Microbial Source Tracking in the Anacostia Watershed

Results from a DOEE study in seven catchments in southeast DC

Picture of Anacostia Riverkeeper

Anacostia Riverkeeper

Anacostia Riverkeeper has worked on Citizen Science Water Quality Monitoring, measuring levels of E. coli for the past five years. As we have collected samples across the watershed, both in District of Columbia waters as well as for smaller monitoring programs in Montgomery and Prince George’s County, we have frequently fielded questions on where the E. coli we find might be coming from. We know it’s there- but how is it getting introduced into our water, and what might be done to thwart it?

E. coli is a bacteria that naturally grows in the guts of warm-blooded animals (birds, dogs, mammals, and even humans!) and the high levels of E. coli that are sometimes found in the Anacostia River can make it unsafe for recreation. Microbial source tracking (MST) is a lab procedure that allows scientists to distinguish the source of fecal contaminants in a water source. Using MST lab procedures, scientists can analyze the E. coli found in the river to identify what types of fecal waste might be entering the waterway.

DOEE (DC’s Department of Energy & Environment) scientist Amir Sharifi recently partnered with a group of scientists at the federal Environmental Protection Agency (EPA) to conduct an MST study in seven tributary catchments in southeast DC (see included map). In this study, published in January of 2023, identified sources of E. coli found in samples collected from November 2019-2020.

Overall, they found the highest levels of E. coli in the summer, particularly after heavy rain events. 44.6% of samples collected had high amounts of E. coli and therefore failed to meet the acceptable use threshold (<410 cfu of E. coli per sample). Similar to what we find in our Citizen Science Water Quality Monitoring, most of these failing events occur after heavy summer rainstorms. Using MST methods, DOEE and EPA scientists were able to gain insights into the sources of E. coli during these failing events.

  • Some human-marked E. coli were found in all catchments. Finding human markers in these catchments was surprising as there is no known sewer outflow in these tributaries like there are in the main-stem of the Anacostia River. At Fort Chaplin, where the human-marked E. coli was particularly high, they were able to identify and remove an illicit gray-water discharge into the stormwater drain. 
  • Dog waste was found to play a major role in fecal contamination in many samples, especially after rain events. This is unsurprising as dog ownership is high in the city, and many pet owners do not properly clean up after their pets. Again at Fort Chaplin, dog-marked E. coli was exceptionally high, leading the authors to recommend pet waste management (providing bags and waste receptacles) at a nearby dog park where none were observed. 
  • Ruminant (deer) -marked E. coli was never found in the catchments during dry conditions, and only trace amounts after extreme rain events. As the sampled areas should not have a large deer population, this is expected, but could have an impact in more rural tributaries as MST studies continue.
  • Avian (bird) -marked E. coli was regularly detected in all catchments regardless of rainfall events. The amount of bird fecal contaminants was higher in areas with more residential buildings, supporting a theory that some microbial pollution comes from residential roofs. Homeowners should consider installing green infrastructure, such as rain barrels or rain gardens, to help filter water coming off their rooftops.

Overall, these findings were an interesting insight into the sources of microbial pollution in the Anacostia River. We look forward to DOEE’s continued efforts in MST sampling, as we expect results in the mainstem of the Anacostia to be quite different as these are impacted by the cities’ combined sewer outflows (CSOs). 

We are initiating MST studies in Maryland’s Anacostia tributaries across Montgomery and Prince George’s county in partnership with University of Maryland professor Dr. Amy Sapkota to fully understand the sources of E. coli across our watershed and help advocate for plans to reduce bacterial levels so the watershed can be safe for all to recreate.

Citation: Diedrich A, Sivaganesan M, Willis JR, Sharifi A, Shanks OC (2023) Genetic fecal source identification in urban streams impacted by municipal separate storm sewer system discharges. PLoS ONE 18(1): e0278548. https://doi.org/10.1371/journal.pone.0278548