Ecosystem Restoration & Biodiversity: Tijuana Estuary Case Study

Restoring a Dynamic Ecosystem to Sustain Biodiversity
Author(s): Joy B. Zedler
Source: Ecological Restoration , March/June 2011, Vol. 29, No. 1/2, Special Theme:
Protection and Restoration–Are We Having an Effect? (March/June 2011), pp. 152-160
Published by: University of Wisconsin Press
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Restoring a Dynamic Ecosystem
to Sustain Biodiversity
Joy B. Zedier
ABSTRACT
Over three decades, Tijuana Estuary became highly modified by frequent storms and runoff events that acte
with intensifying land use to deliver tons of sediment to the salt marsh and its tidal channels. The ma
higher, drier, and more hypersaline, with fewer microtopographic features. The result was reduced bio
an endangered sparrow continued to use the marsh plain, it was not permissible to remove sediment
site. Thus, restoration took on new meaning, and efforts shifted to excavation of disturbed uplands an
novel conditions. When subsequent excavations also accumulated sediment, planning expanded to lar
restored in modules over decades. Sedimentation will likely recur during future stormy periods due to the
Oscillation and global climate change. Thus, biodiversity will best be sustained within an adaptive restor
involving large field experiments that show how to sustain all of the native species somewhere in the estu
single module can provide all essential habitats.
Keywords: flood, salt marsh, sedimentation, tidal influence, Tijuana Estuary
Estuarieswetlands
wetlandsareand
vulnerable
are vulnerable
to floodother downstream to flood-
ing and sedimentation during catastrophic storms. Given that climate
is changing toward more frequent
and extreme storm events, coastal
But where sediments accumulate isfar
hypothetically possible, but adaptation to novel conditions and continual
faster than sea level rises, the marsh
efforts
plain can become elevated enough
to to excavate new salt marshes
shift tidal wetland to upland. from
One uplands are more feasible alteror two plant species might adjust
natives
to for highly dynamic ecosystems.
such rapid changes and expand Here,
theirI present the Tijuana Estuary
marshes can be expected to experience
distributions, but most species will
case be
study, which offers both insights
increased flooding and sedimentation.
slow to accommodate change. and suggestions for future restoration.
At the same time as vegetation
For example, the intertidal marshes
that develop at elevations between
adjusts to sediment accretion, rare
Tijuana
and endangered bird species will be
open mud flats and uplands have
Estuary
Experienced Increased
nesting habFlooding and
tidal creek networks that create het-
further threatened if their
erogeneous topography and support
itat declines. Some might persist if a
a mosaic of halophytes, but their per-
preferred plant can sustain appropriate
sistence requires that sedimentation
rates keep up with rates of sea level
rise. When sedimentation compensates for slowly rising sea level over
decades to centuries, the vegetation
can achieve relatively high diversity
Tijuana Estuary is a 500 ha, marshnesting canopies, regardless of whether
Sedimentation
the salt marsh vegetation remains
dominated ecosystem that is partly
diverse. In either case, efforts to restore
managed
as the Tijuana River
National Estuarine Research Reserve.
rare plants are impaired, because resto-
It the
is representative of the Californian
ration in the form of recontouring
topography would not be permitted
Biogeographic Region, which extends
(although salt marshes [soil water >3%
salt] are typically less diverse in plant
in vegetation that either historically
from Pt. Conception south along the
supported endangered birds orBaja
con-California Peninsula (Zedier et al.
species than fresh [0-0.05% salt] or
tinues to support their nesting. Just
1992). Semidiurnal mixed tides keep
brackish [0.05-3% salt] marshes).
how managers should respond to,
theor
estuary mouth open and the main
channels saline.
plan for, future salt marsh conditions
Ecological Restoration Vol. 29, Nos. 1 -2, 201 1
and increasing rarity of several plant
Of the two-dozen halophytes that
species is uncertain. Periodic removal
occupy the intertidal marshes, Pacific
of sediments and reestablishment of
cordgrass {Spartina foliosa) is the most
ISSN 1522-4740 E-ISSN 1543-4079
©201 1 by the Board of Regents of the
University of Wisconsin System.
historical structure and functioning inundation tolerant. It dominates the
152 # March/June 2011 ECOLOGICAL RESTORATION 29:1-2
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1000-1
edges of channels and creeks but is
often mixed with perennial pickle-
1982-83
900-
weed (Sarco cornia pacifica = Salicornia
virginica) at its inland boundary. Pick-
°
leweed and ten other highly salt toler800-
ant halophytes intermix on the broad
marsh plain. Many of the nongrass
species accumulate sea salts and are
succulent. Collectively the creek-edge
and marsh-plain vegetation provides
nesting habitat for two endangered
birds (light-footed clapper rail [Rallus
longirostris levipes' and Belding s Savan-
nah sparrow 'Ammodrammus sandwichensis beldingi ]). In the high marsh
1979-80
E
J 600-
I
~ 500-
$
and transition to upland, subshrubs
O
and clonal grasses (Monanthochlöe lit-
1= 400-
toralis, Distichlis spicata ) grade into
coastal sage scrub. This infrequently
inundated vegetation provides cover
f
sr 700-
a>
& 300-
for the two endangered birds during
1994-95
the extreme high tides of winter and
200-
summer, and it adds foraging habitat
Î
between nesting seasons.
At Tijuana Estuary, monitoring
occurs annually for the salt marsh
vegetation, fish, channel inverte-
brates, and soil salinity (Desmond
et al. 2002, Zedier and West 2008)
and continuously for channel salinity,
dissolved oxygen, and temperature.
The region has low average rainfall
(<30 cm/y), but variability is high
100-
o yf* - > *A| -
1950-51 1958-59 | 1966-67 1974-75 | 1990-91 1998-99
1954-55 1962-63 1970-71 1978-79 1986-87 2002-03
Figure 1. Annual streamflows (for rainfall years, July 1 through June 30) for Tijuan
U.S.-Mexico border. U.S. Geological Survey data compiled by Janelle West (additio
on flooding is in Zedier and West 2008).
both seasonally, due to the Mediterra-
nean-type climate, and over decades,
due to the Pacific Decadal Oscilla-
flowed
from Goat Canyon onto the
brackish to fresh following
storms
(Zedier and West 2008).
tidal marsh plain, where they buried
tion (PDO) (Bromirski et al. 2003). During the period of increased
the benchmarks (steel pipes 20 cm
storminess (1978 to 2005), aboveground)
land use
Although only recently described, the
placed at Mean Higher
PDO is widely recognized as a longchanged along with the growth
High
ofWater
the
by the U.S. Army Corps
term pattern of benign conditions forhuman population in the watershed.
of Engineers prior to 1974. A 50 cm
tall
concrete benchmark (TJE-43) was
several decades followed by repeated
The nearby city of Tijuana (in
Mexico)
half
buried (Zedier 1983). Marsh soil
quadrupled in population (Ganster
episodic storms and flooding. A prime
2000), and hundreds of houses
werealso recorded 25-30 cm of
example is the coastal watershed of
profiles
accreted
sediment based on Cs-137
the Tijuana River (Figure 1). Between packed onto steep, erodible
bluffs
1950 and 1977, the 1,700 mi2
profiles
(Weis et al. 2001). Broader
and slopes just across the
border
(4,400 km2) watershed (mostly from
in
the estuary (which is
entirely
topographic
surveys (Ward et al. 2003,
Wallace et al. 2005, Zedier and West
in the United States). Deep-rooted
Mexico) discharged an average of 2.3
2008)
andsoil
cores of sediment plumes
million m3 of fresh water per rainfall
shrubs that might have held
the
year to the estuary, which was saline
(Callaway
and Zedier 2004) showed
were removed and replaced by
human
that much
of the marsh plain was
(>3.4% salt) throughout that time
structures and unpaved streets.
The
period (Purer 1942, Zedier 1977,
rainstorms of January-February
elevated1980
by at least 10 cm in recent
Even a 5 cm difference in eleWinfield 1980). The average streamcaused one mudslide thatdecades.
dumped
2 m of sediment into Goat
Canyon
flow for 1978 to 2005 jumped nearly
vation
can shift vegetation composition(Wil(Zedier 1977, Zedier et al. 1999,
at the Mexico-U.S. border
50-fold to 113.9 million m3 (Figure
liams and Swanson 1987). Sediments
1), and parts of the estuary became
Varty and Zedier 2008). These recent
March/June 2011 ECOLOGICAL RESTORATION 29:1-2 153
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sediment-accretion rates dwarfed rates
Prior to 1978, estuary channels
supThe
Estuary's Diverse
ported 29 species of fish, butSalt
with
Marsh Became
of sea level rise of about 1-2 mm/y
(Münk 2002, Scavia et al. 2002).
frequent flooding, the fauna shifted
Less Restorable
In 1983 and 1995, the estuary was
affected by major El Niño events in
addition to the PDO. The 1983 sea
salt- tolerant), short-lived species that
could reproduce in one to twodespite
years reintroduction of tidal flushing
storm coincided with high tides, and
toward a few euryhaline (broadly
Biodiversity did not fully recover
in December 1984. Cordgrass grew
and persist despite disruption ( Zedier
wave surges washed unstable dune et al. 1992).
sand into the adjacent channel, sub- The 1984 nontidal drought killed
stantially diminishing the estuary's crabs ( Pachygrapsis crassipes , Hemigraptidal prism and allowing the mouth sis oregonensis) and snails ( Cerithidea
to close to tidal flushing in early April californica ), eliminating food used by
1984. The estuary remained nontidal the clapper rail. Simultaneous reduction in the extent and vigor of cordgrass reduced nesting habitat for the
from the channels and rebuild the
endangered bird, which either died or
dune, in preparation for reopeningemigrated. Drought nearly extirpated
the river/estuary mouth (Zedier et al.two short-lived, shallow-rooted plant
1992). The nontidal period coincidedspecies, sea-blite {Suaeda esteroa) and
with an eight-month period with noannual pickleweed {Salicornia bigelo rainfall; warm dry weather caused highvii). Further support that tidal exclurates of evaporation that concentrated sion during drought caused extreme
salt in channel waters (reaching 6% hypersalinity and loss of plant diversalt) and across the marsh plain (soil- sity came from a diked salt marsh near
water salinity >10% salt, i.e., 3 times Ensenada, Mexico, where those effects
that of seawater) (Zedier et al. 1992).were documented in the same year
until mid-December 1984, while permits were obtained to excavate sand
Tidal exclusion and drought led to (Ibarra-Obando and Poumian-Tapia
the most stressful conditions ever
documented at Tijuana Estuary.
Extreme Events Reduced
Native Biodiversity
1991).
The series of extreme events had
tall again by 1988, and clapper rails
reestablished a viable population by
1991 (Zedier et al. 1992), but the tidal
plain never recovered the diverse state
recorded in 1974 (Figure 2). Instead of
sustaining an abundance of short-lived
plants (annual pickleweed and seablite), the plant community shifted
to long-lived perennials. And instead
of occurring in relatively even abundances, the perennials shifted toward
two dominants, perennial pickleweed
and salt marsh daisy ( Jaumea carnosa).
No species was extirpated, but annual
pickleweed was nearly eliminated, and
both it and sea-blite are still rare where
they were once common.
Flooding and sedimentation associated with the next PDOs (which are
cyclic), exacerbated by global change
(which is directional), could eliminate
one or both species from Tijuana Estu-
severe and lasting impacts on the ary and perhaps from other coastal
intertidal geomorphology, as well as its salt marshes in the region. Shortlived halophytes make the salt marsh
estuarine biota. The changes in marsh
resilient to other types of disturbance
plain elevation and soil salinity are
most well known, but there were also that create shallow depressions and
Floods and drought had numerous
influxes
negative effects on native plants
and of nutrients and contaminants canopy openings. Annual pickleweed
animals. River flooding imported
with every flood. While these chemi- can make an erodible tidal pool into
cal influxes
were not monitored, the a stabilized depression; sea-blite can
nutrients and temporarily lowered
soil
salinity, which stimulated invasions
of treatment plant on Tijuana grow tall stems that a Belding s Savansewage
exotic rabbitfoot grass (PolypogonRiver
mon (7 km upstream of the estu- nah sparrow can use to defend its nest.
speliensis) and sickle grass ( Parapho
- the U.S. side of the border We have yet to quantify the impacts of
ary on
their diminished distributions.
lis incurva), both of which displaced
with Mexico) has limited capacity
native vegetation, especially in
them3 per day), and it frequently Attempts to restore annual pickle(95,000
high marsh (Kuhn and Zedier overflowed,
1997,
adding contaminants of weed and sea-blite by adding seeds to
the natural marsh plain were ineffecunknown amounts to the sediment
Callaway and Zedier 1998, Fellows
tive (Vivian-Smith 2001, Morzariaand Zedier 2005).
load. Layers of nutrient-rich sediment
Low water salinities were lethal
to
overlain onto historical salt marsh soil Luna and Zedier 2007). We learned
later that the critical microsites for
stenohaline macroinvertebrates continued
(those
to support native vegeta-
annual pickleweed are shallow (about
with narrow ranges of tolerance
tion to
and endangered birds, but comsalt). For example, the sand dollar
position and diversity understand- 5 cm deep) depressions, where water{Dendraster excentricus) population
ably shifted toward fewer species and logging stresses perennial pickleweed
crashed in 1978, and large purplegreater dominance - a condition that and allows the annual to germinate
and grow. (Varty and Zedier 2008).
hinged clams {Sanguinolaria nuttalli)
is not easily reversed.
Such
depressions were filled by rapwere replaced by small individuals of
idly
accreting
sediments. Without
false mya ( Cryptomya californien) after
the 1980 floods (Zedier et al. 1992).
waterlogged microsites, perennial
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pickleweed remained dominant and
60-,
salt marsh daisy persisted as a codomi-
4
'
nant (Bonin and Zedier 2008). Flood-
'
ing in 2000 also inundated restoration
plantings, coating young seedlings
with sediment and impairing cord-
grass establishment (Zedier et al.
50 - y
2003)€
One approach to marsh-plain restoration might have been to recontour
the topography to historical elevations
and variations, but neither grading
nor excavating shallow depressions
was permitted due to the continued presence of Beldings Savannah
sparrows. This state-endangered bird
nests in both diverse and monotypie
(perennial pickleweed) salt marshes
within the region, except where tidal
influence is insufficient to discourage terrestrial predators on eggs and
chicks. Nests are typically built just
3-6 cm aboveground (Powell and
Collier 1998). Where inundation
is infrequent, either due to estuary-
mouth closure or sediment accretion
40- ļ
2O1 X
: ''
u ♦ 5 1
£ 30- ♦ V: 1 '
CU
't '
u ': 1
vi
CU ' '
'k''
20 -
I1V
R k X.^^1974
10- ' x *'2004 '
' 1994^Al, '
on the marsh plain, the soil dries and
1984'
fox, dogs, and cats can find nests in
salt marsh canopies that are less than
50 cm tall.
While restoring salt marshes by low-
ering marsh plains in their current
location would potentially enhance
the size and quality of habitat for
the endangered birds, the short-term
effect would be a loss of habitat already
in use. In the long-term, with future
o
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Species sequence
Figure 2. Dominance-diversity (= species-sequence) cur
marsh-plain species over 31 years. The 1974 condition w
marsh was depauperate in 1984, during nontidal drou
recovery, with the marsh still dominated by Sarcocorni
Jaumea carnosa emerging as a second dominant (Zedi
PDOs and global change, the restored
not be jeopardized. Two
opportunities
completing construction.
Now,
sand
is periodielevated rates and frequencies of flood- that collects in the
were basins
a highly disturbed
upland (the
ing and sedimentation. An alterna- cally excavated and
0.7sold,
ha Tidal Linkage,
completed in
but flooding
still moves considerable
material
tive that was considered feasible and
1997) and afine
former salt
marsh that
marsh plains would again experience
recently implemented was to capture
into the salt marsh. While the com-
had accumulated 1-2 m of sediment
sediments upstream in retention bined impacts of changing urban- (the 8 ha Friendship Marsh, combasins in Goat Canyon, on the U.S. ization and increased storminess are
pleted in 2000). In each case, novel
side of the border. However, the con- somewhat mitigated, the novel hydro- conditions posed new challenges.
At the Tidal Linkage, the exposed
struction of two sequential basins, at a logical conditions in the estuary have
cost of $8 million, was not sufficient. not been reversed.
marsh plain was raw subsoil, to which
Sediment deposition on the marsh we added organic sediment from a
November 2004, when the first storm will likely continue to exceed the rate former sewage lagoon to ameliorate
of the season filled and overflowed
of sea level rise, leading to continual harsh growing conditions. In April
1997 we planted eight halophytes in
both basins, allowing excess sediment accretion relative to mean sea level.
to flow across the southernmost salt This realization has led estuary man- near-equal numbers (-810 plants/
marsh. During 2005, the basins were agers to select restoration sites where species), but despite high initial surreexcavated and armored with rock, nesting by endangered species would vivorship, two of the species planted
The project was nearly completed in
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clapper rails had been sighted among
the cordgrass plantings.
The historical salt marsh cannot be
recontoured and the tidal channels
of the Friendship Marsh cannot be
reexcavated to their deep, wide origins
because of endangered birds. The posi-
tive outcome is that Belding's Savannah sparrows and light-footed clapper
rails persist and use both restoration
areas despite novel conditions and
diminished plant diversity. The challenge is to provide new areas for valued
wildlife to expand by creating suitable habitat to compensate for losses
caused by sediment accretion.
Managers realize the difficulty of
sustaining Tijuana Estuary in a stable
physiographic configuration. It is a
small estuary affected by a large water-
shed, and it will always be a dynamic
ecosystem. With changing climate,
Figure 3. Friendship Marsh, a large (8 ha) restoration experiment that was opened to tidal action
in February 2000. The site encountered excessive sedimentation while testing effects of adding
tidal creeks and allowing tidal pools to form. Replicated areas with and without tidal creek
networks ( shaded ovals, left ) and tidal pools ( lower left) demonstrated that multiple scales of topographic heterogeneity aided restoration of habitat for both plants and animals. Dense plantings
of Pacific cordgrass ( Spartina foliosa) formed a dark band between the mudflat and marsh plain
(enlarged In lower right), although sparser plantings on the marsh plain were slow to establish and
spread, a condition that favored shorebird feeding. The tidal creeks accreted sediment ( top right)
but still provided fish access to the marsh plain. Tidal pools produced abundant invertebrates
and became "feeding oases" at high tide (modified from Larkin et ai. 2006).
became dominant; these were perennial pickleweed and salt marsh daisy.
The same shift occurred in the adjacent natural marsh during the years of
frequent flooding and sedimentation
(Zedier and West 2008). Regardless,
endangered terns, Savannah sparrows, and clapper rails used the Tidal
Linkage.
At the 8 ha Friendship Marsh
(Figure 3), the exposed marsh plain
was former wetland soil, albeit com-
pacted. Tidal influence was not
coastal California is expected to experience increased freshwater runoff of
up to 25% by 2034 and 125% by
2099, with increased flashiness (Scavia
et al. 2002). In anticipation of future
PDOs and climate change, the prospects for sustaining biodiversity grow
dimmer.
Restoration Took
added, presumably by holding moison New Meaning
ture and increasing nutrient availability (O'Brien and Zedier 2006). Even if natural land forms and proThe Friendship Marsh was designedcesses are not restorable, salt marsh
to have 50% low marsh and muddiversity and functioning can still be
flat, 25% marsh plain and 25% high sustained. The typical goal of restoramarsh. Within five years, however, the tion is to return specific ecosystems
mudflat accreted enough sediment to some former state. An alterna-
to support marsh-plain vegetation, tive approach is to accept a site as a
trapping the cordgrass between two novel environment that is irreversibly
bands of higher elevation (Wallace altered. Restoration planners acknowl-
et al. 2005). Also, a low spot along edge that much of Tijuana Estuary is
the berm eroded and allowed flood-
novel - either that novel conditions
restored until mid-February 2000.
borne sediments to accrete along theoccur where a site was historically
With tidal restoration, seawater added
west end of the excavated site. Despiteestuarine or that typical estuarine
the intent to excavate an area that
conditions currently occur in novel
salt, but at that time of year, high
would avoid sedimentation, accretion
locations. For Tijuana Estuary, the
rates averaged - 1-2 cm/y, an order oflargest areas available for restoration
crust across most of the marsh plain. magnitude greater than the rate of seaare former agricultural lands within
Cordgrass that was planted exten- level rise (Wallace et al. 2005). Whenthe river floodplain and are not yet
urbanized. Their upstream location
sively at the lower edge of the site the tidal creeks became constricted
survived, especially in plots where aby sediment, we requested remedialreduces the potential to restore fully
soil amendment (kelp compost) wasmeasures, which were denied because tidal conditions.
tides were too infrequent to prevent
the formation of an extensive salt
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To sustain biodiversity under novel
conditions, it is necessary to track
plant and animal populations and
aim to rescue those that are most at
risk, while simultaneously developing plans for a wide range of suitable
habitats, either on site or elsewhere
within the biogeographical region. At
the large scale, varied topography can
provide the heterogeneous landforms
necessary for wetland species diversity
(Morzaria-Luna et al. 2004). At the
small scale, each species has slightly
different requirements, so specific
sites need to include a high variety
of microsites, as in the regions most
natural salt marshes (e.g., San Quintín
Bay; Zedier et al. 1999). Even the
tracks of bulldozers can provide topographic heterogeneity and differential
wetting by tidal inundation, potentially supporting annual pickleweed
(pers. obs.).
Because 90% of the regions coastal
wetland area has been filled and devel-
oped, several dozen species of salt
marsh plants and animals are considered sensitive or at risk of extinction
(Zedier et al. 1992). With so many
species threatened, a regional approach
is needed to sustain all the native biota
where they can best be sustained, even
if they might not have occurred there
historically. In other southern Cali-
Figure 4. Conceptual plan to expand restoration at Tijuana Estuary. Sediments that have accumulated from multiple events over the past 30 years would be excavated to restore tidal marsh
fornia lagoons and estuaries, projects
and channel habitats and create a berm to limit future sediment accretion from severe floods
are being coupled with redesigns of
major coastal highways and bridges,
of the Tijuana River. Several phases of restoration will be needed to complete this 100 ha effort
(summarized from draft plans of the Tijuana River National Estuarine Research Reserve, 2007).
and full tidal flushing can be restored
(SCWRP 2007). Attempts to sustain
biodiversity by providing habitat for
all the species somewhere in the region
contrasts with attempts to return specific ecosystems to some former state.
Such an approach acknowledges the
need to capitalize on novel conditions, such as a mudflat that accretes
enough sediment to support marsh-
Adaptive Restoration
Allows Learning
While Sustaining Salt
Marsh Biodiversity
Friendship Marsh (Figure 5) indicated
the need to restore topographic heterogeneity in order to restore diversity. The design (replicate areas with
and without tidal creek networks)
Adaptive restoration involves a phased
and the large experimental units
approach with each module designed
(-1 ha) led to research funding and
with knowledge gained in previous
rigorous testing of hypotheses about
phases. Ambitious plans (Figurehalophyte
4)
plantings, algae, inverte-
call for 100 ha of habitat restoration to
brates, and fish (Madon et al. 2001;
be
implemented
in
modules
as
funds
O'Brien and Zedier 2006, Larkin et
and it requires that we acknowledge
and sediment-disposal sites become
unknowns and use restoration sites
al. 2008, 2009). The following series
of questions illustrates how future
to test alternative techniques for sup-available. Designing each module
experimentation within an adaptive
porting native species and providingas an experiment allows procedures
to improve with time and outcomes
restoration framework could refine
ecosystem services.
to come closer to expectations. restoration
For
efforts under novel and
plain vegetation and sparrow nesting,
example, experimentation at the 8dynamic
ha
conditions.
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completed. If indentations gradually
erode to form creeks, and if wind fetch
and bioturbation cause pools to form
on the marsh plain, costs of providing
heterogeneous topography would be
reduced.
Will intertidal pools degrade over
time? Outcomes will differ where sedi-
ment supplies are rich (as at Tijuana
Estuary) or scarce (as in Sweetwater
Marsh National Wildlife Refuge, San
Diego Bay) and where sedimentation
interacts with vegetation encroach-
ment to fill in microsites. A mosaic of
pool types (shallow to deep, at both
low and high intertidal elevations)
could be established initially to test for
persistence and biodiversity support.
How should salt marsh plants be
planted in restoration sites? Only
perennial pickleweed recruited withFigure S. Friendship Marsh topography 42 months after excavation (compare with conceptual
ovals with and without tidal creek networks in Figure 3, left). Mudflat and marsh plain areas that
were initially uniform were altered in elevation by sedimentation; tidal creek excavations were
diminished in depth and width by sediments; a few new creeks formed due to erosion, and pools
developed following resuspension and redistribution of sediments (modified from Wallace et
al. 2005). Vegetation has since developed - as intended across the marsh plain and unintended
across the elevated mudflat.
out being planted into the Friendship
Marsh (Morzaria-Luna and Zedier
2007). Other species with limited
dispersal capacity need to be planted
to avoid monotypie vegetation. However, the only planting approaches we
have tested are propagule type (Sul-
Which relative distribution of salt
halophytes (Batis maritima , Jaumea
livan 2001), use of a kelp-compost
marsh habitats constitutes a sustaincarnosa :) would expand vegetatively
soil amendment, and varied spacing
(O'Brien and Zedier 2006). Because
more rapidly than others by sending
able geomorphological state? While
clustered seedlings showed promise in
runners over the edges of the islands
geomorphological changes were docuand trapping sediment to build the
enhancing canopy cover, the technique
mented at Friendship Marsh, hydrocould be refined with further tests of
dynamics need further understandmarsh plain. Plantings of cordgrass
could also enhance accretion rates
spacing and varied assemblages.
ing. Future excavations call for the
(Ward et al. 2003) and minimize Have the restored salt marsh food
50:25:25 geomorphological pattern,
salt crust formation. Future experiwebs developed the complexity of
but small "designer marshes" could
those in natural marshes? West and
ments could compare islands with
test alternative proportions of low,
others (2003) characterized the food
rough
versus smooth surfaces, as well
mid, and high marsh, as well as
a
as islands of multiple depths and
dynamic alternative, namely overexcaweb leading to fish, but birds are often
elevations.
vation to increase mudflat initially and
the desired restoration target. Huspeni
and Lafferty (2004) developed a food
allow subsequent sedimentation andDo tidal creeks need to be incised
or can they be jump-started to extendweb indicator using the list of tremahydrodynamic forces to "self-design"
on their own? Although the 8 ha site todes that parasitize salt marsh snails
the topography.
Can islands of densely planted
was precision-graded to create repli-to indicate the alternative hosts that
cate tidal creek networks, the creeks are also present. This rapid indicator
vegetation accelerate marsh-plain
shifted over time, shrinking in cross-can be used to compare food webs of
formation using an overexcavation
approach? Marsh-plain formation
sectional area and expanding in length restored and natural marshes, as well
and number within six years (Wal-as restoration sites of different age and
might be jump-started by leaving
lace et al. 2005). Future experimenta- other characteristics (e.g., Whitney et
islands of higher topography to accrete
sediment. Small islands could be left
tion could involve excavating only an al. 2007). Further experimentation
indentation at the creek mouth. The with tidal creek and pool topograat the marsh-plain elevation, and spe-
potential for pools to form via self-phy could include snail parasites as a
cies other than perennial pickleweed
could be introduced in dense clusters.
design could also be tested by leaving response variable over time and among
A reasonable hypothesis is that two
rough surfaces after bulldozer work is geomorphological treatments.
158 M March/June 2011 ECOLOGICAL RESTORATION 29:1-2
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What role does nitrogen limitation
play in the interactions of key halophytes? Species distributions, greenhouse and field experimentation, and
microcosm experiments all indicate
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I thank Dr. Ron Thom for inviting this
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sity, however, and larger plots could
Estuary is protected as a National Estuatine Research Reserve, designated by the
National Oceanic and Atmospheric Administration (NOAA); it is also a Ramsar Wet-
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