Pre- and Post-Tunnel Comparison of Nitrogen Dynamics and Microbial Community of the Anacostia River, D.C.

The Anacostia River located in Washington, D.C is one of the most polluted rivers in the United States. To address environmental concerns, DC Water build a storage tunnel beneath the Anacostia River that opened in March 2018 to divert sewage and stormwater from entering the river. To evaluate the effectiveness of the tunnel and examine relationships between flow conditions, nutrient dynamics and microbial communities, samples for nitrogen concentrations and 16S and 18S biodiversity were collected over the course of five years (2013-2017) prior and two years post (2018-2019) tunnel implementation. Previous work has shown that flow has an impact on nitrate (NO₃^-) and ammonium (NH₄⁺) concentrations and NH₄⁺:NO₃^- ratios as well as presence of various phytoplankton taxa. We predicted that after tunnel implementation, nitrogen concentrations would decrease and alter NH₄⁺:NO₃^- ratios, leading to more diatoms and less cyanobacteria. Although there was heavy rainfall in 2018-2019, nitrogen concentrations were slightly lower than pre-tunnel concentrations leading to different plankton communities. While more analysis needs to be done, preliminary 16S data shows that biodiversity was lower in 2018 as opposed to 2017. For instance, there was a higher percentage of transcript reads of Burkholderiales and Chrysophyceae at the lower Anacostia River in 2018. Due to above average rainfall in 2018-2019, the evaluation of the effectiveness of tunnel implementation needs to continue to see if there is any improvement in water quality as indicated by nitrogen levels and biodiversity of the bacterial and phytoplankton community.