Lifespan of marsh units in Eastern Shore of Virginia salt marshes

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Frequently anticipated questions:

What does this data set describe?

Title:
Lifespan of marsh units in Eastern Shore of Virginia salt marshes
Abstract:
The lifespans of salt marshes in Atlantic-facing Eastern Shore of Virginia are calculated based on estimated sediment supply and sea-level rise (SLR) predictions, following the methodology of Ganju and others (2020). The salt marsh delineations are from Ackerman and others (2023). The SLR predictions are local estimates corresponding to increases of 0.3, 0.5 and 1.0 meter in global mean sea level (GMSL) by 2100, as projected by Sweet and others (2022). This work has been a part of the USGS’s effort to expand the national assessment of coastal change hazards and forecast products to coastal wetlands. The aim is to equip 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. (The data release containing lifespan estimates for the Chesapeake Bay-facing portion of the Eastern Shore of Virginia is found here: https://doi.org/10.5066/P9FSPWSF.)
  1. How might this data set be cited?
    Defne, Zafer, Ganju, Neil K., and Ackerman, Kate V., 20240712, Lifespan of marsh units in Eastern Shore of Virginia salt marshes: data release DOI:10.5066/P14GBAVB, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Defne, Z., Ganju, N.K., and Ackerman, K.V., 2024, Lifespan of marsh units in Eastern Shore of Virginia salt marshes: U.S. Geological Survey data release, https://doi.org/10.5066/P14GBAVB.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.9777
    East_Bounding_Coordinate: -75.4740
    North_Bounding_Coordinate: 37.8818
    South_Bounding_Coordinate: 37.0854
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/664c9cbdd34e1955f5a4f45f/?name=mu_lifespan_ESV.png&allowOpen=true (PNG)
    Graphic of shapefile showing lifespan estimates for Eastern Shore of Virginia salt marshes.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2024
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Vector Digital Data Set (Polygon)
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • G-polygon (6358)
    2. What coordinate system is used to represent geographic features?
      The map projection used is WGS 1984 Web Mercator Auxiliary Sphere (Esri Full Name: WGS_1984_Web_Mercator_Auxiliary_Sphere).
      Projection parameters:
      Standard_Parallel: 0.0
      Longitude_of_Central_Meridian: 0.0
      False_Easting: 0.0
      False_Northing: 0.0
      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_1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    mu_lifespan_ESV.shp Attribute Table
    Attribute information associated with the lifespan estimates for the conceptual marsh units of Eastern Shore of Virginia salt marsh system. (Source: USGS)
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Feature geometry. Marsh units are polygon features.
    FID_CMU
    Sequential unique whole number that represents the identification number for each conceptual marsh unit. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:6357
    Units:none
    ATOT_M2
    Total surface area of a marsh unit in square meters. (Source: USGS)
    Range of values
    Minimum:123.826608
    Maximum:1906442.13071
    Units:square meter
    AVEG_M2
    Surface area of vegetated part of a marsh unit in square meters. (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:1628088.8009
    Units:square meter
    MU_ELEV
    Mean elevation of a marsh unit in meters referenced to NAVD88. (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-0.892
    Maximum:2.135
    Units:meter
    MU_ELEVMTL
    Mean elevation of a marsh unit in meters referenced to mean tide level (MTL). (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-0.749
    Maximum:2.307
    Units:meter
    VG_ELEV
    Mean elevation of the vegetated area in a marsh unit in meters referenced to NAVD88. Value is set to -9999 if there is no vegetated area in the marsh unit. (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-0.39
    Maximum:2.065
    Units:meter
    VG_ELEVMTL
    Mean elevation of the vegetated area in a marsh unit in meters referenced to MTL. Value is set to -9999 if there is no vegetated area in the marsh unit. (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-0.377
    Maximum:2.237
    Units:meter
    UVVR
    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. (Source: USGS)
    Range of values
    Minimum:-1.0
    Maximum:1155922.809
    Units:none
    BGRND
    Lifespan for a marsh unit (in years) for nonclimatic background relative sea level rise. Negative lifespan (other than No Data) indicates the estimated lifespan is depleted and loss is imminent. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-33
    Maximum:10000
    Units:year
    GMSL03
    Lifespan for a marsh unit (in years) for global mean sea level rise of 0.3 meters by 2100. Negative lifespan (other than No Data) indicates the estimated lifespan is depleted and loss is imminent. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-14
    Maximum:10000
    Units:year
    GMSL05
    Lifespan for a marsh unit (in years) for global mean sea level rise of 0.5 meters by 2100. Negative lifespan (other than No Data) indicates the estimated lifespan is depleted and loss is imminent. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-11
    Maximum:10000
    Units:year
    GMSL10
    Lifespan for a marsh unit (in years) for global mean sea level rise of 1.0 meters by 2100. Negative lifespan (other than No Data) indicates the estimated lifespan is depleted and loss is imminent. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-7
    Maximum:10000
    Units:year
    FLG
    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. (Source: USGS)
    Range of values
    Minimum:-11100
    Maximum:0
    Units:None
    Entity_and_Attribute_Overview:
    In this dataset, lifespan estimates for each conceptual salt marsh unit in the Eastern Shore of Virginia salt marsh system have been calculated based on the 1-meter resolution raster source 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 elevation is assumed to be 1 meter and 0.01, respectively.
    Entity_and_Attribute_Detail_Citation: USGS

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Zafer Defne
    • Neil K. Ganju
    • Kate V. Ackerman
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Zafer Defne
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov

Why was the data set created?

The purpose of this shapefile is to present lifespan estimates, based on three different SLR estimates (Sweet and others, 2022), for each salt marsh unit in the Eastern Shore of Virginia as defined by the USGS (Ackerman and others, 2023).

How was the data set created?

  1. From what previous works were the data drawn?
    mu_elev_ESV; mu_UVVR_ESV (source 1 of 1)
    Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 2023, Geospatial characterization of salt marshes on the Eastern Shore of Virginia: data release DOI:10.5066/P9E6V0QK, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    From the elevation dataset (online link 2), we used the marsh unit elevation (MU_ELEV) and vegetated fraction elevation (VG_ELEV) as inputs. From the unvegetated to vegetated ratio (UVVR) dataset (online link 3), we used the UVVR as input. Projection was WGS 1984 Web Mercator Auxiliary Sphere. Data was downloaded 02/15/2024.
  2. How were the data generated, processed, and modified?
    Date: 2024 (process 1 of 3)
    This process step was performed by Kate Ackerman, using ArcGIS Pro (ver. 3.2.2). In this and all process steps, for simple operations the name of the geoprocessing tool used is given in capital letters; for complex operations, the name of the geoprocessing tool used is given in capital letters and 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.
    Merge input datasets.
    a) Download elevation (mu_elev_ESV.shp) and unvegetated to vegetated marsh ratio (UVVR) (mu_UVVR_ESV.shp) layers from the publications that cover the salt marshes of Eastern Shore of Virginia.
    b) JOIN the elevation and UVVR datasets to create one shapefile with both datasets in it.
    c) Convert the coordinate system from Web Mercator to the North American Datum of 1983 (NAD 1983) geographic coordinate system and add the coordinates for polygon centroids (X_POINT, Y_POINT) in decimal degrees to the data table using CALCULATE_GEOMETRY_ATTRIBUTES tool.
    d) Export the following variables to a comma separated values file [ESV_mu.csv]: X_POINT, Y_POINT, FID_CMU, UVVR, ATOT_M2, AVEG_M2, mu_ELEV, vg_ELEV, FLG. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Kate Ackerman
    Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2331 (voice)
    508-457-2310 (FAX)
    kackerman@usgs.gov
    Data sources used in this process:
    • mu_elev_ESV
    • mu_UVVR_ESV
    Data sources produced in this process:
    • ESV_mu.csv
    Date: 2024 (process 2 of 3)
    This processing steps was performed by Zafer Defne using VDatum online (VDatum ver. 4.6.1) and Matlab (ver. 2021b).
    Convert datums and calculate lifespan.
    a) Convert marsh unit elevations from the North American Vertical Datum of 1988 (NAVD88) to Mean Tide Level (MTL) referenced elevations.
    Input the ASCII file of latitude and longitude coordinates and elevation from ESV dataset (ESV_mu.csv) to VDatum software, and transform vertical datum from the NAVD88 to MTL. Do this for the marsh unit elevation (MU_ELEV) and elevation of the vegetated part of the marsh unit (VG_ELEV) to calculate MU_ELEV_MTL and VG_ELEV_MTL, respectively. Use value from the nearest Vdatum point for any point where VDatum has no data.
    b) Calculate sediment budget from UVVR based on Ganju and others (2020) with SB=-0.416*log(UVVR)-1.0749, where SB is sediment budget in kilograms per square meter per year, and log() indicates natural logarithm function.
    c) Calculate total sediment flux under background relative SLR (BGRND) with SF=SB*ATOT_M2, where SF is sediment flux in kilograms per year and ATOT_M2 is total surface area of marsh unit in square meters.
    d) Calculate total sediment flux under global mean sea level (GMSL) scenarios (for example, GMSL03 scenario means GMSL rise of 0.3 meters). SLR reduces vegetated marsh area, therefore, causes reduction in sediment flux. The sediment flux under SLR is calculated with SF_SLR=(SB-SLR_RATE*RHO_F)*ATOT_M2, where SF_SLR is sediment flux under SLR, RHO_F is dry bulk density of future deposited sediment. RHO_F was assigned 159 kilograms per cubic meters from Morris and others (2016). SLR_RATE is the SLR rate, calculated as SLR_RATE=(RSL2100+RSL_OFFSET)/100-RSL_VLM, where RSL2100 is the relative sea level by 2100 under a global mean sea level rise scenario, RSL_OFFSET is the offset to initiate the projection at year 2000, and RSL_VLM is the relative sea level contribution from vertical land motion.
    For sea level rise projections, Sweet and others (2022) SLR data within the region were used. A total of 14 points including 7 stations and 7 grid points were within the bounding box with lower left corner of (-76.4647N, 36.8217W) and upper right corner of (-73.0000N, 38.3267W).
    Interpolate the SLR_RATE from 14 points over a regular grid using GRIDDATA function with natural neighbor interpolation (grid size 35 longitudinal by 15 latitudinal points). Assign to each marsh unit the interpolated SLR_RATE value from the nearest grid point. Do this for the three scenarios considered: GMSL rise of 0.3 meters, 0.5 meters and 1.0 meters by year 2100 and calculate sediment flux for each of them.
    e) Total sediment mass in the vegetated plain above MTL is calculated with TS=vg_ELEV_MTL*AVEG_M2*RHO_E, where TS is total sediment mass, AVEG_M2 is the surface area of the vegetated part of the marsh unit and RHO_E is the dry bulk density of existing marsh substrate sediment. RHO_E was assigned 373 kilograms per cubic meters from Morris and others (2016).
    f) Calculate lifespan (in years) for the background relative SLR with the equation BGRND= -TS/SF. Calculate lifespan (in years) for global mean sea level rise by 0.3 meters, 0.5 meters and 1.0 meters by year 2100 scenarios with the equation GMSL= -TS/SF_SLR for each scenario (GMSL03, GMSL05, GMSL10, respectively).
    g) Output Matlab data as a comma separated text file [ESV_lifespan.csv]. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Zafer Defne
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov
    Data sources used in this process:
    • ESV_mu.csv
    Data sources produced in this process:
    • ESV_lifespan.csv
    Date: 2024 (process 3 of 3)
    This processing step was performed by Zafer Defne using ArcGIS Pro (ver. 3.2.2).
    Finalize the feature dataset and change projection.
    a) JOIN lifespan calculation results file [ESV_lifespan.csv] with the marsh unit features using ADD_JOIN and join field as FID_CMU.
    b) For marshes that are more stable, lifespan calculation sometimes results in large numbers that are far beyond the lifespan horizon of interest. Also, positive sediment budget implies unlimited lifespan. For these units, set the maximum lifespan value to 10,000 years.
    c) Set lifespan values to -9999 for units with no vegetated area or with missing elevation values (FLG values that contain any of -1 or -200 values in them) so that they can be labeled as not available or excluded while plotting the data.
    d) Set legend label for lifespan values less than 0 as imminent.
    e) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Input coordinate system= NAD 1983 Geographic coordinate system; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation= WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the lifespan values [mu_lifespan_ESV.shp]. Data sources used in this process:
    • ESV_lifespan.csv
    Data sources produced in this process:
    • mu_lifespan_ESV.shp
  3. What similar or related data should the user be aware of?
    Ganju, N.K., Defne, Z., and Fagherazzi, S., 2020, Are elevation and open-water conversion of salt marshes connected?: Geophysical Research Letters v. 47, issue 3.

    Online Links:

    Morris, J.T., Barber, D.C., Callaway, J.C., Chambers, R., Hagen, S.C., Hopkinson, C.S., Johnson, B.J., Megonigal, P., Neubauer, S.C., Troxler, T., and Wigand, C., 2016, Contributions of organic and inorganic matter to sediment volume and accretion in tidal wetlands at steady state: Earth’s Future v. 4, issue 4.

    Online Links:

    Sweet, W.V., Hamlington, B.D., Kopp, R.E., Weaver, C.P., Barnard, P.L., Bekaert, D., Brooks, W., Craghan, M., Dusek, G., Frederikse, T., Garner, G., Genz, A.S., Krasting, J.P., Larour, E., Marcy, D., Marra, J.J., Obeysekera, J., Osler, M., Pendleton, M., Roman, D., Schmied, L., Veatch, W., White, K.D., and Zuzak, C., 2022, Global and Regional Sea Level Rise Scenarios for the United States: Updated Mean Projections and Extreme Water Level Probabilities Along U.S. Coastlines: NOAA, Silver Spring, MD.

    Online Links:

    Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 2023, Conceptual marsh units of salt marshes on the Eastern Shore of Virginia in Geospatial characterization of salt marshes on the Eastern Shore of Virginia: data release DOI:10.5066/P9E6V0QK, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    The first link is to the data release, the second to the specific dataset referenced in the abstract.

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Marsh units, and water and land boundaries inherit their horizontal accuracy from accuracy of the source data, Eastern Shore of Virginia marsh units. The vertical accuracy of the marsh unit elevation is inherited from the 1-meter resolution 2015 USGS Lidar digital elevation model (DEM). The uncertainty in the lifespan estimates is large because of the nature of the empirical equations used and the uncertainty in the source data. For example, a 20% variation in each of the unvegetated to vegetated marsh ratio (UVVR), elevation, bulk density and sea-level rise variables, when all in favor of reducing lifespan, may result in a combined reduction of 50% in lifespan estimate.
  2. How accurate are the geographic locations?
    Horizontal accuracy is inherited from the source dataset (Conceptual marsh units of salt marshes on the Eastern Shore of Virginia) that delineates the marsh units, and can be considered to be +/-6 meters.
  3. How accurate are the heights or depths?
    Because the elevation values are averaged over delineated polygons, vertical accuracy of marsh unit elevation depends on both the horizontal accuracy of National Wetlands Inventory (NWI) dataset and the vertical accuracy of source elevation data (1-meter 2015 USGS Lidar DEM). The 1-meter 2015 USGS Lidar DEM vertical elevation accuracy was reported to be 0.06 meters. No additional accuracy assessment of the vertical accuracy has been conducted.
  4. Where are the gaps in the data? What is missing?
    The results are specific to the marsh units within the boundaries of the Eastern Shore of Virginia salt marsh system. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries.
  5. How consistent are the relationships among the observations, including topology?
    Negative lifespan indicates the estimated lifespan is depleted and loss is imminent. Some flagged units (see description for the FLG variable) are assigned a lifespan estimate of -9999.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints None
Use_Constraints The lifespan estimate 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.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The dataset contains polygon marsh unit lifespan data (mu_lifespan_ESV.shp and other shapefile components), browse graphic, and the FGDC CSDGM metadata in .xml format.
  3. What legal disclaimers am I supposed to read?
    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, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 12-Jul-2024
Metadata author:
U.S. Geological Survey
Attn: Zafer Defne
Oceanographer
384 Woods Hole Road
Woods Hole, MA

508-548-8700 x2254 (voice)
508-457-2310 (FAX)
whsc_data_contact@usgs.gov
Contact_Instructions:
The metadata contact email address is a generic address in the event the person is no longer with USGS.
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P14GBAVB/mu_lifespan_ESV.faq.html>
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