The Border Environmental Health Initiative: Water Quality in the Transboundary Upper Santa Cruz Basin

_{Limited rainfall, reliance on ground water, high rates of population growth, and poverty combine with a complex binational and bicultural environment to place unique pressures on human and ecosystem health in the US-Mexico border. The Upper Santa Cruz Basin is a microcosm of border complexity including farming, ranching, mining, twin cities, a large human population, industry, trade, and shared surface and ground water. Surface water is scarce and unreliable, making ground water the primary—and in some areas the only—water source. Urban development, mineral contamination, irrigation, sewage effluent, and even global climate change all have the potential to alter the stability of the fragile systems in the borderland region. Declining water tables and increasing use of border ground-water resources by municipal and other water users have raised concerns about the long-term quality and availability of this supply. Despite the critical nature of water in maintaining human and environmental health in the desert southwest, current knowledge is inadequate regarding the manner in which natural and anthropogenic forces interact to limit water quality and quantity.}

_{The U.S. Geological Survey (USGS) Border Environmental Health Initiative is collaborating with U.S. and Mexican scientists involved in environmental and public health in this area. As a first step to addressing this need, a multidisciplinary team of USGS scientists is working to identify risks to animals and people from potential contaminants in water resources within the Upper Santa Cruz Basin, and quantify impacts to ecosystems and human health. This research will track organic and inorganic contaminants as well as pathogens and their surrogates from sources to sinks in soil, water, plants, and animals. Existing ground-water models and a new surface-water model will be used to assess contaminant and sediment transport.}