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BENTHIC MICROALGAL CONTROL OF THE IMPORT OF REACTIVE SILICATE INTO TIDAL MARSHES
Audra E. Luscher
A Thesis Submitted to the
University of North Carolina Wilmington in Partial Fulfillment Of the Requirements for the Degree of
Master of Science
Center for Marine Science
University of North Carolina at Wilmington
Spring 2005
Approved by
Advisory Committee
_______________________________ _____________________________
___________________________________ Chair
Accepted by
____________________________________ Dean, Graduate School
TABLE OF CONTENTS
ABSTRACT……………………………………………………………………………………… iii
ACKNOWLEDGMENTS………………………………………………………………………… v
DEDICATION……………………………………………………………………………………. vi
LIST OF TABLES……………………………………………………………….………………. vii
LIST OF FIGURES……………………………………………………………………………… viii
INTRODUCTION………………………………………………………………….…….……….. 1
STUDY AREA……………………………………………………………………………………. 5
MATERIALS AND METHODS……………………………………………………….…………. 7
Study Site Characteristics…………………………………………………..……………... 7
In Situ Silicate Dosing Experiments………………………………………………………. 7
STATISTICAL DESIGN…………………………………………………………………………. 11
RESULTS……………………………………………………………………………………….....13
DSi Uptake at Variable Physical, Spatial and Temporal Scales………………………….. 13
Relationship between Benthic Microalgal Biomass and DSi Uptake………….…………. 21
Ratio of Silicate Uptake to Chl a Biomass……………………………….……………….. 21
Tidal Marshes and the Estuarine Silicate Budget……………………………….………... 22
DISCUSSION…………………………………………………………………………………….. 29
LITERATURE CITED………………………………………………………………….…………34
APPENDIX……………………………………………………………………………………….. 39
BIOLOGICAL SKETCH……………………………………………………………….………… 42
ii
ABSTRACT
Benthic microalgal community control of water column silicate (DSi) concentrations was
examined along an estuarine salinity gradient in the Cape Fear River estuary, North Carolina,
USA over various spatial, salinity, and seasonal scales. Microcosm experiments in the field used
three treatments (100, 35, and 0 µM potassium silicate) and related DSi uptake to benthic
chlorophyll a biomass.
Silicate uptake was dependent on benthic microalgal biomass (p<0.0015). However,
even when microalgal biomass was zero, a statistical model predicted an average uptake of 1480
µmol DSi hr-1 m-2. While vascular plants likely play a major role in DSi uptake, there were no
significant differences between summer and winter seasons with respect to uptake rates. There
were also no significant differences between uptake rates along marsh edge and marsh interior
despite large differences in mean silicate import rates. Marsh edge generally exported silicate,
while the interior imported silicate. High among sample variations within the edge and within
interior areas were likely caused by non-uniform flux of silicate from sediment and by variations
in the densities of animals that graze microalgal biomass. No statistical differences in salinity
effects were found among sites, but there were large differences in microalgal biomass. At the
high salinity site, the ratio of DSi uptake to chlorophyll a biomass (µmol DSi/mg Chl a) was
20/1, while that ratio increased to 200/1 at the mesohaline site and 500/1 at the oligohaline site.
Tidal marshes contain a large store of biologically active silicate and clearly interact with
the aquatic environment where silica is used by diatoms in the water column and on sediment
surfaces. Based on a ratio of 25 m2 of marsh interior to marsh edge, marshes in the Cape Fear
River Estuary serve as a large sink of silica, importing 1,318,767 kg yr-1. The silicate imported
into tidal marshes estimated by this study represents 12% of the total river silicate load on an
iii
annual basis. Failure of created marshes has sparked investigation into the role silicate plays in
newly established systems. Created marshes may take years to accumulate the reserve of silicate
found in natural systems, thus DSi may be a reasonable proxy of tidal marsh function for created
tidal marshes.
iv
ACKNOWLEDGEMENTS
I wish to thank my advisor, Dr. Courtney Hackney, for his guidance in the development
of the thesis and assistance in graduate school. I also thank Dr. Lawrence Cahoon for the use of
his laboratory equipment and development of this project and Dr. Joan Willey for her insightful
guidance through the newly created Masters in Marine Science Program. Thank you to Dr. Lynn
Leonard for being a superior female mentor in science. Thank you to the UNCW graduate school
for funding.
I want to acknowledge the N.C. Sea Grant and the Division of Coastal Management for
allowing me the time to work on this thesis and the invaluable experiences from my fellowship.
I especially want to thank my Mom, for her continual love and support. Without her help
I would have never been able to fulfill this dream. Kristen and Melanie, my dear sisters, I thank
you for your shoulders and being incredible examples by excelling in your own graduate
programs and as young female professionals. To Dad and Uncle Bob, I thank you for your love
of nature, the ocean, and fishing, which led me to Marine Science.
This work would not have been possible without Miss Dawn Carroll, who showed true
dedication to friendship by helping me in the field at Smith Creek. Thank you to my
Wilmington family for the many laughs and support, especially Shelly Miller and Beth Cummins
who were there since the beginning. I would also like to thank Jen Arp, Amy Clark, Janice
Nearhoof, Suzanne Sexton, Ashley Skeen, Jason Hall, and Gwen Shaughnessy for their
assistance in the field or laboratory. Extreme appreciation is also extended to Yuliya
Lokhnygina for assistance with statistical analysis.
v
DEDICATION
For Robert Lindsay Donnell, my uncle, who influenced and supported my dreams and
aspirations. I miss your presence in my life everyday, but I will always hold you close in my
heart. I will continue to honor you and keep your spirit alive by pursuing grand adventures and
laughing loudly. And for Grace Elizabeth, whose arrival into this world was my biggest
motivation to finish, so I may spend my time showing you the joys of this world and the ocean
just as my uncle did with me.
vi
LIST OF TABLES
Table Page
1. Assignment of factors and corresponding levels to the split-split-split plot experimental design………………………………………………… 12
2. Comparison of mean silicate uptake at three DSi concentrations
(low - 0 µmol, medium -35 µmol, high - 100µmol)…………………………………….. 18 3. A formal model describing the relationship between
silicate uptake and Chl a biomass……….…………………………………….………… 23 4. Calculation of mean rate of import/export at three
marshes from January-August 2001…………………………………………………….. 27
vii
LIST OF FIGURES
Figure Page
1. Dissolved silicate concentration along a salinity gradient ……………………………….. 2 2. Map of Cape Fear Estuary, North Carolina, indicating
sampling sites……………………………………………………………………………... 6
3. Sampling site sediment characteristics. (A) Percent sand and silt/mud and (B) Organic content of sediments at Smith Creek, Mott Creek, and Fort Fisher……………….……………… 9
4. Mean above plant biomass (g/m-2) at Smith Creek, Mott Creek, and Fort Fisher ……………………………………………….……………. 10
5. Average silicate uptake under light and dark treatments ………………………………………………………………………….. 15 6. Average silicate uptake at the control, low, and high
dosing concentrations ……………………………………………………………………16 7. Monthly silicate uptake averaged for
three dosing concentrations……………………………………………………………… 17
8. Mean benthic microalgal biomass (mg Chl a m-2) at Smith Creek (SC), Mott Creek (MC) and Fort Fisher (FF) from January to August 2001……………………………………………………………. 20
9. Monthly average ratio (µmol DSi hr –1/ mg Chl a) of silicate: Chl a biomass at the three dosing concentrations………….……………………………. 24
10. Monthly average ratio (µmol DSi hr –1/ mg Chl a) between silicate uptake
and Chl a biomass at 100 µmol dosing concentration………...………………………… 25
11. Predicted response of the formal model at the Fort Fisher site …………………………………………………………………….26
12. Conceptual model of silicate cycling in the Cape Fear River Estuary, NC…………………………………………………………… .28
viii
INTRODUCTION
Ground water, river water, and recycling of biogenic silica represent sources of silicate to
an estuary. Silicon (Si), an abundant element in soils, participates in the hydrologic cycle in the
soluble form, reactive silicate (DSi). Diatoms, a major primary producer in estuaries, depend on
silicate as a primary nutrient in the development of their structural coverings or frustules.
Vascular plants also utilize and incorporate silicon into their tissues, which is thought to
contribute to defensive capabilities against herbivory and fungal invasion (Epstein 1994) and
structural integrity.
DSi levels in the Cape Fear River Estuary are conservative along a salinity gradient
(Figure 1). Others estuarine systems were documented having similar DSi patterns (Blanchard
1998, Conley 1995, Liss and Pointon 1973, Stephens and Oppenheimer 1972), but temporal and
spatial depletion of silicate has been reported in response to eutrophic conditions in the Baltic
Sea and North Sea (Smayda 1989), the Po River in the northern Adriatic Sea (Justic et al. 1995),
the Chesapeake Bay (Conley and Malone 1992), the Mississippi River and northern Gulf of
Mexico (Rabalais et al. 1996) and the Cape Fear River (Mallin et al. 1997). Anthropogenic
modifications increase levels of nitrogen and phosphorous relative to silicon abundance and alter
trophic pathways. These modifications result in taxonomic shifts in the dominant estuarine
primary producers from diatoms to non-siliceous species such as cyanobacteria and
dinoflagellates (Rocha et al. 2002, Nilsson et al. 1991, Officer and Ryther 1980).
Studies of silicon cycling focus primarily on open water/oceanic systems (Nelson et al.
1995, Treguer et al. 1995, Calvert 1983, and Demaster et al. 1981). Investigations related to
estuarine systems focus on import/export of terrestrially derived silicon from
1
y = -74.841x + 2534.2
0
500
1000
1500
2000
2500
3000
3500
0 5 10 15 20 25
Salinity (ppt)
Silic
ate
(ug
l-1)
R = 0.92
Figure 1. Dissolve silicate concentrations along a salinity gradient in the Cape Fear River Estuary. (Mallin et al. 1997)
2
estuaries (Conley 1995, Conley and Malone 1992). Rivers carry significant amounts of both
solid amorphous or biogenic (BSi) and dissolved silica (DSi) into estuaries. Average riverine
DSi concentrations in the Chesapeake Bay were found to reach 150 µmol L-1 with BSi
concentrations averaging 28.0 µmol L-1 (Conley and Malone 1992). The global contribution of
BSi by rivers to the ocean’s silica budget is 1.05 ± 0.20 Tmol Si yr –1, which is 16% of the gross
riverine silicon load to the world ocean (Conley 1995).
No complete model describing silicon cycling in dynamic estuarine systems exist. Only a
paucity of studies address silicon budgets within an estuary and the mechanism that allow
marshes to accumulate large quantities of biogenic silica (Norris and Hackney 1999, Preziosi
1998). In the Cape Fear River Estuary, NC, tidal marshes showed increased silica storage in the
porewaters and sediments along the estuarine salinity gradient (Preziosi 1998). Vascular plants
(Spartina alterniflora and Juncus roemerianus) were identified as a sink of silicate in tidal marsh
systems through active uptake (Skeen and Hackney, 1999) and storage of silicate in tissues
(Norris and Hackney 1999). Tidal marshes accumulate large quantities of biogenic silica and
function as traps of this nutrient (Hackney et al. 2000).
The high concentration of silica in tidal marshes is thought to be the source of silicon for
benthic diatoms (Hackney et al. 2000). Benthic microalgae require significantly more silicate
than the planktonic varieties (Sigmon and Cahoon 1997). The standing stock biomass of benthic
microalgae can also vary significantly within tidal marshes. For Example, standing biomass
ranged from 73 to 127 mg Chl a m-2 under Spartina alterniflora, while biomass under Juncus
roemerianus was around 59 mg Chl a m-2 (Sullivan and Currin 2000). Benthic diatoms require
large amounts of DSi to build their protective frustules (Davis 1976, Busby and Lewin 1967).
Upon death, the frustules are often deposited into sediments, where they dissolve and release DSi
3
into the water column and interstitial pore waters (Sundbäck and Snoeijis 1991, Blackburn and
Henriksen 1983, Hopkinson and Wetzel 1982). In general, DSi is more concentrated in sediment
pore waters than in the water column mainly due to the dissolution of diatom frustules
(DeMaster 1981, Iler 1979).
Biological uptake by planktonic diatoms is a major factor in modifying the form of Si
transported by rivers (Conley 1995). This uptake is not well understood for the benthic diatoms,
but is likely as important since benthic forms can intercept and regulate nutrient fluxes along the
sediment-water interface through direct uptake (Sarawut et al. 2003, Welker et al. 2002, Sigmon
and Cahoon 1997, Sundbäck and Snoeijis 1991, Darley et al. 1979). Silicate uptake by benthic
diatoms under natural conditions in tidal marshes has not been quantified.
This study examined patterns of silicate import into tidal marshes 1) in different parts of
the estuary (high, medium, and low salinity marshes), 2) under varying DSi concentrations in
floodwater, 3) at different times of the year, 4) in the interior versus marsh edge, and 5) under
dark conditions. Benthic microalgal influence on DSi uptake was also evaluated.
4
STUDY AREA
The Cape Fear River ( 33º N and 78º W), North Carolina (Figure 2) estuary extends 45
km in length from mouth to the head near Wilmington, N.C. and spans on average 1.6-3.6 km in
width. Salinities within the estuary range from 0 ppt near Wilmington, NC to 35 ppt at the
river’s mouth (Woerner and Hackney, 1997). Tidal salt marshes cover approximately 90 km2 of
the estuary (Weinstein 1979).
The study was conducted within three marshes with different salinities (Figure 2).
Typically, Smith Creek is oligohaline, Mott Creek is mesohaline and Fort Fisher is euhaline.
Two sub sites within each marsh were established. The edge sub-site was approximately 2 m
and the interior sub-site approximately 12 m from the edge of the marsh. All marsh sites were
inundated regularly by semi-diurnal tides, but had different sediment compositions (Figure 3a),
organic content (Figure 3b), and vegetation types (Figure 4).
5
North Carolina
Northeast Cape Fear
River
Fort Fisher
Wilmington
Atlantic Ocean
Mott Creek
Smith Creek
N
15 km
Cape Fear River
Figure 2.
Map of the Cape Fear Estuary, North Carolina, indicating sampling sites.6
MATERIALS AND METHODS
Study Site Characteristics
Five sediment cores were randomly collected in summer of 2001 from all six sub-sites.
Percent sand fraction was extracted using a 63-micrometer stainless steel wet sieve. Sub-
samples of the cores were dried for 24 hr in a 32º C drying oven, weighed, and transferred into a
combustion oven for 3 hr at 300º C. The samples were cooled, weighed again, and the percent
organic content of soil at each site was based on the mass lost during combustion.
Above ground biomass of vascular plants was harvested at each sub-site in five 0.25 m2
quadrats between the end of July and beginning of August 2001 to determine standing stock.
Plant material was dried outdoors for 3 weeks, then dried in a 32º C oven for 24 hr and mass was
determined.
In Situ Silicate Dosing Experiments
Cylindrical microcosms, constructed of acrylic plastic (30 cm in length and 5 cm inner
diameter), were used to determine silicate (DSi) uptake rates. The microcosms, embedded
approximately 7 cm into the marsh substrate, were dosed with approximately 100 ml of a silicate
solution of either 0, 35, or 100 µM prepared using a potassium silicate fertilizer, Pro-Tek®.
Instant Ocean® salt was used to prepare saltwater that varied for each site depending on the
natural salinity range: 7ppt for Smith Creek, 14 ppt for Mott Creek, and 27 ppt for Fort Fisher.
The three DSi concentrations were replicated in 10 microcosms for each sub-site, with half kept
in dark conditions using an opaque, black plastic tarp. A total of 60 microcosms were deployed
monthly at each site from January to August 2001.
7
A tightly banded plastic covering prevented extraneous silicate from entering the
microcosm. Silicate solutions were in contact with the substrate for three hours then a minimum
of 20 ml was removed using 60 ml syringes. The sediment sample contained within each core
was removed and frozen for Chlorophyll a (Chl a) analysis.
Silicate analyses followed using the reduced molybdolsilicic acid spectrophotometry
method of Strickland and Parson (1968) for reactive silicate. Initial DSi concentrations (0 hr)
were compared to the DSi content in solution after the exposure period (3hr). The difference
between the concentrations indicated the silicate uptake/release over the 3 hr inoculation period.
DSi µmol L-1 hr-1m-2 was ([µmoles DSiinitial] – [µmoles DSi final] * salinity conversion factor)/ (3hr
* 0.0019625 m2).
Chl a biomass (mg Chl a m-2) determination followed Whitney and Darley (1979) except
20 ml of acetone was used in the initial Chl a extraction and the 13.5 ml hexane extraction was
reduced to 10 ml. A 2.3 cm (inner diameter) core was used to sample
Chl a and calculated as mg Chl a m-2 = [1.82 x 11.05(663o –663a) * (1.45 x 0.02)]/0.00041548
m2.
8
A.
0.0
25.0
50.0
75.0
100.0
Site
Perc
ent
Silt/MudSand
SC E SC I MC E MC I FF E FF I
B
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Site
Perc
ent
EdgeInterior
SC MC FF
Figure 3. Sampling site sediment characteristics. (A) Percent sand and silt/mud content and (B) Percent organic matter of sediments at Smith Creek (SC), Mott Creek (MC), and Fort Fisher (FF) for the edge (E) and interior (I) sub sites. Vertical bars equal ± 1 standard error.
9
0.0
500.0
1000.0
1500.0
2000.0
2500.0
Site
Mea
n D
ry B
iom
ass (
g) m
-2
SC E MC I FF E
S. alterniflora P. australis
SC I MC E FF I
J. Romerianus
Figure 4. Mean above ground plant biomass of major plant species (g m-2) at Smith Creek (SC), Mott Creek (MC) and Fort Fisher (FF) for the edge (E) and Interior (I) sub-sites. Vertical bars equal ± 1 standard error.
10
STATISTICAL DESIGN
JMP In and S.A.S. statistical software were used to determine statistical relationships
among sampling sites, sampling sub-sites, light treatments, DSi concentrations, and month. All
data were found to be normally distributed and statistical significance for all tests was
established at p < 0.05.
Data were analyzed using a split-split-split plot statistical design and Tukey-Kramer all
pairs comparison tests. The split- split-split plot statistical design split the experimental units of
the subplot levels three times (Table 1). The design utilized DSi concentration as the sub-
sample (observations taken 5 times for the same experimental unit under the same conditions).
This assumption allowed data to be analyzed using the average of the 5 observations for each
combination of factors and aided the analysis when a replicate was missing. The Chlorophyll a
biomass was considered a covariate and not controlled in the experiment.
Table 1. Assignment of factors and corresponding levels to the split-split-split plot experimental design.
11
Plot Experimental
Level
Factor
Levels
Assumptions
Main Plot Units
Month
8 (Jan-Aug 2001)
The same site at different months was viewed as a different location.
1º Subplot Units
Sub-site
2 (edge and
interior marsh)
2º Subplot Units
Light Treatment
2 (light and dark
conditions)
3º Subplot Units
[Silicate]
3 (0, 35 and 100
µmol)
First Split Second Split Third Split*
All sub-plot levels were considered a completely randomized design. The levels under the factors were not randomized to different experimental units.
* Three way interactions and subsequent pairwise comparisons between site, month, and dosing concentration could not be used to demonstrate the interaction effects on silicate uptake as the error term for the “site” variable was confounded with the blocks in the split-split-split plot analysis.
12
RESULTS
Silicate Uptake at Variable Physical, Spatial, and Temporal Scales
The rate of silicate (DSi) uptake was averaged over the entire sampling period (January –
August 2001) at the three sites (n= 425 for Mott Creek, n = 367 for Fort Fisher, and n=342 for
Smith Creek). Silicate uptake was greater under light conditions (327 µmol DSi hr-1m-2 ± 114)
compared to dark conditions (167 µmol DSi hr-1m-2 ± 98), but were not significantly different
(p<0.1934, Figure 5). All two-way interactions were also not statistically significant. Data for
the light and dark treatments were pooled for the remaining statistical comparisons.
The DSi concentration of the dosing solution applied to the chambers affected the rate at
which silicate was imported/exported from the marsh. Significant differences in silicate uptake
were detected among the three dosing concentrations (p<0.0001, Figure 6). Tukey-Kramer all
pair comparisons found significant differences between 0 and 35 µmol concentrations (p <
0.001), 35 and 100 µmol concentrations (p < 0.001), and 0 and 100 µmol concentrations (p <
0.001).
Silicate uptake was not significantly different among months (p < 0.1603, Figure 7), but
the interaction between dosing concentration and month was significant (p < 0.0015). Silicate
uptake was found to be significantly lower at the 0 µmol concentration and greatest at the 100
µmol concentration over all months (Figure 7). In fact, DSi fluxed from the surface into the
overlying waters when they were low in that nutrient.
Silicate import rates (Table 2) into the three sites (p > 0.0983) and at edge and interior
sub-sites (p > 0.0754) were not significantly different despite large differences in mean uptake
rates due to high variability within treatments. The interaction between sub-site and dosing
concentration was also not significant (p> 0.6895). Silicate exchange between water and
13
sediment ranged between -2413 µmol DSi hr-1m-2 ± 96 (an export of silicate at 0 µmol at Mott
Creek) and 788 µmol DSi hr-1m-2 ± 89 (an import of silicate at 100 µmol at Smith Creek) at the
interior sub-sites. At the edge sub-sites –1170 µmol DSi hr-1m-2 ± 88 of silicate was exported at
0 µmol at Fort Fisher and 2484 µmol DSi yr-1m-2 ± 101 was imported at 100-µmol doses at Mott
Creek.
14
-600
-400
-200
0
200
400
600
800
1000
1200
1400
Si u
mol
hr-
1 m
-2
k
Figure 5. Average silicaFisher, Mott Creek and S1 standard error.
Dar
Site
Total FF MC SC
Light
te uptake under light and dark treatments at three marsh sites (Fort mith Creek) and at the average over all sites (total). Error bars denote ±
15
-1500
-1000
-500
0
500
1000
1500
2000
2500
0 umol 35 umol 100 umol
DSi Dosing Concentration
DSi
Upt
ake
(um
ol h
r-1
m-2
)
Figure 6. Average silicate uptake (all sites combined) at the control (0 µmol), low (35 µmol), and high (100 µmol) dosing concentrations. Tukey Kramer all pairs comparison indicated DSi uptake at all concentrations were independent of each other. Error bars denote ± 1 standard error.
16
-3000
-2000
-1000
0
1000
2000
3000
4000
5000
DSi
um
ol h
r-1
m-2
Figure 7. Monthllow - 35 µmol, anSmith Creek). ErKramer all pairs cwhile a double as
**
Jan
Feb Mar
0 umol
y silicate uptake averaged high - 100 µmol) comror bars denote ± 1 standomparison showed 35 µterisk indicates that all c
**
** *AprMay
month
30 umol
d over three dosibine for three maard error. A singmol and 100 µmoncentrations we
17
*
*Jun Ju
l
100
ng concentratiorsh sites (Fort Fle asterisk ind
ol concentratiore independent
*
Aug
umol
n (control - 0 µmol, isher , Mott Creek and
icates that Tukey-n were independent, of each other.
Table 2. Comparison of mean reactive silicate uptake at three DSi concentrations (low - 0 µmol, medium -35 µmol, high - 100µmol). Mean silicate uptake and standard deviation was calculated separately for the six sub-sites at three silicate treatments (n=10) from January-August 2001. Positive numbers indicate mean import into the marsh, while negative numbers signify mean export of reactive silicate. Smith Creek Mott Creek Fort Fisher _ DSi Dose (µmol) 0 35 100 0 35 100 0 35 100 Edge Uptake -788 706 939 -987 485 2484 -1170 –704 583 (µmol hr-1m-2) ± SE 89 91 130 71 109 101 88 131 134 Interior Uptake -1023 904 1805 -2413 -1405 1537 -139 649 1516 (µmol hr-1m-2) ± SE 85 93 153 96 120 166 86 76 85
18
Benthic Microalgal Biomass Chlorophyll a concentrations were highest at the high salinity site (Figure 8). Significant
differences in benthic microalgal biomass existed between the sites, with the highest values at
the high salinity sites (p<0.0001), but no statistically significant difference was found between
the sub-sites (p>0.1056) or among months (p< 0.1994). All two-way interactions were also not
significant (p>0.05).
19
Figure 8. Mean benthic microalgal biomass (mg Chl a m-2) at Smith Creek (SC) with n = 420, Mott Creek (MC) with n= 480, and Fort Fisher (FF) with n = 480 for the edge and interior sub sites from January-August 2001. Data are not available for April 2001 at Smith Creek. Vertical bars equal ± 1 standard error.
0.0
40.0
80.0
120.0
160.0
200.0
240.0
280.0
mg
Chl
a m
-2
Edge
Interior
Month
J JJ JJJJ JJ A A AA AMM MM M M FFF
FF MC SC
20
Relationship between Benthic Microalgal Biomass and Silicate Uptake
A statistical model was developed that describes the import of reactive silicate into tidal
marshes (Table 3). Silicate uptake is linearly dependent on the Chl a biomass in this model for
each combination of site, sub-site, month, light treatment, and dosing concentration. The slope
generated by the model indicates that average algal biomass had a significant effect on the
import of silicate into the marsh (p<0.0015). Differences in the slopes between models
generated for each combination of treatment factors were significantly affected by the
concentration (p<0.001) of the overlying surface water and the position (sub-site) within the
marsh (p<0.0179).
Ratio of Silicate Uptake to Chl a Biomass
The relationship between silicate uptake and Chl a prompted the development of a model
based on the ratio of silicate uptake to Chl a biomass (Figure 9). In this model silicate exchange
was dependent only on the month (p< 0.0356) and concentration of the overlying surface water
(p < 0.001) and no significant interaction (p>0.3010) was found between Chl a biomass and sub-
site. The difference among sites is demonstrated at the 100 µmol dosing concentration (Figure
10).
Higher BMA biomass during warm and cold seasons at Fort Fisher controlled the import
of silicate into the marsh when DSi levels were high (Figure 10). The ratio between DSi Flux
and Chl a biomass at Fort Fisher was approximately 20:1 (µmol DSi hr-1 m-2: mg Chl a m-2)
compared to 200:1 at Mott Creek and 500:1 at Smith Creek. At other sites low BMA biomass
exerted little control over uptake. The extrapolation of this suggests that when benthic Chl a
21
biomass is zero, silicate continues to flux into the marsh at a rate of 1480 µmol DSi hr-1 m-2, this
represents the silicate influx not controlled by BMA biomass (Figure 11).
Tidal Marshes and the Estuarine Silicate Budget
The edge sub-sites showed a pattern of export, suggesting an edge effect, although
significance was not detected due to the high level of variability between samples (Table 4). The
maximum export value (12,234 µmol DSi hr-1m-2) occurred at the Fort Fisher edge sub-site at
DSi concentration equal to 0 µmol in May 2001. Extrapolating the rate of silicate uptake into
yearly import by Cape Fear River tidal marshes indicates that large quantities of silicate are
removed from floodwaters each year, particularly by the interior portions of the marsh (Figure
12).
22
Table 3. A formal model describing the relationship between silicate uptake and Chl a biomass established from a split-split-split plot statistical design. The assumptions for the model indicate error terms (εij
(1), εijk(2), εijkl
(3), and Eijklm) have normal distribution with mean 0 and variance . All errors are independent, which corresponds with the assumption that all
observations are independent and the blocks, effects, and interactions in the model are fixed.
2)3,2,1( andEσ
,)()(
)()()()()(
)()()()3(
)2()1(
ijklmijklmijklm
ijklmijklmijklmlmkmjmmijkl
kljllijkjkkijjiijklm
Ebb
bbb
RY
++
++++++++
++++++++++=
δθγθ
βθαθθγδβδαδδε
βγαγγεαββεαµ
δγ
βα
* Terms in parentheses denote the interactions between the factors
Fixed Effect Variable
Silicate uptake Y Overall mean µ Block Ri (Fort Fisher, Mott Creek, Smith Creek) Month αjSub-site βk (edge vs interior marsh) Treatment γl (light vs dark conditions) Concentration δm (0, 35, and 100 µmol) Chl a Biomass bijklmMain plot error εij
(1) (variation between the main plot exp. units) 1st level error εijk
(2) (variation between the 1st level sub-plot exp. units) 2nd level error εijkl
(3) (variation between the 2nd level sub-plot exp. units) Model error Eijklm (variation between the 3rd level sub-plot exp. units)
-60
-40
-200
0
200
400
600
800
jan feb mar may jun jul aug
DSi
Upt
ake
: Chl
a B
iom
assA.
0Mean ratio =500:1 at 100 µmol
0Month0 umol 35 umol 100 umol
23
-1500
-1000
-500
0
500
1000
1500
jan feb mar apr may jun jul aug
Month
DSi
Upt
ake
: Chl
a B
iom
ass
0 umol 35 umol 100 umol
B.
-
-
-30
-20
-10
0
10
20
30
40
jan feb mar apr may jun jul aug
DSi
Upt
ake
: Chl
a B
iom
assC.
Figure 9. Monthly ave(0 µmol), low (35 µmoMott Creek and (C) Fo
40Mean ratio = 20:1 at 100 µmol
50ral)rt
Mean ratio = 200 at 100 µmol
Month
0 umol 35 umol 100 umol
ge ratio between silicate uptake and chlorophyll a biomass at the control , and high (100 µmol) dosing concentrations at (A) Smith Creek (B) Fisher.
24
-600
-400
-200
0
200
400
600
800
jan feb mar apr may jun jul aug
Month
DSi
Upt
ake:
Chl
a B
iom
ass
SC MC FF
Figure 10. Monthly average ratio between silicate uptake and chlorophyll a biomass at the high (100 µmol) dosing concentrations for Smith Creek (SC), Mott Creek (MC), and Fort Fisher (FF). Data are not available for April 2001 at Smith Creek.
25
0
500
1000
1500
2000
2500
0 40 80 120 160
Chl a biomass (mg m-2)
Silic
ate
Upt
ake
(mol
hr-
1 m
-2)
DSi Uptake (µmol hr-1 m-2) = 3400.14 (Chl a Biomass) + 1.4 x 10 ^ 6
Figure 11. Predicted response of the formal model at the Fort Fisher site, indicating the relationship is representative of silicate uptake as a function of Chl a biomass over the entire sampling period and averaged over the three concentrations, light treatments, and sub-sites. Vertical bars equal ± 1 standard error calculated from pooled variance of the formal model.
26
Table 4. Calculation of mean rate of import/export in three marshes from January-August 2001 from individual square meters of edge and interior marsh and from a single linear meter of marsh edge assuming that each meter of marsh edge is bordered by 25 meters of marsh interior. Smith Creek Mott Creek Fort Fisher Interior Edge Interior Edge Interior Edge Sub-site average rate 566 948 584 -682 659 -410 (µmol hr-1m-2) ± SE 89 127 152 112 127 128 Interior:Edge Rate 15,120 13,940 16,087 (µmol hr-1) Mean export/import per linear meter of all sites combined in the Cape Fear 15,049 River Estuary (µmol hr-1) Total annual import of DSi to tidal marshes 1,318,767 in the Cape Fear River Estuary (kg yr-1) *Total import per year calculated based on estimated area (8.9 Km2) of intertidal marshes in the Cape Fear River Estuary, NC (Weinstein 1979) and assuming 1 m2 of marsh edge is supported by 25 m2 of marsh interior is 5,357,444,000 (µmol hr—1)
27
Discussion
The conservative behavior of silicate (DSI) along an estuarine salinity gradient is well
documented in the literature (Stephens and Oppenheimer 1972, Liss and Pointon
Cape Fear River
Northeast Cape Fear
River
DSi Import into Estuary
At
Fort Fisher
Site
Edge Interior
Subsite
Mott Creek
Site
Edge Interior
Subsite
Smith Creek
Site
Edge Interior
Subsite
Estuary DSi
Legend DSi Surface H2O Concentration High Low Wetland Type FW Swamp Salt Forest Marsh Net Import of Silicate Net Export of Silicate
Figur
Eth
lantic Ocean
Import
Edge:Interior 1.32 x 106 kg yr-1
e 12: Conceptual model of s
DSi xport to e Ocean
DISCUSSION ilicate cycling in the Cape Fear River Estuary, NC.
28
DISCUSSION
Reactive silicate (DSi) concentrations in an estuary generally behave conservatively
along a salinity gradient and are higher in head waters when riverine waters, enriched with
particulate and DSi, enter the estuary (Stephens and Oppenheimer 1972, Liss and Pointon 1973,
Calvert 1983, Wollast and Mackenzie 1988, Conley 1995, and Blanchard 1998). However, the
utilization and removal of DSi from estuarine waters through biological uptake by phytoplankton
(Conley 1995), plants (Norris and Hackney 1999, Skeen and Hackney, 1999) and benthic
microalgae (Sigmon and Cahoon 1997, Darley et al. 1979, Sundbäck and Snoeijis 1991) cause
DSi cycling in estuaries to be more complex then previously described. In highly eutrophic
conditions, deviations in DSi from conservative mixing have been found in association with
microalgal blooms (Smayda 1989, Justic et al. 1995, Conley and Malone 1992, Rabalais et al.
1996, Mallin 1997).
Tidal marshes are coupled to the estuarine system through biogeochemical cycling of
silicon (Hackney et al. 2000, Preziosi 1999). This study further supports this conclusion by
identifying dynamic exchanges in the flux of silicate along the sediment-water interface. Tidal
marshes import DSi from estuarine floodwaters primarily in interior portions of the marsh. Since
the majority of the marsh area in the Cape Fear Estuary is interior, the rate of import is higher
than the average of the interior versus edge in Table 2. Based on the estimated total area of tidal
marshes in the Cape Fear River Estuary, 8.9 Km2, (Weinstein 1979) and a conservative estimate
of 1 m marsh edge: 25 m marsh interior (Minello and Rozas 2002), a predicted import of 15,049
µmol hr-1 for all site combined was identified, which is equivalent to 1.3 x 106 kg DSi yr-1
imported into Cape Fear Estuary tidal marshes. In 1997, the total discharge of water from the
Cape Fear River Estuary was estimated at over 7.7 x 109 m-3 (Cahoon pers. comm. May 20,
29
2004, Carolina Power and Light 1979). Assuming an average silicate concentration of 50 uM,
the river transported over 1.08 x 107 kg DSi yr-1 through the estuary. The amount of silicate
imported into tidal marshes calculated by this study represents 12% of that total river silicate
load. Given the ratio of interior to marsh edge (Minello and Rozas 2002) established for Texas
marsh systems, this is an underestimate for marshes in this geographic area where the ratio is
certainly higher than 25:1. Therefore, the import and storage of silicate by interior tidal marshes
is likely much greater than reported and a more significant portion of the total riverine load.
Biological uptake of DSi from estuarine waters appears to be an important mechanism
importing silica in tidal marshes (Hackney et al. 2000, Skeen and Hackney 1999, Norris and
Hackney 1999). The slope generated by the model indicated a positive relationship between
BMA concentration and silicate removal from estuarine floodwaters (p=0.0015). However,
BMA control on DSi concentration appears to be rather minimal with respect to other biological
and physical factors (Figure 11). At Fort Fisher, even when no BMA are present, the model
predicts an import of 1480 µmol DSi hr-1m-2 (Figure 11). Another source of silicate for BMA is
likely the reservoir of DSi in the pore waters of the marsh. The variability in BMA biomass
between sites appears to be a function of salinity, sediment, and vegetation characteristics and is
highest in higher salinity marshes.
The irregularity in short-term exchanges of silicate made it difficult to identify biological
control of silicate through active uptake. Silicate did flux from sediments into the overlying
floodwaters, a pattern easily observed in the control treatments (0 µmol) (Figure 6 and 7). With
sites combined, the flux occurred at an average rate of approximately 1200 µmol DSi hr-1 m-2.
However, examining silicate movement at all dosing concentrations (0, 35, 100 µM), a net
import of silicate into tidal marshes was identified.
30
Silicate import/export was not statistically affected by changes in light exposure or
position within the marsh, although the mean silicate uptake was elevated under light conditions
(Figure 5) at the euhaline site high in BMA and along marsh edges (Table 3). In all likelihood
the response of light and the edge effect were real, but could not be detected due to spatial
unevenness in BMA and micro-topographic variability in silicate flux along the marsh surface.
The edge effect of DSi flux was a response to the hydrologic head generated from the marsh
draining at low tide. Yelverton and Hackney (1986) found that over 34000 l yr-1 of porewaters
was exported through a 1 x 25m transect in a NC tidal marsh with 90% of the flux occurring
within 2 m of the marsh edge.
Removal of DSi from surface water is also a likely result of uptake by emergent
vegetation. Vascular plants have been shown to take up silicate through a substrate in a linear
fashion versus concentration (Skeen and Hackney 2001), i.e. higher [DSi] leads to greater rates
of uptake. The fibrous root mat that develops along the marsh surface could be intercepting the
silicate, but this phenomenon was not detected by increased silicate removal when above ground
plant biomass was high during the summer growing season.
Significant seasonal patterns were not found in Chl a concentration, although dramatic
differences were found between sites. However, there was a trend of greater BMA biomass
during the winter/early spring months, a pattern noted by other studies (Sigmon and Cahoon
1997, Sullivan and Currin 2000). Seasonal variability in Chl a biomass results from shading or
lack of shading by vascular plants (Sullivan and Currin 2000, Wainright et al. 2000) and feeding
pressure from benthic grazers during active grazing periods, which can produce extreme
patchiness. Grazing can influence taxonomic shifts in the dominant algal species, switching
from diatoms (high silicate need) to cyanobacteria (low silicate need).
31
Silicate cycling in estuaries clearly links tidal wetlands with aquatic environments. The
role intertidal marshes play in removing and cycling the supply of DSi in an estuary may
determine the sensitivity of an estuary to eutrophication. For instance, the limitation of DSi in
Baltic Sea and North Sea (Smayda 1989), the Po River/ northern Adriatic Sea (Justic et al. 1995,
and), Chesapeake Bay (Conley and Malone 1992), Mississippi River/ northern Gulf of Mexico
(Rabalais et al. 1996) and Cape Fear (Mallin 1997) relative to nitrogen and phosphorous
concentrations has caused taxonomic shifts in the major primary producers (Officer and Ryther
1980, Nilsson et al. 1991). Silicate depletion in the waters of Lake Michigan resulted from
increased uptake by diatom species under eutrophic conditions (Shelske and Stoermer 1971).
This shift in species abundance ultimately can affect the transfer of energy to higher trophic
levels and could have an impact on economically important fisheries (Haines 1977 and 1979).
The aerial extent of tidal marsh and salinity may influence the role tidal marshes play
with respect to Si cycling in an estuary. Newly establish marshes are usually flood-dominated
systems and net importers of sediments and organic material, but export mineral nutrients
(Boorman et al. 1995). Once a tidal marsh is established there are two major reservoirs of silica,
dissolved silica in interstitial porewaters (Preziosi 1998) and solid biogenic silica stored in
vegetation (Norris and Hackney 1999) and sediments (Preziosi 1998). Deposition of silica-
enriched frustules of dead benthic microalgae is suggested as another mechanism for delivering
silicate into tidal marshes sediments (Hackney et al. 2000). Created tidal marshes may require
many years before reaching import/export of BSi similar to nearby reference marshes. Assessing
abundance of biogenic silicate stored in sediments could be an important indicator of the
health/longevity and function of created marshes. Maximizing the linear extent of marsh edge in
32
restoration projects would increase the benefits of the created marsh to the estuarine system by
delivering more DSi to the aquatic community.
33
LITERATURE CITED
Blackburn, T.H. and Henriksen, K. 1983. Nitrogen cycling in different types of sediments from Danish waters. Limnology and Oceanography 28:477-493. Boorhman, L.A. Hazelden, J. Andrews, R. and Wells, J.G. 1994. Organic and nutrient fluxes in four north-west European salt marshes. In Changes in fluxes in estuaries: implication from science and management, Dyer and Orth, ed. Olsen and Olsen Fredensborg. Busby, W.F. and Lewin, J. 1967. Silicate uptake and silica shell formation by synchronously dividing cells of the diatom Navicula pelliculosa. Journal of Phycology. 3:127-131. Calvert, S.E. 1968. Silica balance in the ocean and diagenesis. Nature London. 219 (5157): 919-920. Carmen, K.R. Fleeger, J.W. and Pomarico,S.M. 1997. Response of benthic food web to hydrocarbon contamination. Limnology and Oceanography 42: 561-571. Carolina Power and Light Company. 1979. Dye tracer and current meter studies: Appendix A. Cape Fear River, NC 1976, 1977, and 1978. Carolina Power & Light Company. Southport, NC. Creach, V. Schricke, M.T., Bertru, G. and Mariotti, A. 1997. Stable isotopes and gut analyses to determine feeding relationships in saltmarsh macroconsumers. Estuarine, Coastal and Shelf Science 44: 599-611. Conley, D.J. and Malone, T.C. 1992. Annual cycle of dissolved silicate in Chesapeake Bay: implication for the production and fate of phytoplankton biomass. Marine Ecology Progress Series 81: 121-128. Conley, D.J. 1995. Riverine contributions of biogenic silica to the oceanic silica budget. Limnology and Oceanography 42 4: 774-777. Darley W.M., Ohman, C.T., Wimpee, B.B. 1979. Utilization of dissolved organic carbon by natural populations of epibenthic salt marsh diatoms. Journal of Phycology 15:1-15. Davis, C.O. 1976. Continuous culture of marine diatoms under silicate limitation. Journal of Phycology 12:291-300. DeMaster, D.J. 1981. The supply and accumulation of silica in the marine environment. Geochem Cosmochim Acta 45:1715-1732. Epstein, E. 1994. The anomaly of silicon in plant herbivory. Proceedings of the National Academy of Sciences USA. 91, 11-17.
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Hackney, C.T., L.B. Cahoon, C. Preziosi, and A.Norris. 2000. Silicon is the link between tidal marshes and estuarine fisheries: a new paradigm. Pages 531-540 in Concepts and Controversies in Tidal Marsh Ecology, M. Weinstein, ed. Klewer Press. Haines, E.B. 1977. The origin of detritus in Georgia salt marshes. Oikos 2 9:254-260. Haines, 1979. Interactions between Georgia salt marshes and coastal water: A changing paradigm. Pages 35-46 in R.J. Livingston, editor. Ecological Processes in Coastal and Marine Systems. Plenum Press, New York. Hopkinson, C.S. and Wetzel, R.L., 1982. In situ measurements of nutrient and oxygen fluxes in a coastal marine benthic community. Marine Ecology Progress Series 10: 29-35. Iler, R.K. 1979. The Chemistry of silica. Solubility, polymerization, colloid, surface properties, and biogeochemistry. Wiley, Chichester. Justic. D., Rabalais, N.N., Turner, R.E. ad Dortch,Q. 1995. Changes in nutrient structure of river-dominated coastal waters: stoichiometric nutrient balance and its consequences. Estuarine, Coastal, and Shelf Science 40: 339-356. Liss, P.S. and Pointon, M.J. 1973. Removal of dissolved boron and silicon during estuarine mixing of sea and river waters. Geochimica et Cosmochimica Acta. 6: 1493-1498. Mallin, M.A., Cahoon, L.B., McIver, M.R., Parsons, D.C. and Shank, G.C. 1997. Nutrient limitation and eutrophication potential in the Cape Fear River and New River estuaries. UNC WRRI Report #313, 78pp. Minello, T.J. and Rozas, L.P. 2002. Nekton in Gulf Coast wetlands: Fine-scale distributions, landscape patterns, and restoration implications. Ecological-Applications. 12 (2): 441-455. Nelson, D.M., P. Tréguer, and B. Quéguiner. 1995. Production and dissolution of biogenic silica in the ocean: revised global estimates, comparison with regional data and relationships to biogenic sedimentation. Global Biogeochemical Cycles 9: 359-372. Nilsson, P., B. Jonson., I.L. Swanberg, K. Sundback. 1991. Response of marine shallow-water sediment system to and increased load of organic nutrients. Marine Ecology Progress Series 71:275-290. Norris, A. and C. Hackney. 1999. Silica content of a mesohaline tidal marsh in North Carolina. Estuarine, Coastal and Shelf Science 49: 597-605. Officer, C.B. and J.H. Ryther. 1980. The possible importance of silicon in marine eutrophication. Marine Ecology Progress Series 71: 275-290.
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Preziosi, C. 1998. Patterns of silica distribution in tidal marshes of the Cape Fear River Estuary. Masters thesis. University of North Carolina at Wilmington, Wilmington, North Carolina, USA. Rabalais, N.N. Turner, R.E. Justic, D., Dortch, Q., Wiseman, W.J. and Gupta, B.K.S. 1996. Nutrient changes in the Mississippi River and system responses on the adjacent continental shelf. Estuaries 19: 386-407. Rocha, C. Galvao, H. and Barbosa, A. 2002. Role of transient silicon limitation in the development of cyanobacteria blooms in the Guadiana estuary, south-western Iberia. Marine-Ecology-Progress-Series. 228: 35-45. Sigmon, D.E. and L.B. Cahoon. 1997. Comparative effects of benthic microalgal and phytoplankton on dissolved silica fluxes. Aquatic Microbial Ecology 13: 275-284. Skeen, A. and C. Hackney. 1999. Silicate uptake by smooth cordgrass, Spartina alterniflora, grown under various silicate concentrations. Undergraduate Honors thesis. University of North Carolina at Wilmington, Wilmington, North Carolina, USA. Sarawut, S., Yu Ichi,S., Kuninao,T., and Shigeru, M.. 2003. The influence of environmental variability on silicate exchange rates between sediment and water in a shallow-water coastal ecosystem, the Seton Inland Sea, Japan. Marine-Pollution-Bulletin. 47 (1-6): 10-17. Schelske, C.L. and Stoermer, E.F. 1971. Eutrophication, silica depletion, and predicted changes in algal quality in Lake Michigan. Science 173: 423-424. Smayda, T.J. 1989. Primary production and the global epidemic of phytoplankton blooms in the sea: a linkage? In Novel Phytoplankton Blooms (Cosper, E.M., Bricely, V.M. and Carpenter, E.J., eds) Coastal and Estuarine Studies No. 25, Springer-Verlag, New York, pp. 449-483. Stephens, C.F. and Oppenheimer, C.H. 1972. Silica contents in the Northwestern Florida Gulf Coast. Contributions in Marine Science. 16: 99-108. Strickland, J.D.H. and Parsons,T.R. 1968. A practical handbook of seawater analysis. Bulletin 167, Fisheries Research Board Canada, 311p. Sullivan, M.H. and C.A. Moncreiff. 1988. Primary production of edaphic algal communities in a Mississippi salt marsh. Journal of Phycology. 24:49-58. Sullivan, M.H. 1990. Edaphic algae are important component of salt marsh food webs: evidence from multiple stable isotope analyses. Marine Ecology Progress Series 6 2: 149-159.
36
Sullivan, M.H. and C.A. Currin. 2000. Community structure and functional dynamics of benthic microalgae in salt marshes. pp. 81-106 in Concepts and Controversies in Tidal Marsh Ecology. M. Weinstein, ed. Klewer Press. Sundback, K. and Snoeijis, P. 1991. Effects of nutrient enrichment on microalgal community composition in a coastal shallow-water sediment system: an experimental study. Botanica Marine. 34: 341-358 Tréguer, P.D., M. Nelson, A.J. van Bennekom, D.J. Demaster, A. Leynaert, and B. Quéguiner. 1995. The silica balance in the world ocean: A reestimate. Science 2 68: 375-379. Wainwright, S.C., Weinstein, M.P., Able, K.W., and Currin, C.A. 2000. Relative importance of benthic microalgae, phytoplankton and detritus of smooth cordgrass Spartina alterniflora and the common reed Phragmites australis to brackish-marsh food webs. Marine Ecology Progress Series 200: 71-91. Weinstein, M.P. 1979. Shallow marsh habitats as primary nurseries for fishes and shellfish, Cape Fear River, North Carolina. Fishery Bulletin 77:339-357. Weissburg, M. 1992, Functional analysis of fiddler crab foraging: sex specific mechanisms and constraint in Uca pugnax. Journal of Experimental Marine Biology and Ecology 156: 105-124. Welker,C., Sdrigotti,E., Covelli,S., and Faganeli,J. 2002. Microphytobenthos in the Gulf of Trieste (Northern Adriatic Sea): Relationship with labile sedimentary organic matter and nutrients. Estuarine Coastal and Shelf Science. 55 (2): 259-273 Whitney, D.E. and Darley, W.M. 1979. A method for the determination of Chl a in samples containing degraded products. Limnology and Oceanography. 24: 183-0187. Woerner, L.M. and Hackney, C.T. 1997. Distribution of Juncus roemerianus in North Carolina marshes: the importance of physical and abiotic variables. Wetlands. 17, 84-291. Wollast, R. and McKenzie, F.T. 1983. The global cycle of silica. In Silicon Geochemistry and Biogeochemistry (Aston, S.R., ed.). Academic Press, London, 39-76.
37
Yelverton, G.F. and Hackney, C.T. 1986. Flux of dissolved organic carbon and pore water through the substrate of a Spartina alterniflora marsh in North Carolina. Estuarine, Coastal and Shelf Science 22:255-267.
38
Appendix 1. Solutions to fixed effects for the formal model, established from the data set. Estimates for the fixed effects can be used to predict silicate uptake relative to the various parameters studied in this experiment using the equation on page 20.
Effects Factors Model Estimate Standard DF t-value Symbol Error
intercept µ 2833.26 938.08 13 3.02
site Fort Fisher Ri -1624.06 679.66 13 -2.39
Mott Creek -639.35 591.92 13 -1.08 Smith Creek 0 month Apr αj 135.36 1437.16 13 0.09
Aug -1868.81 1289.04 13 -1.45 Feb 63.84 1221.22 13 0.05 Jan 1136.99 1261.05 13 0.9 Jul -3002.56 1237.26 13 -2.43 Jun -1491.64 1270.95 13 -1.17 Mar -561.77 1256.29 13 -0.45 May 0 sub-site edge βk 75.94 1032.5 15 0.07
interior 0 light treatment dark γl -122.75 447.58 37 -0.27
light 0 concentration 0 umol δm -3651.74 554.75 151 -6.58
35 umol -2097.48 529.01 151 -3.96 100 umol 0 Chl a Biomass bijklm -1.28 7.45 151 -0.17
month*subsite Apr/edge αj * βk 1547.46 1530.51 151 1.01
Apr/interior 0 Aug/edge 634.69 1341.02 151 0.47 Aug/interior 0 Feb/edge 256.02 1355.34 151 0.19 Feb/interior 0 Jan/edge 2241.25 1351.86 151 1.66 Jan/interior 0 Jul/edge 695.33 1338.35 151 0.52 Jul/interior 0 Jun/edge 1211.14 1343.39 151 0.9 Jun/interior 0 Mar/edge 1722.21 1338.58 151 1.29 Mar/interior 0
39
Appendix 1. cont’d May/edge 0 May/interior 0
month*light trt Apr/dark αj * γl -671.2 577.99 151 -1.16
Apr/light 0 Aug/dark -173.21 526.78 151 -0.33 Aug/light 0 Feb/dark -732.56 516.66 151 -1.42 Feb/light 0 Jan/dark -988.84 517.38 151 -1.91 Jan/light 0 Jul/dark -785.78 521.52 151 -1.51 Jul/light 0 Jun/dark -654.69 519.45 151 -1.26 Jun/light 0 Mar/dark -1097.01 518.6 151 -2.12
Mar/light 0 May/dark 0 May/light 0
month*conc Apr/ 0 umol αj * δm -322.32 755.04 151 -0.43 Apr/ 35 umol -698.15 732.04 151 -0.95 Apr/ 100 umol 0 Aug/ 0 umol 379.34 681.1 151 0.56 Aug/ 35 umol -23.01 672.76 151 -0.03 Aug/ 100umol 0
Feb/ 0 umol 313.82 670.85 151 0.47 Feb/35 umol 378.89 652.85 151 0.59 Feb/ 100 umol 0 Jan/ 0 umol -1048.31 684.61 151 -1.53 Jan/ 35 umol -554.46 662.15 151 -0.84 Jan/ 100 umol 0 Jul/ 0 umol 2446.29 675.28 151 3.62 Jul/ 35 umol 1541.74 648.7 151 2.34 Jul/ 100umol 0 Jun/ 0 umol -393.95 685.2 151 -0.57 Jun/ 35 umol 44.23 647.35 151 -0.07 Jun/ 100 umol 0 Mar/ 0 umol -122.1 670.43 151 -0.18 Mar/ 35 umol -188.61 646.11 151 -0.29 Mar/ 100 umol 0 May/ 0 umol 0
May/ 35 umol 0 May/ 100 umol 0
40
Appendix 1 Cont’d Chl a biomass*month Apr bijklm* αj 8.24 8.96 151 0.92 Aug 13.06 10.45 151 1.25 Feb 13.45 8.63 151 1.56 Jan -0.43 7.21 151 -0.06 Jul 19.75 11.7 151 1.69 Jun 16.31 8.91 151 1.83 Mar 3.65 10.36 151 0.35 May 0
subsite*light trt edge/dark βk * γl 31.96 268.08 151 0.12 edge/light 0 interior/dark 0 interior/light 0 edge/ 0 umol -658.85 334.56 151 -1.97 edge/ 35 umol -418.22 334.67 151 -1.25 edge/ 100 umol 0 interior/ 0 umol 0
interior/ 35 umol 0 interior/ 100 umol 0 Chl a biomass * edge bijklm* βk -9.98 4.17 151 -2.39 subsite interior 0 light trt*conc dark/ 0 umol γl * δm 860.69 326.36 151 2.64 dark/ 35 umol 671.1 327.14 151 2.05 dark/ 100 umol 0 light/ 0 umol 0 light/ 35 umol 0 light/ 100 umol 0 Chl a biomass*light trt dark bijklm * γl 0.78 1.82 151 0.43 light 0
0 umol 12.83 2.34 151 5.48 35 umol 7.18 2.3 151 3.13 100 umol 0
41
BIOLOGICAL SKETCH
Audra Elizabeth Luscher was born on July 25, 1975, in Merced, California. She lived
most of her childhood in Idaho and Washington State. She graduated from California State
University at Long Beach in June 1998 with a B.S. degree in Marine Biology and a minor in
Chemistry. In June 1998, she was selected as a University of Georgia Marine Institute
undergraduate intern. She moved to Sapelo Island, Georgia and worked with Dr. Steven
Pennings. The experience had a profound influence on her interest to study in South Atlantic
marsh systems. In August 1999, she entered the graduate program in Marine Science at the
University of North Carolina at Wilmington where she worked under the direction of Dr.
Courtney Hackney. As a graduate student, Ms. Luscher was selected as the first North Carolina
Sea Grant Coastal Management Fellow and began working in coastal hazards and resource
management at the N.C. Division of Coastal Management. The fellowship focused on
determining management strategies to protect wetlands influenced by sea level changes and
coordinating the revision of the North Carolina estuarine shoreline stabilization regulations. Ms.
Luscher was hired in October 2002 as a full time Natural Resources Planner for the Maryland
Division of Coastal Zone Management. She graduated with her Masters in the spring of 2005.
She has aspirations to continue working in marine policy, but also would like to live and work
abroad.
42
