David C. Walters Tyler C. Messerschmidt Matthew L. Kirwan Glenn R. Guntenspergen 20250516 spreadsheet https://doi.org/10.5066/P138FBAF Sediment accretion measurements were made at the SMARTX warming experiment at the Smithsonian Environmental Research Center's Global Change Research Wetland. Feldspar marker horizons were established at the beginning of the experiment in 2016 in the warming plots, and were subsequently buried over time by wetland accretion of both organic and inorganic matter. These data include the measurements (via cryogenic coring) of the depth to the marker horizon layer, which can be used to calculate the accretion rate of the wetland, and the organic content of the accretion material, which was determined via Loss On Ignition. These data reflect the accretion of the different vegetation communities (C3 vs. C4) and temperature gradients (+1.7C, +3.4C, +5.1C, ambient) and atmospheric CO2 conditions (elevated CO2 vs. control). Accretion measurements were collected to monitor change in wetland elevation over time. 20160515 20250314 ground condition Complete None planned Global Change Research Wetland at Smithsoinian Environmental Research Center in Edgewater, MD -76.551833 -76.545868 38.876935 38.872191 ISO 19115 Topic Category elevation USGS Thesaurus wetland ecosystems sedimentation USGS Metadata Identifier USGS:68237b30d4be025fcee55c24 None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. David Walters US Geological Survey Biologist mailing and physical

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Laurel MD 20708 USA 2404590010 davidwalters@usgs.gov Depth to the marker horizon layer was measured to the nearest millimeter. Organic content via loss on ignition was measured on samples minimum 0.3g using a mass balance with precision to mg. Standard weights were used to ensure the balance was properly calibrated. Data fall within expected ranges and all data were checked for duplication and omission Data represent only the specific wetland area in which they were collected (the Smithsonian's Global Change Research Wetland) and should be considered in regards to the vegetation community, temperature manipulation, and atmospheric CO2 conditions of the experimental plots from which they were sampled. One feldspar marker horizon subplot was installed in each SMARTX plot. Feldspar was laid into ~15cm by 50cm rectangular subplots, in a layer ~1-2cm. Feldspar was laid over top of the marsh surface, on top of and in between the existing vegetation. Over time, the feldspar marker horizon was then buried, with organic and inorganic sediment accreting on top of it. 20160501 Cryogenic coring was conducted to sample the marker horizon plots, following the method established by the NPS protocol (Lynch et al., 2015). A copper "bullet" was inserted into the wetland, through the accretion material and the buried marker horizon layer, and then liquid nitrogen was pumped into the bullet, causing the sediment to freeze to the sides. The bullet was then removed, with the frozen sediment and feldspar layer attached as a cryocore. The depth from the wetland surface to the visible feldspar marker horizon layer was then measured in three places on each cryocore. After measuring, the accretion material (ie- the sediment on top of the marker horizon layer) was then removed and stored in labelled sample bags, sealed, and placed in cold storage to be processed in the lab. This process was completed for each plot in the SMARTX experiment. 20250312 Accretion material was then processed to determine the soil organic content via loss on ignition (LOI) following the method of Heir et al. (2001). Soil samples were dried to a constant weight at 55 degrees C, ground and homogenized with mortar and pestle, placed into pre-weighed porcelain crucibles, dried again to a constant weight at 55 degrees C, weighed, then placed into a muffle furnace at 550 degrees C, and weighed again. The difference between the sediment dry weight and the combusted sediment weight (accounting for crucible weight) determines the LOI, which is then calculated as a percent of the sediment dry weight. 20250328 Accretion data.csv Comma Separated Value (CSV) file containing data. Producer Defined VegetationCommunity Denotes which of the two plant community sites (C3 or C4) the sample was collected from Producer Defined C3 C3 plant community site, dominated by Schoenoplectus americanus Producer defined C4 C4 plant community site, dominated by Spartina patens Producer defined Transect One of six replicate transects, number 1-6. Transects 1-3 are located in the C3 community site and transects 4-6 are located within the C4 community site. All temperature and CO2 manipulations vary along the transects. Producer Defined 1 6 Treatment The experimentally manipulated temperature and/or CO2 treatment for the plot from which the accretion sample was collected. Producer Defined Ambient Ambient temperature control. No CO2 manipulation, and no increase in soil temperature. Producer defined +1.7 C Soil temperature increased to 1.7 degrees C greater than ambient. No CO2 manipulation. Producer defined +3.4 C Soil temperature increased to 3.4 degrees C greater than ambient. No CO2 manipulation. Producer defined +5.1 C Soil temperature increased to 5.1 degrees C greater than ambient. No CO2 manipulation. Producer defined eCO2 Ambient Ambient temperature control. Also experienced elevated CO2 manipulation. Producer defined eCO2 +5.1 C Soil temperature increased to 5.1 degrees C greater than ambient. Also experienced elevated CO2 manipulation. Producer defined Outside Control Control plots located outside the experimental area. No CO2 manipulation, and no increase in soil temperature. Producer defined Depth1.mm First of three depth measurements made on the accretion sample, measured (in millimeters) from the surface of the wetland to the feldspar marker horizon layer Producer Defined na The feldspar marker horizon was not found Producer defined 10 52 millimeters 1.0 Depth2.mm Second of three depth measurements made on the accretion sample, measured (in millimeters) from the surface of the wetland to the feldspar marker horizon layer Producer Defined na The feldspar marker horizon was not found Producer defined 15 54 Depth3.mm Third of three depth measurements made on the accretion sample, measured (in millimeters) from the surface of the wetland to the feldspar marker horizon layer Producer Defined na The feldspar marker horizon was not found Producer defined 15 53 MeasurementDate Date that the accretion measurements were conducted for the given sample Producer Defined Dateformat: YYYY-MM-DD YearsElapsed Number of years elapsed since the marker horizons were established, which is used to calculate the rate of accretion Producer Defined 4.45 8.87 Years LossOnIgnition.% The percent of sediment weight that was lost on ignition, an estimate of the soil organic content Producer Defined na The feldspar marker horizon was not found Producer defined 28.3 72.04 GS ScienceBase U.S. Geological Survey mailing address

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Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/xxxxxxxx None 20250527 David Walters US Geological Survey Biologist mailing and physical

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Laurel MD 20708 USA 2404590010 davidwalters@usgs.gov FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata FGDC-STD-001.1-1999