干旱区生态环境知识资源中心

The Colorado River delta in Mexico has been partially revegetated following 20 years of water flows from the United States. Lake Powell, the last major impoundment built on the river, filled in 1981. Since then, flood flows in the main channel of the river have occurred in El Nino cycles, and have returned native trees and other vegetation to the riparian corridor. This vegetation provides a migration route for endangered southwestern willow flycatchers (Empidonax traillii) and other migratory birds moving from Mexico to the United States for summer nesting. Agricultural drain water from the Wellton-Mohawk Irrigation District conveyed to the delta since 1977 has created Cienega de Santa Clara, a 4200-ha Typha domengensis marsh containing the largest remaining population of the endangered Yuma clapper rail (Rallus longirostris yumanensis), plus numerous species of migratory and resident waterfowl. Populations in the marine part of the delta have been severely affected by the lack of river flow, but some species have responded positively to renewed flows. Currently, there are 170,000 ha of natural areas in the lower delta in Mexico, containing riparian, wetland and intertidal habitats. Much of this land as well as the adjacent marine zone is protected in the Biosphere Reserve of the Upper Gulf of California and Colorado River Delta. Natural resource managers, scientists and non-governmental environmental groups in Mexico and the United States are exploring conservation measures that can provide water and protection for these areas for the future. (C) 2001 Academic Press.