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

Hypoxia in the Surf Zone of the Hypoxia in the Surf Zone of the Grand Strand: Likely CausesGrand 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.

• 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.

Horry County Beach Closingsn = 10 sites

116 125

215

593

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2000 2001 2002 2003

Nu

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NRDC (2004) Testing the Waters 2004: A Guide to Water Quality at Vacation Beaches

Violation of Enterococcus Swimming Criteria

Violations of Federal Swimming Criteria for Enterococcus Along Grand Strand Beaches

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34.5 35.0 35.5 36.0

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DO (ppm) % Saturation

Temperature (oC) Salinity

2nd Ave N. Pier 7/20/2004

Bottom Water Quality: Longitudinal Transect Along Pier

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25.0

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28.0

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0 2 4 6Bottom Depth (m)

DO

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34.6

34.8

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35.6

35.8

36.0

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3 m

?Low DO5 m

Longitudinal Model of Hypoxic Zone

Pier

+ 100 to 200 m

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

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Withers Swash Midway Swash

Flounder runs start

Cold Event

Hypoxia first observed

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

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

DO Concentration in Bottom Water During Hypoxic Event

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GardenCity

Surfside MyrtleBeach

State Park

SpringmaidPier

2nd Ave N.MB

ApachePier

CherryGrove Pier

DO

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pm

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7/20/047/22/047/23/04

NOAA Estuarine Eutrophication Criteria Biological Stress >2 ppm, < 5 ppmHypoxic >0 ppm, < 2 ppmAnoxic 0 ppm

Off Shore

8.01

8.07 8.06

8.20

8.09

7.83

8.02

7.6

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Garden City Garden City Surfsidenearshore

Surfsideoffshore

Myrtle BeachState Park

Pier

2nd Ave Pier Apache Pier,nearshore

Mea

n p

HpH measurements along Grand Strand, July 23, 2004

Surf Zone and Near Shore Dissolved Oxygen Percent Saturation

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Sampling Date

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DO

2nd Ave N Springmaid Pier Surf Zone (25th Ave N)

Cherry Grove Pier Apache Pier

Cold Event

Bottomwater

Rain No Rain

Rain

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

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

Surf Zone and Near Shore Chlorophyll a Levels

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2/26 3/12 3/27 4/11 4/26 5/12 5/27 6/11 6/26 7/11 7/27 8/11

Sampling Date

Ch

l a (

pp

b)

2nd Ave N Springmaid Pier Surf Zone (25th Ave N)

Cherry Grove Pier Apache Pier

NOAA Estuarine Eutrophication Criteria Surface ConcentrationHypereutrophic >60 ppbHigh >20 ppb, < 60 ppbMedium >5 ppb, < 20 ppbLow >0 ppb, <5 ppb

Bottomwater

Cold Event

Rain No Rain Rain

Total Nitrogen Concentration in the Surf Zone and Near Shore

0.000

0.050

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0.150

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0.350

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0.450

4/23 5/3 5/13 5/23 6/2 6/12 6/22 7/2 7/12 7/22 8/1Sampling Date

Co

nce

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pp

m N

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2nd Ave N Springmaid Pier Surf Zone (25th Ave N)

Cherry Grove Pier Apache Pier

NOAA Estuarine Eutrophication Criteria Maximum Dissolved Surface ConcentrationHigh >1ppmMedium >0.1 ppm, < 1 ppmLow >0 ppm, <0.1 ppm

Bottomwater

Cold Event

Total Phosphorus Concentration in the Surf Zone and Near Shore

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

4/23 5/3 5/13 5/23 6/2 6/12 6/22 7/2 7/12 7/22 8/1Sampling Date

Co

nce

ntr

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pp

m P

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2nd Ave N Springmaid Pier Surf Zone (25th Ave N)

Cherry Grove Pier Apache Pier

NOAA Estuarine Eutrophication Criteria Maximum Dissolved Surface ConcentrationHigh >0.1ppmMedium >0.01 ppm, < 0.1 ppmLow >0 ppm, <0.01 ppm

Bottom water

Cold Event

Nitrogen to Phosphorus Ratio in the Surf Zone and Near Shore

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4/23 5/3 5/13 5/23 6/2 6/12 6/22 7/2 7/12 7/22 8/1

Sampling Date

N/P

2nd Ave N Springmaid Pier Surf Zone (25th Ave N)

Cherry Grove Pier Apache Pier

Bottom water

Cold Event

N deficient growth

P deficient growth

Guildford and Hecky, 2000

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

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

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

Is this a one-time event?

Should we be worried?

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1990 1995 2000 2005 2010 2020 2030

Year

Horry County Population Growth Projections

Permanent Overnight Day

Future Frequency of Hypoxia

• Frequency of Upwelling– Global Climate Change

• Stormwater Runoff– Global Climate Change– Increase in population & impervious cover

Potential Impacts

• Hard Bottom Communities

• Fisheries– Overfishing

• Harmful Algal Blooms

< 0.5 m sediment cover

Potential Hard Bottom Habitat

3 m

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

Hard Bottoms start

Potential Impacts

• Hard Bottom Communities

• Fisheries– Overfishing

• Harmful Algal Blooms

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

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

Surf Zone and Swashes, Myrtle Beach, SC

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Drainage Basin 2 (ditch) Drainage Basin 1 (pool)