Anthony Campbell
NRS534: Fragmented Landscapes
May 2, 2017
The Changing Salt Marsh Landscape
Wetlands have been in long-term decline across the Continental United States (CONUS). Salt
marshes in particular have continued to decline since wetlands garnered federal protection under the
Clean Water Act. These losses are driven in part by urbanization of the coastal zone and resulting
indirect stressors. The inclusion of wetlands in the Clean Water Act marked a paradigm shift in the
management of wetland environments, however the required mitigation is not always enforced leading
to wetland loss (Kelly, 2001). This paper seeks to explore the use of landscape ecology to understand
salt marsh landscape pattern and the dynamics of change. Salt marshes like most ecosystems are
adapted to natural disturbances such as hurricanes and sea level fluctuation. It is important to
understand these natural changes as well as human influenced change due to invasive species such as
the Common reed (Phragmites australis) or loss of predation causing increased herbivory from species
such as Sesarma reticulatum (Holdredge, Bertness & Altieri, 2008). Regional sea level rise is also a major
concern with some areas experiencing greater regional sea level rise such as the Gulf of Mexico due to
gas extraction or the Chesapeake with subsidence, a residual effect of the Laurentide glacier. Hydrology
and elevation are two major factors in determining salt marsh pattern. These two aspects of the marsh
will be altered by sea level rise, understanding their role in current patterns can inform our
understanding of future change. To understand change we need suitable metrics and indicators of salt
marsh function. This paper seeks to understand our knowledge of salt marsh pattern, functional
indicators, and salt marsh change.
The first section of this paper will explore the salt marsh landscape pattern and how it is
impacted by channel type and proximity (Sanderson, Ustin & Foin, 2000), geochemistry of the
porewater (Moffett & Gorelick, 2016), the impact of scale on functional indicators (Kelly, Tuxen &
Stralberg, 2011), and the role of elevation on vegetation zonation (Zedler et al., 1999). Often it is not
feasible to collect a data including elevation, porewater, vegetation, and aerial imagery which makes it
important for studies measuring salt marsh change to have salt marsh landscape attributes and
indicators that relate to vegetation pattern. Functional indicators can be used to understand changes
and the impact of those changes. Studies utilize a variety of indicators including species composition
(Griffen, Theodose, & Dionne, 2011), areas of salt marsh die-off in relation to channels (Schepers et al.,
2017), and hydric soils and urbanization of the surrounding area (Wigand et al., 2004). The final section
will discuss the important role salt marshes play as habitat for species including disturbance impact on
rabbits (Schmidt et al., 2011), nekton use as impacted by salt marsh size (Meyer & Posey, 2014), and salt
marsh landscape metrics in relation to a sparrow (Moffet et al., 2014). Salt marsh are an important
ecosystem under extensive pressure from human derived stressors. Landscape ecology offers important
methods for both increasing our understanding of salt marsh composition and using salt marsh
composition to understand change.
Salt marshes are often thought to be determined by physical factors such as elevation and the
resulting inundation regime. Several of the papers explored indicators of salt marsh pattern. Species
richness was found to be greater within 10 m of a channel, and mosquito ditches did not share this
greater diversity (Sanderson, Ustin & Foin, 2000). This was especially interesting as you would think
mosquito ditches after being on the landscape for >50 years would serve a similar function to natural
channels. In addition to salt marsh channels having greater species richness, another study found that
on the West Coast low marsh was not a uniform community (Zedler et al., 1999). The lack of a
vegetation community was counter to the theoretical view of these salt marshes complicated by a lack
of California cordgrass (S. foliosa) in areas of low elevation (Zedler et al., 1999). However, these low
elevation areas were further from the bay and could have an atypical inundation regime compared to
low marsh/cordgrass habitat. The vegetation zonation could be further complicated by the invasion of
smooth cordgrass (Spartina alterniflora) which frequently replaces S. foliosa, but was not a large
component of the study. Analysis of these salt marshes currently and the impact of S. alterniflora
invasion and hybridization with S. foliosa would be interesting. The impact of invasive species on salt
marshes can be large such as in China’s prograding coast where S. alterniflora has colonized low
elevation areas leading to increases in gross primary production (Sun et al., 2016) and a loss of native
species. Further analysis of the role of invasive species in causing and being impacted by change is
needed.
The geochemistry of salt marsh vegetation plots sampled in 6 cm increments of depth was
found to be significantly different between many of the California salt marsh vegetation species (Moffett
& Gorelick, 2016). The ability to determine vegetation based on trace metals was partly due to
differences in the hydrology of certain species i.e. depth of reducing conditions and when these were
similar the differences were harder to determine (Moffett & Gorelick, 2016). The study additionally
found a limited impact of channel proximity on geochemistry (Moffett & Gorelick, 2016). The vegetation
type was a more important attribute than channel proximity, making these measures possibly
independent of channel proximity which found greater species richness in the other studies. The soil
geochemistry ultimately a more complex way to understand salt marsh zonation than using elevation,
however it does give a rich dataset. The salt marsh pattern especially on the West coast is complex, and
many of these analyses are important to be done regionally to understand differences in salt marsh
zonation with consideration towards invasive species and their impact on salt marshes.
Disturbance is an important aspect of salt marsh ecosystems both storm events and human
impacts. There is evidence that even following regulation requiring mitigation of wetlands, there
continues to be significant losses at permitted sites (Kelly, 2001). These finding were particularly
disturbing as no mitigation was required at the majority of these sites (Kelly, 2001). There is a possibility
that changes were being driven by other stressors, which is an important component of understanding
salt marsh change. Building on this study would be interesting to see how enforcement and mitigation
of wetlands has improved. Understanding salt marsh change in relation to climate change and sea level
rise is a particularly important research field. The possibility that species richness, particularly forb
richness, can be determined by location attributes such as proximity to upland, channel and panne area.
Demonstrating the types of data that can be gleaned from landscape indicators related to elevation and
hydrology without directly sampling either one (Griffin, Theodose & Dionne, 2011). Determining past
salt marsh change has been proposed as a way to better understand the spatial variation of the salt
marsh (Schepers et al., 2017). A major consideration with salt marshes is the role of nitrogen in these
systems. Studies exploring the role that surrounding urban areas and hydric soils have on salt marsh
nitrogen load was novel but ultimately found seasonal variation to be a larger determinate (Wigand et
al.,2004). This analysis could inform development in land surrounding salt marshes to limit the negative
impact to estuaries from nitrogen. Salt marshes are changing and there are many indicators of these
changes such as species richness, expansion of non-vegetated mudflat, and open water in the salt marsh
interior.
Salt marshes are an important habitat for a large number of species and commonly heralded for
their high biodiversity. Nekton are often labor intensive to measure and study and many of these
species spawn in salt marshes. Comparing three marsh types including small island marsh, large island
marsh and expansive fringe marsh found greater nekton density in the expansive fringe marsh and low
numbers of larva and juveniles in the small island marsh (Meyer & Posey, 2014). The study makes clear a
functional difference in salt marsh size for certain nekton species spawning use. Exploring additional
differences such as landscape composition between these salt marshes would have been a good way to
further understand what nekton need from salt marsh habitat. The role disturbance plays in
combination with salt marsh species was explored for the lower key marsh rabbit, finding that rabbit
occurrence was most impacted by the storm event in freshwater wetland areas (Schmidt et al., 2011).
This makes sense given the greater impact of hurricanes on freshwater wetlands. Remote sensing was
used to quantify salt marsh metrics and their impact on sparrow occurrence, of the 31 analyzed patch
metrics Mean Core Area Index and Patch Core Area Coefficient of Variation were found to be
significantly related to sparrow occurrence (Moffett et al., 2014). Several choices when calculating
metrics were noteworthy such as excluding all upland from metrics, 50 m buffers, and comparing salt
marshes by general age. The study’s approach would be interesting to apply to other species and
regions. The importance of scale and MMU and the impact these can have on salt marsh metrics was
explored showing that large MMU and scale altered many metrics significantly (Kelly, Tuxen & Stralberg,
2011). The importance of using appropriate scale/MMU or even multiple scales might be one of the
reasons many studies favor landscape attributes instead of compositional metrics. Salt marshes are
important habitat and a variety of characteristics including patch size, salinity, proximity to salt marsh,
and total marsh size can all be important when understanding species use and occurrence.
Coastal urbanization continues to drive stressors on salt marshes across the CONUS,
understanding salt marsh change can provide an understanding of these stressors. Landscape ecology is
an important method for understanding salt marsh losses driven by urbanization and other disturbance.
The pattern of salt marsh vegetation is an important component of understanding salt marsh baselines,
habitat recovery, ecosystem function, and change. Salt marshes provide critical habitat for many species
this role can be impacted by disturbance (Schmidt et al., 2011), salt marsh size and type (Meyer & Posey,
2014), and even the patch characteristics (Moffett et al., 2014). The composition of salt marshes is
determined by small variations in topography and hydrology resulting in a complex pattern of
vegetation, however these physical characteristics might be less important in the face of other human
induced changes (Holdredge, Bertness & Altieri, 2008). Landscape ecology provides a more nuanced
understanding of salt marsh pattern with landscape indicators providing important insight into the
change experienced by these ecosystems.
Annotated Bibliography:
Griffin, P.J., Theodose, T. & Dionne, M. 2011, "Landscape patterns of forb pannes across a
northern New England salt marsh", Wetlands, vol. 31, no. 1, pp. 25-33.
The articles premise was how perennial forb patches respond to landscape variables. The
spatial pattern of forb pannes is proposed as a way to track larger salt marsh change in Maine or
other northern areas where these landscapes occur. Forb pannes have been shown to respond to
warming with colonization by S. patens. Shannon diversity index and the Evar index were used
to quantify species richness in each panne. They were evaluated as early indicator of change. The
species variables were tested with regression using geospatial variables too. Connections
between individual species and geospatial variables such as proximity to upland, creek edge, and
panne area. The article did not mention spatial autocorrelation which I would think should have
been tested for. The idea that these geospatial variables indicate the underlying
hydrogeomorphological processes determining forb pannes is interesting. Further study to
determine if this land cover type would indeed be an early indicator of salt marsh response to
warming will be interesting. The clustering along river edge and pools is especially interesting in
light of many other studies in this literature review demonstrating greater species richness along
channels. These communities within the marsh are very different than many other salt marsh
communities and need to be understood. How these areas are being determined by elevation
might give another element to future studies of the communities, especially given previous
research they cite which describes forbs in relation to elevated areas around pools.
Meyer, D.L. & Posey, M.H. 2014, "Influence of salt marsh size and landscape setting on salt
marsh nekton populations", Estuaries and coasts, vol. 37, no. 3, pp. 548-560.
The study explored an often difficult to quantify aspect of salt marshes. The study could
have been additionally interesting if they quantified more of the differences between the three
salt marshes examined. The basic question of this study was how salt marsh landscapes impact
nekton populations in the immediate vicinity do. This study looked at the impact of salt marsh
type and landscape on nekton populations, the salt marshes were split into three broad types
including small island marshes, large island marshes and expansive fringe marshes. The study
was interesting as it is focused on behavioral landscape ecology. The many marsh variables
examined were interesting but lacked structural and composition attributes of the salt marsh. The
variables such as mean distance to salt marsh were informative. The study found that expansive
fringe marsh had higher densities of the two nekton species analyzed in several months and years
when compared with both small and large island marshes. The study had rich temporal
measurements of nekton presence, however no exploration of salt marsh characteristics besides a
few broad attributes. It would be interesting to see how configuration and other landscape
characteristics differed between the sites. One fascinating aspect of the study was the low
numbers of larva and juveniles found in small island marshes for Fundulus heteroclitus.
Suggesting that the size of the salt marshes is one limiting factor for the spawning activities of
this species.
Sanderson, E.W., Ustin, S.L. & Foin, T.C. 2000, "The influence of tidal channels on the
distribution of salt marsh plant species in Petaluma Marsh, CA, USA", Plant
Ecology, vol. 146, no. 1, pp. 2941.
The article used vegetation transects to understand geospatial characteristics of the salt
marsh vegetation. It would have been interesting if they expand on the analysis by classifying
and quantifying how these transect based lessons were reflected on a marsh wide basis. The
study looked at two sites in California salt marshes adjacent to a pond and river. The plot
composition was analyzed in comparison to site, tidal stream order, constructed channel, and put
into a cluster analysis. The differences found between constructed (mosquito ditches) and natural
channels in the salt marsh, surprising given how long many of these ditches have been on the
landscape. The lack of increase between the first 10m and the next 10m away from constructed
channels was no different. This is surprising given how long constructed channels have been on
the landscape, however they may have very different depth, width, and morphology. It makes it
clear the complexity of managing salt marshes whether for mitigation or other purposes it is
often very hard to replicate these systems due to the small variations in a channel increasing
species richness and not. Constructed channels had little distance to the “background” vegetation
or non-salt marsh vegetation and low species diversity. Channel were shown to increase species
richness with an additional 1.6 species within 10 m of a channel, this include all channel sizes.
Channels as a conduit for species richness is interesting and has a downside which has been
shown in other studies with invasions such as Phragmites spreading via constructed channels.
The study demonstrates the importance of tidal channels, and is certainly an important lens
through which to examine salt marsh.
Schmidt, P.M., McCleery, R.A., Lopez, R.R., Silvy, N.J., Schmidt, J.A. & Perry, N.D. 2011,
"Influence of patch, habitat, and landscape characteristics on patterns of Lower Keys
marsh rabbit occurrence following Hurricane Wilma", Landscape Ecology, vol. 26, no.
10, pp. 1419-1431.
This article interested me as it is a combination of behavioral ecology, disturbance, and
landscape ecology. They studied Hurricane Wilma in 2005 and the impact of habitat use of the
marsh rabbit. The analysis used Hawth’s Analysis Tools (ArcGIS extension) calculated patch
size and distance between patches with occurrence pre and post storm. Patches were surveyed
three times and then rabbit occurrence was determined. Seems like radio telemetry might have
been a better way to analysis the occurrence and use. The study saw patch abandonment Post
Hurricane which did not entirely recover in surveys two years following the disturbance. The
conclusion that patch abandonment mostly occurred in freshwater wetland patches is interesting
but not surprising given the impact salt water intrusion can have on these environments. The
paper could have discussed in additional detail the fragmentation of the various salt marsh
islands or even shown a change map to make this data clearer.
Zedler, J.B., Callaway, J.C., Desmond, J.S., Vivian-Smith, G., Williams, G.D., Sullivan, G.,
Brewster, A.E. and Bradshaw, B.K., 1999. Californian salt-marsh vegetation: an
improved model of spatial pattern. Ecosystems, 2(1), pp.19-35.
The paper uses extensive elevation and vegetation measurements across two west coast
salt marshes in Mexico and California to critique established elevation based zonation. The study
looks at both the relationship of elevation to vegetation in the salt marsh and distance to the bay
and channels. The paper was an interesting exploration of structural terminology, and I found the
lack of clustering in the vegetation types in the salt marsh plain more interesting. The conclusion
that low marsh should be referred to as cordgrass habitat was informative. The terminology was
deemed important due to the burgeoning interest in restoration. The other interesting finding was
the need to include many channels during restoration. The finding that elevation alone does not
determine the habitat range of S. foliosa. This makes sense given that elevation in conjunction
with tidal inundation are major drivers of plant communities in the salt marsh. The articles
extensive measurements of both elevation and vegetation type led to an added understanding of
the salt marsh landscape. However, these types of measurements are not always possible for
understanding a salt marsh so indicators i.e. species communities and standardized zonation’s are
important.
Schepers, L., Kirwan, M., Guntenspergen, G. & Temmerman, S. 2017, "Spatio
‐temporal
development of vegetation die
‐off
Limnology
in a submerging
and
coastal marsh"
Oceanography, vol. 62, no. 1, pp. 137-150.
A study looking at salt marsh die-off in the Chesapeake Bay, in particular how to salt
marsh pools related to channels across time and space. The idea to quantify the salt marsh
landscape to understand the pattern of change in space and time and how they relate is an
interesting one. The study site has lost 51% of salt marsh vegetation to open water but much of
this open water is in the interior of the salt marsh. Examining pattern to get a greater
understanding of the processes dictating the interior loss of salt marsh vegetation is the papers
major goal. The finding that die-off started in area’s over 75 m from a main channel is interesting
and could be explained by a combination of little sediment deposition and sea level rise. They
propose a similarity between long-term die-off from 1930s to now and the spatial gradient from a
channel back into a salt marsh. They propose a further time-space substitution to study landscape
change. The idea is interesting and I am curious to see how they implement it and what results it
furnishes in the future.
Moffett, K.B. and Gorelick, S.M., 2016. Relating salt marsh pore water geochemistry patterns to
vegetation zones and hydrologic influences. Water Resources Research, 52(3), pp.17291745.
An interesting paper with dense results leading to complex figures that are not the
clearest. The paper use porewater sampling as a method to understand both vegetation and
hydrological pattern in the salt marsh environment. Porewater pattern in the salt marsh is
interesting as it is impacted by both the vegetation and hydrology of the sampling sites. The
sampling was done in five salt marsh zones both perpendicular and parallel to salt marsh
channels, to understand the impact of hydrology and vegetation. The sampling was done at 6 cm
increments from 8 to 44 cm depths in the soil and then these were tested for trace metals, the
surface water during flood and ebb tides were also sampled. The impact of trace metals is
interesting as I have not heard of them as an indicator of salt marsh pattern before especially
given that sodium was not analyzed. Differences between flood/ebb tides make sense as these are
coming from very different sources. The geochemistry profiles were very unique for some
vegetation and were very similar for Spartina alternfilora and Distichlis spicata. This was an
interesting result and perhaps explained by the similarity in the depth of the oxic zone between
the two vegetation types. The geochemistry and sampling at 6 cm increments from 8 cm to 44
led to being able to determine the start of the anoxic zone in each sampling location by the Fe
content, I found this an interesting method though time consuming method for determining the
division. I also wonder how different these results would be in a salt marsh with much less clay
content, as the study site had 61% clay. Paper raises many continuing questions such as the
impact of the winter season on these characteristics, and sets up many more studies on the topic.
The finding that proximity to the creek bank had limited impact, could also be impacted by the
clay content limiting drainage.
Kelly, N.M. 2001, "Changes to the landscape pattern of coastal North Carolina wetlands under
the Clean Water Act, 1984–1992", Landscape Ecology, vol. 16, no. 1, pp. 3-16.
This study immediately intrigued me with the unique premise of combining permit
analysis, policy critique, and landscape analysis. The study combined permits applied for with
USACE for wetland alteration with how these permitting actions and the resulting alterations
impacted the surrounding wetlands both from mitigation and alteration. The study looks at
structural loss of wetland habitat, which they suggest may in the future be linked with functional
loss. The concept that the landscape structure may be linked to functional processes of the
wetlands is interesting and something to look for in the literature following this somewhat early
paper. The permit record and C-CAP were used to quantify salt marsh change both usedd
Cowardins 1979 classification methodology which facilitated the comparison. Though I wonder
how a higher resolution and thematically specific classification would impact the comparison.
The anniversary dates of imagery had 46 cm of tidal difference which may have impacted
change between dates to a degree. The study did not use ancillary data such as available aerial
imagery, to more closely follow the C-CAP protocol which seems like an unnecessary
precaution. The study period had only 109 permits of which 27 were granted to alter emergent
estuarine wetlands and had area estimates. The study found a loss of 20.23 ha in the permit
record and 151.76 ha in the remote sensing image, which seems low for an 8-year study period.
However, given its only loss within buffers of the permit site it makes sense. Most lose in the
larger area surrounding the mitigation site makes it possible that other sources of change are
being included in the analysis. Salt marshes in many places continue to decline after reclamation
was curtailed by section 404 of the clean water act. To me it seems entirely possible these losses
were from other activity than the construction. The paper mentions signature landscape curves
and Figure 5 explains them as just area of wetlands as you get further from the permit site. The
papers conclusion that wetland management should utilize more GIS and remote sensing, has
been met since this paper was written which is encouraging. The conclusion to include potential
impacts to the surrounding area when permitting would be good. The lack of a mention of
possible other stressors that could be altering salt marsh during the study period was an
oversight.
Moffett, K.B., Law, J., Gorelick, S.M., Nur, N. & Wood, J.K. 2014, "Alameda song sparrow
abundance related to salt marsh vegetation patch size and shape metrics quantified from
remote sensing imagery", San Francisco Estuary and Watershed Science, vol. 12, no. 3.
I enjoyed this paper as it was written in an interesting and accessible way, however it was
a little landscape metric heavy. This paper is a study which looks at bird occurrence in relation to
landscape metrics including patch size, configuration, compactness, and degree of dissection.
The species of interest was M. m. pusillula a bird that occurs in west coast tidally influenced salt
marshes and has been linked with many landscape and site characteristics including salinity,
channelization, and tall bulrush. The study seeks to test configuration of the salt marsh and its
impact on the song sparrow, a gap left by previous research which included the surrounding
landscape and few metrics. I understand using a wider array of metrics although the class
textbook warned against throwing the kitchen sink at a study. Additionally, removing the
surrounding landscape seems peculiar as these areas could influence salt marsh composition and
bird occurrence. Aerial imagery acquired was RGB and in the winter time, which may have less
of an impact on the west coast salt marsh, but phenology would be expected to play a large role
in what species are mapped during that time frame. Classification process seems very labor
intensive with reclassification of water from varying vegetation patches, most likely due to the
use of RGB imagery. The 50 m buffer around point count stations were clipped to the salt marsh
boundaries, this seems to be reason enough to include areas outside the salt marsh in the
landscape quantification. The study calculated 31 metrics which overlap significantly in what
types of attributes are being measured, however these were subset based on correlation. Though
if you wanted to subset based on variables with low correlation why not include even more
metrics? The study idea to test the salt marshes configuration, in contrast to studies testing the
salt marsh as an entire patch. However multiple approaches could be taken, including larger
buffers and quantify entire salt marsh landscape metrics to compare between the 10 salt marshes.
The study presents “salt and pepper” effect as a limitation i.e. single pixels of one class
surrounding by another due to pixel based classification. This could have been minimized, as the
article suggests by utilizing object-based classification which would have been a good way to
conduct the study. I think the study lacked a robust comparison between the three salt marsh age
categories of ancient, centennial and restored. I would be particularly interested in how these
three sites varied in song sparrow occurrence and even salt marsh metrics.
Kelly, M., Tuxen, K.A. and Stralberg, D., 2011. Mapping changes to vegetation pattern in a
restoring wetland: Finding pattern metrics that are consistent across spatial scale and
time. Ecological Indicators, 11(2), pp.263-273.
The research wanted to examine metrics in relation to both time and scale, to find a
robust metric. Previous research showed edge to be a metric very influenced by changes to scale.
They proprose the use of MMU to measure the impact of scale, however this seems like in most
studies a difficult thing to change, they accomplish it with filters. The site being a restoration site
is particularly interesting, the site went from 0 % vegetated to vegetated in a 10-year period. The
study states that though imagery was acquired at drastically different tides, low to mid/high tide
there was no concern of the impact on vegetation classification. This should have been shown
through some analysis. The minimum mapping unit analysis is exhaustive with a huge range
amounting to over a hundred images with eleven metrics for each image calculated. Three types
of responses linear, stair-stepped, and erratic, the authors point out these behaviors shifted across
scales. The majority of metrics seem to be relatively stable in small grain sizes and across MMU.
The only exceptions were the extreme MMU of 100, 200, 500 times the grain size, which are
unlikely to be used in a study. They found that metrics were less impacted by grain size than
MMU, which is not surprising given the large range of MMU used compared to only 20x grain
size. The recommendation of a multiscale analysis for restoration in particular is a good
approach to determining real change in the restoration site. I do wish this paper spent more time
discussing the restoration, or even comparing with a natural salt marsh site. I do feel that a multiscale approach may not always be feasible. I am additionally interested in how object-based
classification methods would influence landscape metrics, especially given the quantitative
methods available to determine an appropriate scale for those methodologies.
Sun, C., Liu, Y., Zhao, S., Li, H. & Sun, J. 2016, "Saltmarshes Response to Human Activities on
a Prograding Coast Revealed by a Dual-Scale Time-Series Strategy", Estuaries and
Coasts, pp. 1-18.
The paper is incredibly dense with formulas and in depth discussion of the methodologies
used to compare flux towers with both Landsat and MODIS data. These aspects do give way to
an interesting discussion about the differences between native and exotic salt marsh vegetation
GPP. The paper focuses on GPP of salt marsh vegetation in the prograding coast of China around
the Yangtze River outlet. It is always interesting to read about our native plants as invasive
species across the world. EC towers for the measurement of GPP is something I have not heard
of and is very interesting. They show good agreement between LAI and NDVI for the salt marsh
sites, this agrees with other research on the matter. The papers maps display GPP for four years
across the study period, though they mask land outside the study scope which curtails the visual
appeal of the maps. The study demonstrates the GPP increased significantly due to the S.
alterniflora invasion, this is not surprising given that the vegetation rapidly colonizes the
prograding areas. I do wonder what sort of impact Phragmites australis, in New England has on
GPP of our salt marshes. Their assessment of the technique was again rather dense, though they
do discuss important life history traits that may not be entirely included in the study. The
limitations of coarse resolution satellite imagery make sense as they are trying to understand a
heterogenous landscape with significant vegetation change across a 500-m pixel. I would be
interested in see a similar method conducted for very high resolution remote sensing data.
Wigand, C., McKinney, R.A., Chintala, M.M., Charpentier, M.A. & Groffman, P.M. 2004,
"Denitrification enzyme activity of fringe salt marshes in New England (USA)", Journal
of environmental quality, vol. 33, no. 3, pp. 1144-1151.
One important ecosystem service of salt marshes is there denitrification. This study
examines salt marshes within Narragansett bay to understand if the relationship between nitrogen
load and DEA (Denitrification Enzyme Activity). The study also examined the landscape and
urbanization within 200km buffers surrounding the salt marsh to understand both hydric soil as a
potential sink and land use as a source. The inclusion of hydric soils in the analysis is an
interesting element of understanding salt marsh denitrification. The manipulative study adding
Nitrogen and Phosphorous to the DEA analysis is interesting in showing that these systems in RI
are nitrogen limited, as the nitrogen amendments had significantly greater DEA than both
phosphorous amendments and controls. The lack of significance in DEA to % hydric and
residential land use seems to suggest other seasonal variations such as precipitation was shown to
have more of a role in driving DEA. The study is an interesting look at using landscape attribute
to understand geochemistry of the salt marsh environment.
Holdredge, C., Bertness, M.D. and Altieri, A.H., 2009. Role of Crab Herbivory in Die
New England Salt Marshes. Conservation Biology, 23(3), pp.672-679.
‐Off of
The study examined the impact of Sesarma reticulatum on S. alterniflora die-off through
several experiments including limiting crab access to salt marsh and examining historic aerial
imagery. Similar to the manipulative study in the Wigand et al., paper this study uses the in situ
experiment to better understand an important aspect of the ecosystem. The study is particularly
interesting as it shows that in some salt marshes herbivory can be the driving force in altering the
pattern and causing salt marsh die-off. They state that previous ideas of elevation and inundation
determining salt marsh pattern are less important as human induced change is the overarching
driver of change now. The differences between landscape factors between those salt marshes
with herbivory from Sesarma and those without could have been any interesting addition to the
study. That time of linkage could provide a way to determine the cause of losses through aerial
imagery or other means. The study is perhaps the least landscape ecology based of those
explored in the literature review, but does demonstrate any interesting aspect of the salt marsh
environment.