Mean tidal range of marsh units in eastern Long Island salt marsh complex, New York
This data release contains coastal wetland synthesis products for the geographic region of eastern Long Island, New York, including the north and south forks, Gardiners Island, and Fishers Island. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence wetland health. Through scientific efforts initiated with the Hurricane Sandy Science Plan, the U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands with the intent of providing Federal, State, and local managers with tools to estimate the vulnerability and ecosystem service potential of these wetlands. For this purpose, the response and resilience of coastal wetlands to physical factors need to be assessed in terms of the ensuing change to their vulnerability and ecosystem services.
Welk, Robert, Defne, Zafer, and Ganju, Neil K., 20200331, Mean tidal range of marsh units in eastern Long Island salt marsh complex, New York: data release DOI:10.5066/P91H426U, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.6096
Ordinates (y-coordinates) are specified to the nearest 0.6096
Planar coordinates are specified in Meter
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.0.
The flattening of the ellipsoid used is 1/298.257223563.
Table containing attribute information associated with the dataset.
(Source: Producer defined)
Internal feature number.
Unique whole numbers that are automatically generated.
Coordinates defining the features.
Unique whole number that represents the identification number for each conceptual marsh unit.
Range of values
Total surface area of a marsh unit in square meters
Range of values
Surface area of vegetated part of a marsh unit in square meters. Value is set to -9999 if there is no vegetated area in the marsh unit.
Range of values
Mean tidal range in meters averaged over a marsh unit
Range of values
Marsh unit flag indicating anomalous marsh units based on elevation, surface area, and absence of vegetation. FLG values indicate: (-1) no vegetated area; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-200) greater than 25% of marsh unit has hydroflattened area (and has -9999 as its elevation value; (-1000) marsh unit surface area less than 900 m2; and (0) no flag. Combination of negative values indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m2.
Range of values
In this dataset, tidal range for each conceptual salt marsh unit in the eastern Long Island salt marsh complex has been calculated based on a 0.0005 arc degrees interpolated VDatum dataset. Decimal values in the attribute table are a result of double precision calculations while significant digits are considered in defining the attribute measurement resolutions. Therefore, the smallest unit increment for area values and tidal range is assumed to be 1 meter and 0.01, respectively.
The purpose of this shapefile is to calculate mean tidal range in each marsh unit. Analysis of mean tidal range is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. Biomass production is positively correlated with mean tidal range in salt marshes along the Atlantic coast of the United States. Recent studies support the idea that enhanced stability of the marshes can be attributed to increased vegetative growth due to increased tidal range. This dataset displays the spatial variation of mean tidal range (i.e. Mean Range of Tides, MN) in the eastern Long Island salt marsh complex. MN was based on the calculated difference in height between mean high water (MHW) and mean low water (MLW) using the VDatum (v3.5) database ( http://vdatum.noaa.gov/ ).
This process step and all subsequent process steps were performed in ArcMap (ver. 10.7.1) using tools from ArcToolbox, unless otherwise stated. For complex operations, names of specific tools used are given in CAPITAL letters (any critical parameters used are given in parentheses, separated by a semicolon, immediately after the tool name). The input and output file names are provided in [square brackets] when necessary. Units for length and area calculations are meters (m) and square meters (m2) unless otherwise stated.
Calculate values for each marsh unit. DISSOLVE(Input features=[CMU_ELI]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First) to dissolve the vegetated and unvegetated classes in each marsh unit. FLG flags anomalous marsh units based on the absence of vegetation, the elevation, and the surface area, and is set to (-1) no vegetated area; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-1000) marsh unit surface area less than 900 m2; and (0) no flag. Combination of negative values indicates a combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m2. PROJECT(Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain
Data sources used in this process:
Date: 2019 (process 2 of 6)
Calculate Mean Range of Tides using the VDatum (v3.5) database covering this region
(http://vdatum.noaa.gov/download.php ). Create a 0.0005 arc degrees (~50 meters) spaced point dataset in Matlab (ver. 2012b) for the eastern Long Island domain. Calculate the mean range of tides (MN) as MN=MHW-MLW, where MHW is the mean high water level and MLW is the mean low water level in the VDatum database, and interpolate to the point dataset. The resulting comma-separated file includes columns for latitude, longitude and MN.
Date: 2019 (process 3 of 6)
Create a raster surface dataset from the feature points.
a) Import points from [MN.csv] to ArcMap using MAKE XY EVENT LAYER with the North American 1983 Continuously Operating Reference Station datum (GCS NAD 1983 CORS96) coordinate reference system.
b) Create a raster surface with inverse distance weighting in Spatial Analyst toolbox. IDW.SpatialAnalyst(Output Cell Size=0.0001 degree; Power=2; Search Radius=Variable; Number of Points=12) to obtain [MN_raster_idw.tif].
Date: 2019 (process 4 of 6)
Clip the raster to marsh boundaries. A buffer zone is created around the marsh boundaries to facilitate alternative interpolation and clipping options in future studies.
a) Create 300 m buffer around the marsh polygon [mu_diss.shp] to create a clipping mask [mu_buff300m.shp]. BUFFER(Side type= Full; Method =Geodesic; Dissolve type= All).
b) Clip the raster with the clipping mask. EXTRACT BY MASK to obtain [MN_ELI.tif].
Date: 2019 (process 5 of 6)
Calculate values for each marsh unit.
a) Clip the raster with the polygon features by using EXTRACT BY MASK to obtain [mn_idw_mu.tif].
b) ZONAL STATISTICS AS TABLE(Feature Zone Data=[mu_diss.shp]; zone field=FID_CMU; Value Raster=[mn_idw_mu.tif]; Output Table=mu; Statistics type=MEAN)
c) ADD JOIN(Layer name=[mu_diss.shp]; Input join field=FID_CMU; Join Table=mu; Output join field=FID_CMU) to marsh units layer based on the "FID_CMU" field
d) Export dataset as a shapefile [mu_MN_ELI.shp] and keep the 'mu_MEAN" and "mu_ATOT_M2" fields from the join operation.
e) SELECT BY ATTRIBUTES FROM [CMU_ELI] where "CLASS"= 'vegetated', and join field "APGN_M2" from CMU_ELI.shp on the feature dataset [mu_MN_ELI.shp].
f) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Input coordinate system=NAD 1983 UTM Zone 18N; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the final conceptual marsh units [mu_MN_ELI.shp].
Date: 06-Aug-2020 (process 6 of 6)
Added keywords section with USGS persistent identifier as theme keyword.
Person who carried out this activity:
How well have the observations been checked?
Marsh units and water and land boundaries inherit their accuracy from the source data, eastern Long Island marsh units. Mean range of tides is calculated from the VDatum database, then interpolated on a raster surface and averaged at each marsh unit. If a marsh unit does not overlap with any raster cell center, it is assigned the value of the raster cell with the largest overlap.
How accurate are the geographic locations?
Horizontal accuracy for the polygon boundaries is inherited from the source layer, the conceptual marsh units, and is considered to be +/- 6 meters. The point cloud used for calculating tidal range with VDatum had a 0.0005 arc degree (~50-meter) resolution that was interpolated over a 0.0001 arc degree raster prior to clipping and calculating the mean value for each marsh unit.
Where are the gaps in the data? What is missing?
The results are specific to the marsh polygons as defined within the boundaries of the eastern Long Island salt marsh complex. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries.
How consistent are the relationships among the observations, including topology?
Polygons do not overlap and mean tidal range is positive. During processing of conceptual marsh units, small polygons (less than 9 square meters) were assumed to be marginal and were assigned the classification from the surrounding majority value. This resulted in polygons that were removed from the dataset and FID CMU values that are not sequential.
The mean tidal range for each marsh unit is defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information.
Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.