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Submarine Groundwater Discharge (SGD) and its Importance to Coral Reef Ecosystems, West Hawaii
Eric Grossman, U.S. Geological [email protected]
D. Oki, D. Foote, P. Swarzenski, M. Field (USGS)K. Knee, A. Paytan
(Stanford, UCSC)B. Burnett (FSU)
C. Glenn (UH)
S. Beavers (NPS)
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Submarine Groundwater Discharge (SGD) Why is it a concern?
10-16% global freshwater input to ocean;
Locally, ≤100%
100% nutrient Input10-100x ocean concentrations
“Out of sight, out of mind”
Groundwater use, runoff, waste disposal altering quantity and quality
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Window into aquifer
Submarine Groundwater Discharge (SGD) What is it?
PPT
rechargerunoff
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Composition? Fate? Kaloko-Honokohau
NHP
Johnson et al (In Press)
Pesticides, metals, petroleum, PPCP?
land
ocean
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How much fresh groundwater enters coast? Nutrient?
SGD Nitrogen(MGal/day)
(Kg/d)
Kaloko:
2-3 45-70W. Hawaii: <1,400
2000-3500Knee et al (2008); Grossman et al (In Prep)
Grossman et al (In Prep)
Since 1990sNO3
(2x)PO4
(5x)Parsons et al 2008
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SGD Fluxes to Coral Reefs Worldwide
Maui (104%)
Aqaba (3%)Florida Keys (13%)
Mauritius (76%)
Relative to Kona (in percent)
After Paytan et al (2006)
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SGD –
Importance to Coral Reefs
Phase shiftsalgal, cyanobacteria?
Community structure
Octocorals
~ SGD/nutrients
Buffer to
thermal bleaching?
Chronic and episodic disturbance
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Importance of West Hawaii Coral Reefs coral reef cover & diversity
Friedlander et al. 2008
0
5
10
15
20
25
30
Niihau Kauai Oahu Molokai Lanai Maui Hawaii
Cor
al c
over
(%)
OtherPorites lobataPorites compressaPocillopora meadrinaMontipora patulaMontipora flabellataMontipora capitata
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Importance of West Hawaii Coral Reefs Ecosystem structure & services
Friedlander et al. 2008
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Niihau Molokai Hawaii Lanai Kauai Maui Oahu
Bio
mas
s (to
n ha
-1)
ApexPlanktivoresSecondaryHerbivore
Human Population
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since mid-1970s
Modeled ~50% ↓
in freshwater discharge (KAHO)
Oki et al 1999
Increase in withdrawals (MGal/Day)Time
Dec
reas
e in
dis
char
ge (%
) Wells installed since mid-1970s
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Data from Hawaii Commission on Water Resource Management
Measured Water Level Declines5-10 ft (coastal)15-20 ft (high elevation)
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Modeled 1-ft water table drawdown at coastDecrease in SGD? Saltwater intrusion?
Oki et al 1999
Projected 46% increase in development by 2020
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Ground Water System -
Linkages
Need interdisciplinary models/tools to
1) predict complex ecosystem responses
2) Public & agency buy-in to assess trade-offs between ecosystem functions and human well being
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Conclusions:
Submarine groundwater discharge is a major process affecting coral reefs and coastal ecosystems
-
Spatially/temporally variable
-
Source of nutrients (10-100x seawater)- SGD ↓, nutrient/contaminant ↑
with development -
Uncertain impacts/linkages:
Groundwater use
Land-use (quantity, quality, flow paths)
Climate change
Sea-level rise
Need models/tools to assess trade-offsbetween water use andecosystem-economic sustainability
http://coralreefs.wr.usgs.gov