges. However, because of the extensive erosion changes in the bank profile and in site topography, the river channel is now much more variable in depth, width and velocity for variable discharges. Since bank-stabilizing Russian olives are now absent, the river has eroded 125 to 150 feet (37.5–45 m) of bank line, with river width increased by 15 percent. New bar formation has occurred downstream as the eroded bank material has been relocated.
Over 8,000 cottonwood seedlings and a smaller number of coyote willow, saltcedar and Russian olive were established during the first flood season. Most of the cottonwoods died before the second season, but the remaining patches are conspicuous in places (some were six to seven feet (1.8–2.1 m) tall in 2001) and account for more cover than do survivors of other woody species. They occur in sandy-loamy soils that characterize much of the site. Relative saline soils at the northern end of the experimental area supported large sunflower stands the first summer. These were largely replaced by sweet clover the second summer. Cockleburs and horseweed are common toward the site’s southern end.
The new bar habitat greatly increased the number and diversity of animals using the site. A number of bird and arthropod species were detected on the new bar that were not present in the adjacent mature bosque. Beavers were active cutting young cottonwoods and willows, but as of the summer of 2001 had not had a large impact on the new vegetation overall. Animal use of the bar will likely change as the vegetation changes over the years, but overall the project was beneficial to animal populations.
The AOP provides a good demonstration of the type of new restoration projects currently being done along the Middle Rio Grande Valley. It also shows the effectiveness of bulldozer ecology.
An endangered species is an animal or plant that may very soon go extinct. When extinct, every one of that species is gone; not one is alive anywhere. That species is gone from the Earth forever. The term “extirpated” is used when a species no longer occurs in a given locality, such as the Middle Rio Grande Valley, but still survives in other places (also referred to as “locally extinct.”) A threatened species is reduced in numbers and is on its way to becoming endangered and then going extinct. The purpose of listing a species as threatened or endangered is to restore the species to a point where its populations are stable and no longer in need of special protection. The federal Endangered Species Act offers protection both for a listed species directly and for the ecosystems or habitats on which it depends.
The federal government, through the United States Fish and Wildlife Service, lists species as threatened, endangered or extinct. The state government, through the New Mexico Game and Fish Department, makes its own list of state endangered, threatened or extinct species. Some species may appear on one list and not the other, or they may be on both lists. The New Mexico Natural Heritage Program, a program within the Biology Department at the University of New Mexico, also ranks plant and animal species, and plant communities, as to their endangerment status and monitors these species closely.
Fifty percent of fishes native to the Middle Rio Grande Valley are no longer here. Many things have contributed to this local extinction: pollution, reduced water flow, dams, increased erosion on land leading to more sediment in the water, and introduction of non-native fish species.
Some interesting fish had life cycles that included living in the freshwater Rio Grande and over 1,500 miles (2,400 km) away in the Gulf of Mexico. The American eel and freshwater, or sheepshead, drum are no longer found in New Mexico due to the dams and diversion structures in the Rio Grande. The American eel, Anguilla rostrata, spawns at sea, in the Sargasso Sea to be exact. The females travel up freshwater rivers and can live for 50 years before making the trip out to the ocean. The males stay in the ocean and near shore areas, but when females arrive they travel in groups, along the sea floor, to the spawning area where they mate and die. It takes three years for the young to get back to fresh water. Today eels are still in the Mississippi River valley having been found as far upstream as North Dakota and other rivers of the eastern Atlantic and from Greenland to Brazil. The freshwater drum, Aplodinotus grunniens, today lives primarily in the salt–fresh-water mixed zone of the mouth of rivers. It still comes up the Rio Grande a short ways, but cannot make it very far. Remains have been found in archeological sites in the Middle Rio Grande Valley—evidence that drum made up a significant component of the fishery of the pre-alteration Middle Rio Grande.
The following species are in the “Who Lives Where?” bosque animal activity and are currently (or have been in the past) threatened, endangered or extinct.
Rio Grande Silvery Minnow, Hybognathus amarus
federal: endangered; state: endangered
The silvery minnow was placed on the federal endangered species list in 1994. Today you can find this minnow swimming only in the river between Cochiti Dam and Elephant Butte Reservoir, particularly in the more southern reaches. It is endangered because of poor water quality, changes in the structure of the riverbed, and lack of water in the river due to irrigation and drought. The minnows lay eggs with the peak spring flows, and the young develop in quiet backwater areas after overbank flooding. (See Chapter 2, Introduction, for more information.)
Rio Grande Bluntnose Shiner, Notropis simus simus
Last collected in 1964 near Pena Blanca. Extinction suspected as a result of its habitat periodically drying up due to water diversions, dams, and drought (loss of spawning sites by desiccation), and possibly competition with introduced species. The Pecos bluntnose shiner (Notropis simus pecosensis) is listed as a federal and state threatened species.
Shovelnose Sturgeon, Scaphirhynchus platorhynchus
extinct in New Mexico (extirpated)
Only one voucher specimen of this fish has been found in New Mexico (in 1875); however, archaeological evidence indicates the fish was eaten in earlier times. One theory to explain this fish’s early extinction in New Mexico relates to the sturgeon’s reproductive habits. Since adult fish return to their birthplace to reproduce, any changes to that one spot (such as removing water for irrigation) would affect the entire population of shovelnose sturgeons.
Northern Leopard Frog, Rana pipiens
All five species of leopard frogs in New Mexico are being carefully monitored. The northern leopard frog was listed on the Navajo Endangered Species List as “threatened” in 1997 but has not been placed on state or federal lists even though many local populations have been lost. Although scientists are not sure exactly why leopard frogs have declined dramatically, many suspect that competition with and predation by introduced bullfrogs or predation by introduced fish may be major factors. Other reasons leopard frogs may be declining are damage to their habitat, pollution, and commercial harvesting.
Greater Sandhill Crane, Grus canadensis
Although not currently listed as endangered or threatened, greater sandhill cranes were rare in the 1930s primarily due to loss and degradation of wetland habitats. The Bosque del Apache National Wildlife Refuge was established in 1939 in part to provide wintering habitat for greater sandhill cranes, and now populations have recovered enough that the species is no longer considered endangered. The whooping crane (Grus americana) is listed as endangered at the state level.
Bald Eagle, Haliaeetus leucocephalus
federal: threatened; state: threatened
Once widespread throughout the United States, a decline in the southern and eastern parts of the bald eagle’s range in the 1900s led to its federal listing as endangered. A ban on DDT helped populations recover and by mid-1995 it was down-listed to threatened. By 1999 it was proposed for delisting since populations appear secure. Major threats remain, however, including habitat loss, disturbance by humans, chemical contamination, decreased food supply and illegal shooting.
Yellow-billed Cuckoo, Coccyzus americanus
federal: candidate; state: not listed
Yellow-billed cuckoos are considered a candidate species at the federal level, which means there is enough information on potential threats and the vulnerability of the species to propose listing as endangered or threatened. In the west, yellow-billed cuckoos nest in riparian woodlands with tall cottonwoods and willows. The local subspecies needs large patches of dense riparian forest with fairly dense understory to nest, so it is particularly affected by loss and degradation of habitat.
Southwestern Willow Flycatcher, Empidonax traillii extimus
federal: endangered; state: endangered
The southwestern willow flycatcher was listed as endangered at the federal level in
1995 and at the state level in 1996. It nests in dense willows that overhang wetland habitat. This habitat has been dramatically reduced in the last few decades. When the river was straightened, wetland areas were drained for agriculture. Wetlands were also reduced by the loss of spring flooding. Another contributing factor to the southwestern willow flycatcher’s decline is parasitism by brown-headed cowbirds. Cowbirds lay their eggs in the nests of other birds, leaving those parents to raise the cowbird chicks. Cowbird eggs hatch earlier than the residents’ eggs, and nest- lings are generally bigger and stronger. Cowbird chicks are more aggressive and out-compete others for food. Although native, brown-headed cowbirds expanded their range with the clearing of forests and the introduction of cattle. They have had a dramatic effect on many species in the Southwest.
Little Brown Bat, Myotis lucifugus occultus
federal: candidate for listing; state: not listed
The little brown bat is currently not listed but the local subspecies is considered vulnerable and is being tracked. This bat forages over open water and needs roosting sites close to open water. Its decline is thought to be related to a loss of roosting sites.
Meadow Jumping Mouse, Zapus hudsonius luteus
federal: not listed; state: threatened
This mouse lives in marshlands and wet meadows. Its numbers declined when marshes and meadows were drained in the 1930s. Today, the areas where they are found are far from each other and are only small patches of habitat. They often now live along ditches or drains with willows and other vegetation.
In the Middle Rio Grande Valley, there are many species that have only recently taken up residence. These plants and animals are taking over areas that native spe- cies have lived in for thousands of years. There are many reasons that non-native species may be successful, but in general they arrive here without the animals or plants adapted to eat or compete with them in their native environment.
There are three introduced trees that are very common in parts of the Middle Rio Grande Valley: tamarisk/saltcedar (Tamarix chinensis), Russian olive (Elaeagnus angustifolia), and Siberian elm (Ulmus sp.). In general they are increasing because human-caused changes in the river valley provide favorable conditions for them to grow.
Tamarisk trees flower and produce seeds throughout the growing season; their reproduction is not restricted to spring/early summer as are native cottonwoods. When bare ground is colonized late in summer by tamarisk, it will not be bare in the spring when cottonwoods are sending out seeds. Both Russian olive and Sibe- rian elm can sprout in shaded areas, under the canopy of the cottonwoods, and are becoming very common in the bosque.
Fires in the bosque are much more common today than in previous centuries. Human-caused fires from factors such as fireworks destroy many acres of the bosque each year. Cottonwoods can survive low- to moderate-severity fires, and can re-sprout after high-severity fires, but survivorship of the above-ground tree tends to be low after high-severity fires. Although the sprouts can grow quickly, it takes some time before they are able to produce seed. Both tamarisk and Russian olive can re-sprout after fires, while above-ground parts of the plants tend to be killed. These species, however, often can reestablish after fires more quickly than cottonwoods with new seeds coming from plants off the burned site, since they produce seeds for a longer period than do cottonwoods. Also, tamarisks that survive a fire can increase flowering and seed production, again giving it an advantage in re-establishment over cottonwoods.
Cavity-nesting birds (such as nuthatches, chickadees, and woodpeckers) are an important part of the bosque ecosystem. They use the large cottonwoods to build their nests, but they have not been seen nesting in tamarisk or Russian olive. These introduced trees do not provide suitable cavity sites. If the number of native trees in the Rio Grande bosque continues to decline while introduced tree species increase, we may see a change in some of the wildlife along our river corridor.
The isopods, commonly called pillbugs (Armadillidium vulgare) and woodlice (Porcellio laevis), were brought to this continent in the holds of ships. Ships carried dirt as ballast on their trips to North America, but then dumped the soil to load cargo bound for Europe. Isopods spread from these deposits. In the Rio Grande Valley the isopod has become the major detritivore (eater of dead plant material). Crickets filled this role before, but are now reduced in numbers. Crickets do well in areas that receive spring flooding, but isopods tend to be more numerous in drier sites.
Although native to the eastern U.S., it is unknown whether bullfrogs (Rana catesbeiana) are native to New Mexico. They were introduced throughout the west to provide a source of frog legs for people to eat, and this is probably how they got into the Middle Rio Grande. Bullfrogs are large frogs that eat almost anything they can capture and swallow, even ducklings! They are known for eating other frogs and have been blamed for the decline of several species. The northern leopard frog may have declined in part due to predation by bullfrogs.
Non-native fishes have been introduced to the Middle Rio Grande both accidentally and by intentional Game and Fish stocking programs. There has been a correspond- ing reduction in the numbers and distribution of native fishes as the new species compete for food or prey directly on native species. In some cases an introduced relative is hybridizing with the native species. Species of mosquito fish have been introduced to control mosquitoes in the valley, as some mosquito fish eat mosquito larvae. The installation of Cochiti Dam has changed the temperature of the water and the amount of water released downstream throughout the year; those conditions change the fish able to survive in the reach below the dam.
European starlings (Sturnus vulgaris) were introduced into Central Park, New York City in 1890; by 1952 they were found across the United States. They primarily eat insects but also eat seeds and scavenge garbage. They nest in cavities and so compete directly with native cavity-nesting birds. Starlings nest early in the year and are very aggressive about claiming nest holes. They even evict the large woodpeckers that excavated the hole! Many species of birds are now reduced in numbers due in part to competition from starlings.
House sparrows (Passer domesticus) were introduced to St. Louis in 1875 from England, after initial introductions in the 1850s to Brooklyn died. By 1940 they had spread throughout the United States by nesting in boxcars. They live in and around buildings, close to humans. Like starlings, house sparrows start nesting earlier in the year than native birds and so can claim prime nesting habitat (they nest in cavities but can also build a bulky nest in dense vegetation). They may even appropriate nests of other birds, killing eggs and nestlings if occupied. House sparrows tend to have several broods a year.
House mice (Mus musculus) move along with humans into an area. They have large numbers of young that can reproduce when only two months old. Although they are not common in bosque sites away from the city, in the Albuquerque bosque they are often captured in areas of dense vegetation, especially near water. They do not tend to be in areas of mature cottonwoods. With more human development in or near the bosque, and a shift in vegetation, house mice will likely spread into more areas. The Norway rat (Rattus norvegicus) was also introduced to the valley and is found in agricultural areas, but is not very common in the bosque.
Feral cats eat native rodents and birds. They also eat native lizards, and have caused a dramatic decline in the local lizard populations. Feral dogs roam in packs and eat many native species. They easily destroy ground-nesting birds such as ducks and geese.
Introduced and non-native species have had, and continue to have, a great impact on the native plants and animals of the Middle Rio Grande bosque. Many of these introductions happened years ago. The people releasing the animals or bringing in the plants did not know the effects they would have. It is with hindsight that we wish some of these species had not been brought here. Today, we should not repeat the mistakes of the past. Do not release unwanted pets into the bosque. An unwanted kitten or puppy should be taken to Animal Control or the Humane Society. Don’t vacation in another state and bring home a wild animal, such as a turtle for a pet, then let it go in the bosque when you can’t take care of it any more. We have a rich and diverse population of plants and animals particularly adapted to the Middle Rio Grande Valley. We should work hard at learning about the natural ecosystem and keeping our native species with us.
River of Change - Two Approaches (93kB PDF)
Download all of Chapter 4 (3.2 mB PDF)
- Changing River (534 kB PDF)
- Cottonwood Creation (179 kB PDF)
- Who Lives Where? (952 kB PDF)
- Who Grows Where? (591 kB PDF)
- Working Water (318 kB PDF)
- Bosque Chaos (1407kB PDF)
Who Lives Where Spanish Cards (645.24kb PDF)
Who Grows Where Spanish Cards (469.07kb PDF)
Spanish Activities (338.42kb PDF)