SaltMarshMetrics2022

Town within which the largest portion of the marsh unit is located

Region within the NH seacoast having broadly similar tidal regime

Computed as marsh unit area / edge length for each marsh unit. A low value represents more edge which means exposure and increased risk of loss, and is a negative.

Computed as the Unvegetated area / Vegetated area within each marsh unit. Computed using the marsh extent layer OCM generated as part of the marsh habitat mapping project because it includes the non-vegetated classes. Polygons were derived from the raw marsh clump dataset with a 10 meter buffer to enclose/capture small pannes, pools, and creeks that were not included in the marsh polygons. A low value represents more vegetation and is a positive, while a high value indicates higher amount of unvegetated surface and is a negative.

Percent impervious cover within 150 meter buffer of each marsh unit. Computed using “Impervious Surfaces in the Coastal Watershed of NH and Maine, High Resolution – 2021” (NH GRANIT). A high value represents more impervious cover and potentially polluted runoff that can negatively impact marsh habitat.

Percent natural cover within 150 meter buffer of each marsh unit. Computed using NOAA 2016 C-CAP BETA 10m land cover data and derived from all the natural cover classes. A high value represents more natural cover that can absorb runoff and filter pollutants and is a positive.

Percent agricultural cover within 150 meter buffer of each marsh unit. Computed using NH 2015 Land Use data and derived from the "Agricultural Land" and "Other Agricultural Land" classes. A high value can result in more potentially polluted runoff and is a negative.

Count number of different species of rare animals and plants within the marsh unit (occurrences provided by NH Natural Heritage Bureau, Dec. 2022).

Estimated from water quality samples. Computed by intersecting marsh units with USGS SPARROW catchments, calculated the area-weighted average of the “tn” value.

Computed as a line density raster dataset (feet per acre); and the metric represents the maximum value for any portion of the marsh unit (ditch presence verified using recent orthophotos). Value increases with ditch density, and is a negative.

Computed as percent area of each marsh unit, using the data layer “nh_salt_marsh_habitats_20191010_Phrag_only”. Value increases with higher potential impact from invasive plants, and is a negative.

Computed Shannon diversity index based on habitat types mapped in the data layer “nh_2013_salt_marsh_habitats_20200123” within each marsh unit. The value, Shannon index, increases as both the richness and the evenness of the community increase, and is a positive.

Computed as the proportion of migration space immediately adjacent to marsh unit boundary that has berms present. Berms are based on TPI, derived from the LiDAR DEM using a raster calculator equation: ("tpi" > 0.1) & ("slopedeg" < 8), where tpi = elevation – focal mean of elevation in a 8x8 neighborhood. Marsh units buffered by 16m and clipped to migration space, measured amount of berm area in that resulting area. Value increases with berm presence and is a negative.

Computed by averaging the "AVG_KFACT" attribute from the Area- and Depth-Weighted Averages of Selected SSURGO Variables for the Conterminous United States and District of Columbia data set across soil units contained in the MUPOLYGON feature class from the gSSURGO database. It is a unitless erodibility factor ranging from 0 to 0.64, which quantifies the susceptibility of soil particles to detachment by water. Soils resistant to detachment have low values < 0.15 and erodible soils that easily detach have values > 0.4. This metric is a Negative, higher erodibility indicates higher vulnerability and lower resilience.

Mean tidal range computed for each marsh unit. Units are meters. Tidal range values represent the height from Mean Lower Low Water to Mean Higher High Water as derived from NOAA's Vdatum model. Higher value indicates larger tidal range and better resilience, it is a Positive.

Percent of marsh unit below Mean Higher High Water (MHHW). Computed using tidal surface generated from NOAA's Vdatum model. It is a Negative - more area below MHHW indicates higher vulnerability and lower resilience.

Percent of marsh unit below Mean Tide Level (MTL). Computed using tidal surface generated from NOAA's Vdatum model. It is a Negative.

Percent of shoreline within marsh unit that is hardened. Computed by dividing the length of New Hampshire’s shorelinestructureinventory.shp by the length NHShoreline.shp contained within a 10 meter buffered version of each marsh unit. Higher value indicates more impediment to migration, and is a negative.

Migration space represents the area into which marsh units may migrate under future sea level rise scenarios. Unioned marsh units with the 2022 SLAMM results ("salt marsh persistent" and "salt marsh potential" status for the 1.5 meter SLR by 2100 scenario which represents the high end of the range for this region). Calculated area (sq. meters) contiguous with each marsh unit. Higher value indicates marsh persistence, and is a positive.

This represents the degree to which each marsh unit will be connected to adjacent marsh units under future sea level rise scenarios. This was computed by using the combined 2025, 2050, and 2075 marsh migration areas (persistent and potential) under the 2-meter SLR scenario and counting the number of connections with adjacent marsh units. The count was scaled by the total lengths of the connections for each marsh unit. Higher value indicates better connectedness and is a positive.

The sinuosity of shoreline within each marsh unit. (from Anderson and Barnett, 2017: "An intricate shoreline with lots of inlets and variable physical characteristics provides diverse habitat options and harbors greater ecological diversity than a simple shoreline, and creates resilience by dividing and distributing inundation levels." Computed using NOAA's Environmental Sensitivity Index shoreline and the Sinuosity python script provided by Esri, using ESI shoreline segments intersected with 10m buffered marsh units. Since the sinuosity script generates values from 0-1, Data Notes for the New Hampshire Salt Marsh Plan, April 2023 page 6 where 1 is a straight feature, we multiplied the sinuosity index by -1 so that values closer to 0 were scored higher in the quantile index. A value closer to 0 is a more complex shoreline, and is a positive.

Higher score = Good current condition, higher resilience on scale 1-100

Higher score = More adaptation potential, higher resilience on scale 1-100

Equally weighted sum of Condition + Vulnerability(inverted) + Adaptation. High Score = high overall resilience, good condition, low vulnerability, more adaptation potential

high/low designation indicates whether the marsh unit is in the top half or lower half of all marshes in NH based on the current condition score

high/low designation indicates whether the marsh unit is in the top half or lower half of all marshes in NH based on the vulnerability score

high/low designation indicates whether the marsh unit is in the top half or lower half of all marshes in NH based on the adaptation potential score

Computed as the Unvegetated area / Vegetated area within each marsh unit estimated for the year 2100 at intermediate sea level rise.

For each metric, NH Fish and Game calculated decile breaks to create 10 equal bins within the raw data, and then assigned a rank score to each marsh unit based on the corresponding bin: 1-10. We multiplied metrics with a negative impact by negative 1, so that scores within an element (Condition, Vulnerability or Adaptation) are on a consistent scale, e.g., from poor condition to good condition. For example, a high percentage of phragmites was transformed to a low decile score so that it would correspond with poor condition and low resilience. Quantile scores are available within the attribute table accessible through Data Viewer to enable users to learn more about an individual marsh and see how it compares to other marshes in NH.

For each metric, NH Fish and Game calculated decile breaks to create 10 equal bins within the raw data, and then assigned a rank score to each marsh unit based on the corresponding bin: 1-10. We multiplied metrics with a negative impact by negative 1, so that scores within an element (Condition, Vulnerability or Adaptation) are on a consistent scale, e.g., from poor condition to good condition. For example, a high percentage of phragmites was transformed to a low decile score so that it would correspond with poor condition and low resilience. Quantile scores are available within the attribute table accessible through Data Viewer to enable users to learn more about an individual marsh and see how it compares to other marshes in NH.