Sustainability and avian biodiversity tensions in wastewater management in arid zones

Biodiversity is increasingly threatened by anthropogenic and climatic changes around the globe. Many animals lose the habitats where they can settle and reproduce successfully or are affected in their migratory movements due to disturbance and a lack of stop-over sites. For instance, wetlands are declining worldwide with strong impacts on millions of resident and migratory birds relying on them. Artificial wetlands, such as wastewater treatment ponds can serve an important role in meeting habitat needs of wetland and water-dependent birds. Yet these sites are also altered by technological upgrades geared to more efficient water usage, with largely unknown consequences for avian biodiversity. Here, we systematically determine the relationship between wastewater treatment plants (WTPs) and avian biodiversity across various levels of technological WTP advancement, along the Nile in Egypt, which is a major bird migration flyway. We show that WTPs host large numbers of resident and migratory birds, however the most advanced treatment technologies have significantly lower abundance, species richness and species diversity compared to less advanced WTPs. In contrast, lower-technology WTPs with water availability and spill-over ponds and with a presumably higher water quality displayed higher species diversity. WTP type also affected the avian community composition, with smaller and less diverse species communities in the technologically most advanced WTPs with no open water surface. The results underscore ecological trade-offs associated with water-saving technologies, especially in arid regions where natural wetlands are limited or absent. We advocate for a balanced approach to wastewater management that integrates human resource efficiency and biodiversity conservation. Our findings have broader implications for trade-offs in resource management, emphasizing the need for multi-stakeholder involvement and nature-based scientific approaches. Our study lays the groundwork for establishing wastewater treatment policy that meets both the needs of humans and of wildlife, and more broadly, how wastewater treatment can contribute to biodiversity conservation and meeting sustainable development goals.