Chesapeake Bay Program Tidal Monitoring and Analysis Workgroup meeting December 2, 2010 Matt Hall

1. Frequency-Duration Analysis of Continuous Dissolved Oxygen Data Lower Potomac River Case Study Image or Graphic Chesapeake Bay Program Tidal Monitoring and Analysis Workgroup meeting December 2, 2010 Matt Hall mhall@dnr.state.md.us

2. Questions about DO criteria and living resources • How do individual criteria failures (based on distributional analysis) translate to conditions experienced by living resources (duration at or below criteria levels)? • 2. Were durations at or below measured tolerances (i.e., LC50) violated in the Potomac River between 2006 and 2008? • I adapted frequency-duration methodology developed by Greb and Graczyk (1995) to answer these questions. • Greb, S. R. and Graczyk, D. J. (1995), FREQUENCY-DURATION ANALYSIS OF DISSOLVED-OXYGEN CONCENTRATIONS IN TWO SOUTHWESTERN WISCONSIN STREAMS. JAWRA Journal of the American Water Resources Association, 31: 431–438.

3. Methodology • Sampled all DNR continuous monitors in Potomac River between 2006 and 2008. Cut datasets to include only June through September to guard against major seasonal influences. • SAS program to determine the length of time (consecutive 15 minute intervals) the data fell below the threshold in question. • For monthly and weekly criteria, retained longest monthly or weekly duration per interval, respectively. • For instantaneous criteria and LC50’s, used full set of durations. • Cumulative frequency plots of duration (years pooled).

4. Piscataway Fenwick Mattawoman Blossom Point Wicomico Beach Pope’s Creek Breton Bay Swan Point Piney Point 2006 St. George’s Creek 2007 2008 Percent failure for DO thresholds (5 mg/l) over all three years

5. Preliminary results – Monthly mean criterion Breton Bay Piney Point 47.65% overall failure 16.64 % overall failure

6. Results – Weekly mean criterion Breton Bay Piney Point 28.65% overall failure 7.53 % overall failure

7. Results – Instantaneous minimum Breton Bay Piney Point 16.28% overall failure 3.95 % overall failure

8. Results – Juvenile spot LC50 Breton Bay Piney Point 0.7% overall failure 0.17 % overall failure Juvenile spot (Leiostomus xanthurus) 1 hour LC50 for DO = 0.5 mg/L (at 6.9 salinity and 28°C) Median salinity BBY=11.69 PNY=13.32 Median temp BBY=26.91° PNY=26.21°

9. Results – Juvenile menhaden LC50 Breton Bay Piney Point 0.93% overall failure 0.21 % overall failure Juvenile menhaden (Brevoortia tyrannus) 2 hour LC50 for DO = 0.7 mg/L (at 6.9 salinity and 28°C) Median salinity BBY=11.69 PNY=13.32 Median temp BBY=26.91° PNY=26.21°

10. Conclusions and further analysis ideas • When failures of monthly and weekly criteria occurred, they were of long duration (>10 hours) around half the time. • When failures of the instantaneous minimum occurred, they were of long duration (>10 hours) 15 - 20% of the time. • Failures of spot and menhaden LC50’s did not occur often. When they did occur, they violated the LC50 duration around 40% of the time. The exception was the Breton Bay spot LC50 failure duration which was around 60% of the time. • Further analysis and refinement: • Analyze years separately • Calculate maximum failure duration per month or week for those criteria (or some other way of matching criteria periods) • Match timing of age classes for different LC50 species to con mon dates • Use alternative species for oligohaline and tidal fresh stations