Understanding the rates and patterns of tidal wetland elevation changes relative to sea-level is essential for understanding the extent of potential wetland loss over the coming years. Using an enhanced and more flexible modeling framework of an ecosystem model (WARMER-2), we explored sea-level rise (SLR) impacts on wetland elevations and carbon sequestration rates through 2100 by considering plant community transitions, salinity effects on productivity, and changes in sediment availability. We incorporated local experimental results for plant productivity relative to inundation and salinity into a species transition model, as well as site-level estimates of organic matter decomposition. The revised modeling framework includes an improved calibration scheme that more accurately reconstructs soil profiles and incorporates parameter uncertainty through Monte Carlo simulations. Using WARMER-2, we evaluated elevation change in three tidal wetlands in the San Francisco Bay Estuary, CA, USA along an estuarine tidal and salinity gradient with varying scenarios of SLR, salinization, and changes in sediment availability. We also tested the sensitivity of marsh elevation and carbon accumulation rates to different plant productivity functions. Wetland elevation at all three sites was sensitive to changes in sediment availability, but sites with greater initial elevations or space for upland transgression persisted longer under higher SLR rates than sites at lower elevations. Using a multi-species wetland vegetation transition model for organic matter contribution to accretion, WARMER-2 projected increased elevations relative to sea levels (resilience) and higher rates of carbon accumulation when compared with projections assuming no future change in vegetation with SLR. The new WARMER-2 modeling framework is widely applicable to other tidal wetland ecosystems and can assist in teasing apart important drivers of wetland elevation change under SLR.

Accurate input data are important for making site-specific projections of tidal wetlands into the future. We developed bias-corrected digital elevation models (DEM) using the LEAN approach (LiDAR Elevation Adjustment with NDVI). LEAN DEMs were used as the initial elevation for model projections. Further, we conducted elevation and vegetation surveys across each study site to characterize elevation profiles of dominant species, which were used to inform organic productivity functions in WARMER-2.

Habitat projections from the WARMER-2 model for four tidal wetland sites in San Francisco Bay estuary under the constant sediment scenario, plus 0.2 ppt per decade salinity scenario, and the community transition organic productivity function under a 99 cm by 2100 sea-level rise scenario. Results are the average from one hundred Monte Carlo simulations.

Projections of marsh elevation change with WARMER-2 across five regions of the San Francisco Bay Delta (Cache Yolo, South Delta, North Delta, Central Delta, and Suisun). The model was run across a range of initial elevations for each region and for scenarios of sea-level rise (30, 61, 91, 122, 152, 183, 305 cm by 2100), sediment availability (historic, constant, declining, and increase), and with and without a temporally dynamic tidal range. Results from the Delta Simulation Model 2 hydrodynamic model were used to calculate rates of tide range increase with sea-level rise. WARMER-2 was calibrated using soil cores from Callaway et al 2012 (Rush Ranch and Browns Island cores), and a soil core from Miners Slough.

The research was conducted at eight tidal marshes in coastal estuaries spanning the Washington and Oregon coastlines from Padilla Bay in northern Washington to Bandon located at the mouth of the Coquille River in southern Oregon. The researchers performed bathymetric surveys, created digital elevation models, measured historic rates of mineral and organic matter accumulation, conducted vegetation surveys, deployed water level data loggers, and produced WARMER wetland accretion model projections for each study site. This collection contains data for all of the above across a number of different datasets. Users should investigate the metadata for each item for more information about it's purpose, methods, quality, and characteristics.

We used WARMER, a 1-D cohort model of wetland accretion (Swanson et al. 2014), which is based on Callaway et al. (1996), to examine SLR projections across each study site. Each cohort in the model represents the total organic and inorganic matter added to the soil column each year. WARMER calculates elevation changes relative to MSL based on projected changes in relative sea level, subsidence, inorganic sediment accumulation, aboveground and belowground organic matter productivity, compaction, and decay for a representative marsh area. Each cohort provides the mass of inorganic and organic matter accumulated at the surface in a single year as well as any subsequent belowground organic matter productivity (root growth) minus decay. Cohort density, a function of mineral, organic, and water content, is calculated at each time step to account for the decay of organic material and auto-compaction of the soil column. The change in relative elevation is then calculated as the difference between the change in modeled sea level and the change in height of the soil column, which was estimated as the sum of the volume of all cohorts over the unit area model domain. The total volume of an individual cohort is estimated as the sum of the mass of pore space water, sediment, and organic matter, divided by the cohort bulk density for each annual time step. Elevation is adjusted relative to sea level rise after each year of organic and inorganic input, compaction, and decomposition. We parameterized WARMER from the elevation, vegetation, and water level data collected at each site. We evaluated model outputs between 2010 and 2110 using marsh elevation zones defined above.Model inputs Sea-level rise scenariosIn WARMER, we incorporated a recent forecast for the Pacific coast which projects low, mid, and high SLR scenarios of 12, 64 and 142 cm by 2110, respectively (NRC 2012). We used the average annual SLR curve as the input function for the WARMER model. We assumed the difference between the maximum tidal height and minimum tidal height (tide range) remained constant through time, with only MSL changing annually.Inorganic matterThe annual sediment accretion rate is a function of inundation frequency and the mineral accumulation rates measured from 137Csdating of soil cores sampled across each site. For each site, we developed a continuous model of water level from the major harmonic constituents of a nearby NOAA tide gauge. This allowed a more accurate characterization of the full tidal regime as our water loggers were located above MLLW. Following Swanson et al. (2014), we assumed that inundation frequency was directly related to sediment mass accumulation; this simplifying assumption does not account for the potential feedback between biomass and sediment deposition and holds suspended sediment concentration and settling velocity constant. Sediment accretion, Ms,at a given elevation, z, is equal to, where f(z) is dimensionless inundation frequency as a function of elevation (z), and Sis the annual sediment accumulation rate in g cm-2 y-1.Organic matterWe used a unimodal functional shape to describe the relationship between elevation and organic matter (Morris et al. 2002), based on Atlantic coast work on Spartina alterniflora. Given that Pacific Northwest tidal marshes are dominated by other plant species, we developed site-specific, asymmetric unimodal relationships to characterize elevation-productivity relationships. We used Bezier curves to draw a unimodal parabola, anchored on the low elevation by MTL at the high elevation by the maximum observed water level from a nearby NOAA tide gauge. We determined the elevation of peak productivity by analyzing the Normalized Difference Vegetation Index (NDVI; (NIR - Red)/(NIR + Red)) from 2011 NAIP imagery (4 spectral bands, 1 m resolution; Tucker 1979) and our interpolated DEM. We then calibrated the amplitude of the unimodal function to the organic matter input rates (determined from sediment

We used WARMER, a 1-D cohort model of wetland accretion (Swanson et al. 2014), which is based on Callaway et al. (1996), to examine SLR projections across each study site. Each cohort in the model represents the total organic and inorganic matter added to the soil column each year. WARMER calculates elevation changes relative to MSL based on projected changes in relative sea level, subsidence, inorganic sediment accumulation, aboveground and belowground organic matter productivity, compaction, and decay for a representative marsh area. Each cohort provides the mass of inorganic and organic matter accumulated at the surface in a single year as well as any subsequent belowground organic matter productivity (root growth) minus decay. Cohort density, a function of mineral, organic, and water content, is calculated at each time step to account for the decay of organic material and auto-compaction of the soil column. The change in relative elevation is then calculated as the difference between the change in modeled sea level and the change in height of the soil column, which was estimated as the sum of the volume of all cohorts over the unit area model domain. The total volume of an individual cohort is estimated as the sum of the mass of pore space water, sediment, and organic matter, divided by the cohort bulk density for each annual time step. Elevation is adjusted relative to sea level rise after each year of organic and inorganic input, compaction, and decomposition. We parameterized WARMER from the elevation, vegetation, and water level data collected at each site. We evaluated model outputs between 2010 and 2110 using marsh elevation zones defined above.Model inputs Sea-level rise scenariosIn WARMER, we incorporated a recent forecast for the Pacific coast which projects low, mid, and high SLR scenarios of 12, 64 and 142 cm by 2110, respectively (NRC 2012). We used the average annual SLR curve as the input function for the WARMER model. We assumed the difference between the maximum tidal height and minimum tidal height (tide range) remained constant through time, with only MSL changing annually.Inorganic matterThe annual sediment accretion rate is a function of inundation frequency and the mineral accumulation rates measured from 137Csdating of soil cores sampled across each site. For each site, we developed a continuous model of water level from the major harmonic constituents of a nearby NOAA tide gauge. This allowed a more accurate characterization of the full tidal regime as our water loggers were located above MLLW. Following Swanson et al. (2014), we assumed that inundation frequency was directly related to sediment mass accumulation; this simplifying assumption does not account for the potential feedback between biomass and sediment deposition and holds suspended sediment concentration and settling velocity constant. Sediment accretion, Ms,at a given elevation, z, is equal to, where f(z) is dimensionless inundation frequency as a function of elevation (z), and Sis the annual sediment accumulation rate in g cm-2 y-1.Organic matterWe used a unimodal functional shape to describe the relationship between elevation and organic matter (Morris et al. 2002), based on Atlantic coast work on Spartina alterniflora. Given that Pacific Northwest tidal marshes are dominated by other plant species, we developed site-specific, asymmetric unimodal relationships to characterize elevation-productivity relationships. We used Bezier curves to draw a unimodal parabola, anchored on the low elevation by MTL at the high elevation by the maximum observed water level from a nearby NOAA tide gauge. We determined the elevation of peak productivity by analyzing the Normalized Difference Vegetation Index (NDVI; (NIR - Red)/(NIR + Red)) from 2011 NAIP imagery (4 spectral bands, 1 m resolution; Tucker 1979) and our interpolated DEM. We then calibrated the amplitude of the unimodal function to the organic matter input rates (determined from sediment

The overarching goal of this research was to use site-specific data to develop local and regionally-applicable climate change models that inform management of tidal wetlands along the Pacific Northwest coast. The overarching questions were: (1) how do tidal marsh site characteristics vary across estuaries, and (2) does tidal marsh susceptibility to sea-level rise (SLR) vary along a latitudinal gradient and between estuaries? These questions are addressed in this data collection with three specific objectives: (1) measure topographical and ecological characteristics (e.g., elevation, tidal range, vegetation composition) for tidal marsh and intertidal mudflats, (2) model SLR vulnerability of these habitats, and (3) examine spatial variability of these projected changes along the latitudinal gradient of the California coast.

The overarching goal of this research was to use site-specific data to develop local and regionally-applicable climate change models that inform management of tidal wetlands along the Pacific Northwest coast. The overarching questions were: (1) how do tidal marsh site characteristics vary across estuaries, and (2) does tidal marsh susceptibility to sea-level rise (SLR) vary along a latitudinal gradient and between estuaries? These questions are addressed in this data collection with three specific objectives: (1) measure topographical and ecological characteristics (e.g., elevation, tidal range, vegetation composition) for tidal marsh and intertidal mudflats, (2) model SLR vulnerability of these habitats, and (3) examine spatial variability of these projected changes along the latitudinal gradient of the California coast.

This dataset consists of raster geotiff outputs from modeling vertical accretion and carbon accumulation in the Nisqually River Delta, Washington, USA. These rasters represent projections of future habitat type, change in surface elevation above Mean Sea Level, and total sediment carbon accumulation since 2011 in coastal wetland habitats. Projections were generated in 20-year increments for 100 years for five amounts of sea-level rise, three amounts of suspended sediment concentrations, and two alternative configurations of the U.S. Interstate-5 causeway as it crosses the Nisqually River to either prevent or allow inland habitat migration (a total of 30 scenarios). The full methods and results are described in detail in the parent manuscript, “Can coastal habitats rise to the challenge? Resilience of estuarine habitats, carbon accumulation, and its value to sea-level rise for adaptation planning in a Puget Sound estuary” (2022).