Resolving uncertainties in sewage subsidies to urban aquatic ecosystems using continuous sensing and stable isotopes

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

The presence of sewage in urban streams and rivers poses significant risks to human and environmental health: pathogens increase costs to treat drinking water and make recreation dangerous whereas excess nutrients from runoff and waste can cause algal blooms that can decimate aquatic ecosystems and limit recreational uses. This project addresses interactions between urban streams and urban water infrastructure systems. Sewage pipes flow by gravity, and thus are often deliberately installed in stream channels. As pipes age and leak, stream-sewer interactions and contamination are more likely. Currently, 45 major US cities have domestic sewer and storm drains combined into the same pipe system. When it rains, excess wastewater combines with stormwater, and can flow directly into streams and rivers through a combined sewer overflow. Despite the prevalence of this problem, neither of the two national centers of urban stream research in Baltimore and Phoenix include watersheds with combined sewer overflows. For this project, a nest of in-stream sensors will be established within an urban stream in Pittsburgh, PA. Sensors will collect water quality measurements at 15-minute intervals and give unprecedented insight as to how sewage leaks and overflows affect urban stream water quality at finely resolved time scales. This project will broadly benefit society by deepening understanding of a significant health risk, strengthening relationships between academia and local watershed associations, and educating the public about water quality, public health, and ongoing monitoring efforts. Due to altered hydrology and anthropogenic nutrient subsidies, there remains a critical need to understand the impacts of urban infrastructure systems on stream nutrient loads. This research investigates the elusive connection between catchment pipe infrastructure and ecological impacts in urban aquatic ecosystems by measuring finely-resolved changes in nitrate concentrations and other water quality parameters, evaluating the effects of sewage subsidies on in-stream gross primary productivity, and exploring changes in nitrate mobilization and transport during storm events. This will be accomplished using an unusual combination of stable isotope tracers (nitrate, water) and continuous sensing to disentangle the convoluted signals of watershed transport and transformation of nutrients in urban systems. Nine Mile Run, an urban stream in Pittsburgh, PA with buried headwaters, co-located sewer pipe infrastructure, and combined sewer overflows, will be the focus of the study. A water quality station featuring an ultraviolet nitrate analyzer and a multi-parameter water quality sonde will measure high frequency water chemistry over a two-year period. In-situ sensors, along with an ISCO autosampler, will capture and reveal the full range of daily variations, as well as mid-storm changes, that have not been visible with previous grab sampling. This combination of data on the sources, timing, and delivery of both nitrate and water will allow for better characterization of solute flow paths, elucidate when and how wastewater-groundwater-surface water interactions are occurring, and the effects they have on catchment transport, stream productivity, and stream biogeochemistry. This project will broadly benefit society by deepening understanding of a significant health risk and educating the public about water quality, public health, and ongoing monitoring efforts. It will also expand upon ongoing efforts by the Pittsburgh Collaboratory for Water Research, Education and Outreach to strengthen collaborations between University of Pittsburgh researchers with communities and to continue building a graduate program centered on community-engaged water research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.