Mean tidal range of marsh units in eastern Long Island salt marsh complex, New York (ver. 3.0, May 2026)

This process step and all subsequent process steps were performed by the same person, Robert Welk, 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.
b) Establish marsh unit boundaries. Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE (Input features=[CMU_ELI.shp]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First). PROJECT (Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N) the feature dataset to obtain dissolved marsh units [mu_diss.shp].

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.

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].

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].

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) Add field "FLG" to flag anomalous marsh units based on absence of vegetation, elevation, surface area, and tidal range extrapolation. The flags are calculated in their respective shapefile (i.e., elevation flags are calculated in the elevation shapefile). Set FLG to: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than the 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-1000) marsh unit surface area less than 900 square meters; (-10000) mean tidal range of marsh unit is extrapolated; 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 square meters.
g) 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].

Added keywords section with USGS persistent identifier as theme keyword.

Version 2 updates. Updates were performed in ArcGIS Pro 2.8.8. Duplicate marsh units were manually identified and compared to make sure the most appropriate duplicate marsh unit was deleted. Seventy-six duplicate marsh units were identified (out of 2828) in Mecox Bay, Sagaponack Pond and Georgica Pond and have been removed. After the duplicate marsh units were deleted, the elevation, hydroflattened percentage and elevation flag values were recalculated. Authorship was updated to include Kate Ackerman.

Version 3 Updates. All updates were completed in ArcGIS Pro 3.4.3, using the version 2 of the dataset as the starting dataset. In the original dataset, each marsh plain was not subdivided into smaller parcels ("marsh units") because two processing steps were not completed. For Version 3, these processing steps were completed, resulting in each marsh plain being properly subdivided into these smaller marsh units. Using the new marsh units, UVVR and elevation values were recalculated. Tide range values were carried over from the original (larger) marsh plain polygons and applied to the new, smaller marsh units.
However, exposure potential (SCoRR) values and shoreline change values could not be recalculated at the marsh unit scale. They remain unchanged and still represent the larger marsh plain polygons. In the SCoRR and shoreline change datasets, the field FID_CMU has been renamed to MP to indicate that those polygons correspond to marsh plains, not the newly created marsh units. In the title of the data release for exposure potential and shoreline change, the words "marsh units" were changed to "marsh plains." Throughout the exposure potential and shoreline change metadata, the term 'marsh unit' is still used, but readers should understand that it actually refers to the marsh plain. Previous versions of the data can be obtained by contacting whsc_data_contact@usgs.gov.

Assign tidal range values from previous marsh units to new marsh units created in revision 3 using a spatial join. ADD SPATIAL JOIN (Target Features=[mu_MN_ELI_New.shp], Join Features=[mu_MN_ELI_Old.shp], Match Option=Within, Permanently Join Fields).

Removed the web services distribution formats in preparation for ScienceBase moving platforms and those services no longer being available.