Revisiting \u3csup\u3e228\u3c/sup\u3eTh as a Tool for Determining Sedimentation and Mass Accumulation Rates

The use of 228Th has seen limited application for determining sedimentation and mass accumulation rates in coastal and marine environments. Recent analytical advances have enabled rapid, precise measurements of particle-bound 228Th using a radium delayed coincidence counting system (RaDeCC). Herein we review the 228Th cycle in the marine environment and revisit the historical use of 228Th as a tracer for determining sediment vertical accretion and mass accumulation rates in light of new measurement techniques. Case studies comparing accumulation rates from 228Th and 210Pb are presented for a micro-tidal salt marsh and a marginal sea environment. 228Th and 210Pb have been previously measured in mangrove, deltaic, continental shelf and ocean basin environments, and a literature synthesis reveals that 228Th (measured via alpha or gamma spectrometry) derived accumulation rates are generally equal to or greater than estimates derived from 210Pb, reflecting different integration periods. Use of 228Th is well-suited for shallow (\u3c15 cm) cores over decadal timescales. Application is limited to relatively homogenous sediment profiles with minor variations in grain size and minimal bioturbation. When appropriate conditions are met, complimentary use of 228Th and 210Pb can demonstrate that the upper layers of a core are undisturbed and can improve spatial coverage in mapping accumulation rates due to the higher sample throughput for sediment 228Th

Revisiting 228Th as a tool for determining sedimentation and mass accumulation rates

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tamborski, J., Cai, P., Eagle, M., Henderson, P., & Charette, M. Revisiting 228Th as a tool for determining sedimentation and mass accumulation rates. Chemical Geology, 607, (2022): 121006, https://doi.org/10.1016/j.chemgeo.2022.121006.The use of 228Th has seen limited application for determining sedimentation and mass accumulation rates in coastal and marine environments. Recent analytical advances have enabled rapid, precise measurements of particle-bound 228Th using a radium delayed coincidence counting system (RaDeCC). Herein we review the 228Th cycle in the marine environment and revisit the historical use of 228Th as a tracer for determining sediment vertical accretion and mass accumulation rates in light of new measurement techniques. Case studies comparing accumulation rates from 228Th and 210Pb are presented for a micro-tidal salt marsh and a marginal sea environment. 228Th and 210Pb have been previously measured in mangrove, deltaic, continental shelf and ocean basin environments, and a literature synthesis reveals that 228Th (measured via alpha or gamma spectrometry) derived accumulation rates are generally equal to or greater than estimates derived from 210Pb, reflecting different integration periods. Use of 228Th is well-suited for shallow (<15 cm) cores over decadal timescales. Application is limited to relatively homogenous sediment profiles with minor variations in grain size and minimal bioturbation. When appropriate conditions are met, complimentary use of 228Th and 210Pb can demonstrate that the upper layers of a core are undisturbed and can improve spatial coverage in mapping accumulation rates due to the higher sample throughput for sediment 228Th.This research was undertaken thanks in part to funding from the Canada First Research Excellence Fund, through the Ocean Frontier Institute. This project was supported by U.S. Geological Survey Coastal and Marine Hazards and Resources Program. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. PC acknowledges the support of the Natural Science Foundation of China (NSFC) through Grants No. 92058205

Pore water exchange-driven inorganic carbon export from intertidal salt marshes

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tamborski, J. J., Eagle, M., Kurylyk, B. L., Kroeger, K. D., Wang, Z. A., Henderson, P., & Charette: 1774-1792, https://doi.org/10.1002/lno.11721.Respiration in intertidal salt marshes generates dissolved inorganic carbon (DIC) that is exported to the coastal ocean by tidal exchange with the marsh platform. Understanding the link between physical drivers of water exchange and chemical flux is a key to constraining coastal wetland contributions to regional carbon budgets. The spatial and temporal (seasonal, annual) variability of marsh pore water exchange and DIC export was assessed from a microtidal salt marsh (Sage Lot Pond, Massachusetts). Spatial variability was constrained from 224Ra : 228Th disequilibria across two hydrologic units within the marsh sediments. Disequilibrium between the more soluble 224Ra and its sediment-bound parent 228Th reveals significant pore water exchange in the upper 5 cm of the marsh surface (0–36 L m−2 d−1) that is most intense in low marsh elevation zones, driven by tidal overtopping. Surficial sediment DIC transport ranges from 0.0 to 0.7 g C m−2 d−1. The sub-surface sediment horizon intersected by mean low tide was disproportionately impacted by tidal pumping (20–80 L m−2 d−1) and supplied a seasonal DIC flux of 1.7–5.4 g C m−2 d−1. Export exceeded 10 g C m−2 d−1 for another marsh unit, demonstrating that fluxes can vary substantially across salt marshes under similar conditions within the same estuary. Seasonal and annual variability in marsh pore water exchange, constrained from tidal time-series of radium isotopes, was driven in part by variability in mean sea level. Rising sea levels will further inundate high marsh elevation zones, which may lead to greater DIC export.This research was undertaken thanks in part to funding from the Canada First Research Excellence Fund, through the Ocean Frontier Institute. Additional funding was provided by the U.S. Geological Survey (USGS) Coastal & Marine Geology Program and the USGS Land Change Science Program's LandCarbon program

Soil organic carbon development and turnover in natural and disturbed salt marsh environments

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(2), (2021): e2020GL090287, https://doi.org/10.1029/2020GL090287.Salt marsh survival with sea‐level rise (SLR) increasingly relies on soil organic carbon (SOC) accumulation and preservation. Using a novel combination of geochemical approaches, we characterized fine SOC (≤1 mm) supporting marsh elevation maintenance. Overlaying thermal reactivity, source (δ13C), and age (F14C) information demonstrates several processes contributing to soil development: marsh grass production, redeposition of eroded material, and microbial reworking. Redeposition of old carbon, likely from creekbanks, represented ∼9%–17% of shallow SOC (≤26 cm). Soils stored marsh grass‐derived compounds with a range of reactivities that were reworked over centuries‐to‐millennia. Decomposition decreases SOC thermal reactivity throughout the soil column while the decades‐long disturbance of ponding accelerated this shift in surface horizons. Empirically derived estimates of SOC turnover based on geochemical composition spanned a wide range (640–9,951 years) and have the potential to inform predictions of marsh ecosystem evolution.This work was supported by NSF (OCE1233678) and NOAA (NA14OAR4170104 and NA14NOS4190145) grants to ACS, USGS Coastal & Marine Geology Program, and PIE‐LTER (NSF OCE1238212 and OCE1637630).2021-06-1

Impoundment increases methane emissions in Phragmites‐invaded coastal wetlands

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sanders‐DeMott, R., Eagle, M., Kroeger, K., Wang, F., Brooks, T., Suttles, J., Nick, S., Mann, A., & Tang, J. Impoundment increases methane emissions in Phragmites‐invaded coastal wetlands. Global Change Biology, 28(15), (2022): 4539– 4557. https://doi.org/10.1111/gcb.16217.Saline tidal wetlands are important sites of carbon sequestration and produce negligible methane (CH4) emissions due to regular inundation with sulfate-rich seawater. Yet, widespread management of coastal hydrology has restricted tidal exchange in vast areas of coastal wetlands. These ecosystems often undergo impoundment and freshening, which in turn cause vegetation shifts like invasion by Phragmites, that affect ecosystem carbon balance. Understanding controls and scaling of carbon exchange in these understudied ecosystems is critical for informing climate consequences of blue carbon restoration and/or management interventions. Here, we (1) examine how carbon fluxes vary across a salinity gradient (4–25 psu) in impounded and natural, tidally unrestricted Phragmites wetlands using static chambers and (2) probe drivers of carbon fluxes within an impounded coastal wetland using eddy covariance at the Herring River in Wellfleet, MA, United States. Freshening across the salinity gradient led to a 50-fold increase in CH4 emissions, but effects on carbon dioxide (CO2) were less pronounced with uptake generally enhanced in the fresher, impounded sites. The impounded wetland experienced little variation in water-table depth or salinity during the growing season and was a strong CO2 sink of −352 g CO2-C m−2 year−1 offset by CH4 emission of 11.4 g CH4-C m−2 year−1. Growing season CH4 flux was driven primarily by temperature. Methane flux exhibited a diurnal cycle with a night-time minimum that was not reflected in opaque chamber measurements. Therefore, we suggest accounting for the diurnal cycle of CH4 in Phragmites, for example by applying a scaling factor developed here of ~0.6 to mid-day chamber measurements. Taken together, these results suggest that although freshened, impounded wetlands can be strong carbon sinks, enhanced CH4 emission with freshening reduces net radiative balance. Restoration of tidal flow to impounded ecosystems could limit CH4 production and enhance their climate regulating benefits.This project was supported by USGS-NPS Natural Resources Preservation Program #2021-07, U.S. Geological Survey Coastal & Marine Hazards and Resources Program and the USGS Land Change Science Program's LandCarbon program, and NOAA National Estuarine Research Reserve Science Collaborative NA14NOS4190145. R Sanders-DeMott was supported by a USGS Mendenhall Fellowship and partnership with Restore America's Estuaries

Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Eagle, M. J., Kroeger, K. D., Spivak, A. C., Wang, F., Tang, J., Abdul-Aziz, O. I., Ishtiaq, K. S., O’Keefe Suttles, J., & Mann, A. G. Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands. The Science of the Total Environment, 848, (2022): 157682, https://doi.org/10.1016/j.scitotenv.2022.157682.Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO2 in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30–70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m−2 y−1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y−1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.This project was supported by the U.S. Geological Survey Coastal and Marine Hazards and Resources Program and the USGS Land Change Science Program's LandCarbon program, NOAA National Estuarine Research Reserve Science Collaborative NA14NOS4190145, and MIT Sea Grant 2015-R/RC-141. Contributions of Abdul-Aziz were also supported by NSF CBET Environmental Sustainability Award No. 1705941. Our stakeholder partners, including the Cape Cod National Seashore, Waquoit Bay National Estuarine Research Reserve, and the Bringing Wetlands to Market project team, and Towns and Conservation Commissions, including Eastham, Barnstable, Brewster, Yarmouth, Denis, Sandwich and Orleans, were instrumental in providing research support and site access

Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating relative sea-level rise

Salt marshes respond to sea-level rise through a series of complex and dynamic bio-physical feedbacks. In this study, we found that sea-level rise triggered salt marsh habitat restructuring, with the associated vegetation changes enhancing salt marsh elevation resilience. A continuous record of marsh elevation relative to sea level that includes reconstruction of high-resolution, sub-decadal, marsh elevation over the past century, coupled with a lower-resolution 1500-year record, revealed that relative sea-level rose 1.5 ± 0.4 m, following local glacial isostatic adjustment (1.2 mm/yr). As sea-level rise has rapidly accelerated, the high marsh zone dropped 11 cm within the tidal frame since 1932, leading to greater inundation and a shift to flood- and salt-tolerant low marsh species. Once the marsh platform fell to the elevation favored by low-marsh Spartina alterniflora, the elevation stabilized relative to sea level. Currently low marsh accretion keeps pace with sea-level rise, while present day high marsh zones that have not transitioned to low marsh have a vertical accretion deficit. Greater biomass productivity, and an expanding subsurface accommodation space favorable for salt marsh organic matter preservation, provide a positive feed-back between sea-level rise and marsh platform elevation. Carbon storage was 46 ± 28 g C/m2/yr from 550 to 1800 CE, increasing to 129 ± 50 g C/m2/yr in the last decade. Enhanced carbon storage is controlled by vertical accretion rates, rather than soil carbon density, and is a direct response to anthropogenic eustatic sea-level rise, ultimately providing a negative feedback on climate warming

The Coastal Carbon Library and Atlas: open source soil data and tools supporting blue carbon research and policy

Quantifying carbon fluxes into and out of coastal soils is critical to meeting greenhouse gas reduction and coastal resiliency goals. Numerous ‘blue carbon’ studies have generated, or benefitted from, synthetic datasets. However, the community those efforts inspired does not have a centralized, standardized database of disaggregated data used to estimate carbon stocks and fluxes. In this paper, we describe a data structure designed to standardize data reporting, maximize reuse, and maintain a chain of credit from synthesis to original source. We introduce version 1.0.0. of the Coastal Carbon Library, a global database of 6723 soil profiles representing blue carbon‐storing systems including marshes, mangroves, tidal freshwater forests, and seagrasses. We also present the Coastal Carbon Atlas, an R‐shiny application that can be used to visualize, query, and download portions of the Coastal Carbon Library. The majority (4815) of entries in the database can be used for carbon stock assessments without the need for interpolating missing soil variables, 533 are available for estimating carbon burial rate, and 326 are useful for fitting dynamic soil formation models. Organic matter density significantly varied by habitat with tidal freshwater forests having the highest density, and seagrasses having the lowest. Future work could involve expansion of the synthesis to include more deep stock assessments, increasing the representation of data outside of the U.S., and increasing the amount of data available for mangroves and seagrasses, especially carbon burial rate data. We present proposed best practices for blue carbon data including an emphasis on disaggregation, data publication, dataset documentation, and use of standardized vocabulary and templates whenever appropriate. To conclude, the Coastal Carbon Library and Atlas serve as a general example of a grassroots F.A.I.R. (Findable, Accessible, Interoperable, and Reusable) data effort demonstrating how data producers can coordinate to develop tools relevant to policy and decision‐making.Department of Energy, Grant/AwardNumber: COMPASS-FME; Division of Environmental Biology, Grant/AwardNumber: DEB-1655622; National Oceanicand Atmospheric Administration, Grant/Award Number: NA22OAR4310148; National Science Foundation, Grant/Award Number: DGE-1842473; Pew Charitable TrustsGlobal Change Biolog

Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ~~2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals. Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual¿centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual ¿14C record for this same time period, two large ¿14C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal¿ centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light¿dark couplets at decadal¿centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake

Temporal variability in chemical cycling of the subterranean estuary and associated chemical loading to the coastal ocean

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014.Cataloged from PDF version of thesis.Includes bibliographical references.At the land-ocean interface, terrestrial groundwater interacts with seawater to form a subterranean estuary, which can play host to dynamic biogeochemical cycling of nutrients, trace metals and radionuclides. This chemically altered groundwater enters the ocean through submarine groundwater discharge (SGD), a process that is driven by a number of physical processes acting on aquifers and the coastal ocean. In this thesis, seasonal variability in chemical cycling and associated loading to the coastal ocean was observed in a monthly time series within the Waquoit Bay (MA, USA) subterranean estuary. The position of the aquifer mixing zone moved seaward with an increase in hydraulic gradient, resulting in low salinity conditions and reduced mixing, while a decrease in gradient led to landward movement, high salinity groundwater and enhanced mixing. At this location, seasonal variability in sea level, not groundwater level, was the dominant variable driving the hydraulic gradient and therefore SGD. Fluxes of sediment bound cations to the ocean increased coincidently with sea level rise due to desorption. There was enhanced nitrogen attenuation during winter, potentially due to longer groundwater residence times, with greater nutrient delivery to coastal waters during the spring and summer bloom. Interannual climate fluctuations that control sea level and precipitation may ultimately control the timing and magnitude of chemical and water flux via SGD. In addition to temporal variability, aquifer lithology influences chemical export. This thesis also demonstrates that SGD from karst subterranean estuaries may play a role in local and global element budgets. The potential for the chemical signature of SGD to be recorded in the coral record was tested through a combination of coral culture experiments and field and modeling studies in the Yucatan Peninsula. Coral barium was well correlated with precipitation for a twelve-year record, with coral geochemistry reflecting the passage of a hurricane in 2002. While additional complexities in deciphering coral records remain, this proxy offers the potential to extend SGD records into the past.by Meagan Joan Eagle Gonneea.Ph. D