2006 Severn Water Quality Monitoring Project--Description

Background
In recent years, hypoxia (low levels of dissolved oxygen) has become recognized as the major water quality problem for the Chesapeake Bay, and has negatively impacted other fresh and marine water bodies world-wide.  Hypoxia is known to develop as a result of nutrient-fueled overgrowth of phytoplankton, which end up sinking to the bottom and being consumed by oxygen-depleting decay bacteria.  Estuaries are particularly vulnerable to hypoxia because of the restricted vertical mixing of bottom salty water with oxygen-rich fresher surface water.  Extensive monitoring by the Chesapeake Bay Program has shown the development of large volumes of hypoxic water in the deep portions of the Chesapeake every summer, with the levels of hypoxia correlating with the annual input of nutrients. Efforts to monitor dissolved oxygen levels in tributaries such as the Severn have been limited, and it is generally assumed that hypoxia is much less likely in these shallower waters with greater contact with atmospheric oxygen.  However, data from the DNR Severn monitoring station at the Rte 50 bridge shows consistent summer hypoxia near the 25 foot deep bottom.  Additional DNR monitoring at the head of the tidal Severnfor two summers showed hypoxia even in shallow water at a one meter depth.  Another reason for concern is that the Severn's traditionally good yellow perch population has declined in recent years in spite of stocking efforts by the DNR Fisheries Division, and a detailed study of this problem has laid much of the blame to hypoxia in the fresher Severn creeks.   Finally, preliminary monitoring of the Severn's Saltworks Creek by Pierre Henkart in the summer of 2004 revealed bottom hypoxia in depths as shallow as 6 feet.  Taken together, there was clear evidence of summer hypoxia in the Severn, but without a more complete and wide-ranging monitoring program, the extent of the problem was difficult to assess.  In the spring of 2006, the Severn Riverkeeper Program and the Arlington Echo Outdoor Education Center collaboratively developed this Monitoring Project to provide a more detailed picture of the Severn's water quality, with a major focus on dissolved oxygen levels.

Strategy and Resources
In order to characterize the Severn's hypoxia during the summer of 2006, the Monitoring Project monitored the Severn at multiple stations from Annapolis to its tidal head at Indian Landing every 1-2 weeks.  This Project was headed by Pierre Henkart, a semi-retired NIH scientist with a bachelor's degree in chemistry, a PhD in biochemistry and molecular biology, postdoctoral research in marine biochemistry, and many years of activity on the Chesapeake. The Project was based on a collaboration between the Severn Riverkeeper Program and Arlington Echo Outdoor Education Center, allowing the full length of the river to be monitored using the Riverkeeper's boat and personnel based in Saltworks Creek, and boats and personnel based at Arlington Echo on the upper Severn near Indian Landing.  The Riverkeeper purchased two YSI 85 meters capable of measuring dissolved oxygen (DO), salinity, and temperature, and Arlington Echo purchased one identical instrument.  The Riverkeeper Program assigned intern Allison Albert to work on this project along with Dr. Henkart, Riverkeeper Fred Kelly and various volunteers. Arlington Echo assigned staffer Suzanne Kilby and two college student interns, Jessica Childs and Ashley Fussell, to obtain water quality data from the upper Severn.  All monitoring personnel were trained in the use of the meter and data handling by Pierre Henkart, who was present on all but one Riverkeeper monitoring trips.  Helpful advice in many areas was provided by NOAA's Dr. Peter Bergstrom, who accompanied one monitoring trip to provide quality control for the DO measurements.  A detailed list of monitoring personnel is included in the monitoring results spreadsheet.

Monitoring
A series of monitoring stations in the Severn mainstem and selected Creeks was established, and a guide using both GPS and visual line-ups was developed to allow monitors to make repeated measurements at the same position.  The creek stations were selected as representative of others based on the character of their entrance channels (shallow vs deep, straight vs curved), and included several from each side of the Severn.  The stations are shown on the accompanying map. Monitoring each station consisted of anchoring the boat using established line-ups, and lowering the YSI probe to ~0.5 meter off the bottom as determined by feeling the weight suspended below the probe contact the bottom.  Monitoring personnel then recorded dissolved oxygen levels (both percent saturation and concentration in mg/liter), salinity and temperature.  Numbers from the meter screen were recorded on a paper datasheet mounted on a clipboard.  The probe was then raised 1-2 meters and the readings repeated to provide a profile of the entire water column, with 4-5 points taken at most stations.  The Riverkeeper boat typically used both meters at each station to provide duplicate values.

    By August, it became clear that some monitoring stations were consistently showing bottom dissolved oxygen levels below 1 mg/l, and the accuracy of our meters at these low levels was open to question.  A water sampling device (LaMotte, JT-1) was then used to obtain near-bottom water samples at these stations to allow olefactory assessment of the presence of hydrogen sulfide (H2S), a product of anaerobic bacterial metabolism.  The presence of H2S confirmed that these stations were truly anoxic, i.e., DO levels <0.2 mg/l.  No H2S-positive samples were obtained when metered bottom DO levels were >0.2mg/l. 

      Results--dissolved oxygen  │   Discussion--dissolved oxygen    │  Results--salinity  │   Discussion--salinity