Investigating Anthropogenic Impacts and Environmental Factors on Bacterioplankton Community Dynamics in the Potomac River

Abstract

The Potomac River is a part of a watershed that spans multiple states, rural and urban regions
and is affected by disturbances, including sewage overflow, runoff, and excess nutrients.
Bacterioplankton play an important ecological role in the Potomac River because of their ability
to recycle nutrients and serve as river health indicators. For this study, we set out to see how
spatial and temporal factors affect bacterial concentrations in relation to anthropogenic activity.
We collected data from two sites in the Potomac River area that have experienced cyanobacteria
blooms: Gunston Cove and Hunting Creek. The Potomac Science Center Pond was also included
in the study for comparison of bacteria found in the differing environments. At each site, we
collected 1L of water in a Nalgene bottle, filtered it with a 0.22 μm Sterivex filter in the
laboratory, and then placed it in the -80° C freezer. The filter was then later used for DNA
extraction, sequence analysis, and taxonomic identification of bacterioplankton. A 10 mL aliquot
of water was preserved in 3.7% formalin for microscopy. Fixed samples were stained with
acridine orange, filtered through a 0.22 μm black polycarbonate filter, and viewed with an
epifluorescence microscope to record bacterial abundance counts. The Hunting Creek and
Gunston Cove samples were not able to produce a signal. However, an ongoing algal bloom was
detected in the pond samples, which had high abundances of cyanobacteria with counts
increasing as the bloom progressed