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Water Management Study: Upper Rio Grande Basin c. Ecosystem Oegradation.-Parts of the Basin's ecosystem are under extreme stress. The river below Elephant Butte Dam has been extensively canalized and exhibits little ofthe habitat characteristics that existed prior to the development of industrial agriculture in the area (Pittenger 1992). The closure of dams in this reach, dewatering of the river bed, degradation of water quality, and channel-maintenance activities, such as vegetation removal and mowing, have severely compromised the biological integrity of the plant and animal communities that historically occurred in this reach. The loss of 71 percent of the native fish species in this area indicates the severity of the impact. ~~ ;.~ In 1994 the U.S. Fish & Wildlife Service listed the Rio Grande silvery minnow as an endangered species, observing that the species, once prevalent throughout the Rio Grande, now can be found only in some places in the Middle Rio Grande (U.S. Fish and Wildlife Service 1994). The minnow is the sole survivor of a guild offive similar species that once inhabited the Rio Grande. In the Middle Rio Grande half of the original fish fauna have disappeared. Between 1918 and the 1980s this area has experienced the elimination of all the saltgrass meadow (48,603 acres), and nearly half (17,498 acres) of the timber and brush dominated by cottonwoods, and seen 17,833 acres become dominated by exotic species (Crawford et al. 1993b). Much of the riparian cottonwood forest, known as the bosque, is now functionally detached from the river and will experience marked change under current resource-management practices (Crawford et al. 1996). f:~ ~~ <: ;< d. Global Climate Change.-The prospect of global climate change promises to exacerbate the demands for water and related resources in the Upper Rio Grande Basin. Models of global climate predict that the accumulation of carbon dioxide and other greenhouse gases will produce global warming and other climatic changes over the next century. There is no single way to show the potential effects of these changes, but one study highlights the potential impact. Drawing on a large body of past research showing that the price of agricultural land is related to the net earnings farmers expect to derive from the land in the foreseeable future, Robert Mendelsohn and two co-authors estimated the potential impact global warming would have on the farmers' net earnings and, hence, on the price of agricultural land (Mendelsohn et al. 1994). They determined that a warming of 70 F, even with an 8 percent increase in precipitation, would cause farm land prices to decline by $200-450, and perhaps by as much as $1000 per acre (1992 prices) throughout most of the Upper Rio Grande Basin. .'-;' 1-;.. .,". .~ f ~: :~?:r ,;j ~>: \,~ (.' ":' 74 .- i t) 0. 5 ,t ~ ',,! '-.; 'j (:..~ ~;.~ r~' li~ ~~