From accident to management: The Cienega de Santa Clara ecosystem

The 1977 creation of the Cienega de Santa Clara, an 18,000ha wetland (6500ha cattail marsh with 11,500ha of open water lagoons and mudflats) in Sonora, Mexico, was the unintended consequence of the solution to reduce the salinity of the U.S. water deliveries to Mexico. Under the 1944 Water Treaty, the U.S. was obliged to deliver water to Mexico. But the water that was delivered from the U.S. harmed crops in Mexico because it included brackish agricultural runoff from fields in the Lower Colorado River basin. In 1972, Minute 242 to the Treaty called for a reduction in the salinity of U.S. deliveries. As a result, the U.S. diverted the agricultural runoff to a desiccated Colorado Delta floodplain in Sonora, Mexico, inadvertently creating the Cienega de Santa Clara, a wetland that now provides habitat for protected species (Desert Pupfish and the Yuma Clapper Rail), and wintering grounds for more than 200,000 migratory waterbirds. In June 1993, the wetland became part of Mexico's Upper Gulf of California and Colorado River Delta Biosphere Reserve. The Yuma Desalting Plant, completed in 1992, was constructed by the U.S. to desalinate the agricultural runoff that flows to the Cienega. The high cost of operation and abundant Colorado River flow have kept the plant idle. However, the past decade of drought in the Colorado Basin has now made the agricultural runoff a valuable resource to meet growing U.S. water demands, but operating the plant could risk damage to the Cienega wetlands. In response, a binational collaboration of government agencies, environmental groups and university scientists began working together to protect and study this wetland. Replacement flows and environmental monitoring during the 2010–2011 trial run of the Yuma Desalting Plant are prompting a shift from passive to active management of this binational ecosystem. The purpose of this paper is to identify management practices that could help maximize the ecological benefits of water flows. The suggested management practices are based on historical variations in quantity, timing and quality of inflows, occasional dredgings and wildfires. The most important management recommendation is a formal allocation of water of adequate volume and quality. The agreement reached in 2010s Minute 316 to the Treaty is a precedent for successful efforts to protect shared ecosystems along the U.S.–Mexico border. El inicio en 1977 del desarrollo de la Cienega de Santa Clara, un humedal de 18,000hectáreas (650