Sediment cores were collected from three sites within the Plum Island Ecosystems Long-Term Ecological Research (PIE-LTER) domain in Massachusetts to obtain estimates of long-term marsh decomposition and evaluate shifts in the composition and reactivity of sediment organic carbon in disturbed marsh environments. Paired sediment cores were collected from three sites on the marsh platform and from three ponds; these cores were about 100 and 50 centimeters in length, respectively. The marsh sites had similar elevations, at about 1.41 to 1.51 meters relative to the North American Vertical Datum of 1988, and similar salt marsh grass communities, dominated by Spartina patens, S. alterniflora, and Distichlis spicata. Permanently inundated ponds within each site had comparable depths (0.24–0.30 meters) but varied in size (between 643 and 7,149 square meters; Spivak et al., 2017, 2018). The U.S. Geological Survey analyzed radioisotope concentrations for lead-210, radium-226, cesium-127, and beryllium-7 from six marsh cores and three pond cores to develop an age model for each core. This data release includes calculated percent dry bulk density and raw radioisotope data for these cores. Spivak, A.C., Gosselin, K., Howard, E., Mariotti, G., Forbrich, I., Stanley, R., and Sylva, S.P., 2017, Shallow ponds are heterogeneous habitats within a temperate salt marsh ecosystem: Journal of Geophysical Research-Biogeosciences, 122(6), 1371-1384. Spivak, A. C., Gosselin, K. M., and Sylva, S.P., 2018, Shallow ponds are biogeochemically distinct habitats in salt marsh ecosystems: Limnology and Oceanography, 63(4), 1622-1642.

Sediment cores were collected from three sites within the Plum Island Ecosystems Long-Term Ecological Research (PIE-LTER) domain in Massachusetts to obtain estimates of long-term marsh decomposition and evaluate shifts in the composition and reactivity of sediment organic carbon in disturbed marsh environments. Paired sediment cores were collected from three sites on the marsh platform and from three ponds; these cores were about 100 and 50 centimeters in length, respectively. The marsh sites had similar elevations, at about 1.41 to 1.51 meters relative to the North American Vertical Datum of 1988, and similar salt marsh grass communities, dominated by Spartina patens, S. alterniflora, and Distichlis spicata. Permanently inundated ponds within each site had comparable depths (0.24–0.30 meters) but varied in size (between 643 and 7,149 square meters; Spivak et al., 2017, 2018). The U.S. Geological Survey analyzed radioisotope concentrations for lead-210, radium-226, cesium-127, and beryllium-7 from six marsh cores and three pond cores to develop an age model for each core. This data release includes calculated percent dry bulk density and raw radioisotope data for these cores. Spivak, A.C., Gosselin, K., Howard, E., Mariotti, G., Forbrich, I., Stanley, R., and Sylva, S.P., 2017, Shallow ponds are heterogeneous habitats within a temperate salt marsh ecosystem: Journal of Geophysical Research-Biogeosciences, 122(6), 1371-1384. Spivak, A. C., Gosselin, K. M., and Sylva, S.P., 2018, Shallow ponds are biogeochemically distinct habitats in salt marsh ecosystems: Limnology and Oceanography, 63(4), 1622-1642.

We conducted vegetation surveys concurrently with elevation surveys at every fourth elevation point (~25% of the elevation points) (Figure 5). 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) and Cook et al. (2013). We located 69 tidal wetland species in 2,154 vegetation plots across the nine estuaries in the study. Common species included Carex lyngbyei, Sarcocornia perennis, Distichlis spicata, Deschampsia cespitosa, Juncus balticus and Potentilla anserina. The frequency of several common species varied markedly across the sites. Distichlis spicata dominated the flora at five of the nine sites, but was relatively uncommon at Port Susan and Grays Harbor. Deschampsia cespitosa, a middle to high marsh tussock-forming species was frequent at the three Oregon sites and at Willapa but much less common in Puget Sound marshes. The high marsh rush, Juncus balticus, was most frequent at Siletz and absent or rare at Willapa and Padilla. Carex lyngbyei occurrence was variable regionally, ranging from >75% frequency at Bull Island to near absence at Padilla (it did not occur in any surveyed plots, but a few plants were observed at the upland margin of the site in late 2014). See appendices for detailed site specific results.We delineated marsh zones using long-term NOAA tidal data combined with our site-specific elevation and water level data and examined plant abundance in these major zones across the sites. At many sites, plant composition tended to vary by zone, but not necessarily in consistent ways across the region. For instance, at Bandon, Sarcocornia perennis was the most abundant high marsh species (with Deschampsia cespitosa most abundant in middle and low marsh), while S. perennis was the most abundant plant in low marsh at Grays Harbor (Carex spp. dominated in mid-marsh and Potentilla anserina dominated high marsh). Vertical zonation of plant assemblages was less pronounced at other sites, including Nisqually where Distichlis spicata had the highest mean cover in all three major marsh zones. Low marsh habitat was common at Bull Island, Willapa, Nisqually, and Port Susan. Common species in this zone included Sarcocornia perennis, Distichlis spicata, Carex lyngbyei, and Triglochin maritima. Middle tidal marsh was present at all of the sites and particularly common at Skokomish. Common species included all of the aforementioned taxa and Deschampsia cespitosa, Juncus balticus and Agrostis stolonifera. High marsh was only common at Bandon, Siletz, Willapa, Grays Harbor and Padilla. Common high marsh species included many species found in other zones, but also included Potentilla anserine and Atriplex prostrata. Transition zone habitat (defined as wetland flooding at least once per year but no more than once per month) was limited at most of our study sites. Zonation of individual species per site are illustrated in the respective appendices.

We conducted vegetation surveys concurrently with elevation surveys at every fourth elevation point (~25% of the elevation points) (Figure 5). 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) and Cook et al. (2013). We located 69 tidal wetland species in 2,154 vegetation plots across the nine estuaries in the study. Common species included Carex lyngbyei, Sarcocornia perennis, Distichlis spicata, Deschampsia cespitosa, Juncus balticus and Potentilla anserina. The frequency of several common species varied markedly across the sites. Distichlis spicata dominated the flora at five of the nine sites, but was relatively uncommon at Port Susan and Grays Harbor. Deschampsia cespitosa, a middle to high marsh tussock-forming species was frequent at the three Oregon sites and at Willapa but much less common in Puget Sound marshes. The high marsh rush, Juncus balticus, was most frequent at Siletz and absent or rare at Willapa and Padilla. Carex lyngbyei occurrence was variable regionally, ranging from >75% frequency at Bull Island to near absence at Padilla (it did not occur in any surveyed plots, but a few plants were observed at the upland margin of the site in late 2014). See appendices for detailed site specific results.We delineated marsh zones using long-term NOAA tidal data combined with our site-specific elevation and water level data and examined plant abundance in these major zones across the sites. At many sites, plant composition tended to vary by zone, but not necessarily in consistent ways across the region. For instance, at Bandon, Sarcocornia perennis was the most abundant high marsh species (with Deschampsia cespitosa most abundant in middle and low marsh), while S. perennis was the most abundant plant in low marsh at Grays Harbor (Carex spp. dominated in mid-marsh and Potentilla anserina dominated high marsh). Vertical zonation of plant assemblages was less pronounced at other sites, including Nisqually where Distichlis spicata had the highest mean cover in all three major marsh zones. Low marsh habitat was common at Bull Island, Willapa, Nisqually, and Port Susan. Common species in this zone included Sarcocornia perennis, Distichlis spicata, Carex lyngbyei, and Triglochin maritima. Middle tidal marsh was present at all of the sites and particularly common at Skokomish. Common species included all of the aforementioned taxa and Deschampsia cespitosa, Juncus balticus and Agrostis stolonifera. High marsh was only common at Bandon, Siletz, Willapa, Grays Harbor and Padilla. Common high marsh species included many species found in other zones, but also included Potentilla anserine and Atriplex prostrata. Transition zone habitat (defined as wetland flooding at least once per year but no more than once per month) was limited at most of our study sites. Zonation of individual species per site are illustrated in the respective appendices.

The accretion history of fringing salt marshes in Narragansett Bay, Rhode Island, was reconstructed from sediment cores. Age models, based on excess lead-210 and cesium-137 radionuclide analysis, were constructed to evaluate how vertical accretion and carbon burial rates have changed during the past century. The Constant Rate of Supply (CRS) age model was used to date six cores collected from three salt marshes. Both vertical accretion rates and carbon burial increased from 1900 to 2016, the year the data were collected. Cores were up to 90 cm in length with dry bulk density ranging from 0.07 to 3.08 grams per cubic centimeter and carbon content 0.71 % to 33.58 %.

This dataset includes multi-sensor core logger (MSCL) data of sediment cores collected in southern Cascadia (offshore northern California) aboard the M/V Bold Horizon in September-October 2019.

This dataset includes multi-sensor core logger (MSCL) data of sediment cores collected in southern Cascadia (offshore northern California) aboard the M/V Bold Horizon in September-October 2019.

This dataset presents radiocarbon data from 87 samples from sediment cores collected in southern Cascadia (offshore northern California) aboard the M/V Bold Horizon in September-October 2019. Sample ages were determined by the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility and the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry (KCCAMS) facility at the University of California, Irvine (UCI).

This dataset presents radiocarbon data from 87 samples from sediment cores collected in southern Cascadia (offshore northern California) aboard the M/V Bold Horizon in September-October 2019. Sample ages were determined by the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility and the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry (KCCAMS) facility at the University of California, Irvine (UCI).

This dataset presents specific activities of cesium-137 in picoCuries per gram from sediment cores collected from Cargill Marsh, South San Francisco Bay, California on June 21, 2022, and December 14, 2023. The cores were collected with hand driven push cores to assess sediment accumulation on the marsh.