Unvegetated to vegetated ratio of marsh units in Massachusetts salt marshes
This data release contains coastal wetland synthesis products for Massachusetts, developed in collaboration with the Massachusetts Office of Coastal Zone Management. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and tidal range are calculated for smaller units delineated from a digital elevation model, providing the spatial variability of physical factors that influence wetland health. 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.
Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 20210929, Unvegetated to vegetated ratio of marsh units in Massachusetts salt marshes: data release DOI:10.5066/P97E086F, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.
Suggested citation: Ackerman, K.V., Defne, Z., and Ganju, N.K., 2021, Geospatial Characterization of Salt Marshes for Massachusetts: U.S. Geological Survey data release, https://doi.org/10.5066/P97E086F.
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 meters
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS 84.
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.
Internal feature number.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
Unique whole numbers used to identify each conceptual marsh unit.
Range of values
Total surface area of a marsh unit.
Range of values
Surface area of the vegetated part of a marsh unit.
Range of values
Ratio of unvegetated surface area to vegetated surface area. Ordinarily, UVVR ranges from zero (completely vegetated) to infinity (completely unvegetated). However, it is assigned the value of -1 when completely unvegetated.
Range of values
Marsh unit flag indicating anomalous marsh units based on absence of vegetation, elevation, surface area and tidal range extrapolation. FLG values indicate: (-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 m^2; (-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 m^2.
Range of values
In this dataset, the salt marshes of Massachusetts have been delineated to conceptual salt marsh units to facilitate unit by unit evaluation of response and resiliency of the marsh system to physical and biogeochemical drivers. Each unit is also analyzed based on the vegetated and unvegetated surface area coverage, the ratio of which can be an independent measure of marsh health for salt marshes on the Atlantic and Pacific coasts of the United States. UVVR is calculated as the ratio of unvegetated area to vegetated area in a marsh unit. 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 UVVR is assumed to be 1 meter and 0.001, respectively.
The purpose of this shapefile is to calculate the ratio of unvegetated area to vegetated area (UVVR) in each marsh unit. Analysis of unvegetated to vegetated marsh ratio is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. An unvegetated area to vegetated area ratio was defined as a potential indicator of the current state of a salt marsh unit. UVVR was calculated based on U.S. Department of Agriculture National Agriculture Imagery Program (NAIP) 0.6-meter resolution imagery.
Danielson, J., and Tyler, D., 20160501, Topobathymetric Model for the New England Region States of New York, Connecticut, Rhode Island and Massachusetts, 1887 to 2016: U.S. Geological Survey, Reston, VA.
This process step and all subsequent process steps were performed by the same person, Kate Ackerman, 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 (m^2) unless otherwise stated.
a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 19N.
b) Prepare elevation datasets. For the USGS NED tiles: MOSAIC TO NEW RASTER; PROJECT the new raster to NAD_1983_UTM_Zone_19N; and RESAMPLE the new raster to 1m. MOSAIC TO NEW RASTER the USGS 1m DEM tiles. PROJECT the USGS CoNED raster to NAD_1983_UTM_Zone_19N. MOSAIC TO NEW RASTER the USGS CoNED raster, USGS 1m DEM raster, and the USGS NED raster, with the order of precedence: the USGS CoNED, USGS 1m DEM raster, USGS NED raster.
c) Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE(Input features=[CMU_MA.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 19N) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
d)Create a rectangular polygon that covers the domain [extent.shp]. CLIP the mosaicked elevation dataset by the boundaries polygon [elev_mosaic.tif].
Person who carried out this activity:
U.S. Geological Survey
384 Woods Hole Road
Woods Hole, MA
508-548-8700 x2331 (voice)
Data sources used in this process:
USGS 1m DEM
Data sources produced in this process:
Date: 2021 (process 2 of 3)
Prepare a mask polygon to define analysis boundaries. In order to account for the possible influence of the surrounding terrain on the analysis, a mask area larger than the salt marsh extent is first created [UVVR_mask.shp]. At the end of the analysis the results are clipped to the boundaries of the salt marsh area [MU_mask.shp]. Both [UVVR_mask.shp] and [MU_mask.shp] are edited to determine which interior polygons are removed.
a) EXPORT features from NWI dataset after SELECT("ATTRIBUTE" LIKE 'E2%EM%' OR "ATTRIBUTE" LIKE 'E2AB3%' OR "ATTRIBUTE" LIKE 'E2EM%' OR "ATTRIBUTE" LIKE 'E2SS%' OR "ATTRIBUTE" LIKE 'E2US4%') to select from estuarine intertidal areas of 1) emergent wetland, 2) scrub-shrub area, 3) rooted vascular aquatic bed, 4) organic unconsolidated shore classes [NWI_exclusive_select.shp].
b) BUFFER(Input features=[NWI_exclusive_select.shp]; Linear unit=5 meters; Dissolve type=All) to obtain the mask polygon [buff5m.shp] and ELIMINATE POLYGON PART(Condition=Percentage; Percentage=99; Eliminate contained part only) to obtain [UVVR_mask01.shp]. Apply buffer with -5 meters to obtain [MU_mask01.shp].
c) EXPORT features from NWI dataset after SELECT("ATTRIBUTE" NOT LIKE 'E%' OR "ATTRIBUTE" LIKE '%FO') to obtain features that are not estuarine or are forested estuarine [NWI_inclusive_select.shp]. MULTIPART TO SINGLEPART to separate individual polygons [NWI_inclusive_single.shp].
d) To exclude the voids in the NWI map during the analysis, these interior polygons need to be removed from the mask. ERASE [NWI_exclusive_select.shp] from [extent.shp] and MULTIPART TO SINGLEPART to get [NWI_exc_voids_single.shp].
e) SYMMETRICAL DIFFERENCE (Input features=[buff5m.shp], Update features=[UVVR_mask01.shp], Join attributes= All) and MULTIPART TO SINGLEPART to obtain [UVVR_mask01_buff5m_diff_single.shp]. Do a SPATIAL JOIN (Target Features=[UVVR_mask01_buff5m_diff_single.shp], Join Features= NWI wetlands for all of MA; Join operation=join one to one; Keep all target features; match option= intersect) to obtain [UVVR_nwi_sjoin.shp]. Select records that have a null value for the “attribute” field and generate a shapefile of the selected records [NWI_voids_single.shp].
f) SELECT BY LOCATION from [NWI_inclusive_single.shp] that are completely within the [MU_mask01.shp] and SELECT BY LOCATION from [NWI_voids_single.shp] that are completely within the [MU_mask01.shp] and SELECT BY LOCATION from [NWI_exc_voids_single.shp] that are completely within the [MU_mask01.shp]. If any additional polygons need to be removed from the mask include them in a new feature layer [erase_mask_manual.shp]. MERGE all four resulting shapefiles to generate polygons to be excluded [erase_inside.shp] from the final masks.
g) ERASE [erase_inside.shp] from [MU_mask01.shp] to obtain [MU_mask.shp], and ERASE [erase_inside.shp] from [UVVR_mask01.shp] after BUFFER [erase_inside.shp] by -5 meters, to obtain [UVVR_mask.shp].
Data sources used in this process:
Data sources produced in this process:
Date: 2021 (process 3 of 3)
Compute vegetated and unvegetated areas by image processing.
a) MOSAIC TO NEW RASTER the NAIP tiles for this region.
b) EXTRACT BY MASK from the elevation raster [elev_mosaic.tif] and the NAIP imagery raster using [UVVR_mask.shp] polygon. Rescale the elevation raster values to the same range with 8-bit NAIP imagery (0 to 255) using min-max scaling. Perform ISO CLUSTER UNSUPERVISED CLASSIFICATION with 5 input bands: the Near Infrared, Blue, Green, and Red from the NAIP imagery and the rescaled elevation raster; with 32 classes and a minimum class size of 5000 cells. RECLASSIFY the classified raster by visually comparing the NAIP imagery to obtain the unvegetated-vegetated raster [UVVc.tif].
c) Dissolve unvegetated regions smaller than a threshold value to the surrounding vegetated regions and vice versa to clean the UVV raster. For this purpose, use the REGION GROUP(Number of neighbors=4; Zone grouping method=Within; Add Link field to output) to get the [UVV_region.tif], and TEST("Count" < 9) to set a threshold value of 9 raster cells [lt9.tif]. Use RASTER CALCULATOR to toggle the value of the Link field in the region raster [Map algebra expression=Con("%lt9.tif%", ~Lookup("%UVVc_region.tif%","LINK"),Lookup("%UVVc_region.tif%","LINK"))], where the test raster indicates regions with areas smaller than the threshold.
d) RASTER TO POLYGON(Simplify polygons=False) and CLIP with the final marsh complex outline [mu_diss.shp] to obtain [UVVc_filt_clip.shp].
e) REPAIR GEOMETRY, ADD GEOMETRY ATTRIBUTES(Geometry properties=Area_geodesic; Area unit=Square_meters), CALCULATE FIELD(Python_9.3 expression; Field name=gridcode, Expression=filt(!gridcode!, !AREA_GEO!), Code Block= def filt(gridcode, AREA_GEO):/if gridcode== 0 and AREA_GEO < 9:/return 1/else:/return gridcode) and DISSOLVE(Create multipart features=False) to get filtered, clipped and dissolved unvegetated-vegetated polygons [UVVc_filt_clip_diss.shp].
f) INTERSECT the dissolved conceptual marsh units [mu_diss.shp] with unvegetated-vegetated polygons [UVVc_filt_clip_diss.shp], REPAIR GEOMETRY, and calculate the area of unvegetated and vegetated polygons in each marsh unit. To do this ADD GEOMETRY ATTRIBUTES(Geometry properties=Area_geodesic; Area unit=Square_meters) to get [UVV_poly.shp], and DISSOLVE(Input features=[UVV_poly.shp]; Dissolve fields=FID_CMU, gridcode; Statistics field=gridcode.MEAN) and REPAIR GEOMETRY to get [UVV_poly_diss.shp]. Edit the fields to have "TYP", "APGN_M2", and "ATOT_M2" fields for type of polygon indicating vegetated or unvegetated, surface area of the polygon, and total surface area of the marsh unit, respectively. Visually inspect and manually remove marsh units that are fully forested due to polygon artifacts that are a result of buffering.
g) Add field "UVVR" and calculate unvegetated to vegetated ratio based on "TYP", "APGN_M2" and "ATOT_M2" fields. If the vegetated area is zero for a marsh unit set the value of UVVR to -1.
h) DISSOLVE(Input features=[UVV_poly_diss.shp]; Dissolve fields=FID_CMU, gridcode; Statistics field=UVVR, ATOT_M2 and FLG with Statistics type= First for all) to obtain [mu_UVVR_MA.shp].
i) 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 m^2; (-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 m^2.
j) SELECT BY ATTRIBUTES FROM [CMU_MA.shp] where "TYP"= 'vegetated,' and join field "APGN_M2" from [CMU_MA.shp] on the feature dataset [mu_UVVR_MA.shp] and rename this field "AVEG_M2."
k) 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 19N; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the UVVR for each marsh unit [mu_UVVR_MA.shp].
Data sources used in this process:
How well have the observations been checked?
Marsh unit boundaries and water and land boundaries inherit their accuracy from the source data, the conceptual marsh units. Vegetated and unvegetated polygon accuracy is based on the 0.6-meter resolution National Agriculture Imagery Program (NAIP) products, and the elevation datasets (USGS CoNED, USGS 1-meter DEM, and USGS NED).
Where are the gaps in the data? What is missing?
The results are specific to the marsh polygons as defined within the boundaries of Massachusetts salt marshes. Sliver polygons of open salt water along the marsh edges may also be included in some instances as a result of geoprocessing. In some marsh units there are small sliver gaps due to coupling of artifacts of the NWI (e.g., NWI polygons for ditches that are classified as riverine) and geoprocessing when the marsh polygons were closer than 10 meters at a specific section that is followed by a wider distance (e.g., access roads, fringing forests, etc.). The effect of these slivers on the calculations is negligible. For example, in marsh units 5958 and 5965 the sliver gaps are a result of the geoprocessing steps that remove riverine polygons. Other examples include marsh units 165, 308, 648, 3441, 5613. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries. Occasionally, marsh units are retained in this dataset even though the imagery displayed extreme change (e.g., partially or completely converted to water) from the NWI wetland delineation.
How consistent are the relationships among the observations, including topology?
Topological errors that occurred during geoprocessing were automatically removed by the topological rules used for the analysis. The polygons were checked for correct geometry and do not overlap. Small polygons (less than 9 m^2) were assumed to be marginal and were assigned the classification from the surrounding majority value. In one area (around marsh unit 6125), there are marsh units that have straight lines for boundaries; this is due to larger areas of hydro-flattened bathymetry/elevation values that do not allow the basin analysis to identify ridge lines between basins. These marsh units have a flag that shows that the hydro-flattened area of the marsh unit is greater than 25 percent of the marsh unit area.
A visual comparison between NAIP imagery was performed at randomly selected sites to verify the land and water boundaries. Marsh polygons without any vegetation were assigned a UVVR value of -1. The UVVR of 5 marsh units (FID_CMU= 3559, 3561, 3562, 3564, 3570 in the Weymouth Fore River) was manually adjusted to -1 after examining the imagery.
The unvegetated to vegetated ratio 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.
Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.