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Hypoxia in the Surf Zone of the Grand Strand: Likely Causes

Hypoxia in the Surf Zone of the Grand Strand: Likely Causes. Azure Bevington, Susan Libes, Joseph Bennett, Amanda Hall, Neil Capper and Eric Tosso, Coastal Carolina University, Conway, SC. Serendipity. Being in right place at the right time doing something else.

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Hypoxia in the Surf Zone of the Grand Strand: Likely Causes

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  1. Hypoxia in the Surf Zone of the Grand Strand: Likely Causes Azure Bevington, Susan Libes, Joseph Bennett, Amanda Hall, Neil Capper and Eric Tosso, Coastal Carolina University, Conway, SC

  2. Serendipity • Being in right place at the right time doing something else. • Assessing the impact of new discharge pipe at 25th Ave S on eutrophication status of nearshore. • Hypothesis: Stormwater runoff through discharge pipes contributes to nutrient loading in the nearshore.

  3. Violations of Federal Swimming Criteria for Enterococcus Along Grand Strand Beaches

  4. DO (ppm) % Saturation Temperature (oC) Salinity 2nd Ave N. Pier 7/20/2004

  5. Bottom Water Quality: Longitudinal Transect Along Pier

  6. 0 m 3 m ? Low DO 5 m Longitudinal Model of Hypoxic Zone Pier + 100 to 200 m

  7. Time-line • Surface Cooling: July 1 – July 30 • Rain fall • 7/9, 1.0 inches • 7/18, 2.2 inches • Sampling • 7/20: 2nd Ave N and Springmaid • 7/22: 2nd Ave N and Springmaid • 7/23: Cherry Grove and Apache + DNR transects • Flounder Jubilee • July 15 – 23 • July 23 – 28: tapered down

  8. Rain Fall Amounts Near Locations of Major Freshwater Input to Surf Zone

  9. Time-line • Surface Cooling: July 1 – July 30 • Rain fall • 7/9, 1.0 inches • 7/18, 2.2 inches • Sampling • 7/20: 2nd Ave N and Springmaid • 7/22: 2nd Ave N and Springmaid • 7/23: Cherry Grove and Apache + DNR transects • Flounder Jubilee • July 15 – 23 • July 23 – 28: tapered down

  10. pH measurements along Grand Strand, July 23, 2004

  11. Rain No Rain Rain

  12. Time-line • Surface Cooling: July 1 – July 30 • Rain fall • 7/9, 1.0 inches • 7/18, 2.2 inches • Sampling • 7/20: 2nd Ave N and Springmaid • 7/22: 2nd Ave N and Springmaid • 7/23: Cherry Grove and Apache + DNR transects • Biotic Impacts • Flounder Jubilee • Benthic invertebrate kills at Huntington Beach and Pawleys Island

  13. Causative Agents • Coastal Upwelling • Summer Cooling • Plankton Bloom • Elevated Chlorophylls • Nutrients • Stormwater Runoff • Pipes and swashes discharge on beach • Off-shore discharge pipes • Raw Sewage Spill

  14. Rain No Rain Rain

  15. P deficient growth N deficient growth Guildford and Hecky, 2000

  16. Causative Agents • Coastal Upwelling • Summer cooling • Plankton Bloom • Elevated Chlorophylls • Nutrients • Stormwater Runoff • Pipes and swashes discharge on beach • Off-shore discharge pipes • Raw Sewage Spill

  17. Stormwater Runoff • Tidal Creeks (swashes) • Withers Swash: 35 to 40 cfs non-rain, 12 MGD • Midway Swash: 10 to 15 cfs non-rain, 4 MGD • Pipes on Beach Face • Diameter ( 2 to 3’) • 100+ • Outfall Pipes (n = 3) • 25th Ave S • Two individual pipes • 1222’ • 60” diameter • Installed June 2003 • 32.35 cfs during 50-yr non-hurricane storm (8.6” in 24 hr) • Catchment area is 189 acres

  18. Causative Agents • Coastal Upwelling • Summer cooling • Plankton Bloom • Elevated Chlorophylls • Nutrients • Stormwater Runoff • Pipes and swashes discharge on beach • Off-shore discharge pipes • Raw Sewage Spill in NMB • July 13: few hundred gallons • July 21: 5000 gallons

  19. Is this a one-time event? Should we be worried?

  20. Future Frequency of Hypoxia • Frequency of Upwelling • Global Climate Change • Stormwater Runoff • Global Climate Change • Increase in population & impervious cover

  21. Potential Impacts • Hard Bottom Communities • Fisheries • Overfishing • Harmful Algal Blooms

  22. Potential Hard Bottom Habitat < 0.5 m sediment cover

  23. Hard Bottoms start 3 m Typical 4 s waves along Grand Strand constrain wind mixing to upper 3 m (Gayes, pers. comm.)

  24. Potential Impacts • Hard Bottom Communities • Fisheries • Overfishing • Harmful Algal Blooms

  25. Needs • Monitoring • Define normal for Nearshore Waters • Now using estuarine criteria • How much of these events are natural • Translate this into management guidelines • Reduction of nonpoint loads

  26. Acknowledgments • Bob Van Dolah, Mel Bell, George Reikerk, Dean Cain, SC DNR • Denise Sanger, SC DHEC OCRM • Alan Lewitus, South Carolina Algal Ecology Laboratory • Bob Pender, Ryan Day, Burroughs and Chapin Center for Marine and Wetland Studies

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