3 
chapter 11 
Shortnose Surgeon Temperature 
Sensitivity Analyses 
For water column temperatures greater than 29°C, documented as stressful to short- 
nose sturgeon, EPA established a Chesapeake Bay open-water dissolved oxygen 
criterion of 4.3 mg liter -1 instantaneous minimum to protect survival of this listed 
sturgeon species (U.S. EPA 2003). An investigation was conducted to determine if 
there were water column habitats within Chesapeake Bay and its tidal tributaries 
where water column temperatures routinely exceed 29°C. States would need to apply 
the 4.3 mg liter -1 instantaneous minimum dissolved oxygen criterion in such open- 
water habitats. 
Bottom water temperature data were examined for the June through September 
period for the years 1996 through 2002 for all Chesapeake Bay tidal water quality 
monitoring stations throughout the mainstem Bay and tidal tributaries. Observations 
greater than 29°C at a station were expressed as a percentage of the total number of 
observations at the station for the 1996 through 2002 summer time period. These 
percentages were then interpolated and displayed on a map (Figure II-1). Due to the 
high density of stations within the District of Columbia’s tidal waters, this region 
was examined in greater detail (Figure II-2). 
Areas with a higher percentage of tidal water temperatures above 29°C were almost 
exclusively in the tidal fresh and oligohaline regions of the tidal tributaries. The tidal 
fresh James and Appomattox rivers had the highest percentages with 16^40 percent 
of the summer bottom water temperatures exceeding 29°C. In the Northeast, Elk, 
Bohemia, Sassafras, and tidal fresh segmemts of the Chester, Patuxent, Potomac, 
Rappahannock, Mattaponi and Pamunkey rivers, temperatures exceeded 29°C 5-15 
percent of the time. 
Examining the District of Columbia’s water quality monitoring stations’ bottom 
temperature data, it appeared that there were some stations with fairly high percent¬ 
ages of temperatures exceeding the 29°C temperature threshold (Figure II-2). But on 
closer examination, these stations were infrequently sampled and, therefore, the 
percentages were misleading. Based on a more strict evaluation of the total number 
of exceedences by station, it did not appear that elevated bottom water temperatures 
chapter ii 
Shortnose Sturgeon Temperature Sensitivity Analyses 
