0058423
Impacts of Dredging and Inlet Bypassing on the Inter-tidal Ecology of Pea Island National Wildlife Refuge (12 Years of Sand Bypassed from Oregon Inlet to Pea Island)
Dennis Stewart US Fish and Wildlife Service and Robert Dolan University of Virginia
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• Cape Hatteras National Seashore
• Pea Island National Wildlife Refuge
• National Wildlife Refuge System Improvement Act of 1997
• Compatibility Determination
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Fundamental Questions
• Anticipated physical impacts to beach?
• What are the ecological implications?
• Compatible with mission and purpose?
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Table 1. Statistical Summary
Location Sand Size S.D. Heavy Minerals Percent Fine Sand (In mm) (Dark Minerals) (‹0.25mm)
Pea Island Swash zone 0.57mm 1.3 2.5% 32%
Oregon Inlet 0.26mm 2.4 11% 50% Spit
Ocean Bar 0.45mm 3.3 6% 33%
Oregon Inlet 0.22mm 2.0 10% 60% Channel
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Significant Impacts
• 1. Burial (>4cm without wave runup) • 2. Finer grains & high % heavy mineral
• Degree of impact correlated with: – Frequency – Volume –Placement
Trend in mean grain size from 1990-2002, mid swash zone, Pea Island, NC.
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0.9
0.8
0.7
0.6
0.5 R = 0.68 2 0.4 R = 0.46
0.3
0.2
Average mean grain size (mm) size meanAverage grain 0.1
0 1988 1990 1992 1994 1996 1998 2000 2002 2004
Dredge Disposal Data 3 1200000 Hopper Dredge 1000000 Pipeline Dredge 800000 600000 400000 200000 0
Volume of sand deposited y Volume deposited sand of 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
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Trend in heavy mineral content of the Mid-Swash Zone 1992-2002
18.00
16.00
14.00
12.00
10.00
R = 0.81 8.00 R2 = 0.65
6.00 Mineral Abundance (%) 4.00
2.00
0.00 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Dredge Disposal Data ) 3
1200000 Hopper Dredge 1000000 Pipeline Dredge 800000 600000 400000 200000 0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Volume of sand deposited (y
Trend of decline in Emerita counts taken from 1990-2002 along Pea Island, NC.
30.00
25.00
20.00 R = 0.72 R2 = 0.52 15.00
10.00
5.00 Count average per sandcore per Countaverage
0.00 1988 1990 1992 1994 1996 1998 2000 2002 2004
-5.00
Dredge Disposal Data
1200000 Hopper Dredge 1000000 Pipeline Dredge 800000 ) 3 600000 (y 400000 200000 0
Volume of sand deposited 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
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Trend of Donax counts taken from 1993 – 2002 along Pea Island.
20.00
18.00
16.00
14.00
12.00
10.00 R = 0.14 8.00 R2 = 0.02 6.00
Count sand per average core 4.00
2.00
0.00 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Dredge Disposal Data Hopper Dredge
1000000 Pipeline Dredge 800000
) 600000 3
(y 400000 200000 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Volume of sand deposited
Trend of Amphipod counts taken from 1996-2002 along Pea Island, NC. 14.00
12.00
10.00
8.00 y = -0.8869x + 1779.9 R2 = 0.2623 6.00
4.00 Count per sandaverage core
2.00
0.00 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Dredge Disposal Data Hopper Dredge 900000 Pipeline Dredge 800000 700000 600000 )
3 500000
(y 400000 300000 200000 100000 0 Volume of sand deposited sand deposited Volume of 1995 1996 1997 1998 1999 2000 2001 2002
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CONCLUSIONS
• NEW METHODS – Node/Inter-node Disposal – Others?
• REVISIT DREDGING MORATORIUM WINDOWS – Least biological activity – Peak biological activity
• MONITORING IS CRITICAL – Data for adaptive management – Input for compatibility decision
• MUST MAINTAIN SCIENTIFIC OBJECTIVITY – Will involve some risks
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