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Article

Geomorphic Comparison of Three Globally Significant Wetland Landscapes

by
Jessica Sullivan
1,*,
Michael Foster
1,
James Chassereau
2 and
Robert Sullivan, Jr.
3
1
Department of Biological, Environmental and Earth Sciences, University of South Carolina Aiken, Aiken, SC 29803, USA
2
Savannah River Site Biomass Facility-Ameresco, Aiken, SC 29831, USA
3
Aiken County Sheriffs Office, Aiken, SC 29801, USA
*
Author to whom correspondence should be addressed.
Environments 2025, 12(12), 458; https://doi.org/10.3390/environments12120458
Submission received: 17 September 2025 / Revised: 19 November 2025 / Accepted: 25 November 2025 / Published: 26 November 2025
(This article belongs to the Special Issue Monitoring and Assessment of Environmental Quality in Coastal Ecosystems, 4th Edition)
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Abstract

Salt marshes are dynamic coastal environments that play a critical role in sediment transport, nutrient cycling, and carbon sequestration. However, the geomorphic factors that influence water flow and material exchange in and between marshes of different size, shape and type remain poorly understood. In this study, we compare the morphology of three distinct marsh landscapes within the ACE Basin, South Carolina: a natural salt marsh (Ethan’s Island), a reclaimed agricultural marsh (Alligator Marsh), and a natural marsh at the upland forest interface (Hannah’s Marsh). Using high-resolution digital elevation models and estimates for drainage density and drainage efficiency, we quantify the similarities and differences in morphology between the different marsh types, and discuss potential implications of our findings in regard to water flow and material exchange. We found that drainage density and drainage efficiency are not always positively correlated and, importantly, the agricultural marsh displays the highest drainage efficiency, despite a drainage density that is comparable to the natural marshes. This finding reveals that the unique linear, interconnected structure of creek networks in the agricultural marsh yields higher efficiency. Further, we found that the natural marsh with the most complex, meandering and fragmented creek networks displayed the lowest drainage efficiency, despite having the highest drainage density. Together, these findings suggest that both drainage density and drainage efficiency should be considered separately, and that drainage efficiency is largely influenced by the structure and spatial arrangement of creek networks with a marsh. Given the relatively higher drainage efficiency of the ag-marsh landscapes, we speculate that such landscapes may enhance the flow of water and sediment between inland areas and the coastal ocean, a process that can help marshes migrate landward as sea levels rise.

1. Introduction

Salt marshes remain the focus of intensive study due to their ecosystem functions and, more recently, in response to the unknown effects of sea-level rise on their overall stability [1,2]. Salt marshes function as intertidal floodplains, storing water and sediment with each tidal cycle or storm event [1,2,3]. Typically, these low-relief landscapes serve as depositional environments for marine and terrestrial sediments, with complex overmarsh currents producing variable patterns of suspended and dissolved material exchange with the sedimentary surface [4,5,6,7,8,9,10]. Salt marshes are highly productive with a net primary production that ranges from 650 to 3700 g dry biomass m−2yr−1 [11,12] and are important nursery habitats for economically important fisheries [13,14,15,16]. They also help protect terrestrial lowlands from erosive tidal and wave energy [1,3,17] and have a high capacity for carbon storage and sequestration [18,19,20,21,22,23,24,25,26]. As such, the restoration, enhancement, and conservation of coastal marshes are becoming increasingly important [27].
The ecosystem services provided by marsh environments are sustained by process-form feedback that operates within the context of a complex geomorphic setting [28,29,30,31,32,33,34]. For instance, a study recently combined field observations and numerical modeling to show that current directions and speed vary substantially over relatively short time and space scales, and that this flow complexity arises from the submergence and emergence of subtle marsh topography [32,35]. Additionally, Lidar-based analyses have highlighted how microtopographic variations shape sediment deposition patterns, underscoring the need for precise geomorphic knowledge [36]. To accurately assess the function, structure and overall stability of marshes, we must deepen our understanding of the geomorphic controls on flow and sedimentation within and between marsh systems, and with adjacent upland regions. This is important because such interactions influence spatial and temporal aspects of marsh migration in response to sea level rise [37,38]. Recent studies have emphasized that the ability of marsh landscapes to migrate inland is a first-order determinant of their overall survival under accelerated sea-level rise, with models incorporating topographic and sediment dynamics showing variable migration success [37,38,39]. Nevertheless, there remains a paucity of robust data to characterize the geomorphic factors that influence inland marsh migration and, consequently, this process is not fully accounted for in predictive models which tend to overestimate marsh vulnerability to sea-level rise [37,40,41].
One reason for our poor constraint on overall marsh stability is that studies of inland marsh expansion are largely limited to forests, shrub land [42] and residential areas [43], although agricultural fields are abundant features of coastal plain landscapes worldwide and are more exposed to projected sea-level rise than other upland regions [44,45]. Furthermore, the low elevation and gentle slope of agricultural lands are likely to increase the potential for landward marsh expansion as waters rise [37,46,47,48,49]. As such, about half of the marsh restoration projects in the southeastern US [50,51], and in other coastal regions worldwide [50,51,52,53,54,55] occurred in areas with an agricultural past. Large-scale wetland restoration projects are also planned for coastal areas of Louisiana and Maryland, where broad expanses of agricultural lands are common [51]. In addition to these engineered “ag-marsh” systems, naturally restored marshes reclaimed by sea-level and land use changes are also common, particularly in the southeastern US.
Despite the rise in ag-marsh landscapes in the last decade, few studies have looked at how the unique morphology of ag-marshes affects water and sediment exchange [35,56]. Artificial drainage infrastructures in the form of ditches, channels and canals are ubiquitous features of ag-marshes, and these features may enhance hydraulic connectivity of water and sediment between terrestrial uplands and the sea [57,58,59,60,61,62,63,64,65,66], and increase inundation extent and frequency within adjacent uplands [63,64,67]. Hence, such marsh types may act as preferential corridors for inland marsh migration as waters rise [68]. Nevertheless, there is a paucity of work to quantify how ag-marsh landscapes compare to natural marsh systems regarding structure and function [69]. In this study, we provide a geomorphic comparison of three ACE Basin marsh sites along a salt marsh—forest continuum that encompasses a natural salt marsh, a reclaimed ag-marsh, and a forest-marsh transition zone. The proposed field sites are located within the Ashepoo, Combahee, and Edisto (ACE) River Basin, SC. We quantitatively compare the geomorphic structure of the marsh sites using drainage density and drainage efficiency as metrics and discuss our findings in the context of marsh structure and function. This work is important because it can help identify and prioritize coastal wetland landscapes that are most capable of facilitating the transfer of water, sediment, and nutrients in and between marsh systems, and between ocean and inland areas [70]. Such information is needed to inform coastal management and policy in the context of natural and anthropogenic change within our coastal margins [71].

2. Description of Study Sites

The study investigates the morphology of three distinct marsh sites located within the Ashepoo, Combahee, and Edisto (ACE) Basin of the southeastern North American coastal plain (Figure 1).
The ACE Basin stands out as one of the largest undeveloped estuaries in the USA, with a drainage area of ~8000 km2 [72]. The basin comprises diverse habitats, including pine and hardwood forests, freshwater, brackish, and saltwater tidal marshes, barrier islands, and beaches, establishing itself as the preeminent estuarine resource in South Carolina [73]. Despite its pristine condition, the ACE Basin has not escaped the impacts of both recent and historical land use practices such as agriculture, silviculture, aquaculture, impoundments, controlled burning, and forestry [74,75]. Agricultural activities in the basin ceased in the late 1800s, allowing natural processes to reclaim many of these landscapes [76,77]. In 1992, the ACE Basin was designated as a National Estuarine Research Reserve (NERR) site by the National Oceanic and Atmospheric Administration to promote long-term research, education, coastal training, and stewardship.
The first field site, Ethan’s Island, is a ~0.15 km2 natural salt marsh located ~10 km inland from the ocean (Figure 1A). The site receives semidiurnal tides along its northern border via a subtidal distributary channel of the South Edisto River. The salt marsh is unrestricted in flow along all other borders. Two primary intertidal creeks traverse the eastern and western perimeters, and each is flanked by natural levees. These natural levees gradually lose their distinctiveness as they extend into the marsh interior (Figure 1A). Discontinuities in the levees create hydraulic links, facilitating the flow of water between the primary intertidal creeks and the marsh platform through secondary intertidal creeks. The salinity fluctuates between 30 and 35 ppt.
The second site is Alligator Marsh, an abandoned rice field marsh that has been “reclaimed” by natural tidal processes for the past ~200 years (Figure 1B). The 0.30 km2 “ag-marsh” is located 17 km from the coastal ocean. The marsh is open to flow along its entire perimeter, and receives diurnal tides via Fishing Creek, a subtidal channel which feeds the system from the east (Figure 1B). Within the study area, Fishing Creek splits into two distributed subtidal channels: one that flows along the eastern boundary of the marsh, and a second that forms the northern and western boundaries of the site. On the marsh platform, artificial drainages in the form of canals, ditches, and dikes incise the landscape. Most of these features are linear, while some form meanders and distributary creeks (Figure 1B). Salinity ranges from 22 to 32 ppt.
The third field site, Hannah’s Marsh, is a 0.03 km2 marsh-forest transition zone, located ~16 km from the ocean and located immediately southwest of Alligator Marsh (Figure 1C). Hannah’s marsh is the smallest of the three sites and is unique in that it shares a direct connection to the ag-marsh landscape, Alligator Marsh, via the main subtidal channel that forms the southeastern edge of the site. The marsh shares its northwestern boundary with a forested upland area, forming a marsh-forest transition zone. Field observations of the site reveal freshwater vegetation die-off, indicating encroachment of the salt marsh into the forested area. The salinity ranges from 22 to 23 ppt.

3. Methods

3.1. Digital Elevation Models

A 2012 lidar point cloud dataset was obtained for Colleton and Charleston Counties, SC, sourced by the South Carolina Department of Natural Resources. The lidar dataset has a vertical accuracy of 0.08 m to 0.11 m root-mean-square error on open and vegetated terrain, with ground returns spaced nominally at 0.7 m. Lidar tiles were projected to NAD 1983 HARN State Plane South Carolina and North American Vertical Datum 1988 for horizontal and vertical projections, respectively. The raw point cloud data was processed to generate a bare-earth Digital Elevation Model (DEM) by first applying the LP360 Adaptive TIN Ground Filter algorithm to the lidar tiles. This tool classifies points as “ground returns” by creating and refining the TIN based on an initial set of ground seed points. It then iteratively adds new points to the TIN that are within a specified angular threshold and maximum distance from the current ground seed points [78,79]. Here, we prescribed an angular threshold of 6 degrees and a threshold distance of 0.1 m above the ground seed points. This meticulous filtering process is essential for removing dense vegetation canopy, which often obscures the true marsh surface [78,79,80]. Then, within the same software, triangulation was applied to generate bare-earth digital elevation models (DEMs) at a resolution of 1 m × 1 m for each of the marsh study sites.

3.2. Creek Network Extraction, Drainage Density and Drainage Efficiency

Elevation histograms were generated for each marsh site to determine the elevation range associated with geomorphic subclasses [32,80,81]. Using Spatial Analyst tools in ESRI ArcGIS version 10.8.2, the DEM surfaces were classified according to the histogram subclasses, and the percentage area of each landcover type was calculated. Creek networks were identified for each DEM using the elevation contour associated with the intertidal creek geomorphic subclass. The accuracy of the channel extraction was evaluated through visual inspection of the DEM and field observations. The length of the intertidal creek contour was then computed and divided by 2 to estimate the total creek length for each marsh site [32,33]. A sinuosity ratio was also computed for each intertidal creek by dividing the actual channel length (ACL) by the straight-line distance (SLD) between the creek mouth and the creek head (Equation (1)).
S = A C L   ( m ) S L D   ( m )
Excluding the area associated with subtidal channels, the drainage density of each marsh site was estimated by dividing the total creek length by the area of the marsh interior [26,56]:
D d = ∑ i n t e r t i d a l   c r e e k   l e n g t h   ( m ) A r e a   o f   M a r s h   I n t e r i o r   ( m 2 )
Drainage efficiency was then estimated using the approach outlined by [82,83,84]. Specifically, the mean unchanneled path length, l, representing the average distance a water particle at a point on the marsh platform travels before reaching a conduit, was estimated [82,83,85]. This was achieved by using the Spatial Analyst Cost-Distance tool to estimate the shortest path from each grid cell of the DEM to the nearest intertidal creek edge, and assuming topographically driven flow. This tool generates a scalar field over the entire marsh area. The mean unchanneled path length is then divided by the inverse of drainage density, or the Hortonian length (Hl, after [82]), to yield a nondimensional metric for drainage efficiency [78]:
D e =   l   ( m ) 1 / D d

4. Results

4.1. Marsh Morphology

The elevation histogram derived from Ethan’s Island DEM shows values ranging from −4.7 m to 1.36 m (Figure 2).
The distribution is unimodal with a peak that is centered on a mode of 0.71 m. The mean elevation for the site is 0.45 ± 1.2 (standard deviation) which is less than the mode, indicating a negative skew. From left to right there are five breaks in the histogram slope which represent the elevation range of different geomorphic subclasses (Figure 2a). Specifically, the lowest elevations are associated with the subtidal channels that flank the study site to the west, north, and east (Figure 3), and extend to 0.09 m.
The subtidal area accounts for 14% of the total site area (Table 1).
The next break in slope marks the transition from subtidal channels to intertidal creeks, which extend to 0.65 m elevation (Figure 2a) and occupy 7% of the marsh area (Table 1). The intertidal creeks at Ethan’s Island are relatively straight with an average sinuosity value of 1.1 ± 0.10 (Table 1) and tend to incise the marsh platform from the eastern and western flanks (Figure 3). However, these fragmented creek networks do not appear to form lateral connections across the marsh interior (Figure 3). Higher up in the tidal framework is the marsh platform, which can be subdivided into low marsh (0.65–0.79 m) and high marsh (0.79–1.1 m) (Figure 2a). The low marsh occupies 20% of the marsh area (Table 1) and forms an apparent trough connecting the heads of individual creek networks (map figure). Most of the site comprises high marsh, which takes up 48% of the total area. The highest elevations range from 1.1 to 1.37 (Figure 2a) and are associated with levees that occupy 11% of the area and tend to border subtidal channels and intertidal creeks (Figure 3).
The elevation distribution for Hannah’s Marsh ranges from −1.5 m to 1.62 m with a mean value of 0.55 ± 0.62 (Figure 2b). The histogram shows a unimodal distribution with a peak centered at a mode of 0.74 m. The lowest elevations occupy 5% of the total area (Table 1) and form the main subtidal channel that borders the marsh to the southeast (Figure 3). Intertidal creeks form between 0.30 m and 0.60 m and occupy 16% of the site (Table 1). The creek features of Hannah’s Marsh form along the subtidal channel to the east (Figure 3) and are more sinuous than those at Ethan’s Island, with an average sinuosity ratio of 1.2 ± 0.15 (Table 1). The low marsh and high marsh platform range from 0.60 to 0.74 m, and 0.74 to 0.95 m, respectively. The low marsh occupies 30% of the site, while the high marsh takes up 39% (Table 1). The highest elevations are associated with levees, which range from 0.95 m to 1.62 m (Figure 2b) and take up 10% of the site area.
Alligator Marsh elevations range from −3.9 to 1.53 m (Figure 2c). The histogram shows a unimodal distribution with a mode of 0.76. The mean elevation is 0.37 m ± 0.99. Two main subtidal channels account for 17% of the study site (Table 1) and surround the marsh site along the northern, western, and eastern borders (Figure 3). Intertidal creeks form between −0.30 m and 0.60 m (Figure 2c) and occupy 8% of the marsh site. As stated earlier in the narrative, the spatial arrangement of intertidal creeks for Alligator Marsh is unique and reflects the agricultural history of the site. Specifically, intertidal creeks incise the marsh interior along predominantly linear paths (average sinuosity value of 1.07 ± 0.03), with an east–west orientation (Figure 3). In most cases, individual creek networks form apparent connections between the two separate subtidal systems flanking the marsh (Figure 3). The low marsh occupies 10% of the marsh site and ranges from 0.60–0.70 m (Figure 2), followed by the high marsh which extends from 0.70 to 0.96 m and occupies 50% of the site (Table 1). Levees form at elevations of 0.96–1.53 m and take up 15% of the marsh area.

4.2. Drainage Density and Drainage Efficiency

A total of 11 intertidal creeks were identified from the DEM for Ethan’s Island (Table 1), with a total creek length of 1425 m (Table 1). Dividing the total creek length by the area of the marsh interior, excluding the area of the subtidal channel (155,876 m2), yielded a drainage density of 0.01 m−1. Given a Hortonian length, Hl of 35.05 and a mean unchanneled path length of 23.58 m (Table 1), the drainage efficiency was estimated to be 4.24.
The largest marsh site, Alligator marsh, also has the highest number of intertidal creeks. There is a total of 23 creeks with a total length of 3430 m. Dividing the total creek length by the area of the marsh interior (257,079 m2) resulted in a drainage density of 0.01 m−1. The Hl for Alligator marsh is 100 and the mean unchanneled path length is 22.23 m. This yielded a drainage efficiency of 4.50 (Table 1).
A total of 7 intertidal creeks were identified for Hannah’s Marsh (Table 1). The creek networks form complex networks that have a southeast to northwest orientation (Figure 3) and have a total length of 717 m (Table 1). Dividing the total creek length by the area of the marsh interior (42,825 m2) yielded a drainage density of 0.02 m−1. Taking the inverse of the Dd yielded a Hortonian length, Hl, of 50. The mean unchanneled path length for the site was 15.9 m, revealing a drainage efficiency of 3.14 (Table 1).
A comparison of metrics between the three marsh sites reveals a drainage density of 0.01 m−1 for both Ethan’s Island and the ag-marsh, Alligator marsh (Table 1). The smallest marsh site, Hannah’s Marsh, exhibits the highest drainage density, with a value of 0.02 m−1. On the other hand, Hannah’s marsh has a drainage efficiency of 3.14, which is the lowest efficiency of the three sites (Table 1). Further, Alligator marsh displays the highest drainage efficiency (4.50), which is 6% higher than that of Ethan’s Island, despite having the same drainage density (Table 1). This outcome is likely a result of the relatively shorter mean unchanneled path distance of Alligator Marsh with respect to Ethan’s Island.

5. Discussion

Drainage density is commonly used to quantify a marsh’s ability to move water in and out of a system [82,86,87,88,89,90,91,92], yet our results demonstrate that drainage density does not always correlate positively with drainage efficiency. While drainage density can provide a useful metric to describe how dissected a marsh landscape is, it does not account for the structure or spatial layout of the creek networks which play a key role in circulation pathways during flood and ebb [32,33,93,94]. On the other hand, drainage efficiency accounts for the spatial orientation of creek networks, particularly those that may enhance the potential for hydraulic connectivity across the system. Here, in the case Alligator Marsh, the unique morphology of the ag-marsh landscape, which is characterized by historically engineered, predominantly linear drainages, increased the potential for hydraulic connections from one side of the marsh to the other, resulting in a higher drainage efficiency than the other two marsh sites (Hannah’s Marsh and Ethan’s Island) even though the drainage density was lower than Hannah’s Marsh and comparable to Ethan’s Island (Table 1). This finding reinforces the assertion that drainage density and drainage efficiency should be considered separately in morphological studies of marsh landscapes, as the latter provides a more relevant measure of hydraulic function [90,92]. Indeed, recent studies have demonstrated that drainage efficiency, albeit a static metric, is relevant for processes (i.e., marsh plant invasion) that depend on how well water, sediments, seeds, etc., move across and throughout a marsh system [86], and that improving the drainage efficiency can yield better ecological/hydrological functioning over and above just having a certain density of channels [92].
This finding on the relatively higher drainage efficiency of the ag-marsh landscape with respect to its natural counterparts is important because it highlights a potentially important quality of ag-marsh landscapes in facilitating enhanced movement of water and sediment within and between marsh systems that is a direct result of their unique geomorphic structure. In particular, we speculate that the predominantly linear structure and spatial layout of the ag-marsh creeks, with creek heads that form apparent connections with the heads of creeks on the opposite sides of the system, may facilitate a unique type of hydraulic connectivity. This is important, given that such hydraulic connections have been shown to greatly impact overmarsh circulation patterns and water pathways between flood and ebb tide [33,90,91,92,93,94,95]. We further speculate that the increased hydraulic connectivity of the ag-marsh landscape may also reduce water residence times by creating “short-circuiting” pathways for water and sediment on the outgoing tide [33]. This potentially expedited transport enabled by the linear drainage features contrasts with the more sinuous, topographically controlled flow in natural marshes. Hence, we contend that the ag-marsh landscapes may play an important role in the efficient exchange of water and sediments within and between individual marsh systems. Future efforts are required, however, to further investigate our assertions through field assessment and numerical modeling.
This finding on the potential significance of ag-marsh landscapes in enhanced water and material exchange may also have important implications for temporal and spatial patterns of inland marsh migration in the context of sea level rise. Marsh survival is highly dependent on their ability to migrate to higher ground as waters rise [37,40,96,97,98]. Given their position between the coastal ocean and terrestrial uplands, ag-marsh landscapes are likely to share boundaries and/or hydraulic connections to marsh-forest transition zones. The engineered linear drainages and canal characteristics of former ag-marsh landscapes may act as preferential corridors for enhanced transmission of tidal water and sediment far inland towards terrestrial upland areas [61,62]. This enhanced inland water delivery, facilitated by a relatively higher drainage efficiency, could accelerate the salinization and inundation of adjacent uplands, thereby promoting marsh migration into abandoned agricultural fields and forest edges—a process increasingly recognized as critical for marsh persistence under the slow press of sea level rise [45,48,61,66,68,96].
Ag-marsh landscapes are abundant within the ACE Basin, SC [97], as well as in many other coastal areas worldwide [98,99], and often share a common boundary with terrestrial uplands [72,100,101,102,103,104]. If these landscapes are indeed more hydraulically efficient than their natural counterparts, they represent a critical, yet under-studied, resource for offsetting future marsh losses along the seaward margins. Their unique geomorphic structure could make them ideal targets for conservation and restoration efforts aimed at proactively facilitating inland transgression in the face of sea level rise.
Altogether, these findings suggest that ag-marsh landscapes may play an important, albeit unexplored, role in marsh function and stability. This study provides a necessary framework for future field and modeling studies that can further assess how the geomorphic legacy of ag-marsh landscapes influences the dynamics of circulation, material cycling, and water residence times in and between marsh systems. Such work will help support the findings presented herein and add accuracy to predictions of the fate of coastal wetlands worldwide in the context of natural and anthropogenic change.

6. Conclusions

This study provides a quantitative geomorphic comparison of three globally significant wetland landscapes in the ACE Basin, SC. Using high-resolution DEMs and drainage metrics for drainage density and drainage efficiency, we demonstrate that drainage density and drainage efficiency are not necessarily correlated, and that drainage efficiency is a more relevant metric for predicting marsh hydraulic function. In particular, we found the Alligator Marsh (ag-marsh) displayed the highest drainage efficiency (4.50) despite having a drainage density of 0.01 m−1, comparable to the natural salt marsh, Ethan’s Island. Conversely, Hannah’s Marsh, with its more complex and fragmented creek networks, had the highest drainage density (0.02 m−1), but the lowest efficiency (3.14). This demonstrates that the spatial structure and connectivity of the creek network, captured by the drainage efficiency metric, are the dominant controls on hydraulic performance. We contend that the unique, linear creek structure inherited from the historical artificial ditching in Alligator Marsh may promote more enhanced water and material exchange by minimizing the mean unchanneled path length, thereby increasing hydraulic efficiency compared to the more sinuous, fragmented creek networks of natural marshes. Future work should build upon the findings presented here by integrating field-based measurements and numerical modeling to further investigate the geomorphic controls of ag-marsh landscapes on the dynamics of water and sediment delivery in and between marsh systems, an important process influencing spatial and temporal patterns of inland marsh retreat as sea levels rise.

Author Contributions

Conceptualization, J.S.; methodology, J.S., M.F., J.C. and R.S.J.; formal analysis, J.S. and M.F.; investigation, J.S., M.F., J.C. and R.S.J.; writing—original draft preparation, J.S.; writing—review and editing, J.S. and M.F.; visualization, J.S.; supervision, J.S.; project administration, J.S.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Science Foundation CAREER Grant, award number: 2041366.

Data Availability Statement

The original data presented in the study are openly available in FigShare at https://doi.org/10.6084/m9.figshare.30148567.v1; https://doi.org/10.6084/m9.figshare.30148564.v1.

Acknowledgments

The authors would like to thank the SCDNR Staff for their project support and assistance with field work and site access.

Conflicts of Interest

Author Jessica Sullivan was employed by the University of South Carolina Aiken. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Environments 12 00458 g001
Figure 1. The ACE Basin, SC, consists of the Ashepoo, Combahee and Edisto River basins. The marsh study sites are (A) Ethan’s Island, a natural salt marsh located closest to the coastal ocean, (B) Alligator Marsh, a reclaimed agricultural marsh, and (C) a natural marsh adjacent to the forested upland. Hannah’s Marsh and Alligator marsh are connected by a main subtidal channel denoted with the white box.
Figure 1. The ACE Basin, SC, consists of the Ashepoo, Combahee and Edisto River basins. The marsh study sites are (A) Ethan’s Island, a natural salt marsh located closest to the coastal ocean, (B) Alligator Marsh, a reclaimed agricultural marsh, and (C) a natural marsh adjacent to the forested upland. Hannah’s Marsh and Alligator marsh are connected by a main subtidal channel denoted with the white box.
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Figure 2. Elevation histograms for (a) Ethan’s Island (b) Alligator marsh, and (c) Hannah’s Marsh. The vertical and horizonal axis mark the frequency of elevation and elevation values, respectively. Vertical dashed lines mark the slope breaks associated with geomorphic classifications.
Figure 2. Elevation histograms for (a) Ethan’s Island (b) Alligator marsh, and (c) Hannah’s Marsh. The vertical and horizonal axis mark the frequency of elevation and elevation values, respectively. Vertical dashed lines mark the slope breaks associated with geomorphic classifications.
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Figure 3. The DEMs for (a) Hannah’s Marsh, (b) Ethan’s Island, and (c) Alligator Marsh are shown. Shades of black to white represent the geomorphic subclasses for elevations associated with subtidal channels, intertidal creeks, low marsh, high marsh, and levees, as identified from histogram slope breaks. Note the linear nature of the ag-marsh landscape (c) relative to the natural marshes (a,b).
Figure 3. The DEMs for (a) Hannah’s Marsh, (b) Ethan’s Island, and (c) Alligator Marsh are shown. Shades of black to white represent the geomorphic subclasses for elevations associated with subtidal channels, intertidal creeks, low marsh, high marsh, and levees, as identified from histogram slope breaks. Note the linear nature of the ag-marsh landscape (c) relative to the natural marshes (a,b).
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Table 1. Table showing metrics used for geomorphic comparison between the three study sites. The metrics include total creek length (m), average sinuosity, drainage density, unchanneled path distance, and drainage efficiency.
Table 1. Table showing metrics used for geomorphic comparison between the three study sites. The metrics include total creek length (m), average sinuosity, drainage density, unchanneled path distance, and drainage efficiency.
Hannahs Marsh Ethan’s IslandAlligator Marsh
Min Elevation (m)−1.5−4.7−3.87
Max Elevation (m)1.71.361.52
Mean Elevation (m)0.54 (±0.62)0.45 (±1.2)0.37 (±0.99)
Total Marsh Area (m2)45,014181,526311,460
Area of Marsh Interior (m2)42,825155,876257,079
Subtidal channel (m2)2189 (5%)25,650 (14%)54,381 (17%)
Intertidal creeks (m2)7314 (16%)12,156 (7%)24,037 (8%)
Low Marsh (m2)13,449 (30%)36,422 (20%)29,821 (10%)
High Marsh (m2)17,712 (39%)87,580 (48%)154,956 (50%)
Levee (m2)4350 (10%)19,718 (11%)48,265 (15%)
# Int Creeks71123
Total Creek Length (m)71714253430
Avg. S1.20 (0.15)1.10 (0.10)1.07 (0.03)
Dd (m−1)0.020.010.01
l (m)15.923.5822.23
De3.144.244.50
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Sullivan, J.; Foster, M.; Chassereau, J.; Sullivan, R., Jr. Geomorphic Comparison of Three Globally Significant Wetland Landscapes. Environments 2025, 12, 458. https://doi.org/10.3390/environments12120458

AMA Style

Sullivan J, Foster M, Chassereau J, Sullivan R Jr. Geomorphic Comparison of Three Globally Significant Wetland Landscapes. Environments. 2025; 12(12):458. https://doi.org/10.3390/environments12120458

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Sullivan, Jessica, Michael Foster, James Chassereau, and Robert Sullivan, Jr. 2025. "Geomorphic Comparison of Three Globally Significant Wetland Landscapes" Environments 12, no. 12: 458. https://doi.org/10.3390/environments12120458

APA Style

Sullivan, J., Foster, M., Chassereau, J., & Sullivan, R., Jr. (2025). Geomorphic Comparison of Three Globally Significant Wetland Landscapes. Environments, 12(12), 458. https://doi.org/10.3390/environments12120458

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