SMARTX Elevation Data_2016-2020

The Salt Marsh Accretion Response to Temperature Experiment (SMARTX) was conducted in the Kirkpatrick Marsh, part of the Smithsonian’s Global Change Research Wetland (GCReW). Six replicate transects within the Kirkpatrick Marsh, three in each of the dominant plant communities, were established in 2016. A heating gradient consisting of an ambient temperature plot and heated plots raised to +1.7, +3.4, and +5.1 °C above ambient temperatures was established along each transect. Soil surface elevations were tracked using surface elevation tables (SETs). SETs were installed in each plot to measure soil surface elevation. Elevation benchmarks were installed outside of the experimental plot in June 2016 by driving a series of stainless-steel rods through the entire soil profile to “refusal” (approximately 12.5 meters, but ranging from 6 to 13.5 meters) and then permanently anchored. SET benchmark vertical stability over time was assessed by periodically surveying them relative to each other with a Trimble S5 Total Station and no significant differences in elevation were found. Elevation measurements were collected from approximately 60 “pins” that are 4.5 mm apart and measure the distance from a parallel bar attached to the anchored benchmark to the ground surface, and recorded to the nearest millimeter. This resulted in high-precision measurements of soil surface elevations relative to the base of the benchmark. Measurements were taken every June, August, and January since warming began on June 1, 2016. In addition to this, measurements were taken more frequently (every two months from March 2019 to February 2020) to examine inter-annual variability in marsh elevation. To determine long term trends, marsh surface elevation was regressed against time for each individual SET pin resulting in approximately 60 estimates of linear elevation trends for each plot. Pin linear regressions across replicate plots (~180 linear regressions per treatment) were then averaged together to estimate the average long-term change in elevation at the treatment level. The data in this dataset represent the change in elevation between June 2016 and February 2020 at the pin-level on sheet "PinChange" and at the plot-level on sheet "PlotChange". Within the sheets, the column labeled “PlotLabel” represents the plant community, replication, and warming treatment respectively by the hundreds, tens, and ones place value. “4” and “3” in the hundreds place differentiates between the C₄ and C₃ plant communities. Numbers 1 through 6 in the tends place indicate the heating gradient replications. In the ones place, “0” represents ambient temperature treatments while “1”, “2”, and “3” represent elevated temperature treatments in ascending order.