Urban expansion in the Sao Paulo Metropolitan Area is causing stream food webs to collapse, with ecological interactions falling from 190 to just three.
Across thirty micro-watersheds in the Upper Tiete region, from fully forested to fully urbanized, urbanization does not merely reduce biodiversity. It selectively favors small organisms and eliminates the very small, medium-sized and large species whose feeding relationships keep stream ecosystems functioning.
The damage appears early. Even with only 12.5% urban coverage, complex ecological connections are diminished, meaning degradation begins with the first stages of development rather than gradually.
Energy flow in the most urbanized streams falls by up to 1,446-fold, weakening the ability of waterways to break down toxic pollutants and process organic matter. That raises the risk that untreated substances reach downstream reservoirs supplying more than 22 million residents, including the Billings Reservoir.
Protecting forested streams and restoring degraded waterways with wastewater treatment, improved water quality and bank vegetation is essential to rebuild biodiversity, ecological interactions and energy flows.