millennial pre-settlement stability of sedge meadow ... w... · millennial pre-settlement stability...
TRANSCRIPT
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Millennial Pre-settlement Stability of
Sedge Meadow Habitats in Two Piedmont River Valleys
William Hilgartner1, Dorothy Merritts2, Robert Walter2, Michael
Rahnis2, Christopher Berhardt3 , Jeff Hartranft4, Ali Neugebauer2,
Mark Voli2, Hanna Jantzi2, Amy Moser2, and Candace Grand Pre2
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Carex stipata Carex stricta
Carex crinita Eleocharis ovata**
This presentation focuses on a paleoecological analysis of fossil seeds from core and river bank samples, combined with pollen
analysis, geomorphic data and land use history of two river sites in Maryland and Pennsylvania
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First Site: Little Falls, northern Baltimore County, Maryland,
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Little Falls, Baltimore Co., Maryland
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Site of Core LFC1
Holocene hydric layer
Legacy Sediment
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River Bank Stratigraphy
Post-settlement Silt & Clay Layer aka “Legacy Sediment”
Holocene Hydric Layer
Late Pleistocene Gravel Layer
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Core LFC 1
C-14 Date Intercept Age = 4,970 yr BP
C-14 Date Intercept Age = 300 yr BP
56 cm
0 cm
Black clay & plant fragments 10 YR 2/1
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RESULTS: Macrofossil Profile LFC1
Analyst: W. Hilgartner
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Pollen Profile LFC1
Ragweed Increase ca. A.D. 1730
Increase in Alder
Analyst: C. Bernhardt
Oak decline
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Ragweed Increase 6.0 cm = ca. A.D. 1730 Alder increase
0 cm = ca. A.D. 1775
C-14 = 4970 BP
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Sorensen’s Index of Similarity
Note: Consistent indices > 40% from 4300 BP to 1775
Initial establishment of Carex stricta ~4300 BP
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Results: A stable tussock sedge wetland
persisted from 4300 yr BP until A.D. 1775.
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Hydrology of Prehistoric Wetland at
Little Falls …Absence of
paleo-channels
- springs from
Valley margin;
- ground water
table at 1.0 cm;
- saturated soil
Tussock Sedge Wetland, Great Marsh, Chester Co., PA
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Initial habitat change began ca. A.D. 1730 when Carex stricta declined and Alder (Alnus serrulata) became
established
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Burial between 1775 and 1835
The tussock sedge wetland (tsw) was rapidly buried within 60 years between ca. A.D. 1775 and 1835, when 1.0 – 2.0 m of silt and clay sediment (Legacy Sediment - LS) accumulated in a reservoir behind a downstream mill dam.
tsw
LS
5,000 BP
A.D. 1775
A.D. 1835
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18th to 20th Century Dams at Little Falls
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14
So
ren
so
n's
In
de
x
Matrix Point
GRAPH 2: Sorensons Indices Comparing Seed Species in Pairs of Surface Samples
STUDY AREA
Mill Dam
Mill DamSaw Mill
Railroad Spur
Dam (?)
Grist & Saw Mill Dam
Paper Mill Dam(partly rebuilt)
Water surface
Reservoir fill terrace
Distance (ft)
Ele
va
tio
n (
ft)
20,000
400
350
300
10,000 0
LITTLE FALLS: Elevation Profile
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Breach of the mill dam created an incised, high-banked
meandering river channel …..
This incision exposed the legacy sediment and underlying prehistoric
tussock sedge wetland, periglacial gravel, and bedrock.
LS
BW
VB
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Lateral sediment samples show tussock sedge wetland extent (23 m)
Carex stricta
Carex stricta Alluvial Fan interrupts wetland
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The Second Site:
Big Spring Run, Lancaster Co., PA
Holocene Hydric layer
Legacy Sediment
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Big Spring Run, Lancaster Co., Pennsylvania
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Macrofossil Sampling Site
Big Spring Run
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160± 40
140± 40
90 ± 40
270 ± 40 230 ± 40
230 ± 40
850 ± 40
1220 ± 40
2860 ± 40 3000 ± 40
All but one date on single nut.
Big Spring Run, PA, Buried Wetland Soil Radiocarbon (AMS) Dates Dates and Paleo-seed Sampling
European settlement 1709
Macrofossil sample column
0 170 cm
C-14 dates and Depths of the Macrofossil Sampling Site
120 cm 72 cm
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Pollen in upper layers of the sample column
(85 cm – 114 cm)
Ragweed increase
Decline in oak & hickory
Analyst: C. Bernhardt
O:R = A.D. 1730
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160± 40
140± 40
90 ± 40
270 ± 40 230 ± 40
230 ± 40
850 ± 40
1220 ± 40
2860 ± 40 3000 ± 40
All but one date on single nut.
Big Spring Run, PA, Buried Wetland Soil Radiocarbon (AMS) Dates Dates and Paleo-seed Sampling
European settlement 1709
Macrofossil sample column
0 170 cm
Pollen Date Added (in red)
72 cm
A.D. 1730
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Carex prasina type (n =165) -drooping sedge Obligate wetland perennial
0 5 10 15 20
72768084889296
100104108112116120124128132136141147157
Number of Seeds
De
pth
(cm
)
795 BP 1540 BP 3000 BP
Wet Meadow
72
80
88
96
104
112
120
128
136
144
152
160
De
pth
(cm
)
Dandelion seed at 106 cm
Oak:ragweed Horizon (Pollen Date)
ca. 1730 at 102 cm
Initial settlement 1709 at 120 cm?
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Eleocharis obtusa (n = 125)- blunt spikerush (syn: E. ovata) Obligate wetland perennial
0 10 20 30 40 50 60 70 80
72
76
80
84
88
92
96
100
104
108
112
116
120
124
128
132
136
141
147
157
Number of Seeds
De
pth
(cm
)
795 BP 1540 BP 3000 BP
Mud Flat
72
80
88
96
104
112
120
128
136
144
152
160
De
pth
(cm
)
Wet Meadow
ca. 1730
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Alisma plantago-aquatica (n =27)- water plantain
Obligate wetland, aquatic (up to 15-cm water depth)
0 1 2 3 4 5 6 7 8
72
76
80
84
88
92
96
100
104
108
112
116
120
124
128
132
136
141
147
157
Number of Seeds
De
pth
(cm
) 795 BP 1540 BP 3000 BP
Pond
Mud Flat
72
80
88
96
104
112
120
128
136
144
152
160
De
pth
, cm
Wet Meadow
ca. 1730
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A.D. 1730
Pre-settlement Habitat Stability Based on the Continual Presence of C. stipata & C. prasina
Carex stipata (green bar)
Carex stipata (green bar)
Eleocharis
Alisma
Carex hystericina
Carex prasina type
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Sorensen’s Similarity - BSR Samples
-20
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140 160 180
Pe
rce
nt
Sim
ilari
ty
Depth (cm)
Pre-settlement Period Post-settlement Period
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Summary….. Pre-settlement Wetland Stability…
…was maintained over millennia despite these disturbances: - a high charcoal/drought period, ca. 4,000 - 4200 BP, - presumed high abundance of beaver activity - tropical storms and flooding events - prehistoric human disturbance. This long-term wetland stability indicates… - a forested watershed (~100% forest cover) acted as a storm and erosion
buffer - low sedimentation rates entered the valley (0.01 cm/yr at both sites) - constant water table level and stable hydrology - no ponds from beavers in either valley - no main channel; instead low flow anastomosing system
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Post-settlement Habitat Change
A sudden period of rapid sedimentation from deforestation combined with multiple mill ponds and dams during the 18th and 19th centuries was the first event in > 4,000 years to produce succession and decline in these wetlands.
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Sedge meadow wetlands, especially tussock sedge
wetlands are the favored habitat of the endangered bog turtle (Glyptemys muhlenbergii) in Maryland and
Pennsylvania
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Decline of Bog Turtle Habitat
The greater extent of prehistoric sedge meadow wetlands and their subsequent reduction by dams may help explain the modern disjunct distribution and decline of the bog turtle.
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One solution to the decline in bog turtle habitat is restoration…removal of the legacy sediment to expose the
underlying sedge meadow wetland.
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Acknowledgements: Funding: Franklin and Marshall College, PA Dept of Environmental Protection, PA Chesapeake Bay
Commission, EPA, and NSF (MRI and NCALM) Students of Franklin and Marshall College; John Hart-Smith of Johns Hopkins University Landowners at Big Spring: Joseph Sweeney (sold property in 2011); The Kirchner family (current owners) Great Marsh owners are Jim Moore and family
Affiliations: • 1 Contact Information: William Hilgartner, Johns Hopkins University and Friends School of Baltimore. Mailing (Home Office)
Address:137 Hopkins Rd, Baltimore, MD 21212. Cell: 443-834 -6116, Email: [email protected] • 2Franklin and Marshall College, Lancaster, PA. • 3U.S. Geological Survey, Reston, VA. • 4 Department of Environmental Protection, Harrisburg, PA.