The approaching obsolescence of 137Cs dating of wetland soils in North America

Drexler, Judith Z.; Fuller, Christopher C.; Archfield, Stacey A.

doi:10.1016/j.quascirev.2018.08.028

Cited by 57 publications

(39 citation statements)

References 93 publications

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“…These three cores have the lowest salinity conditions, with the two marsh sites being mostly freshwater and occasionally brackish (Jiang et al, ; Saha et al, ) and the mangrove core being heavily influenced by managed freshwater discharges from Picayune Strand State Forest. The observation that clear 137 Cs peaks are only visible in the cores from more freshwater conditions supports findings of the limited utility of 137 Cs in saline peat soils (Corbett & Walsh, ; Drexler et al, ; Lynch et al, ; Marchio et al, ).…”

Section: Discussionsupporting

confidence: 74%

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

et al. 2020

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Rates of organic carbon (OC) burial in some coastal wetlands appear to be greater in recent years than they were in the past. Possible explanations include ongoing mineralization of older OC or the influence of an unaccounted‐for artifact of the methods used to measure burial rates. Alternatively, the trend may represent real acceleration in OC burial. We quantified OC burial rates of mangrove and coastal freshwater marshes in southwest Florida through a comparison of rates derived from 210Pb, 137Cs, and surface marker horizons. Age/depth profiles of lignin: OC were used to assess whether down‐core remineralization had depleted the OC pool relative to lignin, and lignin phenols were used to quantify the variability of lignin degradation. Over the past 120 years, OC burial rates at seven sites increased by factors ranging from 1.4 to 6.2. We propose that these increases represent net acceleration. Change in relative sea‐level rise is the most likely large‐scale driver of acceleration, and sediment deposition from large storms can contribute to periodic increases. Mangrove sites had higher OC and lignin burial rates than marsh sites, indicating inherent differences in OC burial factors between the two habitat types. The higher OC burial rates in mangrove soils mean that their encroachment into coastal freshwater marshes has the potential to increase burial rates in those locations even more than might be expected from the acceleration trends. Regionally, these findings suggest that burial represents a substantially growing proportion of the coastal wetland carbon budget.

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Section: Discussionsupporting

confidence: 74%

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

et al. 2020

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“…Accretion rates, measured using 137 Cs, at tidal marsh sites in Siletz Bay, Coos Bay, and Coquille River Estuary (also known as Bandon Marsh) averaged 3.3 ± 1.2 ( n = 3), 3.3 ± 0.1 ( n = 3), and 2.3 ± 0.2 ( n = 3) mm yr −1 , respectively (Thorne et al, ). The range of high marsh SARs in the Coquille was lower in our study (1.1 ± 0.2 to 1.8 ± 0.1 mm yr −1 ), possibly a result in differences between radiometric methods, especially challenges of the 137 Cs methods applied to Pacific NW estuaries (Drexler et al, ). The range of SARs measured in the Salmon River Estuary (1.2 ± 0.2 to 2.9 ± 0.3 mm yr −1 ) was lower than a previously measured rate of 3.0 ± 0.0 mm yr −1 ( n = 2) by Thom () along the northern edge of the estuary.…”

Section: Discussioncontrasting

confidence: 64%

Controls on Sediment Accretion and Blue Carbon Burial in Tidal Saline Wetlands: Insights From the Oregon Coast, USA

2020

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Oregon estuaries provide important opportunities to assess controls on tidal saline wetland carbon burial and sediment accretion as both rates of relative sea level rise (RSLR; −1.4 ± 0.9 to 2.8 ± 0.8 mm yr−1) and fluvial suspended sediment load relative to estuary area (0.23 to 17 × 103 t km−2 yr−1) vary along the coast. We hypothesized that vertical accretion, measured using excess 210Pb in least‐disturbed wetlands within seven Oregon estuaries, would vary with either RSLR or sediment load relative to estuary area, and carbon burial would correlate strongly to sediment accretion. Mean rates of high marsh accretion (0.8 ± 0.2 to 4.1 ± 0.2 mm yr−1) indicate that Oregon tidal wetlands have mainly kept pace with twentieth‐century RSLR with the exception that the accretionary balance in the central coast is negative, suggesting drowning. Experiencing the fastest rates of RSLR, central‐coast estuaries may foreshadow the fates of other Oregon estuaries under future accelerated sea level rise. Comparison of mass accumulation rates with sediment loads, however, indicates low trapping efficiency and therefore no fluvial sediment limitation. Thus, nonlinear feedback between RSLR and sediment accretion may enhance wetland resistance to drowning. Among wetlands keeping pace with or exceeding RSLR, sediment accretion displays no significant relationship with elevation but rather appears controlled by both the rate of RSLR and relative sediment load, highlighting the importance of incorporating both factors into future studies of tidal saline wetlands. Carbon burial rates, controlled by sediment accretion, will likely increase with future accelerated sea level rise.

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“…Methodology biases exist for wetland vertical accretion rates where measurements made over years to decades are usually different for those from the same location made over centuries or millennia (Breithaupt et al, ) and evidence exists that the shorter‐term marker 137 Cs by itself is inadequate to estimate CAR (Drexler et al, ). This methodological bias is also inherent in disentangling the changing CARs over time with variations in rates of RSLR.…”

Section: Discussionmentioning

confidence: 99%

Sea Level Rise Explains Changing Carbon Accumulation Rates in a Salt Marsh Over the Past Two Millennia

et al. 2019

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High rates of carbon burial observed in wetland sediments have garnered attention as a potential “natural fix” to reduce the concentration of carbon dioxide (CO2) in Earth's atmosphere. A carbon accumulation rate (CAR) can be determined through various methods that integrate a carbon stock over different time periods, ranging from decades to millennia. Our goal was to assess how CAR changed over the lifespan of a salt marsh. We applied a geochronology to a series of salt marsh cores using both 14C and 210Pb markers to calculate CARs that were integrated between 35 and 2,460 years before present. CAR was 39 g C·m−2·year−1 when integrated over millennia but was upward of 148 g C·m−2·year−1 for the past century. We present additional evidence to account for this variability by linking it to changes in relative sea level rise (RSLR), where higher rates of RSLR were associated with higher CARs. Thus, the CAR calculated for a wetland should integrate timescales that capture the influence of contemporary RSLR. Therefore, caution should be exercised not to utilize a CAR calculated over inappropriately short or long timescales as a current assessment or forecasting tool for the climate change mitigation potential of a wetland.

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The approaching obsolescence of 137Cs dating of wetland soils in North America

Cited by 57 publications

References 93 publications

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

Controls on Sediment Accretion and Blue Carbon Burial in Tidal Saline Wetlands: Insights From the Oregon Coast, USA

Sea Level Rise Explains Changing Carbon Accumulation Rates in a Salt Marsh Over the Past Two Millennia

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