Tidal Marsh Soil Surveys, Radiocarbon and 137 Cs data

All of these files are Access Databases that contain RTK elevation survey data and the corresponding vegetation surveys that were conducted concurrently. Over 2,000 intertidal plots were sampled for plant cover, frequency of occurrence, and species richness across the six study sites. Approximately 57 vascular plant species were found in the study, including grasses, rushes, forbs and sedges. Vegetated marsh ranged in elevation from approximately local mean tide level (MTL) to the marsh-upland transition zone (upland plots, defined as areas estimated to flood 1 time per year on average, were not considered for further analysis). We assessed vegetation cover and species richness concurrently with elevation surveys at approximately 25% of the elevation points. We visually assessed percent cover of all plant species within a 0.25 m2 quadrat, and recorded the average and maximum height (measured to the nearest centimeter) of each species. Total plant cover in a plot could exceed 100% due to vegetation layering. Vascular plant nomenclature generally follows Baldwin et al. (2012). We used long-term (10 yr) NOAA tide data to assess inundation relationships with local elevation and thereby define the elevation limits of four intertidal habitat zones for evaluation of SLR impacts to marshes along the California coastline: low marsh, middle marsh, high marsh and transitional marsh. First, to determine region-specific relationships between elevation and inundation, we compiled data from all recorded high tides from 2004-2013 at three NOAA tidal stations along the US west coast: San Diego, San Francisco, and Charleston, Oregon (tidesandcurrents.noaa.gov). Using these time series, we determined the percentage of high tides that reached a given elevation. We defined low marsh as all elevations between the lowest vegetation plot and the elevation reached by 50% of all recorded high tides (low marsh flooded at least once daily, on average). We defined middle marsh as habitat flooded by 50-25% of all high tides (flooding once every 1-2 days, on average), and high marsh as elevations flooded by 3-25% of all high tides (flooding at least twice per month, but less than once every other day, on average). We defined transition zone marsh as habitat flooded by 0.14-3% of all high tides (flooding at least once annually, but no more than twice per month, on average). Mudflat occurred between local mean-lower low water (MLLW) and the lowest extent of emergent tidal marsh vegetation; subtidal habitat occurred. Using the regional NOAA data, we determined the z* ranges that corresponded to the four marsh zones as defined above.

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