Lifespan of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia

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What does this data set describe?

Title:
Lifespan of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia
Abstract:
The sediment-based lifespan of salt marsh units in Assateague Island National Seashore (ASIS) and Chincoteague Bay is shown for conceptual marsh units defined by Defne and Ganju (2018). The lifespan represents the timescale by which the current sediment mass within a marsh parcel can no longer compensate for sediment export and deficits induced by sea-level rise. The lifespan calculation is based on vegetated cover, marsh elevation, sediment supply, and sea-level rise (SLR) predictions after Ganju and others (2020). Sea level rise scenarios are present day estimates corresponding to the 0.3, 0.5, and 1.0 meter increase in Global Mean Sea Level (GMSL) by 2100 from Sweet and others (2017). 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, including the Assateague Island National Seashore and Chincoteague Bay salt marshes, 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.
References: Defne, Z., and Ganju, N.K., 2018, Conceptual marsh units for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: U.S. Geological Survey data release, https://doi.org/10.5066/P92ZW4D9.
Ganju, N.K., Defne, Z., Fagherazzi, S., 2020, Are elevation and open-water conversion of salt marshes connected?, Geophysical Research Letters, https://doi.org/10.1029/2019GL086703.
Sweet, W.V., Kopp, R.E., Weaver, C.P., Obeysekera, J., Horton, R.M., Thieler, E.R., and Zervas, C., 2017, Global and regional sea level rise scenarios for the United States (Tech. Rep. NOS CO-OPS 083). Silver Spring, MD: National Oceanic and Atmospheric Administration. https://doi.org/10.7289/v5/tr-nos-coops-083.
  1. How might this data set be cited?
    Defne, Zafer, and Ganju, Neil K., 20220526, Lifespan of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P9WSYCAN, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Ganju, N.K., and Defne, Z. 2022, Lifespan of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: U.S. Geological Survey data release, https://doi.org/10.5066/P9WSYCAN.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.4955
    East_Bounding_Coordinate: -75.0962
    North_Bounding_Coordinate: 38.3377
    South_Bounding_Coordinate: 37.8457
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/6267eb10d34e76103ccf4d98?name=mu_lifespan_ASISp.png (PNG)
    Graphic of lifespan estimates under background relative sea level rise in Assateague Island and Chincoteague Bay salt marsh overlaying Esri basemap.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2022
    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 (3352)
    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_ASISp attribute table
    Attribute information associated with the lifespan estimates for the conceptual marsh units of Assateague Island and Chincoteague Bay salt marsh complex. (Source: USGS)
    FID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    FID_CMU
    Sequential unique whole number that represents the identification number for each conceptual marsh units. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:3351
    Units:none
    ATOT_M2
    Total surface area of a marsh unit in square meters. (Source: USGS)
    Range of values
    Minimum:199.285435731
    Maximum:623041.914617
    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:479882.968935
    Units:square meter
    mu_ELEV
    Mean elevation of a marsh unit in meters referenced to NAVD88. (Source: USGS)
    Range of values
    Minimum:-1.269
    Maximum:2.113
    Units:meter
    mu_ELEVMTL
    Mean elevation of a marsh unit in meters referenced to MTL. (Source: USGS)
    Range of values
    Minimum:-1.222
    Maximum:2.212
    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. No data value is -9999. (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-1.086
    Maximum:2.014
    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. No data value is -9999. (Source: USGS)
    ValueDefinition
    -9999No Data
    Range of values
    Minimum:-1.039
    Maximum:2.113
    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:659.179020539
    Units:none
    BGRND
    Lifespan for a marsh unit (in years) for nonclimatic background relative sea level rise. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-1049
    Maximum:10000
    Units:year
    GMSL03
    Lifespan for a marsh unit (in years) for global mean sea level rise of 0.3 meters by 2100. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-18233
    Maximum:10000
    Units:year
    GMSL05
    Lifespan for a marsh unit (in years) for global mean sea level rise of 0.5 meters by 2100. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-927
    Maximum:10000
    Units:year
    GMSL10
    Lifespan for a marsh unit (in years) for global mean sea level rise of 1.0 meters by 2100. (Source: USGS)
    ValueDefinition
    -9999No Data
    10000Value larger than or equal to 10000
    Range of values
    Minimum:-244
    Maximum:10000
    Units:year
    FLG
    Marsh unit flag indicating anomalous marsh units based on absence of vegetation, elevation and surface area. 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; (-1000) marsh unit surface area less than 900 square meters; and (0) no flag. Combination of negative values indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 square meters. (Source: USGS)
    Range of values
    Minimum:-1101
    Maximum:0
    Units:None
    Entity_and_Attribute_Overview:
    In this dataset, lifespan estimates for each conceptual salt marsh unit in the Assateague Island and Chincoteague Bay salt marsh complex has 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
  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 for each marsh unit in Assateague Island National Seashore and Chincoteague Bay.

How was the data set created?

  1. From what previous works were the data drawn?
    mu_elev_ASISp.shp (source 1 of 2)
    Defne, Zafer, and Ganju, Neil K., 2018, Elevation of marsh units in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P9HCTQ66, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    Used the marsh unit elevation (mu_ELEV) and vegetated fraction elevation (vg_ELEV) as inputs. Projection was WGS 1984 Web Mercator Auxiliary Sphere.
    mu_UVVR_ASISp.shp (source 2 of 2)
    Defne, Zafer, and Ganju, Neil K., 2018, Unvegetated to vegetated marsh ratio in Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P9AY52YJ, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution:
    Used the unvegetated to vegetated ratio (mu_UVVR) as input. Projection was WGS 1984 Web Mercator Auxiliary Sphere.
  2. How were the data generated, processed, and modified?
    Date: 2022 (process 1 of 3)
    This process step and subsequent process steps were performed by the same person, Zafer Defne, in ArcGIS Pro (ver.2.8.2) 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.
    a) Download elevation and unvegetated to vegetated marsh ratio (UVVR) datasets for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia from the USGS ScienceBase (https://doi.org/10.5066/P9HCTQ66 and https://doi.org/10.5066/P9AY52YJ, respectively).
    b) Convert the coordinate system to the North American Datum of 1983 (NAD 1983) geographic coordinate system and add the coordinates for polygon centroids to the data table using ADD_GEOMETRY_ATTRIBUTES tool.
    c) Export following variables to a comma separated values file [ASIS_life.csv]: X_POINT, Y_POINT, FID_CMU, UVVR, ATOT_M2, AVEG_M2, mu_ELEV, vg_ELEV. 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:
    • mu_elev_ASISp.shp
    • mu_UVVR_ASISp.chp
    Data sources produced in this process:
    • ASIS_life.csv
    Date: 2022 (process 2 of 3)
    The following processing stepswereperformed by Neil Ganju using VDatum online (VDatum ver.3.9) and Matlab (ver.2018a).
    a) Convert elevations from the North American Vertical Datum of 1988 (NAVD88)to Mean Tide Level (MTL) referenced elevations.
    Upload the ASCII file of latitude and longitude coordinates and elevation to VDatum online , and transform vertical datum from the NAVD88 to MTL. Do this for the marsh unit elevation and elevation of the vegetated part of the marsh unit 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 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 sediment flux for the three scenarios considered: Global mean sea level rise of 0.3 meters, 0.5 meters and 1.0 meters by year 2100.
    Sea-level rise (SLR) reduces vegetated marsh area, therefore, causes reduction in sediment flux. The sediment flux under SLR is calculated with SF_SLR= (SB-(GMSLR-BGRND_RSLR)*RHO_F)*ATOT_M2, where SF_SLR is sediment flux under SLR, RHO_F is dry bulk density of future deposited sediment, GMSLR is the local SLR in meters for a specific global mean sea level rise scenario, and BGRND_RSLR is the non-climatic background relative sea level rise in meters. RHO_F was assigned 159 kilograms per cubic meters from Morris and others (2016). For sea level rise projections, the averages of values from two stations (LEWES and KIPTOPEKE) from Sweet and others (2017) were used: 0.00175 meters for BGRND_RSLR, 0.0051, 0.0066, and 0.0132 meters for GMSLR of 0.3, 05. and 1.0 meters by 2100.
    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) under the 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) Save results as a Matlab data file [ASIS_life.mat].
    References:
    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, 4(4), 110–121. https://doi.org/10.1002/2015EF000334
    Sweet, W.V., Kopp, R.E., Weaver, C.P., Obeysekera, J., Horton, R.M., Thieler, E.R., and Zervas, C., 2017, Global and regional sea level rise scenarios for the United States (Tech. Rep. NOS CO-OPS 083). Silver Spring, MD: National Oceanic and Atmospheric Administration. https://doi.org/10.7289/v5/tr-nos-coops-083. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Neil K. Ganju
    Research Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2252 (voice)
    508-457-2310 (FAX)
    nganju@usgs.gov
    Data sources used in this process:
    • ASIS_life.csv
    Data sources produced in this process:
    • ASIS_life.mat
    Date: 2022 (process 3 of 3)
    The rest of the processing steps were done by Zafer Defne, in ArcGIS Pro (ver.2.8.2) and Matlab (ver.2011b) unless otherwise stated.
    a) Output Matlab data as a comma separated text file and merge with the marsh units features using ADD_JOIN and join filed 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 for flagged units (FLG less than 0) to -9999 so that they can be labeled as not available or excluded while plotting the data.
    d) Set 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 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 lifespan values [mu_lifespan_ASISp.shp]. 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:
    • ASIS_life.mat
    Data sources produced in this process:
    • mu_lifespan_ASISp.shp
  3. What similar or related data should the user be aware of?
    Defne, Zafer, and Ganju, Neil K., 2018, Conceptual marsh units for Assateague Island National Seashore and Chincoteague Bay, Maryland and Virginia: data release DOI:10.5066/P92ZW4D9, U.S. Geological Survey, Reston, VA.

    Online Links:

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

  1. How well have the observations been checked?
    Marsh units, water and land boundary inherit their accuracy from accuracy of the source data, Assateague Island marsh units, and vertical accuracy marsh unit elevation calculated from the 1-meter resolution U.S. Geological Survey Coastal National Elevation Database (USGS CoNED) data with processing date of 2016. 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 contributing in the direction 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 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 NWI dataset and the vertical accuracy of source elevation data, CoNED. CoNED vertical elevation accuracy was 0.2 meters.
  4. Where are the gaps in the data? What is missing?
    The results are specific to the marsh polygons definition within the boundaries of the Assateague Island and Chincoteague Bay 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. Coverage near the domain boundaries in Wallops Bay and Wallops Island is not complete and not suggested for use in analyses (specifically marsh units with FID_CMU= 3, 1659, 1666, 1672 and 1728).
  5. How consistent are the relationships among the observations, including topology?
    Negative lifespan indicates the estimated lifespan is depleted and loss is imminent. Flagged units (see description for the FLG variable) are assigned a lifespan estimate of -10,000.

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? mu_lifespan_ASISp
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 26-May-2022
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)
zdefne@usgs.gov
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_P9WSYCAN/mu_lifespan_ASISp.faq.html>
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