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.