Year 3 Research and Priorities Jeremy Testa Horn Point Laboratory December 9, 2008

1. Year 3 Research and Priorities Jeremy Testa Horn Point Laboratory December 9, 2008 • Primary Scientific Question What C sources are missing from the Bay Program Water Quality model, leading to failed predictions of hypoxic volume? • Relevant Questions from proposal: • B) Production in the flanking shoal areas • (1) same integrated P but less R means more TOC export • (2) benthic primary production as source • (3) spring bloom versus summer production sources • (4) mechanisms for cross-bay transport of TOC

2. Why can’t current water quality models capture oxygen minima? • Current WQ model fails to capture O2 minima in Chesapeake Bay bottom waters • Why? • 1) Transport of C from shoals to deep waters • not part of model • 2) Alternate C source to fuel respiration • not included (“buried C”, primary production)

3. How to investigate? • (1) Do comparison between modeled and measured O2 at all hypoxic stations • (2) Quantify difference as “net respiration” • (3) Distribute “net respiration” over entire hypoxic volume – compute net missing BOD • (4) Investigate possible C sources • Collaborations: • Rebecca and Bill – testbed queries and error analysis • Delaware group – analysis of PP and nutrient load related to “net un-modeled R”

4. To Quantify “Missing Carbon” 1) “Net unmodeled respiration” = Model – OBS 2) “Missing C” = “Net unmodeled Respiration” *V * C/O2 3) Integrate over time with an appropriate scheme to quantify rates Question set 1: Computational details -Match observation to closest model point or average both? -How to interpolate (time + space)? Question set 2: Analysis of missing C -How much C is missing? -Where is the missing C? -When is the C missing? CBP 13k model versus observations Observation Model Cell

5. Initial Analyses Surface vs. Bottom 1) Surface performs better than bottom 2) Model especially bad < 4 mg/l

6. Initial Analyses Spring versus summer 1) Model better in spring 2) No low O2 in spring, however

7. Middle versus Lower Bay 1) During dry year – middle compares favorably, but not lower 2) During wet year – both middle and lower perform poorly

8. Why the shift in relationship between nutrient loading and hypoxia after 1980? • A)Process hypotheses • (1) redox-induced increase nutrient recycling efficiency • (2) loss of biological nutrient sinks (oysters, marshes, SAV) • (3) shoaling of pycnocline & hypsographic threshold • (4) regime shift in oceanographic circulation • B)Artifact hypotheses • (1) abrupt increase in N-loading not apparent in Susquehanna R. • (2) increased O2 sampling intensity yields higher hypoxia volume • (3) aliased interpolation leads to miscalculation of hypoxia volume • (4) shift from N- to P-limitation

9. 2) How have sediment nutrient cycling and oxygen demand contributed • to Chesapeake Bay hypoxia regime shift? • Chesapeake Bay Box Model – Examining shifts in O2, NH4, and DIP net • biogeochemical production from 1960 to present • Examine long-term patterns water O2 uptake and nutrient regeneration • Examine long-term patterns in surface layer productivity and organic fluxes to sediments • Advantages – • Box model already built and has been shown to have high utility in Chesapeake Bay • Model provides a tool to examine past 40 years of O2 and nutrient dynamics • Disadvantages – • Course scale, • Error difficult to quantify • Data limitations for multi-decade analysis

10. CB Box Model?

11. What has not been done?Computations of nutrient production, consumption and transport? July 2003

12. What to do • Derive flux computation from WQ model compare to Box model? • 2) Time series on N flux?

13. July 2003 July 2002 July 1970 July 1965

14. What has been done?Computations of O2 production, consumption and transport?