Trends in Chesapeake Hypoxia/Anoxia Modeling Subcommittee Quarterly Review Feb. 2, 2010

1. Trends in Chesapeake Hypoxia/Anoxia Modeling Subcommittee Quarterly ReviewFeb. 2, 2010 Rebecca R. Murphy and William P. Ball Johns Hopkins University, Department of Geography and Environmental Engineering

2. Outline • Chesapeake Bay Environmental Observatory (CBEO) • Hypoxic volume trends • Stratification trends • Statistical models • Possibility that large-scale climatic forces are affecting hypoxia/stratification • Brief comparison to model output

3. CBEO and Hypoxia Analysis Data Sets Chesapeake Bay Program data USGS River Monitoring Historic CBI data Model outputs etc… New Tools/Methods CBEO website: http://cbeo.communitymodeling.org investigate Generated from data in Hagy et al. (2004) in Estuaries

4. DO Analysis Approach: Analyze hypoxic volume with as much temporal and spatial resolution as possible • Interpolate DO and calculate hypoxic volume for each data collection cruise • Examine time series • Look at where/when changes are occurring in DO patterns

5. Interpolated DO: June-July 2 years

6. rN,vol = 0.31 (p=0.07) rN,vol = - 0.44 (p=0.006) rN,vol = 0.50 (p=0.001) rN,vol = 0.88 (p=4e-17) Data Sources: USGS, CBP

7. Example bottom DO at CB4.3C

8. Example bottom DO at CB4.3C

9. June DO: Oxygen depletion is happening earlier in summer in recent years Stratification: Plays a role in oxygen depletion Approach: • Calculate pycnocline strength • Examine time series • Identify where/when changes are occurring • Look for significant relationships between stratification and hypoxic volume trends Early July DO: More hypoxic volume than anticipated from nutrients alone Nutrients Late July DO: Hypoxic volume follows trend expected from nutrient loads

10. Stratification Strength Calculation Pycnocline Data Source: CBP

11. Stratification Strength Calculation 1. Calculate Brunt Väisälä Frequency 2. Interpolate maximum Brunt Väisälä Frequency (N2) 3. Average max N2 in region of interest Average = 0.015

12. Stratification Trends

13. Analysis: Stratification to Early July Hypoxic Volume (‘85-’09) HypoxicVolEarlyJuly = 6 + 0.8 (StratificationJune) + 2 (StratificationEarlyJuly) + e R2 = 0.74 (p=3e-07)

14. June DO: Oxygen depletion is happening earlier in summer in recent years Changing Climatic Forces (NAO, wind, GSI, sea level rise?) • June • Stratification: • Increasing over time • Causes less vertical mixing of oxygen Early July DO: More hypoxic volume than anticipated from nutrients alone Nutrients • July Stratification: • Not increasing over time • Very variable Climatic Forces Wind speeds much more variable year-to-year in July Late July DO: Hypoxic volume follows trend expected from nutrient loads

15. Possible Climatic Factors NAO • North Atlantic Oscillation • Index has been higher for last 25 years – influences mid-Atlantic climate in multiple ways • Wind direction shifts: (related to NAO) • Winds from south tend to weaken stratification Graph from Jeremy Testa (UMCES) Wind shift and possible relation to hypoxic volume identified by Malcolm Scully (Old Dominion), data=NOAA

16. Possible Climatic Factors: Salinity Changes • Gulf Stream Position (related to NAO) • Index has been higher for last 25 years – means saltier mid-Atlantic waters (Lee and Lwiza 2008) • Sea Level Rise • Evidence of increased Bay salinity (Hilton et al. 2008) Plymouth Marine Laboratory data NOAA data

17. Continuing Work • Investigation of the causes of the increase in early summer stratification and hypoxia • Expanded interpolation efforts into tributaries to examine hypoxia vs. stratification trends

18. Comparison to Model Output 57k output from Mark Noel March ‘09

19. Acknowledgements • Chesapeake Bay Environmental Observatory (CBEO) team, including: • Dr. Michael Kemp and Jeremy Testa (UMCES) • Drs. Dominic Di Toro and Damian Brady (UDel) • Dr. Randal Burns and Eric Perlman (JHU CS) • Data sources: Chesapeake Bay Institute, Chesapeake Bay Program, USGS, NOAA • NSF funding of the CBEO project

20. References • Guo, X. and Valle-Levinson, A. (2008). “Wind effects on the lateral structure of density-driven circulation in Chesapeake Bay.” Continental Shelf Research, 28, 2450-2471. (Univ of Florida) • Hagy, J. D., Boynton, W.R., Wood, C.W., Wood, K.V. (2004). "Hypoxia in the Chesapeake Bay, 1950-2001: long-term changes in relation to nutrient loading and river flows." Estuaries, 27(4), 634-658. • Hilton, T.W., Najjar, R.G., Zhong, L., and M. Li. (2008). “Is there a signal of sea-level rise in Chesapeake Bay salinity?” Journal of Geophysical Research, 113, C09002. (Penn State, UMCES) • Lee, Y.J. and K.M.M. Lwiza. 2008. Factors driving bottom salinity variability in the Chesapeake Bay.Continental Shelf Research 28:1352-1362. (Stony Brook) • Scully, M.E. (2009). “The importance of decadal-scale climate variability to wind-driven modulation of hypoxia in Chesapeake Bay.” Nature Precedings, Posted Jun 2, 2009. (Old Dominion) Data Sources: • CBP: http://www.chesapeakebay.net/data_waterquality.aspx • CBI and other historic data: http://archive.chesapeakebay.net/data/historicaldb/historicalmain.htm • USGS: http://va.water.usgs.gov/chesbay/RIMP/ and http://waterdata.usgs.gov/nwis/monthly/ • NCDC (wind data, Patuxent Naval Air Station: http://cdo.ncdc.noaa.gov/pls/plclimprod/poemain.accessrouter?datasetabbv=DS3505 • NOAA (sea level): http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml • GSI: http://web.pml.ac.uk/gulfstream/default.htm

21. Data Source: USGS

22. Theory: Stratification and Mixing BVF BVF Richardson Number, Ri (Ri: balance between buoyant and shear forces) vertical velocity gradient Ri Vertical Diffusivity, Ez (Munk and Anderson 1948) Ez,0 = Eddy diffusivity with no stratification a,b = coefficients

23. Flow