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Climate Change and the Fate of Coastal Wetlands. Wetland Science and Practice. 33(3)70-77.

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70 Wetland Science & Practice September 2016
Coastal wetlands, including tidal marshes and forests,
provide a number of key ecosystem services, includ-
ing habitat for recreationally and commercially important
nsh and shellsh, protection from wind, waves, storms
and oods, and removal of excess nutrients, namely nitro-
gen (N) and phosphorus (P), from agricultural and urban
runoff (e.g., Tiner 2013). Along the coast, climate change
will be manifested as rising sea level with attendant coastal
ooding and saltwater intrusion. A more immediate impact
which has already been experienced is drought, particularly
in late summer and fall. These processes will lead to migra-
tion of tidal wetlands inland, where possible, and changes
in habitat as freshwater wetlands convert to brackish marsh
or open water (Figure 1).
As part of the National Science Foundation’s Georgia
Coastal Ecosystems Long Term Ecological Research (GCE
LTER) project, scientists from seven institutions of higher
learning, including the University of Georgia, Indiana Uni-
versity, Virginia Institute of Marine Sciences, University of
Houston, University of Florida, Georgia Southern Universi-
ty, College of Coastal Georgia, and the U.S. Environmental
Protection Agency, initiated a eld experiment - Seawater
Addition Long Term Experiment or SALTEx - to investigate
how saltwater intrusion and increased ooding will alter
the direction and pace of change of microbial, plant, and
animal communities and key biogeochemical processes
in a tidal freshwater marsh. SALTEx consists of an array
of eld plots that are used to answer three main questions
regarding sea level rise and saltwater intrusion:
1. How does long-term, chronic (“press”) addition of
diluted seawater affect tidal freshwater marsh structure
and function?
2. What are the effects of periodic pulsing of diluted seawa-
ter to simulate low river ow or
drought conditions?
3. What are the effects of freshwater additions?
The SALTEx site is located on the Alta-
maha River near Sapelo Island, Georgia
(Figure 2). The Altamaha River is the third
largest river on the U.S. East Coast. It is
not dammed along the 200-mile (330 km)
stretch from the conuence of the Oc-
mulgee and Oconee Rivers to the Atlantic
Ocean, making it one of the most ecologi-
cally intact river systems in the East. The
river and estuary contain large areas of tid-
al marsh and forest and extensive alluvial
bottomland hardwood forest upstream.
The tidal freshwater marsh plant com-
munity consists of four dominant species
that are common in freshwater marshes of
the southeastern U.S.: creeping primrose-
willow (Ludwigia repens), smartweed
(Polygonum hydropiper), pickerelweed
(Pontederia cordata), and giant cutgrass
(Zizaniopsis miliacea).
Climate Change and the Fate of Coastal Wetlands
Christopher Craft1, Indiana University, Ellen Herbert, Virginia Institute of Marine Sciences, Fan Li, University
of Houston, Dontrece Smith, University of Georgia, Joe Schubauer-Berigan, U.S. Environmental Protection
Agency, Sarah Widney, Indiana University, Christine Angelini, University of Florida, Steve Pennings, Univer-
sity of Houston, Patricia Medeiros, University of Georgia, Jeb Byers, University of Georgia, and Merryl Alber,
University of Georgia
1 Corresponding author:
FIGURE 1. Aerial view of deteriorating tidal marsh in southeastern Georgia.
Wetland Science & Practice September 2016 71
FIGURE 2. Site map of the GCE LTER (inset). SALTEx’s location is indicated with the
black star.
FIGURE 2. (a) Delivery of seawater-river water mixture to a plot. (b) Press plot
(replicate 3) in July 2015, 15 months after treatments were initiated. Note the loss of
vegetation in the plot as only some giant cutgrass remains, and all other plant species
have disappeared. The four porewater wells are visible in each quarter of the plot.
The SALTEx experiment was initiated in 2012
and consists of 30 eld plots, each 2.5 m on a
side. There are three treatments (Press, Pulse,
and Fresh) and two types of controls (with and
without sides), each consisting of six replicates.
The Press treatment plots receive regular (4 times
each week) additions of a mixture of seawater
and fresh river water (Figure 3a). Pulse plots
receive the same mixture of seawater and river
water during September and October, which is
typically a time of low ow in the river when
saltwater intrusion naturally occurs. The Fresh
treatment plots receive regular additions of fresh
river water. Treatment water is added during low
tide to facilitate its inltration into the soil, and
all plots are inundated by astronomical tides at
high tide.
Response measurements include (1) soil
porewater chemistry and nutrient cycling, (2)
plant community, (3) terrestrial and aquatic
invertebrates, (4) microbial activity, and (5) soil
properties and soil elevation change (Table 1).
Baseline (pre-treatment) data were collected in
2013 and early 2014 and treatments were initi-
ated in April 2014.
Changes in porewater chemistry and microbial
activity were evident almost immediately follow-
ing treatment additions. Porewater chloride and
sulfate (both present in seawater) and salinity
increased within the rst month following Press
additions (Figure 4a). Hydrogen sulde produced
by sulfate-reducing bacteria also increased (Fig-
ure 4b), while the emission of methane (CH4),
a potent greenhouse gas, declined in the Press
plots within six months of the start of treat-
ments. The plant community also was affected
during the rst year of treatments. Creeping
primrose-willow, a succulent groundcover spe-
cies, disappeared from the Press plots during the
rst summer and never recovered. Smartweed
and pickerelweed also declined later during the
rst year. By the second year of treatments, even
the hardy giant cutgrass was in decline in the
Press plots. The reduction of plant biomass led
to reduced carbon uptake by emergent vegeta-
tion, which may lead to long-term declines in soil
carbon sequestration. After 18 months of Press
additions, vegetation in Press plots was nearly
extirpated (Figure 3b) and some Press plots had
lost nearly 2 cm of soil elevation, which we attri-
bute to a loss of roots and rhizomes accompany-
ing the loss of aboveground biomass.
72 Wetland Science & Practice September 2016
Pulse additions of diluted seawater
led to transient increases in porewater
salinity and sulfate that disappeared
once treatments were halted (Figure 4a).
Creeping primrose-willow nearly disap-
peared from Pulse plots after the rst
year, recovering only slightly in year 2.
Other plant species were not affected by
the Pulse addition, nor were greenhouse
gas emissions affected.
Our preliminary ndings suggest that
climate change-driven chronic saltwater
intrusion will lead to rapid changes in mi-
crobial and plant communities with atten-
dant changes in ecosystem services such
as productivity, carbon sequestration, and
greenhouse gas emissions. Of concern is
the loss of vegetation and soil elevation
within the rst two years of Press addi-
tion of diluted seawater. We will continue
treatments for several more years to better
understand the effects of transient low
ow or drought conditions and freshwater
additions on tidal freshwater marshes. In
addition, we plan to follow recovery of
the plots when we discontinue the treat-
ments to see if recovery follows the same
trajectories in the different treatments and
to see how quickly the system recovers, if
at all. SALTEx is complemented by other
work in the GCE LTER that examines
ecosystems at the landscape scale, such
as tracking vegetation productivity and
community changes along the Altamaha
River annually and relating these changes
to salinity and other factors. We also have
a long-term monitoring site at a healthy
tidal freshwater forest to detect any possi-
ble saltwater intrusion in its early stages.
We hope that understanding the response
Porewater: Salinity, chloride, sulfate, sulde, dissolved organic C, inorganic and organic forms of N and P
Plant community: Aboveground biomass, photosynthesis, leaf N and P, benthic microalgae
Animal community: Grasshoppers, insects, crabs, snails
Microbial community: Extracellular enzyme activity, diversity
Ecosystem: Net ecosystem exchange, ecosystem respiration, greenhouse gases (CO2, CH4, N2O)
Soils: Bulk density, C, N, and P content, organic matter quality and composition,
soil elevation, temperature
TABLE 1. Measurements to assess the effects of SALTEx treatments on tidal freshwater marsh structure and function.
FIGURE 3. Concentrations of salinity (a) and sulde (b) in SALTEx treatment plots pre-
(January and March 2014) and post-treatment. Means with an asterisk (*) are signicantly
different from other treatments within the same month.
Wetland Science & Practice September 2016 73
of marshes and forests to salinization will
inform adaptive management strategies of
coastal communities. Stay tuned.
The Georgia Coastal Ecosystems Long
Term Ecological Research site was estab-
lished in 2000 by the National Science
Foundation. It encompasses three adjacent
sounds, the Altamaha, Doboy, and Sapelo,
that vary in freshwater input, and includes
upland, intertidal, and subtidal habitat. The
overarching goal of the GCE LTER is to
understand how variation in source and
amount of freshwater and seawater struc-
ture estuarine habitats and processes and
to identify and predict changes that occur
in response to natural and anthropogenic
perturbations. More than 60 participants
representing 14 academic institutions
and agencies are involved in GCE LTER
research and education programs. The eld
site is based at the University of Georgia
Marine Institute on Sapelo Island and is ad-
ministered by the University of Georgia De-
partment of Marine Sciences. Christopher
Craft is a founding member of the GCE
LTER and serves on its executive commit-
tee ( n
The Wetlands Lab investigates the effects of human
activities such as eutrophication, urbanization, and
climate change on freshwater and estuarine wetlands
and the ecosystem services they support, as well as
how restoration can be employed to re-establish these
services. The Lab actively supports graduate and
undergraduate research, education, and service (http://
Tiner, R.W. 2013. Tidal Wetlands Primer: An Intro-
duction to their Ecology, Natural History, Status, and
Conservation. University of Massachusetts Press,
Amherst, MA.
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... However, both passive monitoring and simulation modelling approaches lack the power to confirm specific process thresholds unless paired with a suite of additional field-based studies. A final approach, which is the subject of this study, is experimental manipulation where a set of experimental "treatment" wetland units are exposed to SLR impacts and compared with a set of experimental "controls" (e.g., Cherry, Ramseur, Sparks, & Cebrian, 2015;Craft et al., 2016;Langley, Mozdzer, Shepard, Hagerty, & Patrick Megonigal, 2013;Lee, De Meo, Thomas, Tillett, & Neubauer, 2016, Rasser, 2009Spalding & Hester, 2007). ...
... The exact details surrounding delivery of these saltwater doses will be dependent on the layout and location of each study site. For example, saltwater additions in the experimental manipulations by Craft et al. (2016) were directly pumped from an adjacent tidal inlet. Given that such a setup is not feasible in all situations, we developed a method to deliver portable salt doses irrespective of nearby saltwater sources. ...
... During these periods we added a standard salt dose volume in proportion to an estimate of sediment pore space volume (soil porosity). In fact, the study by Craft et al. (2016) adopted a similar approach in a location subject to daily tidal cycles when they added salt doses only during low tide to facilitate infiltration. ...
Full-text available
The impact of sea level rise (SLR) on coastal wetlands is dependent on the net effects of increased inundation and saltwater intrusion. The need for accurate projections of SLR impacts has motivated several experimental mesocosm studies aimed at detailed investigations on wetland biogeochemical cycling. However, the degree with which they accurately reproduce field conditions remains unknown because they have primarily been laboratory based using relatively small sediment volumes (10–200 L) treated over short time periods. As a first step towards addressing these issues, we present a novel mesocosm device and portable methodology for long-term SLR simulation via in situ saltwater additions to relatively large sediment volumes (approximately 1,000 L). The device (chamber) consists of two interlocking polycarbonate cylinders with an internal diameter of 1.4 m. Each cylinder has holes drilled in the side to facilitate water exchange. The outer cylinder (collar) can be rotated to one of two possible positions. The first position produces alignment of the inner cylinder holes with the collar holes, whereas the second position offsets the holes to eliminate water exchange and contain salt additions (doses). Our device design and dosing scheme produced higher porewater salinities in the sediments of treatment mesocosms relative to control mesocosm sediments. In addition, we observed low incidence of elevated porewater salinity outside of the chamber walls and no measurable salt contamination of control plots. Widespread SLR simulations in a variety of geographical settings, whether with our proposed design or some other design, would likely help reduce some of the general uncertainties regarding the sensitivity of coastal wetlands to SLR and saltwater intrusion. © 2018 The Authors. Methods in Ecology and Evolution
... Habitat degradation and decreases in coastal wet- lands extent are expected in some locations due to erosion (wave action associated with higher sea levels) and saltwater inundation and intrusion (Michener et al. 1997;Scavia et al. 2002;FitzGerald et al. 2006;USEPA 2011a, b;Jun et al. 2013;Wieski and Pennings 2014;Craft et al. 2016;Thorne et al. 2018). Increased salinity is likely to increase organic matter mineralization and decrease productivity, which can alter the balance between marsh erosion and accre- tion, as well as the quality of the habitat. ...
Full-text available
Anticipated future increases in air temperature and regionally variable changes in precipitation will have direct and cascading effects on United States (U.S.) water quality. In this paper, and a companion paper by Coffey et al., we review technical literature addressing the responses of different water quality attributes to historical and potential future changes in air temperature and precipitation. The goal is to document how different attributes of water quality are sensitive to these drivers, to characterize future risk to inform management responses, and to identify research needs to fill gaps in our understanding. Here we focus on potential changes in streamflow, water temperature, and salt water intrusion (SWI). Projected changes in the volume and timing of streamflow vary regionally, with general increases in northern and eastern regions of the U.S., and decreases in the southern Plains, interior Southwest, and parts of the Southeast. Water temperatures have increased throughout the U.S. and are expected to continue to increase in the future, with the greatest changes in locations where high summer air temperatures occur together with low streamflow volumes. In coastal areas, especially the mid‐Atlantic and Gulf coasts, SWI to rivers and aquifers could be exacerbated by sea level rise, storm surges, and altered freshwater runoff. Management responses for reducing risks to water quality should consider strategies and practices robust to a range of potential future conditions.
Transport of foraminiferal propagules is an important mode of dispersal in benthic foraminifera. Known to occur from tidal marshes and estuaries to deep-water environments, the former are particularly vulnerable to ongoing climate change. Because rising sea levels can have profound implications on local salinity and associated faunal compositions, transport of foraminiferal propagules within these environments can be crucial for local assemblages to respond to changing conditions. Here we focus on a shallow-water environment in southeastern Georgia to evaluate whether propagule transport occurs evenly or whether it shows a predominant direction, such as land- or seaward. Two sites were sampled in the Doboy Sound area: the southern tip of Sapelo Island and a site on the North River located approximately 10 km inland. We applied the propagule method using the fine fraction of the sediments that contains the propagule bank. Experimental conditions in the laboratory included three temperatures (18, 24 and 30°C) and three salinities (15, 25 and 35) to simulate a range of environments that might trigger the growth of various foraminiferal species. While adult in situ assemblages of both sites were at least partly influenced by the adjacent salt marshes, experimentally grown assemblages were dominated by mudflat, estuarine or more open marine species. Thus, propagule transport from the more terrestrial side of the assemblage gradient is limited, while propagules of more marine species can be transported far into the extensive estuarine system of the study area, where they can remain viable within the local propagule banks. Results provide important insights into possible changes in foraminiferal assemblages with rising sea-level on the Georgia coast.
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