From Pipes to Streams: Phosphate's Role in Urban Ecosystems
Since the Flint, Michigan episode, drinking water utilities across the U.S. are using orthophosphate additions to control corrosion from lead pipe networks. However, the use of this type of corrosion inhibitors also provides key nutrients for bacteria that live in the pipe networks and urban streams. Although the stream and drinking water pipe networks are not designed to be hydrologically connected, the pipe network in Pittsburgh (and other cities) is aged and deteriotating. As a result, unintended connections occur in the subsurface, linking leaks from the pipe networks to downgradient stream networks. Our team is evaluating how these connections can change the microbiome of the pipe and stream network. This NSF-funded RAPID project examines changes in the chemistry, nutrient limitation and microbiome of the drinking water pipe and urban streams before and after the initiation of orthophosphate use by the Pittsburgh Water and Sewer Authority.
This research focuses on uncovering the unexpected impacts of orthophosphate (PO43-) treatments on urban stream water quality, emphasizing connections between drinking water infrastructure and downstream ecosystems. Originally applied to reduce lead pipe corrosion, PO43- additions are driving increases in phosphorus concentrations and pipe corrosion byproducts—such as copper, manganese, and iron—in urban streams. Collaborating with a drinking water treatment plant, the study examines significant shifts in stream chemistry influenced by infrastructure leaks, wastewater contributions, and mineral weathering. Nutrient bioassays are showing accelerated eutrophication as a result of the combined availability of nitrogen and phosphorus, with algal biomass continuing to proliferate across urban waterways. This work highlights ongoing ecological risks posed by unintended nutrient transfers from subsurface infrastructure to streams, providing critical insights for urban water management, nutrient mitigation strategies, and further investigations into infrastructure-stream interactions.