Wetland Science & Practice March 2017 13
Many coastal wetlands
attributable to various factors
including land development,
erosion, salinization, and a
lack of sediment inputs (Bar-
ras et al. 2003; Baumann et al.
1984). Additionally, condi-
tions may worsen as impacts
associated with sea level rise
as well as increases in storm
frequency and intensity exac-
erbate marsh stressors (Hauser
et al. 2015). Marshes naturally
exhibit a mosaic of vegetated
and open water areas (Adamo-
wicz and Roman 2005). How-
ever, studies document marsh
fragmentation and subsequent degradation by examining an
increase in the conversion of vegetated areas to open water
(Figure 1; Turner 1997; Day et al. 2000).
Conceptual models of marsh degradation describe three
processes: 1) drowning - whereby accretionary processes
are outpaced by sea level rise, 2) edge retreat - caused
primarily by wave erosion at lower marsh margins, and 3)
marsh pond (sometimes referred to as pools or pannes) col-
lapse - in which open water areas fail to maintain elevation
relative to rising sea level and expand through continued
edge erosion (Mariotti 2016). DeLaune and others (1994)
described the process as pond initiation, in which newly
formed open water areas allow for marsh degradation via
erosion, collapse, and other mechanisms. In response,
wetland restoration projects have been implemented over
the past three decades to stabilize and enhance marsh eco-
systems (Warren et al. 2002). Techniques include erosion
control, invasive species removal, and re-establishment of
natural wetland vegetation and tidal ow regimes (GM-
CHRS 2004; Jackson 2009). Notably, in a recent article
Smith and Niles (2016) highlights the need for improved
approaches to documenting marsh degradation and deter-
mining the potential benets and/or risks associated with
Broome and others (1988) identied important compo-
nents in marsh restoration including elevation of the site in
relation to tidal regime, slope, exposure to wave action, soil
chemical and physical characteristics, nutrient supply, sa-
linity and availability of viable propagules for revegetation.
These factors highlight the need for restoration strategies
that counterbalance subsidence, support a stable platform
for plant growth, and keep pace with expected sea level rise
while maintaining natural patterns of wetland hydrology
and vegetation. The intentional application of sediments
into marsh habitats has the potential to help achieve resto-
ration goals by allowing the marsh to maintain elevation
despite ongoing subsidence or sea level rise.
Dredged materials have been utilized for many years
in wetland creation and restoration projects (Faulkner and
Poach 1996; Craft 1999; Cahoon and Cowan 1988). Com-
monly, materials are deposited within diked containment
areas, adjacent to shorelines, or in open water until target
elevations are reached (Landin et al. 1989; USACE 1983;
Berkowitz et al. 2015). The placement of dredged material
RESEARCH FOR SALT MARSH RESTORATION
1Correspondence author: Jacob.F.Berkowitz@usace.army.mil, 601-634-5218
Marsh Restoration Using Thin Layer Sediment Addition: Initial Soil Evaluation
Jacob Berkowitz1, Christine VanZomeren, and Candice Piercy
U.S. Army Corps of Engineers (USACE), Engineer Research and Development Center (ERDC), Vicksburg, MS
FIGURE 1. Site conditions in a degrading marsh near Avalon, New Jersey, USA in which portions of the marsh
have shifted from vegetated areas to shallow open features that display signs of erosion and subsidence
(left). Within vegetated sections of the marsh, Spartina alterniora roots form a dense root mat that helps to
stabilize marsh soils (right).
14 Wetland Science & Practice March 2017
directly onto the marsh surface remains challenging due to
the need to achieve target elevations while maintaining or
rapidly establishing the native plant communities that sta-
bilize marsh soils (DeLaune et al. 1994). As a result, much
interest has focused on the application of thin layers of
dredged materials within existing marshes to support marsh
elevation while enhancing existing habitat.
Wilbur (1992) dened thin layer placement techniques
as the application of dredged materials to a thickness that
does not transform the receiving habitat’s ecological func-
tions. Others have dened thin layer placement utilizing
a layer thickness criteria ranging from as little as a few
centimeters up to 50 cm. Sediment application typically
occurs via the spraying of uidized dredged materials onto
the marsh surface (Figure 2). Ray (2007) provided a review
of thin layer placement case studies. For example, Reimold
and others (1978) performed initial small-scale studies in
which Spartina alterniora successfully recovered follow-
ing the placement of 23 cm of dredged materials on the
marsh surface. Placement of thick layers reduced or pre-
vented plant recovery by rhizomes (Ford et al. 1999; Schrift
et al. 2008). Other studies examined thin layer placement
techniques designed to restore or enhance
degraded marshes through evaluation of plant
communities (Pezeshki et al. 1992; Ford et al.
1999), invertebrates (Croft et al. 2006), soil
organic matter and bulk density (Slocum et
al. 2005), and marsh resilience following a
disturbance (Stagg and Mendelssohn 2011).
TESTING THIN LAYER SEDIMENT TO RESTORE
DEGRADING SALT MARSH IN NEW JERSEY
Current efforts are utilizing thin layer applica-
tions of dredged materials to address concerns
regarding marsh degradation and enhance-
ment of marsh resilience and habitat within a
large wetland complex located near Avalon,
New Jersey, USA (Figure 3). The S. alternio-
ra-dominated marsh displayed several signs
of instability including erosion, expansion of
open water areas, and fragmentation. Sedi-
ment placement occurred between November
2015 and March 2016. Dredged sediments
were obtained during channel maintenance
from the federally-maintained New Jersey
Intracoastal Waterway following Superstorm
Sandy. Sediment placement depths ranged
from 5-20 cm in vegetated areas and up to
50 cm in open water portions of the marsh.
Primary project goals include stabilization of
the marsh platform, increasing the elevation
of recently developed open water areas to pro-
mote vegetation establishment, and evaluating
the potential benets of thin layer sediment
application for other restoration activities. Sta-
bilization of the degraded Avalon marsh will
also provide continued benets to the barrier
island community of Avalon by maintaining
protection from waves and erosion. Monitor-
ing efforts to document restoration outcomes
began in 2016 and will continue during 2017
FIGURE 2. Site preparation prior to thin layer sediment application included placement
of coir logs to target areas receiving sediment additions (top). Thin layer placement of
dredged materials involves spraying a dredged sediment slurry onto the marsh surface
(bottom). (Photo courtesy of Tim Welp)
Wetland Science & Practice March 2017 15
Project partners will be monitoring responses of veg-
etation, fauna, and other factors to the thin layer placement
effort, while our team is focused on soil physical, nutrient
and biogeochemical properties. Soils provide the physical
substrate supporting plant growth and soil microbial com-
munities have been shown to respond quickly to changes in
the environment (Slocum et al. 2005; Harris 2009). As a re-
sult, we believe that examining soil physical, nutrient, and
microbial properties associated with restoration techniques
remains an important component in evaluating restoration
trajectory and success (Table 1; Berkowitz 2013; Berkowitz
and White 2013). Prior to dredged material placement, soil
core samples were collected in vegetated and open water
areas within the restoration footprint and in adjacent control
regions of the marsh (Figure 4). The combination of pre-
application data with subsequent soil collections will allow
investigation of baseline soil property differences between
vegetated and open water features in the marsh as well as
change detection within control and treatment areas where
thin layer applications have occurred.
Figure 3. Location of the tidal marsh in coastal New Jersey, USA.
Note the location of the New Jersey Intracoastal Waterway, the source
for dredged materials utilized in the thin layer application. The areas
highlighted in white outline the portions of the marsh receiving thin layer
FIGURE 4. Sampling conditions differed between open water areas and S.
alterniora-dominated sections of the marsh as indicated by the lack of
soil stability in the open water areas. (Photo courtesy of Bobby McComas)
Physical properties Anticipated marsh response
Soil horizon development; bulk
density decrease; dredge material
incorporated into the original soil
Soil organic matter
Total dissolved nitrogen
Dissolved organic carbon
Soluble reactive phosphorus
Accumulation of organic C, N, and P;
C sequestration; improved nutrient
cycling over time
Microbial biomass carbon
Potentially mineralizable nitrogen
Microbial biomass nitrogen Microbial communities become
established; marsh functions
dependent on microbes return to
comparable marsh levels
TABLE 1. Soil parameters being evaluated following thin layer sediment application and anticipated marsh response
16 Wetland Science & Practice March 2017
We anticipate the partial recovery of marsh functions
following dredged material placement based upon previous
studies. For example, Craft and others (1999) examined
constructed and planted S. alterniora marshes over a 25-
year period reporting accumulation of soil organic C and
soil N and decreases in bulk density. However, soil proper-
ties did not correspond with values observed in a natural
marsh. Thin layer placement applications may increase
recovery timelines, due to the presence of potential seed
sources for vegetation and microbial populations. Microbial
communities represent a small but active nutrient pool in
the soil environment, regulating biogeochemical cycling
and bioavailability of nutrients (White and Reddy 2001). As
marsh functions develop over time we expect soil horizon
development, organic C, N, and P accumulation, as well as
bulk densities and nutrient cycling to approach levels iden-
tied in the control marsh areas. Analysis of pre-treatment
and initial post-treatment samples collected after thin layer
placement of dredged materials are ongoing and should
lend insight into the implications and potential benets of
restoration techniques utilizing thin layer sediment applica-
tion (Figure 5).
For further information on this project, please feel free
to contact the senior author or the project leads Monica
Chasten from the USACE Philadelphia District and Dave
Golden from the New Jersey Department of Environmental
Protection Division of Fish and Wildlife. n
Research funding for this portion of the Avalon monitoring
effort was provided by the USACE Environmental Manage-
ment and Restoration Research Program (Trudy Estes – Pro-
gram Manager). Jason Pietroski and Kevin Philley assisted
with eld data collection and sample preparation. The Avalon
marsh restoration project was the result of a collaboration
with the USACE Philadelphia District, the New Jersey De-
partment of Environmental Protection Division of Fish and
Wildlife, The Nature Conservancy, and Green Trust Alliance
FIGURE 5. S. alterniora emerging from dredged materials utilized for marsh restoration via thin layer sediment application. The photos were taken
approximately six months (a, b), nine months (c), and 18 months (d) after placement of dredged material.
Wetland Science & Practice March 2017 17
funded jointly through the 2013 Disaster Relief Appropria-
tions Act (Superstorm Sandy recovery) and National Fish
and Wildlife Foundation Hurricane Sandy Coastal Resiliency
Competitive Grant. The authors would also like to acknowl-
edge the project leads Monica Chasten from the USACE
Philadelphia District and Dave Golden from the New Jersey
Department of Environmental Protection Division of Fish
and Wildlife and the dedicated team including Ms. Metthea
Yepsen from The Nature Conservancy and Ms. Jackie Jahn
from GreenVest LLC., and all the other staff from the Green
Trust Alliance and the Stone Harbor Wetlands Institute who
assisted with these projects. Special acknowledgements
are also offered for the dredging contractor, Barnegat Bay
Dredging, Inc. dredge captains and crew whose innovation,
teamwork and dedication contributed greatly to making this
project successful. The authors would like to acknowledge
the assistance of the USACE ERDC Program Managers, Ms.
Linda Lillycrop and Dr. Todd Bridges for continual support
of USACE Philadelphia District efforts to bring the Avalon
marsh restoration project to fruition.
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