Human activities have had substantial impacts on coastal ecosystems in a variety of ways

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Human activities have had substantial impacts on
coastal ecosystems in a variety of ways
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Eutrophication through increased nutrient loading
into coastal watersheds
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The majority of past research has focused on
saltmarsh systems within estuaries. Little
research has been done to investigate how abiotic
factors control ecological structure and function
within oligohaline zones.
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How are estuaries structured and function within
their critical, oligohaline zones?
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• Question 1
• How does the transition in nutrient limitation of
  macrophyte production (from P to N as you
  progress down the estuary) occur? Is it gradual
  or discrete in nature?
• Question 2
• What mechanism(s) controls macrophyte production
  within the estuarine oligohaline zone?
• Is macrophyte production and zonation solely a
  function of interspecific competition for
  nutrients, or a combination of competitive
  ability and stress tolerance?
• Question 3
• Is the location of macrophyte communities found
  within estuarine oligohaline zones static or
  dynamic with respect to longer-term variations in
  freshwater inflow or tidal range?

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These questions will be addressed using a series
of hierarchically nested approaches covering a
range of ecological scales.
Landscape level (1,3)
Freshwater marsh
Community level (2b)
Oligohaline zone
Ecosystem Level (2a)
Salt marsh
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Question 1 How does the transition in nutrient
limitation occur within estuaries?
Landscape level
P-limitation
Freshwater marsh
Oligohaline zone
Decreasing salinity
Salt marsh
N-limitation
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Hypothesis 1 Given the complex biogeochemical
nature of the estuarine oligohaline zone, it is
unlikely that the transition of nutrient
limitation is discrete, and in fact, marsh
macrophyte production may exhibit co-limitation
by both N and P within the oligohaline zone. The
specific limiting nutrient may vary in congruence
with fluctuations in porewater salinity and
sulphide concentrations.
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Increasing P-limitation
Increasing N-limitation
N-availability may control abundance or
productivity
P-availability may control abundance or
productivity
Abundance (g DW m-2) or Productivity (g DW m-2
day-1)
Theoretically expected optimal relationship
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South Carolina
Charleston
Ashepoo-Combahee-Edisto Basin
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Abundance (g m-2)
Fenwick
Freshwater P-limited
Short
Tall
Brackish Zone
St. Pierre
Abundance (g m-2)
Short
Tall
Saltwater N-limited
Big Bay
Abundance (g m-2)
Month
Month
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Freshwater P-limited
Duckblind
Abundance (g m-2)
Brackish Zone
Month
Juncus Zone
Saltwater N-limited
Abundance (g m-2)
Month
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Freshwater P-limited
Wiltown
Brackish Zone
Abundance (g m-2)
Saltwater N-limited
Month
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Freshwater P-limited
plt0.0001 F7,1490119.80
E
E
Brackish Zone
E
C
D
Saltwater N-limited
C
B
A
Sulphide concentration (uM)
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The NP technique does suggest N-limitation
within the saltmarshes along the Edisto River
Short Spartina alterniflora
Tall Spartina alterniflora
H2S
Abundance (g m-2)
Abundance (g m-2)
NP
NP
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Within the Edisto River, the NP technique also
supports the idea that nutrient limitation is
important in controlling production of the
dominant macrophyte species
Wiltown Zizania aquatica
p0.0119 F1,711.360
p0.026 F1,87.427
Abundance (g m-2)
NP
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Within the oligohaline zone of the Edisto River,
the appears to be no relationship between NP
ratios and aboveground production
Juncus zone Juncus roemerianus
Duckblind Spartina cynosuroides
Abundance (g m-2)
Abundance (g m-2)
NP
NP
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Question 2a What mechanisms control macrophyte
production within the estuarine oligohaline zone?
Freshwater marsh
Oligohaline zone
Decreasing salinity
Ecosystem Level (2a)
Salt marsh
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Past research has shown a strong relationship
between nutrient loading and saltmarsh macrophyte
productivity using in situ fertilization
experiments.
Saltmarsh ecosystems are nitrogen limited
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Hypothesis 2a Given past research which has
shown physical factors are superimposed upon
nitrogen limitation within saltmarsh ecosystems,
it is likely that macrophyte production within
the estuarine oligohaline zone is also primarily
controlled by nutrient limitation and will
respond to nutrient additions. Furthermore,
since it is likely that limitation within the
oligohaline zones is dynamic and determined by
the biogeochemical interactions between sulphur,
nitrogen, and phosphorus, it is hypothesized that
macrophyte response will be greatest to additions
of both N and P and equal, but enhanced, to
additions of N or P alone.
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NP
N
P
Production
C
Time
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Plum Island Ecosystem LTER, Rowley MA
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Will use 3 NP factorial fertilization
experiments in a Spartina patens dominated high
marsh community, Spartina alterniflora low marsh
community, and Typha angustifolia marsh within
the estuarine oligohaline zone.
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Response of Spartina alterniflora to fertilization
FNgtPC
pgt0.001
Aboveground Biomass (g m-2)
1999
2000
2001
2002
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Response of Spartina patens to fertilization
FNgtPC
p0.023
Aboveground Biomass (g m-2)
2000
2001
2002
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Response of Typha angustifolia to fertilization
FPgtNC
p0.023
Aboveground Biomass (g m-2)
2001
2000
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Question 2b Is macrophyte production and
zonation solely a function of competitive ability
to obtain nutrients or a combination of nutrient
competition and ability to tolerate physical
stress?
Freshwater marsh
Community level (2b)
Decreasing salinity
Oligohaline zone
Salt marsh
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upward expansion limited by ability to compete
for N
Low Marsh - Spartina alterniflora
Mixed zone
lower boundary determined by ability to
withstand salinity stress
High Marsh - Spartina patens
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Control -- no additons of fertilizer N-only -- 30
M N m-2 yr-1 P-only -- 10 M P m-2 yr-1 NP -- 30
M N and 10 M P m-2 yr-1
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Typha angustifolia
Spartina patens
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NP treatments May and August
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NP treatments May and August
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Artificially created bare patch
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Question 3 Is the location of macrophyte
communities found within estuarine oligohaline
zones static or dynamic with respect to
longer-term variations in freshwater inflow or
tidal range?
Landscape level
P-limitation
Freshwater marsh
Oligohaline zone
Decreasing salinity
Salt marsh
N-limitation
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Hypothesis 3 Given that abiotic stress on system
structure and function is determined by
interaction between freshwater and marine-derived
inputs, and given that these inputs fluctuate
over a multitude of temporal scales, it is likely
that the location of estuarine oligohaline marsh
communities fluctuates in concordance with
longer-term changes in precipitation patterns and
sea level rise.
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Available datasets will be searched to obtain
information on freshwater discharge and sea
level. In addition, sources will be searched for
remotely captured images that can be analysed
using GIS tools.
Freshwater marsh
??
Oligohaline zone
Decreasing salinity
Salt marsh
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