Summary of 2006 Severn Monitoring Project

   In order to assess summer dissolved oxygen levels in the Severn River, a collaborative monitoring project was carried out by teams from the Severn Riverkeeper and Arlington Echo Outdoor Education Center, beginning in June 2006 and extending into the fall of 2006.  Every 1-2 weeks, monitoring was carried out at a series of 18 fixed stations, from near the Chesapeake off the USNA throughout the Severn to the head of the tidal Severn at Indian Landing.  As shown on the map below, stations were chosen throughout the Severn mainstem, Round Bay, and in representative creeks on both shores of the Severn.  Using electronic meters with probes measuring dissolved oxygen, salinity, and temperature, depth profiles were obtained for each of these parameters every 1-2 meters, from the surface to the bottom. 
   Dissolved oxygen (DO) levels near the surface generally showed healthy, near-atmosphere saturated levels as expected.  However, throughout the summer, DO levels near the bottom all averaged below the "healthy" threshold of 5 mg/l, from "moderately hypoxic" (2-5 mg/l) down to the anoxic levels (<0.2 mg/l) characteristic of "dead zones".  These results are depicted by the color coded circles on the map. Stations in Asquith Creek and throughout most of Round Bay showed the lowest levels, which were at or close to anoxic.  Anoxia at these stations was confirmed by easily detectable levels of hydrogen sulfide, a product of anaerobic bacterial metabolism.  Stations nearer the Severn's mouth, and those in most Severn creeks showed milder bottom hypoxia (2-5 mg/l).  Our dissolved oxygen results explain previous studies documenting degradation of the benthic habitat in the Severn, which is most pronounced in and above Round Bay.    
   Salinity measurements from monitoring after the 5-10" rain storm of June 25-27 showed the expected decrease in salinity throughout the Severn.  However, although fresh water was detected at Indian Landing right after the storm, the major source of fresh water entered the Severn from the Chesapeake Bay rather than from the Severn watershed.   This was shown by data from a week after the storm, when the Severn's salinity decreased progressively from its mouth through our station above Round Bay in the Narrows. Measurements over the next week showed the replacement of all of the older saltier water with fresher water from the Bay.  As the dry summer continued into August, saltier water entered the Severn along the bottom from the Chesapeake. These results show that water flows in the Severn are dominated by density-driven exchange from the adjoining Chesapeake. 
   The following pages provide details of this monitoring program:
       Monitoring Program Description   │   DO Results    │   DO Discussion   │  Salinity Results   │  Salinity Discussion.

A PDF version of the entire monitoring report is available here.