Surface Elevation Tables and Marker Horizon (collectively SET-MH) datasets provide a unique opportunity to evaluate tidal marsh accretion rates compared with current and projected sea-level rise. SET is a tool that allows for accurate and repeatable measurements of marsh elevation, while Marker Horizon allows for the measurement of sediment that has deposited on top of the feldspar marker. SETs are deep rod benchmarks with an attachment for a portable leveling device (arm) at fixed directions. The distance from the fixed arm to the marsh surface is measured by lowering a set of pins (usually nine) from the SET to the marsh surface, providing a repeatable and accurate measurement of elevation change. Marker horizon data measure the amount of sediment that is deposited onto the marsh surface, is a layer of white feldspar clay applied to a 0.5x0.5m quadrats associated with each SET. Marker horizons are measured by extracting a plug from the marsh surface using a knife or cryo-core, and measuring the sediment deposited on top of the layer. Together, repeated measurements of SET-MH data separates surface deposition from shallow subsurface processes (e.g., root growth or shallow soil compaction). The ability of a tidal marsh to keep up with sea-level rise was largely due to relative sediment load and to a smaller degree it’s position within the tidal frame.

Surface Elevation Tables (SETs) were installed in 2009 and 2010 using permanent, deep rods driven down into the soil with a demolition hammer, typically about 60-80 feet. The top of the rod lies near the sediment surface, with a receiver end. A Surface Elevation Table is a portable mechanical leveling device that attaches to the receiving end at the top of the deep rod. The SET arm includes a bubble level and a notched collar that allows for the arm to be aligned precisely and repeatedly in the cardinal directions. SETs were installed as triplicates in Reference, Phase II, and as north-south pairs in the 2009 restoration area (Units 1-4). Each SET location was read repeatedly at regular, at least annual intervals. Reading SETs consisted of measurements for nine pins facing the four cardinal directions for a total of 36 measurements per SET, per sampling event. Each pin was measured to the nearest millimeter.

Surface Elevation Tables (SETs) were installed in 2009 and 2010 using permanent, deep rods driven down into the soil with a demolition hammer, typically about 60-80 feet. The top of the rod lies near the sediment surface, with a receiver end. A Surface Elevation Table is a portable mechanical leveling device that attaches to the receiving end at the top of the deep rod. The SET arm includes a bubble level and a notched collar that allows for the arm to be aligned precisely and repeatedly in the cardinal directions. SETs were installed as triplicates in Reference, Phase II, and as north-south pairs in the 2009 restoration area (Units 1-4). Each SET location was read repeatedly at regular, at least annual intervals. Reading SETs consisted of measurements for nine pins facing the four cardinal directions for a total of 36 measurements per SET, per sampling event. Each pin was measured to the nearest millimeter.

SET-MH were installed in 2009 and 2010 with three replicates in Reference and Phase II and with two replicates (north-south) pairs in the 2009 restoration area (Units 1-4). SET-MH were read repeatedly at regular, at least annual intervals. Reading SETs consisted of measurements for nine pins facing the four cardinal directions for a total of 36 measurements per SET, per sampling event. Marker Horizons consisted of a marker, usually white feldspar clay, so that the sediment that accumulated on top of the marker would be visible and measurable to the nearest millimeter. Together, SET-MH provide information on surface elevation changes due to surface accretion (MH) compared to changes that may be due to subsurface processes (such as root growth or groundwater swelling).

Surface elevation tables with marker horizons (SET-MH) measure millimeter-scale changes in elevation over time. A combination of pin measurements (elevation change) and surface deposition measurements (marker horizon) is used to distinguish elevation changes due to belowground and aboveground processes. SET-MHs were installed in 2016 and were measured quarterly across five tidal marshes (Petaluma marsh, San Pablo Bay National Wildlife Refuge, Rush Ranch, Browns Island, and Miners Slough).

Surface elevation tables with marker horizons (SET-MH) measure millimeter-scale changes in elevation over time. A combination of pin measurements (elevation change) and surface deposition measurements (marker horizon) is used to distinguish elevation changes due to belowground and aboveground processes. SET-MHs were installed in 2016 and were measured quarterly across five tidal marshes (Petaluma marsh, San Pablo Bay National Wildlife Refuge, Rush Ranch, Browns Island, and Miners Slough).

Here we provide data used to report on changes in tidal marsh elevation in relation to our network of 20 fixed benchmarks located across a geographically broad network of coastal elevation monitoring stations with standard monitoring protocols. This dataset includes Surface Elevation Table (SET) measurements taken from 10 sites along the US Atlantic coast, ranging from Virginia to Maine. Each site includes 2 SETs where repeat measurements of wetland surface elevation were made from 2005-2019.

Here we provide data used to report on changes in tidal marsh elevation in relation to our network of 20 fixed benchmarks located across a geographically broad network of coastal elevation monitoring stations with standard monitoring protocols. This dataset includes Surface Elevation Table (SET) measurements taken from 10 sites along the US Atlantic coast, ranging from Virginia to Maine. Each site includes 2 SETs where repeat measurements of wetland surface elevation were made from 2005-2019.

To assess the current topography of the tidal marshes we conducted survey-grade elevation surveys at all sites between 2009 and 2013 using a Leica RX1200 Real Time Kinematic (RTK)Global Positioning System (GPS) rover (±1 cm horizontal, ±2 cm vertical accuracy; Leica Geosystems Inc., Norcross, GA; Figure 4). At sites with RTK network coverage (San Pablo, Petaluma, Pt. Mugu, and Newport), rover positions were received in real time from the Leica Smartnet system via a CDMA modem (www.lecia-geosystems.com). At sites without network coverage (Humboldt, Bolinas, Morro and Tijuana), rover positions were received in real time from a Leica GS10 antenna base station via radio link. When using the base station, we adjusted all elevation measurements using an OPUS correction (www.ngs.noaa.gov/OPUS). We used the WGS84 ellipsoid model for vertical and horizontal positioning. We verified rover accuracy and precision by measuring positions at local National Geodetic Survey (NGS) benchmarks and temporary benchmarks established at each site (Table 1). Average measured vertical errors at benchmarks were 1-2 cm throughout the study, comparable to the stated error of the GPS. At each site, we surveyed marsh surface elevation along transects oriented perpendicular to the major tidal sediment source, with a survey point taken every 12.5 m; 50 m separated transect lines. We used the Geoid09 model to calculate orthometric heights from ellipsoid values (m, NAVD88; North American Vertical Datum of 1988) and projected all points to NAD83 UTM zone 10 or zone 11 using Leica GeoOffice (Leica Geosystems Inc, Norcross, GA, v. 7.0.1).We synthesized the elevation survey data to create a digital elevation model (DEM) at each site in ArcGIS 10.2.1 Spatial Analyst (ESRI 2013; Redlands, CA) with exponential ordinary kriging methods (5 x 5 mcell size) after adjusting model parameters to minimize the root-mean-square error (RMS). We used elevation models as the baseline conditions for subsequent analyses in this study including tidal inundation patterns, SLR response modeling, and mapping of sites by specific elevation (flooding) zones.

To assess the current topography of the tidal marshes we conducted survey-grade elevation surveys at all sites between 2009 and 2013 using a Leica RX1200 Real Time Kinematic (RTK)Global Positioning System (GPS) rover (±1 cm horizontal, ±2 cm vertical accuracy; Leica Geosystems Inc., Norcross, GA; Figure 4). At sites with RTK network coverage (San Pablo, Petaluma, Pt. Mugu, and Newport), rover positions were received in real time from the Leica Smartnet system via a CDMA modem (www.lecia-geosystems.com). At sites without network coverage (Humboldt, Bolinas, Morro and Tijuana), rover positions were received in real time from a Leica GS10 antenna base station via radio link. When using the base station, we adjusted all elevation measurements using an OPUS correction (www.ngs.noaa.gov/OPUS). We used the WGS84 ellipsoid model for vertical and horizontal positioning. We verified rover accuracy and precision by measuring positions at local National Geodetic Survey (NGS) benchmarks and temporary benchmarks established at each site (Table 1). Average measured vertical errors at benchmarks were 1-2 cm throughout the study, comparable to the stated error of the GPS. At each site, we surveyed marsh surface elevation along transects oriented perpendicular to the major tidal sediment source, with a survey point taken every 12.5 m; 50 m separated transect lines. We used the Geoid09 model to calculate orthometric heights from ellipsoid values (m, NAVD88; North American Vertical Datum of 1988) and projected all points to NAD83 UTM zone 10 or zone 11 using Leica GeoOffice (Leica Geosystems Inc, Norcross, GA, v. 7.0.1).We synthesized the elevation survey data to create a digital elevation model (DEM) at each site in ArcGIS 10.2.1 Spatial Analyst (ESRI 2013; Redlands, CA) with exponential ordinary kriging methods (5 x 5 mcell size) after adjusting model parameters to minimize the root-mean-square error (RMS). We used elevation models as the baseline conditions for subsequent analyses in this study including tidal inundation patterns, SLR response modeling, and mapping of sites by specific elevation (flooding) zones.