TENUOUS ECOLOGICAL PROGRESS HIGHLIGHTS THE NEED FOR BINATIONAL COOPERATION IN THE SANTA CRUZ WATERSHED NEAR NOGALES

The Santa Cruz River near Nogales, Arizona flows year-round with the release of effluent. In July 2009, upgrades to the treatment process came online at the Nogales International Wastewater Treatment Plant (NIWTP). The ecological response from the biological nutrient removal technologies brought about a rapid shift in water chemistry and biological assemblages in this effluent-dominated stretch of the river: increased dissolved oxygen, decreased in total phosphorus and ammonia, and the return of an endangered native fish species. Sonoran Institute’s 2019 Living River report provides insights into the evolving biogeochemical conditions and extent of the river downstream of the NIWTP. The largest population center along this stretch of the river is in Nogales, Sonora; over 80% of the wastewater delivered to the NIWTP is generated in Mexico. Yet without a binational agreement to ensure that wastewater continues to be delivered to the NIWTP, this restoration is tenuous. Further, infrastructure improvements are needed on both sides of the border. This intersection of restoration ecology, effluent management, and water resource policy highlights the opportunity for binational cooperation to ensure the resilience of the Santa Cruz River ecosystem.