Changing levels of heavy metal accumulation in birds at Tumacacori National Historic Park along the Upper Santa Cruz River Watershed in southern Arizona

Introduction National parks and other protected areas can be influenced by contamination from outside their boundaries. This is particularly true of smaller parks and those with riparian ecosystems. Riparian woodlands provide a critical resource for breeding, migratory, and wintering birds, and support more species than any other vegetation type in southern Arizona (Knopf et al. 1988). The degradation of riparian systems from heavy metal contamination can have detrimental impacts on avian communities and other organisms living within that ecosystem. Animals living in contaminated areas are susceptible to adverse health effects as a result of long-term exposure, and bioaccumulation of heavy metals. Therefore, understanding contamination source locations and how birds are living within a national park or protected area are crucial for making decisions regarding avian species management. The upper Santa Cruz River in southern Arizona is dry throughout most of the annual cycle, but a 35 km stretch that flows through Tumacacori National Historical Park (NHP) was revived to a perennial flow in the mid-1900s, when the river started being filled with treated effluent from the Nogales International Wastewater Treatment Plant (NIWTP). The plant treats sewage and wastewater from both Nogales, Arizona, and Nogales, Sonora, Mexico. Furthermore, the river receives water from intermittent tributaries (e.g., Sonoita Creek) that flow through urban and abandoned mining areas. The Santa Cruz River corridor within the park now supports lush riparian vegetation, but concerns about water quality have arisen because heavy metals, pesticides, and other contaminants have been discovered in this riverine system (King, Zaun, and Velasco 1999; Kirkpatrick, Conway, and LaRoche 2009). Avian monitoring at Tumacacori NHP,