Environmental Geoscience

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Browsing Environmental Geoscience by Title

  • Article
    Accuracy and precision of tidal wetland soil carbon mapping in the conterminous United States
    (Nature Publishing Group, 2018-06-21) Holmquist, James R. ; Windham-Myers, Lisamarie ; Bliss, Norman B. ; Crooks, Stephen ; Morris, James T. ; Megonigal, J. Patrick ; Troxler, Tiffany G. ; Weller, Donald ; Callaway, John ; Drexler, Judith ; Ferner, Matthew C. ; Gonneea, Meagan E. ; Kroeger, Kevin D. ; Schile-Beers, Lisa ; Woo, Isa ; Buffington, Kevin ; Breithaupt, Joshua ; Boyd, Brandon M. ; Brown, Lauren N. ; Dix, Nicole ; Hice, Lyndie ; Horton, Benjamin P. ; MacDonald, Glen M. ; Moyer, Ryan P. ; Reay, William ; Shaw, Timothy ; Smith, Erik ; Smoak, Joseph M. ; Sommerfield, Christopher K. ; Thorne, Karen ; Velinsky, David ; Watson, Elizabeth ; Wilson Grimes, Kristin ; Woodrey, Mark
    Tidal wetlands produce long-term soil organic carbon (C) stocks. Thus for carbon accounting purposes, we need accurate and precise information on the magnitude and spatial distribution of those stocks. We assembled and analyzed an unprecedented soil core dataset, and tested three strategies for mapping carbon stocks: applying the average value from the synthesis to mapped tidal wetlands, applying models fit using empirical data and applied using soil, vegetation and salinity maps, and relying on independently generated soil carbon maps. Soil carbon stocks were far lower on average and varied less spatially and with depth than stocks calculated from available soils maps. Further, variation in carbon density was not well-predicted based on climate, salinity, vegetation, or soil classes. Instead, the assembled dataset showed that carbon density across the conterminous united states (CONUS) was normally distributed, with a predictable range of observations. We identified the simplest strategy, applying mean carbon density (27.0 kg C m−3), as the best performing strategy, and conservatively estimated that the top meter of CONUS tidal wetland soil contains 0.72 petagrams C. This strategy could provide standardization in CONUS tidal carbon accounting until such a time as modeling and mapping advancements can quantitatively improve accuracy and precision.
  • Article
    Author Correction : Accuracy and precision of tidal wetland soil carbon mapping in the conterminous United States
    (Nature Publishing Group, 2018-10-09) Holmquist, James R. ; Windham-Myers, Lisamarie ; Bliss, Norman B. ; Crooks, Stephen ; Morris, James T. ; Megonigal, J. Patrick ; Troxler, Tiffany G. ; Weller, Donald ; Callaway, John ; Drexler, Judith ; Ferner, Matthew C. ; Gonneea, Meagan E. ; Kroeger, Kevin D. ; Schile-Beers, Lisa ; Woo, Isa ; Buffington, Kevin ; Breithaupt, Joshua ; Boyd, Brandon M. ; Brown, Lauren N. ; Dix, Nicole ; Hice, Lyndie ; Horton, Benjamin P. ; MacDonald, Glen M. ; Moyer, Ryan P. ; Reay, William ; Shaw, Timothy ; Smith, Erik ; Smoak, Joseph M. ; Sommerfield, Christopher K. ; Thorne, Karen ; Velinsky, David ; Watson, Elizabeth ; Wilson Grimes, Kristin ; Woodrey, Mark
    This Article corrects an error in Equation 1
  • Preprint
    Bioturbation depths, rates and processes in Massachusetts Bay sediments inferred from modeling of 210Pb and 239 + 240Pu profiles
    ( 2004-07-20) Crusius, John ; Bothner, Michael H. ; Sommerfield, Christopher K.
    Profiles of 210Pb and 239+240Pu from sediment cores collected throughout Massachusetts Bay (water depths of 36-192 m) are interpreted with the aid of a numerical sedimentmixing model to infer bioturbation depths, rates and processes. The nuclide data suggest extensive bioturbation to depths of 25-35 cm. Roughly half the cores have 210Pb and 239+240Pu profiles that decrease monotonically from the surface and are consistent with biodiffusive mixing. Bioturbation rates are reasonably well constrained by these profiles and vary from ~0.7 to ~40 cm2 yr-1. As a result of this extensive reworking, however, sediment ages cannot be accurately determined from these radionuclides and only upper limits on sedimentation rates (of ~0.3 cm yr-1) can be inferred. The other half of the radionuclide profiles are characterized by subsurface maxima in each nuclide, which cannot be reproduced by biodiffusive mixing models. A numerical model is used to demonstrate that mixing caused by organisms that feed at the sediment surface and defecate below the surface can cause the subsurface maxima, as suggested by previous work. The deep penetration depths of excess 210Pb and 239+240Pu suggest either that the organisms release material over a range of >15 cm depth or that biodiffusive mixing mediated by other organisms is occurring at depth. Additional constraints from surficial sediment 234Th data suggest that in this half of the cores, the vast majority of the presentday flux of recent, nuclide-bearing material to these core sites is transported over a timescale of a month or more to a depth of a few cm below the sediment surface. As a consequence of the complex mixing processes, surface sediments include material spanning a range of ages and will not accurately record recent changes in contaminant deposition.
  • Article
    Carbon budget of tidal wetlands, estuaries, and shelf waters of eastern North America
    (John Wiley & Sons, 2018-04-04) Najjar, Raymond G. ; Herrmann, Maria ; Alexander, Richard ; Boyer, Elizabeth W. ; Burdige, David J. ; Butman, David ; Cai, Wei-Jun ; Canuel, Elizabeth A. ; Chen, Robert F. ; Friedrichs, Marjorie A. M. ; Feagin, Russell A. ; Griffith, Peter C. ; Hinson, Audra L. ; Holmquist, James R. ; Hu, Xinping ; Kemp, William M. ; Kroeger, Kevin D. ; Mannino, Antonio ; McCallister, S. Leigh ; McGillis, Wade R. ; Mulholland, Margaret R. ; Pilskaln, Cynthia H. ; Salisbury, Joseph E. ; Signorini, Sergio R. ; St-Laurent, Pierre ; Tian, Hanqin ; Tzortziou, Maria ; Vlahos, Penny ; Wang, Zhaohui Aleck ; Zimmerman, Richard C.
    Carbon cycling in the coastal zone affects global carbon budgets and is critical for understanding the urgent issues of hypoxia, acidification, and tidal wetland loss. However, there are no regional carbon budgets spanning the three main ecosystems in coastal waters: tidal wetlands, estuaries, and shelf waters. Here we construct such a budget for eastern North America using historical data, empirical models, remote sensing algorithms, and process‐based models. Considering the net fluxes of total carbon at the domain boundaries, 59 ± 12% (± 2 standard errors) of the carbon entering is from rivers and 41 ± 12% is from the atmosphere, while 80 ± 9% of the carbon leaving is exported to the open ocean and 20 ± 9% is buried. Net lateral carbon transfers between the three main ecosystem types are comparable to fluxes at the domain boundaries. Each ecosystem type contributes substantially to exchange with the atmosphere, with CO2 uptake split evenly between tidal wetlands and shelf waters, and estuarine CO2 outgassing offsetting half of the uptake. Similarly, burial is about equal in tidal wetlands and shelf waters, while estuaries play a smaller but still substantial role. The importance of tidal wetlands and estuaries in the overall budget is remarkable given that they, respectively, make up only 2.4 and 8.9% of the study domain area. This study shows that coastal carbon budgets should explicitly include tidal wetlands, estuaries, shelf waters, and the linkages between them; ignoring any of them may produce a biased picture of coastal carbon cycling.
  • Article
    Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes
    (Nature Research, 2023-12-12) Reithmaier, Gloria M. S. ; Cabral, Alex ; Akhand, Anirban ; Bogard, Matthew J. ; Borges, Alberto V. ; Bouillon, Steven ; Burdige, David J. ; Call, Mitchel ; Chen, Nengwang ; Chen, Xiaogang ; Cotovicz Jr, Luiz C. ; Eagle, Meagan J. ; Kristensen, Erik ; Kroeger, Kevin D. ; Lu, Zeyang ; Maher, Damien T. ; Perez-Llorens, J. Lucas ; Ray, Raghab ; Taillardat, Pierre ; Tamborski, Joseph J. ; Upstill-Goddard, Rob C. ; Wang, Faming ; Wang, Zhaohui Aleck ; Xiao, Kai ; Yau, Yvonne Y. Y. ; Santos, Isaac R.
    Mangroves and saltmarshes are biogeochemical hotspots storing carbon in sediments and in the ocean following lateral carbon export (outwelling). Coastal seawater pH is modified by both uptake of anthropogenic carbon dioxide and natural biogeochemical processes, e.g., wetland inputs. Here, we investigate how mangroves and saltmarshes influence coastal carbonate chemistry and quantify the contribution of alkalinity and dissolved inorganic carbon (DIC) outwelling to blue carbon budgets. Observations from 45 mangroves and 16 saltmarshes worldwide revealed that >70% of intertidal wetlands export more DIC than alkalinity, potentially decreasing the pH of coastal waters. Porewater-derived DIC outwelling (81 ± 47 mmol m−2 d−1 in mangroves and 57 ± 104 mmol m−2 d−1 in saltmarshes) was the major term in blue carbon budgets. However, substantial amounts of fixed carbon remain unaccounted for. Concurrently, alkalinity outwelling was similar or higher than sediment carbon burial and is therefore a significant but often overlooked carbon sequestration mechanism.
  • Article
    Climate change influences foliar nutrition and metabolism of red maple (Acer rubrum) trees in a northern hardwood forest
    (Ecological Society of America, 2022-02-21) Blagden, Megan ; Harrison, Jamie L. ; Minocha, Rakesh ; Sanders-DeMott, Rebecca ; Long, Stephanie ; Templer, Pamela H.
    Mean annual air temperatures are projected to increase, while the winter snowpack is expected to shrink in depth and duration for many mid- and high-latitude temperate forest ecosystems over the next several decades. Together, these changes will lead to warmer growing season soil temperatures and an increased frequency of soil freeze–thaw cycles (FTCs) in winter. We took advantage of the Climate Change Across Seasons Experiment (CCASE) at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA, to determine how these changes in soil temperature affect foliar nitrogen (N) and carbon metabolism of red maple (Acer rubrum) trees in 2015 and 2017. Earlier work from this study revealed a similar increase in foliar N concentrations with growing season soil warming, with or without the occurrence of soil FTCs in winter. However, these changes in soil warming could differentially affect the availability of cellular nutrients, concentrations of primary and secondary metabolites, and the rates of photosynthesis that are all responsive to climate change. We found that foliar concentrations of phosphorus (P), potassium (K), N, spermine (a polyamine), amino acids (alanine, histidine, and phenylalanine), chlorophyll, carotenoids, sucrose, and rates of photosynthesis increased with growing season soil warming. Despite similar concentrations of foliar N with soil warming with and without soil FTCs in winter, winter soil FTCs affected other foliar metabolic responses. The combination of growing season soil warming and winter soil FTCs led to increased concentrations of two polyamines (putrescine and spermine) and amino acids (alanine, proline, aspartic acid, γ-aminobutyric acid, valine, leucine, and isoleucine). Treatment-specific metabolic changes indicated that while responses to growing season warming were more connected to their role as growth modulators, soil warming + FTC treatment-related effects revealed their dual role in growth and stress tolerance. Together, the results of this study demonstrate that growing season soil warming has multiple positive effects on foliar N and cellular metabolism in trees and that some of these foliar responses are further modified by the addition of stress from winter soil FTCs.
  • Article
    Clumped and conventional isotopes of natural gas reveal basin burial, denudation, and biodegradation history
    (Geochemical Society, 2023-10-13) Kim, Jihyun ; Martini, Anna M. ; Ono, Shuhei ; Lalk, Ellen J. ; Ferguson, Grant A.g. ; McIntosh, Jennifer C.
    Formation and post-genetic alteration of hydrocarbons provide insights into the dynamic and complex geologic, hydrologic, and microbial history of shallow crustal environments. Clumped isotopologues of methane (e.g., Δ13CH3D) have emerged as a proxy for constraining methane formation temperatures in sedimentary basins. However, unrealistically high apparent temperatures and microbial cycling of methane necessitate further investigation into how the generation and biodegradation of hydrocarbons may modify methane clumped isotopologue signatures. This study analyzed and modeled the clumped isotopologues of methane, in addition to traditional gas isotopes, to provide new insights into the origin, thermal maturity, migration, and biodegradation histories of hydrocarbons in the Paradox Basin in the Colorado Plateau. The basin was deeply buried in the geologic past and has been recently incised, leading to rapid denudation, enhanced meteoric circulation, and microbial activity. δ13CCH4 and CH4/ΣC2+ ratios suggest that most natural gases in various reservoirs throughout the basin are thermogenic in origin with variable thermal maturities. However, signatures suggestive of anaerobic oxidation of ethane and propane, and secondary microbial methane generation, exist. In the northeastern part of the basin, Δ13CH3D values in reservoirs above and below the Paradox Formation source rocks are consistent with thermodynamic equilibrium, indicating that the thermally mature hydrocarbons equilibrated at ≥160 °C during maximum burial over 30–80 Ma. Disequilibrium Δ13CH3D values of natural gas in Paradox Formation reservoirs along the southwestern margin of the basin suggest the presence of low-maturity hydrocarbons consistent with the region’s shallower burial history. Models of Δ13CH3D values based on the exchange rate of hydrogen isotopes between methane and water and the basin thermal history support that meteoric recharge and microbial activity, following incision/denudation over the past few million years, promoted anaerobic oxidation of hydrocarbons (particularly ethane and propane), biodegradation of crude oil, and generation of secondary microbial methane in shallow reservoirs.
  • Article
    Cold-water coral distributions in the Drake Passage area from towed camera observations – initial interpretations
    (Public Library of Science, 2011-01-25) Waller, Rhian G. ; Scanlon, Kathryn M. ; Robinson, Laura F.
    Seamounts are unique deep-sea features that create habitats thought to have high levels of endemic fauna, productive fisheries and benthic communities vulnerable to anthropogenic impacts. Many seamounts are isolated features, occurring in the high seas, where access is limited and thus biological data scarce. There are numerous seamounts within the Drake Passage (Southern Ocean), yet high winds, frequent storms and strong currents make seafloor sampling particularly difficult. As a result, few attempts to collect biological data have been made, leading to a paucity of information on benthic habitats or fauna in this area, particularly those on primarily hard-bottom seamounts and ridges. During a research cruise in 2008 six locations were examined (two on the Antarctic margin, one on the Shackleton Fracture Zone, and three on seamounts within the Drake Passage), using a towed camera with onboard instruments to measure conductivity, temperature, depth and turbidity. Dominant fauna and bottom type were categorized from 200 randomized photos from each location. Cold-water corals were present in high numbers in habitats both on the Antarctic margin and on the current swept seamounts of the Drake Passage, though the diversity of orders varied. Though the Scleractinia (hard corals) were abundant on the sedimented margin, they were poorly represented in the primarily hard-bottom areas of the central Drake Passage. The two seamount sites and the Shackleton Fracture Zone showed high numbers of stylasterid (lace) and alcyonacean (soft) corals, as well as large numbers of sponges. Though data are preliminary, the geological and environmental variability (particularly in temperature) between sample sites may be influencing cold-water coral biogeography in this region. Each area observed also showed little similarity in faunal diversity with other sites examined for this study within all phyla counted. This manuscript highlights how little is understood of these isolated features, particularly in Polar regions.
  • Preprint
    The colonial ascidian Didemnum sp. A: Current distribution, basic biology and potential threat to marine communities of the northeast and west coasts of North America
    ( 2006-10-09) Bullard, Stephan G. ; Lambert, Gretchen ; Carman, Mary R. ; Byrnes, J. ; Whitlatch, R. B. ; Ruiz, G. ; Miller, R. J. ; Harris, L. ; Valentine, Page C. ; Collie, Jeremy S. ; Pederson, J. ; McNaught, D. C. ; Cohen, A. N. ; Asch, Rebecca G. ; Dijkstra, Jennifer A. ; Heinonen, K.
    Didemnum sp. A is a colonial ascidian with rapidly expanding populations on the east and west coasts of North America. The origin of Didemum sp. A is unknown. Populations were first observed on the northeast coast of the U.S. in the late 1980s and on the west coast during the 1990s. It is currently undergoing a massive population explosion and is now a dominant member of many subtidal communities on both coasts. To determine Didemnum sp. A’s current distribution, we conducted surveys from Maine to Virginia on the east coast and from British Columbia to southern California on the west coast of the U.S. between 1998 and 2005. In nearshore locations Didemnum sp. A currently ranges from Eastport, Maine to Shinnecock Bay, New York on the east coast. On the west coast it has been recorded from Humboldt Bay to Port San Luis in California, several sites in Puget Sound, Washington, including a heavily fouled mussel culture facility, and several sites in southwestern British Columbia on and adjacent to oyster and mussel farms. The species also occurs at deeper subtidal sites (up to 81 m) off New England, including Georges, Stellwagen and Tillies Banks. On Georges Bank numerous sites within a 147 km2 area are 50-90% covered by Didemnum sp. A; large colonies cement the pebble gravel into nearly solid mats that may smother infaunal organisms. These observations suggest that Didemnum sp. A has the potential to alter marine communities and affect economically important activities such as fishing and aquaculture.
  • Article
    Comparison of atmospheric mercury speciation and deposition at nine sites across central and eastern North America
    (American Geophysical Union, 2010-09-22) Engle, Mark A. ; Tate, Michael T. ; Krabbenhoft, David P. ; Schauer, James J. ; Kolker, Allan ; Shanley, James B. ; Bothner, Michael H.
    This study presents >5 cumulative years of tropospheric mercury (Hg) speciation measurements, over the period of 2003–2009, for eight sites in the central and eastern United States and one site in coastal Puerto Rico. The purpose of this research was to identify local and regional processes that impact Hg speciation and deposition (wet + dry) across a large swath of North America. Sites sampled were selected to represent both a wide range of mercury exposure and environmental conditions. Seasonal mean concentrations of elemental Hg (1.27 ± 0.31 to 2.94 ± 1.57 ng m−3; inline equation ± σ), reactive gaseous mercury (RGM; 1.5 ± 1.6 to 63.3 ± 529 pg m−3), and fine particulate Hg (1.2 ± 1.4 to 37.9 ± 492 pg m−3) were greatest at sites impacted by Hg point sources. Diel bin plots of Hgo and RGM suggest control by a variety of local/regional processes including impacts from Hg point sources and boundary layer/free tropospheric interactions as well as from larger-scale processes affecting Hg speciation (i.e., input of the global Hg pool, RGM formed from oxidation of Hgo by photochemical compounds at coastal sites, and elemental Hg depletion during periods of dew formation). Comparison of wet Hg deposition (measured), RGM and fine particulate Hg dry deposition (calculated using a multiple resistance model), and anthropogenic point source emissions varied significantly between sites. Significant correlation between emission sources and dry deposition was observed but was highly dependant upon inclusion of data from two sites with exceptionally high deposition. Findings from this study highlight the importance of environmental setting on atmospheric Hg cycling and deposition rates.
  • Article
    Comparison of two U.S. power-plant carbon dioxide emissions data sets
    (Americal Chemical Society, 2008-06-25) Ackerman, Katherine V. ; Sundquist, Eric T.
    Estimates of fossil-fuel CO2 emissions are needed to address a variety of climate-change mitigation concerns over a broad range of spatial and temporal scales. We compared two data sets that report power-plant CO2 emissions in the conterminous U.S. for 2004, the most recent year reported in both data sets. The data sets were obtained from the Department of Energy’s Energy Information Administration (EIA) and the Environmental Protection Agency’s eGRID database. Conterminous U.S. total emissions computed from the data sets differed by 3.5% for total plant emissions (electricity plus useful thermal output) and 2.3% for electricity generation only. These differences are well within previous estimates of uncertainty in annual U.S. fossil-fuel emissions. However, the corresponding average absolute differences between estimates of emissions from individual power plants were much larger, 16.9% and 25.3%, respectively. By statistical analysis, we identified several potential sources of differences between EIA and eGRID estimates for individual plants. Estimates that are based partly or entirely on monitoring of stack gases (reported by eGRID only) differed significantly from estimates based on fuel consumption (as reported by EIA). Differences in accounting methods appear to explain differences in estimates for emissions from electricity generation from combined heat and power plants, and for total and electricity generation emissions from plants that burn nonconventional fuels (e.g., biomass). Our analysis suggests the need for care in utilizing emissions data from individual power plants, and the need for transparency in documenting the accounting and monitoring methods used to estimate emissions.
  • Article
    Deciphering the dynamics of inorganic carbon export from intertidal salt marshes using high-frequency measurements
    (Elsevier, 2018-08-25) Chu, Sophie N. ; Wang, Zhaohui Aleck ; Gonneea, Meagan E. ; Kroeger, Kevin D. ; Ganju, Neil K.
    The lateral export of carbon from coastal marshes via tidal exchange is a key component of the marsh carbon budget and coastal carbon cycles. However, the magnitude of this export has been difficult to accurately quantify due to complex tidal dynamics and seasonal cycling of carbon. In this study, we use in situ, high-frequency measurements of dissolved inorganic carbon (DIC) and water fluxes to estimate lateral DIC fluxes from a U.S. northeastern salt marsh. DIC was measured by a CHANnelized Optical Sensor (CHANOS) that provided an in situ concentration measurement at 15-min intervals, during periods in summer (July – August) and late fall (December). Seasonal changes in the marsh had strong effects on DIC concentrations, while tidally-driven water fluxes were the fundamental vehicle of marsh carbon export. Episodic events, such as groundwater discharge and mean sea water level changes, can impact DIC flux through altered DIC concentrations and water flow. Variability between individual tides within each season was comparable to mean variability between the two seasons. Estimated mean DIC fluxes based on a multiple linear regression (MLR) model of DIC concentrations and high-frequency water fluxes agreed reasonably well with those derived from CHANOS DIC measurements for both study periods, indicating that high-frequency, modeled DIC concentrations, coupled with continuous water flux measurements and a hydrodynamic model, provide a robust estimate of DIC flux. Additionally, an analysis of sampling strategies revealed that DIC fluxes calculated using conventional sampling frequencies (hourly to two-hourly) of a single tidal cycle are unlikely to capture a representative mean DIC flux compared to longer-term measurements across multiple tidal cycles with sampling frequency on the order of tens of minutes. This results from a disproportionately large amount of the net DIC flux occurring over a small number of tidal cycles, while most tides have a near-zero DIC export. Thus, high-frequency measurements (on the order of tens of minutes or better) over the time period of interest are necessary to accurately quantify tidal exports of carbon species from salt marshes.
  • Preprint
    Depth of the vadose zone controls aquifer biogeochemical conditions and extent of anthropogenic nitrogen removal
    ( 2017-06) Szymczycha, Beata ; Kroeger, Kevin D. ; Crusius, John ; Bratton, John F.
    We investigated biogeochemical conditions and watershed features controlling the extent of nitrate removal through microbial dinitrogen (N2) production within the surficial glacial aquifer located on the north and south shores of Long Island, NY, USA. The extent of N2 production differs within portions of the aquifer, with greatest N2 production observed at the south shore of Long Island where the vadose zone is thinnest, while limited N2 production occurred under the thick vadose zones on the north shore. In areas with a shallow water table and thin vadose zone, low oxygen concentrations and sufficient DOC concentrations are conducive to N2 production. Results support the hypothesis that in aquifers without a significant supply of sediment-bound reducing potential, vadose zone thickness exerts an important control of the extent of N2 production. Since quantification of excess N2 relies on knowledge of equilibrium N2 concentration at recharge, calculated based on temperature at recharge, we further identify several features, such as land use and cover, seasonality of recharge, and climate change that should be considered to refine estimation of recharge temperature, its deviation from mean annual air temperature, and resulting deviation from expected equilibrium gas concentrations.
  • Article
    Detection and characterization of coastal tidal wetland change in the northeastern US using Landsat time series
    (Elsevier, 2022-04-26) Yang, Xiucheng ; Zhu, Zhe ; Qiu, Shi ; Kroeger, Kevin D. ; Zhu, Zhiliang ; Covington, Scott
    Coastal tidal wetlands are highly altered ecosystems exposed to substantial risk due to widespread and frequent land-use change coupled with sea-level rise, leading to disrupted hydrologic and ecologic functions and ultimately, significant reduction in climate resiliency. Knowing where and when the changes have occurred, and the nature of those changes, is important for coastal communities and natural resource management. Large-scale mapping of coastal tidal wetland changes is extremely difficult due to their inherent dynamic nature. To bridge this gap, we developed an automated algorithm for DEtection and Characterization of cOastal tiDal wEtlands change (DECODE) using dense Landsat time series. DECODE consists of three elements, including spectral break detection, land cover classification and change characterization. DECODE assembles all available Landsat observations and introduces a water level regressor for each pixel to flag the spectral breaks and estimate harmonic time-series models for the divided temporal segments. Each temporal segment is classified (e.g., vegetated wetlands, open water, and others – including unvegetated areas and uplands) based on the phenological characteristics and the synthetic surface reflectance values calculated from the harmonic model coefficients, as well as a generic rule-based classification system. This harmonic model-based approach has the advantage of not needing the acquisition of satellite images at optimal conditions (i.e., low tide status) to avoid underestimating coastal vegetation caused by the tidal fluctuation. At the same time, DECODE can also characterize different kinds of changes including land cover change and condition change (i.e., land cover modification without conversion). We used DECODE to track status of coastal tidal wetlands in the northeastern United States from 1986 to 2020. The overall accuracy of land cover classification and change detection is approximately 95.8% and 99.8%, respectively. The vegetated wetlands and open water were mapped with user's accuracy of 94.6% and 99.0%, and producer's accuracy of 98.1% and 93.5%, respectively. The cover change and condition change were mapped with user's accuracy of 68.0% and 80.0%, and producer's accuracy of 80.5% and 97.1%, respectively. Approximately 3283 km2 of the coastal landscape within our study area in the northeastern United States changed at least once (12% of the study area), and condition changes were the dominant change type (84.3%). Vegetated coastal tidal wetland decreased consistently (~2.6 km2 per year) in the past 35 years, largely due to conversion to open water in the context of sea-level rise.
  • Article
    Distinguishing seawater from geologic brine in saline coastal groundwater using radium-226; an example from the Sabkha of the UAE
    (Elsevier, 2014-02-06) Kraemer, Thomas F. ; Wood, Warren W. ; Sanford, Ward E.
    Sabkhat (Salt flats) are common geographic features of low-lying marine coastal areas that develop under hyper-arid climatic conditions. They are characterized by the presence of highly concentrated saline solutions and evaporitic minerals, and have been cited in the geologic literature as present-day representations of hyper-arid regional paleohydrogeology, paleoclimatology, coastal processes, and sedimentation in the geologic record. It is therefore important that a correct understanding of the origin and development of these features be achieved. Knowledge of the source of solutes is an important first step in understanding these features. Historically, two theories have been advanced as to the main source of solutes in sabkha brines: an early concept entailing seawater as the obvious source, and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations. Ra-226 could uniquely distinguish between these sources under certain circumstances, as it is typically present at elevated activity of hundreds to thousands of Bq/m3 (Becquerels per cubic meter) in subsurface formation brines; at exceedingly low activities in open ocean and coastal water; and not significantly supplied to water from recently formed marine sedimentary framework material. The coastal marine sabkha of the Emirate of Abu Dhabi was used to test this hypothesis. The distribution of Ra-226 in 70 samples of sabkha brine (mean: 700 Bq/m3), 7 samples of underlying deeper formation brine (mean: 3416 Bq/m3), the estimated value of seawater (< 16 Bq/m3) and an estimate of supply from sabkha sedimentary framework grains (<~6 Bq/m3) provide the first direct evidence that ascending geologic brine contributes significantly to the solutes of this sabkha system.
  • Preprint
    Ensuring confidence in radionuclide-based sediment chronologies and bioturbation rates
    ( 2006-09-11) Crusius, John ; Kenna, Timothy C.
    Sedimentary records of naturally occurring and fallout-derived radionuclides are widely used as tools for estimating both the ages of recent sediments and rates of sedimentation and bioturbation. Developing these records to the point of data interpretation requires careful sample collection, processing, analysis and data modeling. In this work, we document a number of potential pitfalls that can impact sediment core records and their interpretation. This paper is not intended as an exhaustive treatment of these potential problems. Rather, the emphasis is on potential problems that are not well documented in the literature, as follows: 1) The mere sampling of sediment cores at a resolution that is too coarse can result in an apparent diffusive mixing of the sedimentary record at rates comparable to diffusive bioturbation rates observed in many locations; 2) 210Pb profiles in slowly accumulating sediments can easily be misinterpreted to be driven by sedimentation, when in fact bioturbation is the dominant control. Multiple isotopes of different half lives and/or origin may help to distinguish between these two possible interpretations; 3) Apparent mixing can occur due simply to numerical artifacts inherent in the finite difference approximations of the advection diffusion equation used to model sedimentation and bioturbation. Model users need to be aware of this potential problem. Solutions to each of these potential pitfalls are offered to ensure the best possible sediment age estimates and/or sedimentation and bioturbation rates can be obtained.
  • Article
    Environmental controls, emergent scaling, and predictions of greenhouse gas (GHG) fluxes in coastal salt marshes
    (John Wiley & Sons, 2018-07-28) Abdul-Aziz, Omar I. ; Ishtiaq, Khandker S. ; Tang, Jianwu ; Moseman-Valtierra, Serena M. ; Kroeger, Kevin D. ; Gonneea, Meagan E. ; Mora, Jordan ; Morkeski, Kate
    Coastal salt marshes play an important role in mitigating global warming by removing atmospheric carbon at a high rate. We investigated the environmental controls and emergent scaling of major greenhouse gas (GHG) fluxes such as carbon dioxide (CO2) and methane (CH4) in coastal salt marshes by conducting data analytics and empirical modeling. The underlying hypothesis is that the salt marsh GHG fluxes follow emergent scaling relationships with their environmental drivers, leading to parsimonious predictive models. CO2 and CH4 fluxes, photosynthetically active radiation (PAR), air and soil temperatures, well water level, soil moisture, and porewater pH and salinity were measured during May–October 2013 from four marshes in Waquoit Bay and adjacent estuaries, MA, USA. The salt marshes exhibited high CO2 uptake and low CH4 emission, which did not significantly vary with the nitrogen loading gradient (5–126 kg · ha−1 · year−1) among the salt marshes. Soil temperature was the strongest driver of both fluxes, representing 2 and 4–5 times higher influence than PAR and salinity, respectively. Well water level, soil moisture, and pH did not have a predictive control on the GHG fluxes, although both fluxes were significantly higher during high tides than low tides. The results were leveraged to develop emergent power law‐based parsimonious scaling models to accurately predict the salt marsh GHG fluxes from PAR, soil temperature, and salinity (Nash‐Sutcliffe Efficiency = 0.80–0.91). The scaling models are available as a user‐friendly Excel spreadsheet named Coastal Wetland GHG Model to explore scenarios of GHG fluxes in tidal marshes under a changing climate and environment.
  • Preprint
    Estimation of groundwater and nutrient fluxes to the Neuse River estuary, North Carolina
    ( 2008-01-12) Spruill, Timothy B. ; Bratton, John F.
    A study was conducted between April 2004 and September 2005 to estimate ground-water and nutrient discharge to the Neuse River estuary in North Carolina. Largest ground-water fluxes were observed to occur generally within 20 m of the shoreline. Ground-water flux estimates based on seepage-meter measurements ranged from 2.86 x 108 to 4.33 x 108 m3 annually and are comparable to estimates made using radon, a simple water-budget method, and estimates derived by using Darcy’s Law and previously published general aquifer characteristics of the area. The lower ground-water flux estimate (equal to about 9 m3 s–1), which assumed the narrowest ground-water discharge zone (20 m) of three zone widths selected for an area west of New Bern, North Carolina, most closely agrees with ground-water flux estimates made using radon (3–9 m3 s–1) and Darcy’s Law (about 9 m3 s–1). A ground-water flux of 9 m3 s–1 is about 40% of the surface-water flow to the Neuse River estuary between Streets Ferry and the mouth of the estuary and about 7% of the surface-water inflow from areas upstream. Estimates of annual nitrogen (333 tonnes) and phosphorus (66 tonnes) fluxes from ground water to the estuary, based on this analysis, are less than 6% of the nitrogen and phosphorus inputs derived from all sources (excluding oceanic inputs), and approximately 8% of the nitrogen and 17% of the phosphorus annual inputs from surface-water inflow to the Neuse River estuary assuming a mean annual precipitation of 1.27 m. We provide quantitative evidence, derived from three methods, that the contribution of water and nutrients from ground-water discharge to the NRE is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment sources of nutrients. Locally high ground-water discharges in the NRE do occur, however, and could help explain the occurrence of localized phytoplankton blooms, submerged aquatic vegetation, or fish kills.
  • Article
    Flow and geochemistry of groundwater beneath a back-barrier lagoon : the subterranean estuary at Chincoteague Bay, Maryland, USA
    (Elsevier B.V., 2009-01-21) Bratton, John F. ; Bohlke, John K. ; Krantz, David E. ; Tobias, Craig R.
    To better understand large-scale interactions between fresh and saline groundwater beneath an Atlantic coastal estuary, an offshore drilling and sampling study was performed in a large barrier-bounded lagoon, Chincoteague Bay, Maryland, USA. Groundwater that was significantly fresher than overlying bay water was found in shallow plumes up to 8 m thick extending more than 1700 m offshore. Groundwater saltier than bay surface water was found locally beneath the lagoon and the barrier island, indicating recharge by saline water concentrated by evaporation prior to infiltration. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied, with buried peats and estuarine muds acting as confining units. Groundwater ages were generally more than 50 years in both fresh and brackish waters as deep as 23 m below the bay bottom. Water chemistry and isotopic data indicate that freshened plumes beneath the estuary are mixtures of water originally recharged on land and varying amounts of estuarine surface water that circulated through the bay floor, possibly at some distance from the sampling location. Ammonium is the dominant fixed nitrogen species in saline groundwater beneath the estuary at the locations sampled. Isotopic and dissolved-gas data from one location indicate that denitrification within the subsurface flow system removed terrestrial nitrate from fresh groundwater prior to discharge along the western side of the estuary. Similar situations, with one or more shallow semi-confined flow systems where groundwater geochemistry is strongly influenced by circulation of surface estuary water through organic-rich sediments, may be common on the Atlantic margin and elsewhere.
  • Article
    Forecasting sea level rise-driven inundation in diked and tidally restricted coastal lowlands
    (Springer, 2023-05-05) Befus, Kevin M. ; Kurnizki, Alexander P. D. ; Kroeger, Kevin D. ; Eagle, Meagan J. ; Smith, Tim P.
    Diked and drained coastal lowlands rely on hydraulic and protective infrastructure that may not function as designed in areas with relative sea-level rise. The slow and incremental loss of the hydraulic conditions required for a well-drained system make it difficult to identify if and when the flow structures no longer discharge enough water, especially in tidal settings where two-way flows occur through the dike. We developed and applied a hydraulic mass-balance model to quantify how water levels in the diked and tidally restricted coastal wetlands and water bodies dynamically respond to sea-level rise, specifically applied to the Herring River Estuary in MA, USA, from 2020 to 2100. Sensitivity testing of the model parameters indicated that primary outcomes were not sensitive to many of the chosen input values, though the terrestrial water input rate to the estuary and the flow coefficient for the hydraulic infrastructure were important. The relative importance of parameters, however, is expected to be site specific. We introduced a drainability metric that quantifies the net water volume drained over every tidal cycle to monitor and forecast how rising water levels on either side of the dike affected the net draining or impounding conditions of the system. Ensembles of model results across parameter and sea-level scenario uncertainties indicated that substantial impoundment of the Herring River Estuary was expected within ~ 20 years with the existing flow structures, a sluice and two flap gates. Simulations with up to three additional gates did not dampen this trend toward impoundment, suggesting that rising impounded water levels are likely even with major construction upgrades. Increasingly impounded diked coastal waterbodies present a hydrologic challenge with socioecological implications due to projected flooding and ecosystem impacts. Solutions to this challenge may be to allow coastal wetland restoration pathways or require substantial and recurring infrastructure improvement projects.