Salt marsh ecohydrological zonation due to heterogeneous vegetation–groundwater–surface water interactions

Moffett, Kevan B.; Gorelick, Steven M.; McLaren, R. G.; Sudicky, Edward A.

doi:10.1029/2011wr010874

Cited by 92 publications

(115 citation statements)

References 95 publications

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“…Many investigations, including field studies and numerical simulations, have been carried out to examine pore water flow in salt marshes under the influence of tides [Moffett et al, 2010;Wilson and Morris, 2012;Wilson and Gardner, 2006;Xin et al, 2010a], evapotranspiration [Boaga et al, 2014;Marani et al, 2006;Ursino et al, 2004], soil properties including stratigraphy [Gardner, 2007;Gardner and Wilson, 2006;Wilson and Morris, 2012;Xin et al, 2009Xin et al, , 2012, inland fresh groundwater input [Gardner et al, 2002;Nuttle and Harvey, 1995], and marsh topography [Gardner, 2005;Moffett et al, 2012;Xin et al, 2013aXin et al, , 2011. While these studies generated important insights into the pore water flow behavior, none of them considered the density effects associated with salinity variations, which commonly exist in surface water and pore water within a marsh system [Cao et al, 2012;Hughes et al, 2012].…”

Section: Introductionmentioning

confidence: 99%

Effects of salinity variations on pore water flow in salt marshes

Shen

Jin

Xin

et al. 2015

Water Resources Research

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Spatial and temporal salinity variations in surface water and pore water commonly exist in salt marshes under the combined influence of tidal inundation, precipitation, evapotranspiration, and inland freshwater input. Laboratory experiments and numerical simulations were conducted to investigate how density gradients associated with salinity variations affect pore water flow in the salt marsh system. The results showed that upward salinity (density) gradients could lead to flow instability and the formation of salt fingers. These fingers, varying in size with the distance from the creek, modified significantly the pore water flow field, especially in the marsh interior. While the flow instability enhanced local salt transport and mixing considerably, the net effect was small, causing only a slight increase in the overall mass exchange across the marsh surface. In contrast, downward salinity gradients exerted less influence on the pore water flow in the marsh soil and slightly weakened the surface water and groundwater exchange across the marsh surface. Numerical simulations revealed similar density effects on pore water flow at the field scale under realistic conditions. These findings have important implications for studies of marsh soil conditions concerning plant growth as well as nutrient exchange between the marsh and coastal marine system.

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Section: Introductionmentioning

confidence: 99%

Effects of salinity variations on pore water flow in salt marshes

Shen

Jin

Xin

et al. 2015

Water Resources Research

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“…However, spectral data sources do not provide the topographic information necessary to fully understand morphodynamic processes: although digital elevation models (DEMs) have been successfully generated from habitat maps in the Venice lagoon (Silvestri et al, 2003), additional influences on halophyte distribution such as groundwater circulation (Moffett et al, 2010(Moffett et al, , 2012 can lead to mismatches between topography and habitats (Hladik et al, 2013). These additional influences on habitat distribution prevent the reliable use of spectral data to infer topography.…”

Section: Introductionmentioning

confidence: 99%

Unsupervised detection of salt marsh platforms: a topographic method

2018

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Abstract. Salt marshes filter pollutants, protect coastlines against storm surges, and sequester carbon, yet are under threat from sea level rise and anthropogenic modification. The sustained existence of the salt marsh ecosystem depends on the topographic evolution of marsh platforms. Quantifying marsh platform topography is vital for improving the management of these valuable landscapes. The determination of platform boundaries currently relies on supervised classification methods requiring near-infrared data to detect vegetation, or demands labourintensive field surveys and digitisation. We propose a novel, unsupervised method to reproducibly isolate salt marsh scarps and platforms from a digital elevation model (DEM), referred to as Topographic Identification of Platforms (TIP). Field observations and numerical models show that salt marshes mature into subhorizontal platforms delineated by subvertical scarps. Based on this premise, we identify scarps as lines of local maxima on a slope raster, then fill landmasses from the scarps upward, thus isolating mature marsh platforms. We test the TIP method using lidar-derived DEMs from six salt marshes in England with varying tidal ranges and geometries, for which topographic platforms were manually isolated from tidal flats. Agreement between manual and unsupervised classification exceeds 94 % for DEM resolutions of 1 m, with all but one site maintaining an accuracy superior to 90 % for resolutions up to 3 m. For resolutions of 1 m, platforms detected with the TIP method are comparable in surface area to digitised platforms and have similar elevation distributions. We also find that our method allows for the accurate detection of local block failures as small as 3 times the DEM resolution. Detailed inspection reveals that although tidal creeks were digitised as part of the marsh platform, unsupervised classification categorises them as part of the tidal flat, causing an increase in false negatives and overall platform perimeter. This suggests our method may benefit from combination with existing creek detection algorithms. Fallen blocks and high tidal flat portions, associated with potential pioneer zones, can also lead to differences between our method and supervised mapping. Although pioneer zones prove difficult to classify using a topographic method, we suggest that these transition areas should be considered when analysing erosion and accretion processes, particularly in the case of incipient marsh platforms. Ultimately, we have shown that unsupervised classification of marsh platforms from high-resolution topography is possible and sufficient to monitor and analyse topographic evolution.

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“…Spectral data sources, however, are not sufficient to provide the topographic information necessary to fully understand morphodynamic processes: although Digital Elevation Models (DEMs) have been successfully generated from habitat maps 25 in the Venice lagoon (Silvestri et al, 2003), additional influences on halophyte distribution such as groundwater circulation (Moffett et al, 2010(Moffett et al, , 2012 can lead to mismatches between topography and habitats (Hladik et al, 2013). These additional influences on habitat distribution prevent the reliable use of spectral data to infer topography.…”

mentioning

confidence: 99%

Unsupervised detection of salt marsh platforms: a topographic method

Goodwin¹,

Mudd²,

Clubb³

2017

Preprint

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Abstract.Salt marshes filter pollutants, protect coastlines against storm surges, and sequester carbon, yet are under threat from sea level rise and anthropogenic modification. The productivity and even survival of salt marsh vegetation depends on the topographic evolution of marsh platforms. Quantifying marsh platform topography is vital for improving the management of these valuable landscapes. Determining platform boundaries currently relies on supervised classification methods requiring near-infrared data 5 to detect vegetation, or demands labor-intensive field surveys and digitization. We propose a novel, unsupervised method to reproducibly isolate saltmarsh scarps and platforms from a DEM, referred to as Topographic Identification of Platforms (TIP).Field observations and numerical models show that saltmarshes mature into sub-horizontal platforms delineated by sub-vertical scarps: based on this premise, we identify scarps as lines of local maxima on a slope raster, then fill landmasses from the scarps upward, thus isolating mature marsh platforms. We test the TIP method using lidar-derived DEMs from six saltmarshes in 10England with varying tidal ranges and geometries, for which topographic platforms were manually distinguished from tidal flats. Agreement between manual and unsupervised classification exceeds 94% for DEM resolutions of 1 m, with all but one sites maintaining an accuracy superior to 90% for resolutions up to 3 m. For resolutions of 1 m, platforms detected with the TIP method are comparable in surface area to digitized platforms, and have similar elevation distributions. We also find that our method allows the accurate detection of local bloc failures as small as 3 times the DEM resolution. Detailed inspection 15 reveals that although tidal creeks were digitized as part of the marsh platform, unsupervised classification categorizes them as part of the tidal flat, causing an increase in false negatives and overall platform perimeter. This suggests our method would have increased accuracy if used in combination with existing creek detection algorithms. Fallen blocs and high tidal flat portions, associated with potential pioneer zones, may also be areas of discordance between our method and supervised mapping.Although pioneer zones prove difficult to classify using a topographic method, it also suggests that these transition areas 20 should be considered when analysing erosion and accretion processes, particularly in the case of incipient marsh platforms.Ultimately, we have shown that unsupervised classification of marsh platforms from high-resolution topography is possibleand sufficient to monitor and analyze topographic evolution.

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Salt marsh ecohydrological zonation due to heterogeneous vegetation–groundwater–surface water interactions

Cited by 92 publications

References 95 publications

Effects of salinity variations on pore water flow in salt marshes

Effects of salinity variations on pore water flow in salt marshes

Unsupervised detection of salt marsh platforms: a topographic method

Unsupervised detection of salt marsh platforms: a topographic method

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