An estimated 10 to 20 tons of reactive nitrogen from sewage flows into Pittsburgh's Monongahela River every year from the Nine Mile Run watershed.
"Leaky sewers are simply not something most people are interested in until they begin to smell it in the stream or see things like a particular fish disappear from the stream," said Bain. "Based on the results from our Nine Mile Run study, this paper forces the wider urban ecology community to more carefully consider this sewage problem."
In order to accurately measure nitrogen's impact on Nine Mile Run, the Pitt team had to first determine how much was coming from leaky sewer systems. Over a two-year period, the researchers collected water samples biweekly from the small stream located in Pittsburgh's East End during both rainy and dry time periods with intensive sampling during one summer storm. Nitrogen concentrations were measured in the samples, and the researchers used this data to estimate sewage contributions to nitrogen in the stream's water. Notably, the results highlighted that sewers in this study basin are leaking consistently, even during dry weather conditions. While the apparent volumes of sewage are concerning, the study also reaffirms the substantial ability of urban systems to hold onto this nitrogen, despite the heavily impacted stream channel and the predominance of paved areas.
"This suggests a pervasive influence of leaking sewerseven during periods without rainfall. This is in addition to the raw sewage contributions during wet weather from combined sewer overflows that are currently the subject of mitigation efforts in Pittsburgh," said Elliott. "Our report highlights the importance of assessing nitrogen leakage from sewers into our waterways, particularly as sewer systems age across the United States."
|Contact: B. Rose Huber|
University of Pittsburgh