What Coastal Marsh Sediments Reveal About Land Use Change; Bodega Bay, CA
Anne M. Fisher (1), Laura K. Rademacher (1), Tessa M. Hill (2), Sarah Myhre (2)
(1)
Dept of Earth and Environmental Sciences, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211 ([email protected])
(2)
Bodega Marine Laboratory & Dept of Geology, University of California, One Shields Ave., Davis, CA 95616
Discussion and Conclusions
RP 1a marsh core was similar to the Bodega Harbor core, with little change in grain size
distribution with depth. RP 2a showed variation in sediment fractions in the first 6
cm, suggesting a recent change in sediment source.
Rail Pond cores exhibit a transition from harbor to separated marsh that
accompanied the development of the road
The harbor core was collected on the opposite side of the road from the marsh, and
theoretically shares deeper sediment layers with the marsh cores. The harbor core had
uniform sediment fractions throughout, suggesting no change in sediment source.
silt and clay
100%
80%
0.063 mm
60%
0.149 mm
40%
0.250 mm
20%
0%
0.420 mm
0--1 1--2 2--3 3--4 4--5 5--6 6--7 7--8 8--9 9-- 10-- 11-- 12-- 13-- 14-10 11 12 13 14 15
depth (cm)
RP 2a
B
650 meters
N
500 meters
C
0.420 mm
BH 1a
100%
silt and
clay
0.063 mm
80%
60%
40%
0.149 mm
20%
0.250 mm
0%
N
Fig. 5 Map of northern Bodega Harbor
with dotted sites of core collection sites.
5
14
--1
1
3
12
--1
8-9
6-7
0.250 mm
4-5
0-1
grain size
N
0.149 mm
depth (cm)
grain size
650 meters
Fig. 2 Aerial
photos of
northern
Bodega Harbor
before and after
road
construction
construction.
Future Work
silt and
clay
0.063 mm
100%
80%
60%
40%
20%
0%
2-3
1972
1942
•Harbor cores include large sand, low silt, and low clay fractions.
•Rail Ponds cores were characterized by smaller grain size (silt and
clay), particularly near the surface
•Lack of silt and clay in harbor sample suggests higher wave energy, which
suspends smaller particles
•Elevated silt and clay in Rail Ponds cores suggests less influence of the
harbor’s wave and tidal action
•Color and grain size analyses between Rail Pond cores may indicate
different rates of sedimentation over time
RP 1a
A
10
--1
•Coastal wetlands have high primary productivity and are an important
terrestrial carbon sink (Choi et al., 2001; Brevik and Homburg, 2003)
•Land use affects rate that carbon is sequestered in terrestrial soils
•1963 road construction around Bodega Harbor separated coastal marshes
from the harbor
Research Question
How has construction of the Westside Road impacted coastal marsh
functions around Bodega Harbor?
H
Hypotheses
th
ffor post-construction
t
t
ti marsh
h deposition
d
iti
(1) More silt and clay accumulate in
coastal marshes
(2) More carbon will accumulate in
Fig. 1 Map with
coastal marshes
location of Bodega
(3) Absence of foraminifera in
Harbor.
(www.50states.com)
coastal marshes
Results
grain size
Introduction
Graphs A, B, C Graphs A and B display core
data from 2 Rail Ponds cores. Graph C displays
data from the Bodega Harbor core, the marine
comparison.
depth (cm)
•9 sediment cores collected around Bodega
Harbor
•Core Processing:
•Sliced in 1 cm segments
•Sediment color analysis
•Samples washed in 63 micron sieve
•Samples sifted in stacked sieves
Color Analysis
Gaffney Point
Fig. 4 Grain size analysis
equipment, including stacked sieves and
balance.
Fig. 3 Sediment collected by
manually pushing cores into the
sediment and scooping the
core up.
Fig. 6 Core RP 1a before it
was sliced into 1 cm samples.
cm
color
0--1
2.5Y
2
Y2
2.5/1,
/1 5Y
Y
3/2
1--2
10YR 2/1
2--3
10YR 2/1
3--4
5Y 2.5/1
4--5
5Y 2.5/1, 5Y 3/2
5--6
5Y 2.5/2, 5Y 3/2
6--7
5Y 2.5/1, 5Y 3/2
7--8
5Y 2.5/1, 5Y 3/2
8--9
5Y 2.5/1,
/ 5Y 3/2
/
9--10
5Y 2.5/1, 5Y 3/2
10--11
5Y 2.5/1, 5Y 3/2
11--12
5Y 2.5/1
12--13
5Y 2.5/2
13--14
5Y 2.5/1
14--15
5Y 2.5/1
•Collect longer (1.2 m) cores in the Rail Ponds to examine the larger
sedimentation trends over time.
References
Brevik, E. C. & Homburg, J. A., 2003. A 5000 year record of carbon
sequestration from a coastal lagoon and wetland complex, Southern
California, USA. Catena 57, 221-232.
0.420 mm
0--1 1--2 2--3 3--4 4--5 5--6 6--7 7--8 8--9 9-- 10-- 11-- 12-10 11 12 13
Methods
•Carbon and nitrogen analysis at UC Davis: these data will indicate how
biomass, sedimentation, and burial has changed over time.
Fig. 7 Color change with
depth in RP 1a core
core.
Color changes indicate
different chemical
composition, source of
sediment, or other
depositional changes
over time in the marsh.
Choi, Y., Wang, Y., Hsieh, Y. P., & Robinson, L., 2001. Vegetation succession
q
in a coastal wetland in northwest Florida:
and carbon sequestration
Evidence from carbon isotopes. Global Biogeochemical Cycles 15, 311319.
Acknowledgements
Biological Indicators
•No foraminifera species observed
in samples
•Organic matter in Rail Ponds
cores was higher in first 6 cm of
the core
I would like to thank the EPA for funding this
project, Bodega Marine Laboratory for use
of their facilities, Jackie Sones and Molly
Engelbrecht for help in researching
historical information, and Kari
McLaughlin, Sverre LeRoy, Sarah
Myhre, and May Roberts for their field
assistance.