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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Flow Directions and Ages of Subsurface Water in a Salt Marsh System Constrained by Isotope Tracing

Salt marshes are dynamic hydrologic systems where terrestrial groundwater, terrestrial surface water, and seawater mix due to bi-directional flows and pressure gradients. Due to the counteracting terrestrial and marine forcings that control these environments, we do not comprehensively understand water fluxes in these complex coastal systems. To understand the water sources, flow directions, and velocities in salt marsh porewater, we employed a combination of geochemical tracers and analytical models across a hillslope-to-salt marsh continuum in a salt marsh experiencing daily inundation of estuarine surface water (SW) from tides and mixing of fresh seasonal groundwater. We used tritium ( 3 H) as a hydrologic tracer to assess porewater ages and stable water isotope ($\delta$ 2 H and $\delta$ 18 O) analyses to separate isotopically distinct estuarine and terrestrial groundwater across different depths and landscape positions in the study transect. We employed electrical conductivity to constrain the role of source mixing and evapotranspiration in salt marsh hydrology. Salinity and stable isotopes revealed that transpiration, rather than evaporation, increased subsurface water salinity to concentrations above estuarine SW during summer. Elevated salinity at depth indicated that salt marsh subsurface water is recharged during the dry growing season. Seasonal recharge patterns drive long-term deep subsurface water dynamics across the salt marsh, with 3 H ages of 3–7 years, and daily tidal cycles drive short-term shallow porewater dynamics with 3 H ages of 0 ± 3.6 years. Furthermore, our conceptual understanding of the spatiotemporal changes in SW-subsurface water interactions at the terrestrial-marine interface quantifies the hydrological constraints we are missing to improve our understanding of biogeochemical cycles within the salt marsh.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Reproductive Responses to Increased Shoot Density and Global Change Drivers in a Widespread Clonal Wetland Species, Schoenoplectus americanus

The expansion of many wetland species is a function of both clonal propagation and sexual reproduction. The production of ramets through clonal propagation enables plants to move and occupy space near parent ramets, while seeds produced by sexual reproduction enable species to disperse and colonize open or disturbed sites both near and far from parents. The balance between clonal propagation and sexual reproduction is known to vary with plant density but few studies have focused on reproductive allocation with density changes in response to global climate change. Schoenoplectus americanus is a widespread clonal wetland species in North America and a dominant species in Chesapeake Bay brackish tidal wetlands. Long-term experiments on responses of S. americanus to global change provided the opportunity to compare the two modes of propagation under different treatments. Seed production increased with increasing shoot density, supporting the hypothesis that factors causing increased clonal reproduction (e.g., higher shoot density) stimulate sexual reproduction and dispersal of genets. The increase in allocation to sexual reproduction was mainly the result of an increase in the number of ramets that flowered and not an increase in the number of seeds per reproductive shoot, or the ratio between the number of flowers produced per inflorescence and the number of flowers that developed into seeds. Seed production increased in response to increasing temperatures and decreased or did not change in response to increased CO2 or nitrogen. Results from this comparative study demonstrate that plant responses to global change treatments affect resource allocation and can alter the ability of species to produce seeds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Timing Value of Marine Renewable Energy Resources for Potential Grid Applications

In this paper, the applicability of marine renewable energy for potential grid applications is presented. We show that many of the unique value streams from marine-based electricity generation stem from their inherent temporal characteristics, especially when compared to wind and solar. Specifically, in this work, we evaluate the timing value for three types of marine energy resources - (a) tidal (b) wave and (c) ocean currents. Firstly, through a suite of novel metrics such as resource availability, persistence and versatility, we evaluate the temporal value characteristics of these resources. Secondly, through a more grid-oriented numerical study, we comment on the potential ramifications of those temporal characteristics in context of energy balancing and effective load carrying capability, for one marine-based resource i.e. wave. Subsequently, we further our understanding of the relative advantages which may be leveraged by operating wave-based generation resources in tandem with more established renewable choices, such as solar and wind. Our results indicate that compared to wind and solar, marine energy resources are consistently more available and persistent on an hourly level, throughout an entire year of operation. In addition to this, wave resources are also seen to reduce both the magnitudes and the degree of volatility in balancing requirements within the power system. Our work not only focuses on sites specific to the Unites States (US), but also includes a parallel study for a location in Great Britain (GB). Results are found to be consistent for sites in both the US and GB, implying that the grid benefits discussed in this work could apply to a number of locations globally.

Bhattacharya, Saptarshi↗
DOE OSTI2019

Modeling assessment of storm surge in the Salish Sea

Here we present a modeling assessment of storm surge in the Salish Sea—a large and complex estuarine system in the Pacific Northwest that is exposed to extratropical cyclones. A method was developed to systematically identify storm surge events in the Salish Sea based on water level records at four representative tidal gauges in the Salish Sea. The maximum storm surge distribution in the Salish Sea was calculated based on model simulations of 34 major historical storm events from 1980 to 2016. The model simulations were validated by field observations of water level and velocity using a suite of model performance metrics. Model results suggest that the maximum storm surge in the Salish Sea is generally in the range of 0.8 m–1.03 m and is heterogeneous in space. The model results also show a strong north-south gradient with larger surge magnitudes occurring in the north that is primarily caused by the southerly wind in winter months. The sensitivity analysis of wind forcing suggested that storm surge in the Salish Sea is dominated by the remote surge from the Pacific Ocean, and the local wind contributes up to approximately 20% of the surge variability. This paper systematically elucidates storm surge characteristics and potential risk in the Salish Sea.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Reducing impacts of artificial ponding in modeling salt marshes using a conductivity-formulated subgrid model

The landforms of salt marsh systems are rather complex, with meandering channel networks cutting through low-lying, extensive marsh platforms. Some small-scale topographic details are critical to flooding and draining processes but cannot be reflected in the Digital Elevation Model (DEM) due to limited measurement resolution and vegetation bias. Numerical models need a grid with high enough resolution to capture the small-scale connectivity to correctly model the small-scale flow processes, making the model computationally unaffordable. Here, in this study, we derived a subgrid model, which couples two flow components, one is the regular subgrid model for simulating the subgrid-resolved flows, and the other is a conductivity-formulated porous flow model for modeling small-scale gut flows unresolved at the subgrid level. The model validation was performed using an idealized case with a narrow slot that was unresolved in the coupled flow model. Model results were compared with a slot-resolved regular subgrid model where only surface flows are solved and suggested that, with a proper model parameterization, the coupled flow model is capable of reproducing flooding and draining processes similar to the slot-resolved subgrid model of surface flow. The model was applied to simulating flooding and draining processes in a meso-tidal salt marsh. The model results demonstrate that the coupled subgrid model can be used to reduce the impacts of artificial ponding that usually occur in numerical simulations of salt marshes with numerous narrow gullies and creeks.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Effects of spatial variability in vegetation phenology, climate, landcover, biodiversity, topography, and soil property on soil respiration across a coastal ecosystem

Coastal terrestrial-aquatic interfaces (TAIs) are crucial contributors to global biogeochemical cycles and carbon exchange. A systematic evaluation of the interaction between coastal catchment properties and carbon dioxide (CO2) emission by soil respiration is significant for assessing carbon dynamics and predicting the future trajectory of atmospheric CO2 concentrations in coastal TAIs. The soil CO2 efflux in these transition zones is however poorly understood due to the high spatiotemporal dynamics of TAIs, as various sub-ecosystems in this region are compressed and expanded by complex influences of tides, changes in river levels, climate, and land use. We focus on the Chesapeake Bay region to (i) investigate the spatial heterogeneity of the coastal ecosystem and identify spatial zones with similar environmental characteristics based on the spatial data layers, including vegetation index (kNDVI), climate, landcover, diversity, topography, soil property, and relative tidal elevation; (ii) understand the primary driving factors affecting soil respiration within sub-ecosystems of the coastal ecosystem. Specifically, we employed hierarchical clustering analysis to identify spatial regions with distinct environmental characteristics, followed by the determination of main driving factors using Random Forest regression and SHapley Additive exPlanations. Maximum and minimum temperature are the main drivers common to all sub-ecosystems, while each region also has additional unique major drivers that differentiate them from one another. Precipitation exerts an influence on vegetated lands, while soil pH value holds importance specifically in forested lands. In croplands characterized by high clay content and low sand content, the significant role is attributed to bulk density. Wetlands demonstrate the importance of both elevation and sand content, with clay content being more relevant in non-inundated wetlands than in inundated wetlands. The topographic wetness index significantly contributes to the mixed vegetation areas, including shrub, grass, pasture, and forest. Additionally, our research reveals that dense vegetation land covers and urban/developed areas exhibit distinct soil property drivers. Overall, there is no one-size-fits-all approach to modeling carbon fluxes in coastal TAIs, and our study highlights the importance of further research and monitoring practices to improve our understanding of carbon dynamics and promote the sustainable management of coastal TAIs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Influence of alveolar mixing and multiple breaths of aerosol intake on particle deposition in the human lungs

Predictive dosimetry models play an important role in assessing health effect of inhaled particulate matter and in optimizing delivery of inhaled pharmaceutical aerosols. Here, in this study, the commonly used 1D Multiple-Path Particle Dosimetry model (MPPD) was improved by including a mechanistically based model component for alveolar mixing of particles and by extending the model capabilities to account for multiple breaths of aerosol intake. These modifications increased the retained fraction of particles and consequently particle deposition predictions in the deep lung during tidal breathing. Comparison with an existing dataset (J. Aerosol Sci., 99:27-39, 2016) obtained under two breathing conditions referred to as slow and fast breathing showed significant differences in 1 µm particle deposition between predictions (slow: 30±1%, fast: 21±1%) and measurements (slow: 43±9%, fast: 30±5%) when the prior version of MPPD (single breath and no mixing, J. Aerosol Sci., 151:105647, 2021) was used. Adding a mixing model and multiple breaths moved the predictions (slow: 34±2%, fast:25±2%) closer to the range of deposition measurements. For 2.9 µm particles, predictions from both the original (slow: 70±2%, fast: 57±2%) and the revised MPPD model (slow: 71±2%, fast: 59±3%) compared well with experiments (slow: 67±8%, fast: 58±10%). This was expected as suspended fraction of 2.9 µm particles was small and thus the addition of alveolar mixing and multi breath capability only slightly increased the retained fraction for particles of this size and greater. The revised 1D model improves dose predictions in the deep lung and support human risk assessment from exposure to airborne particles.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Automated bidirectional coupling of multiscale models of aerosol dosimetry: Validation with subject-specific deposition data

Assessing the toxicity of airborne particulate matter or the efficacy of inhaled drug depends upon accurate estimates of deposited fraction of inhaled materials. In silico approaches can provide important insights into site- or airway-specific deposition of inhaled aerosols in the respiratory system. In this study, we improved on our recently developed 3D/1D model that simulate aerosol transport and deposition in the whole lung over multiple breath cycles. A subject-specific multiscale lung model of a healthy male subject using computational fluid-particle dynamics (CFPD) in a 3D model of the oral cavity through the large bronchial airways entering each lobe was bidirectionally coupled with a recently improved Multiple Path Particle Dosimetry (MPPD) model to predict aerosol deposition over the entire respiratory tract over multiple breaths for four conditions matching experimental aerosol exposures in the same subject from which the model was developed. These include two particle sizes (1 and 2.9 μm) and two subject-specific breathing rates of ~300 ml/s (slow breathing) and ~750 ml/s (fast breathing) at a target tidal volume of 1 L. In silico predictions of retained fraction were 0.31 and 0.29 for 1 μm and 0.66 and 0.62 for 2.9 μm during slow and fast breathing, respectively, and compared well with experimental data (1 μm: 0.31 ± 0.01 (slow) and 0.27 ± 0.01 (fast), 2.9 μm: 0.63 ± 0.03 (slow) and 0.68 ± 0.02 (fast)). Furthermore, these results provide a great deal of confidence in the validity and reliability of our approach.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Hydrocarbon production reduces natural methane seeps in the Santa Barbara channel

Abundant natural hydrocarbon seepage in the Santa Barbara Channel includes large amounts of gas, mainly methane. Numerous seeps are focused along a faulted anticlinal axis where in 1982 ARCO placed two large (900 m 2 each) steel gas capture tents on the seabed adjacent to Platform Holly. The seep rate into the tent at high tide is about 5 percent less compared with low tide (2m tidal range). An earthquake in 2013 (M = 4.8) did not affect seepage rates into the steel tents, indicating that gas was not released by fault dilation. The CO 2 and H 2 S content of the captured gas are anomalously low compared to typical Holly gas due to bacterial and sea water-gas interaction at the seep tent. Platform Holly production had an overall effect of reducing gas seepage into the tents over time. Wells beneath the tents at 1-km depth had a much greater influence on the seepage rate than more distal wells. The nearby wells had a direct effect on seepage rate when they were put on production (seepage decreased) versus shut in (seepage increased). The response time was within hours, indicating a direct hydraulic connection between the reservoir at 1 km subsea and the seabed. Permeability of the approximate 1-km fault pathway between the reservoir and the seep tent is calculated to be about 3 × 10 -14 m 2 (30 millidarcys). Gradually, the seep rate declined from peak flow in 1990 (4.5×10 4 m 3 dy-1) to less than 7.1×10 3 m 3 dy -1 in 2013. In June of 2013, a horizontal well was completed high on the structural anticline between Platform Holly and directly beneath the seep tents. Within three weeks of turning on this new well, seepage into the tents completely ceased, ending more than 30 years of natural methane seepage captured by the tents.

58 GEOSCIENCES↗
DOE OSTI2026

Development and application of an environmental risk register for marine energy device and project developers

The marine energy industry is steadily advancing as more devices are deployed worldwide. However, several challenges and barriers remain, such as lingering uncertainty regarding the potential environmental effects of marine energy devices on marine animals, habitats, and ecosystems. Concerns have led to difficulty navigating permitting and consenting processes and receiving authorization to deploy devices in the marine environment, including extended timelines and costs. Based on existing risk registers, a novel marine energy environmental risk register was created to help the marine energy industry move beyond these barriers. This risk register aims to aid marine energy device and project developers identify and assess potential environmental risks early in device design or project planning, document and track potential environmental interactions, prioritize risks and determine risk responses, and make decisions throughout device or project development. It can also be used as a tool to assist in communicating with regulators and advisors during permitting processes and to inform stakeholder and community engagement efforts. This paper details the methods and process to develop a risk register specific to environmental effects of marine energy and describes two use cases (one for wave energy and another for tidal energy) to highlight example results. Due to the tool's novelty, the paper showcases its application for the marine energy industry and acknowledges limitations and possible future improvements. Overall, the environmental risk register shows promise to support marine energy developers when identifying, tracking, and addressing potential environmental risks and to help successfully navigate permitting and deploy marine energy devices responsibly.

Environmental effects↗
DOE OSTI2024

Total Water Level Prediction at Continental Scale: Coastal Ocean

We demonstrate recent progress made in the simulation of total water level (TWL) at continental scale, using the coastal ocean of US East Coast/Gulf of Mexico coast as an example. A key difference between the continental-scale and small-scale modeling is that the former requires a more accurate vertical datum. Using a geoid-based datum (xGEOID20b), a satellite altimetry product, and a state-of-the-art 3D unstructured-grid model, we significantly improve the accuracy for TWL both near- and off-shore. The average root-mean-square error at all NOAA stations is 14 cm. The non-tidal signals are found to be sensitive to the representation of a large-scale current system near the boundary and extending the domain extent to accommodate this system improves these signals.

Cui, Linlin↗
DOE OSTI2021

Interplay of microbial communities with mineral environments in coralline algae

Coralline algae are worldwide carbonate builders, considered to be foundational species and biodiversity hotspots. Coralline habitats face increasing pressure from human activities and effects related to Global Change, yet their ecological properties and adaptive responses remain poorly understood. The relationships of the algal microbiota with the mineral bioconstructions, as well as plasticity and resilience of coralline holobionts in a changing environment, are of particular interest. In the Gulf of California, Neogoniolithon trichotomum (Rhodophyta) is the main carbonate builder in tidal pools. We performed a multi-disciplinary assessment of the N. trichotomum microstructure using XRD, SEM microscopy and SR-FTIR spectromicroscopy. In the algal perithallus, magnesium-calcite and aragonite were spatially segregated and embedded in a polysaccharide matrix (rich in sulfated polysaccharides). Mg-calcites (18-19 mol% Mg) were the main mineral components of the thallus overall, followed by iron carbonates related to dolomite (ankerite) and siderite. Minerals of late evaporitic sequences (sylvite and bischofite) were also present, suggesting potential halophilic microenvironments within the algal thalli. The diverse set of abundant halophilic, halotolerant and oligotrophic taxa, whose abundance increase in the summer, further suggests this condition. We created an integrated model, based on environmental parameters and the microbiota distribution, that identified temperature and nutrient availability (particularly nitrate and silicate) as the main parameters related to specific taxa patterns. Among these, Hahella, Granulossicoccus, Ferrimonas, Spongiibacteraceae and cyanobacterial Xenococcaceae and Nostocaceae change significantly between seasons. These bacterial components might play relevant roles in algal plasticity and adaptive responses to a changing environment. This study contributes to the understanding of the interplay of the prokaryotic microbiota with the mineral microenvironments of coralline algae. Because of their carbonates with potential resistance to dissolution in a higher pCO 2 world and their seasonally dynamic bacteria, coralline algae are relevant targets to study coastal resilience and carbonated systems responses to changing environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Autonomous sensor suite for evaluating fish-turbine interactions and environmental impacts in marine renewable energy and hydropower

Marine renewable energy (MRE) harnesses ocean-based resources such as waves, tides, currents, and thermal or salinity gradients for sustainable power generation. It has the potential to complement existing renewable resources, support remote communities, and contribute to decarbonization efforts. However, understanding the hydrodynamic forces created by MRE devices and their impacts on marine life is critical for responsible deployment. Here, to address these concerns, advanced sensor devices, including the Marine Sensor Fish (MSF), Sensor Fish Mini (SF Mini), and Flexible Sensor Fish (FSF), were developed to measure interactions between aquatic organisms and MRE systems. This paper details the design, manufacturing, calibration, and field deployment of these sensor suites, highlighting their ability to capture key physical stressors such as shear forces, pressure changes, and collision impacts. The MSF successfully evaluated turbine interactions at a tidal turbine in the Salish Sea, capturing data on turbulence, collision impact, and pressure gradients. The SF Mini validated hydrodynamic conditions in scaled hydraulic models, supporting computational fluid dynamics simulations. The FSF, with its flexible silicone body, measured species-specific impacts in turbulent environments. This research demonstrates the potential of Sensor Fish technology to advance sustainable marine energy systems by reducing biological impacts and informing environmentally sustainable designs.

Ecological impacts↗
DOE OSTI2022

Disturbance legacies regulate coastal forest soil stability to changing salinity and inundation: A soil transplant experiment

Coastal forests worldwide are vulnerable to a dramatic transition from upland to wetland as sea-level rise accelerates and regimes of precipitation and storms change. However, the biogeochemical impacts of shifting salinity and inundation disturbance that foreshadow forest to wetland state transitions are largely unknown. This experiment used a natural salinity gradient in a tidal creek in eastern Maryland, U.S.A., to examine how soil respiration and chemistry may change under novel salinity and inundation disturbance regimes. Soil monoliths were transplanted in a reciprocal design among plots varying in seawater exposure and elevation above the creek. We monitored the monoliths’ carbon dioxide (CO 2 ) flux for two years and performed soil chemical analyses at the end of the experiment. Soil CO 2 flux was affected by changing disturbance regimes and responses were dependent upon the salinity and inundation legacies associated with each study location. Lowland soil CO 2 flux was resistant to changing salinity and inundation disturbance, with transplanted soil monolith chemistry composition in between that of its origin and destination. Conversely, upland soil CO 2 flux was sensitive to changing salinity and inundation disturbance and remained suppressed throughout the 2-year study when exposed to wetter, saline conditions. Additionally, transplanted upland soil chemistry composition was like that of its destination, rather than origin, with upland soils displaying higher pH, base saturation, and nutrient availability relative to lowland soils. Here, we hypothesize that reductions in soil respiration rates were driven by loss of soil nutrients and osmotic and redox stress on microbial communities following exposure to seawater. Together, our results suggest that disturbance legacies shape coastal forest soil responses to changing salinity and inundation disturbance regimes. However, fully understanding the dependence of system responses on disturbance legacies requires future study across a variety of systems and spatial and temporal scales.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Sex-specific respiratory and systemic endocrine effects of acute acrolein and trichloroethylene inhalation

Acrolein and trichloroethylene (TCE) are priority hazardous air pollutants due to environmental prevalence and adverse health effects; however, neuroendocrine stress-related systemic effects are not characterized. Comparing acrolein, an airway irritant, and TCE with low irritancy, we hypothesized that airway injury would be linked to neuroendocrine-mediated systemic alterations. Male and female Wistar-Kyoto rats were exposed nose-only to air, acrolein or TCE in incremental concentrations over 30 min, followed by 3.5-hr exposure to the highest concentration (acrolein - 0.0, 0.1, 0.316, 1, 3.16 ppm; TCE - 0.0, 3.16, 10, 31.6, 100 ppm). Real-time head-out plethysmography revealed acrolein decreased minute volume and increased inspiratory-time (males>females), while TCE reduced tidal-volume. Acrolein, but not TCE, inhalation increased nasal-lavage-fluid protein, lactate-dehydrogenase activity, and inflammatory cell influx (males>females). Neither acrolein nor TCE increased bronchoalveolar-lavage-fluid injury markers, although macrophages and neutrophils increased in acrolein-exposed males and females. Systemic neuroendocrine stress response assessment indicated acrolein, but not TCE, increased circulating adrenocorticotrophic hormone, and consequently corticosterone, and caused lymphopenia, but only in males. Acrolein also reduced circulating thyroid-stimulating hormone, prolactin, and testosterone in males. Furthermore, acute acrolein inhalation resulted in sex-specific upper respiratory irritation/inflammation and systemic neuroendocrine alterations linked to hypothalamic-pituitary-adrenal axes activation, which is critical in mediating extra-respiratory effects.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Periodicity Analysis of Earthquake Occurrence and Hypocenter Depth Near Parkfield, California, 1994–2002 Versus 2006–2014

In central California, periodic earthquake occurrence suggests a relationship with annual hydrological, atmospheric, thermal, and tidal loadings. Here, in catalogs of declustered earthquakes within 100 km from Parkfield, CA, we study a semiannual periodicity for the monthly number of ≤7.2-km-deep earthquakes and the monthly median hypocenter depth over 1994–2002 and 2006–2014. Peak-trough months in fitted periodic components differ between time spans and event populations. Deeper earthquakes present no semiannual and a weak annual periodicity. Although modeled pore pressure shows a Spring peak, when added to the elastic Coulomb stress from surface hydrospheric loads, it fails to predict a 6-month periodicity for 2006–2014. In 1994–2002, the pore-pressure amplitude appears to be of same order as the elastic stress and may have had a stronger effect. In 2006–2014, we did not find load model parameters explaining the observed pattern or apparent changes following the 2003 San Simeon and 2004 Parkfield earthquakes.

58 GEOSCIENCES↗
DOE OSTI2021

Climate Change and Changes in Compound Coastal-Riverine Flooding Hazard Along the U.S. Coasts

The cooccurrence of coastal and riverine flooding leads to compound events with substantial impacts on people and property in low-lying coastal areas. Climate change could increase the level of compound flood hazard through higher extreme sea levels and river flows. Here, a bivariate flood hazard assessment method is proposed to estimate compound coastal-riverine frequency under current and future climate conditions. A copula-based approach is used to estimate the joint return period (JRP) of compound floods by incorporating sea-level rise (SLR) and changes in peak river flows into the marginal distributions of flood drivers. Specifically, the changes in JRP of compound major coastal-riverine flooding defined based on simultaneous exceedances above major coastal and riverine thresholds, are explored by midcentury. Subsequently, the increase in the probability of occurrence of at least one compound major coastal-riverine flooding for a given period of time is quantified. The proposed compound flood hazard assessment is conducted at 26 paired tidal-riverine stations along the Contiguous United States coast with long-term data and defined flood thresholds. We show that the northeast Atlantic and the western part of the Gulf coasts are experiencing the highest compound major coastal-riverine flood probability under current conditions. However, future SLR scenarios show the highest frequency amplification along the southeast Atlantic coast. The impact of changes in peak river flows is found to be considerably less than that of SLR. Climate change impacts, especially SLR, may lead to more frequent compound events, which cannot be ignored for future adaptation responses in estuary regions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Sea Level-Driven Marsh Migration Results in Rapid Net Loss of Carbon

Sea level rise alters coastal carbon cycling by driving the rapid migration of coastal ecosystems, salinization of freshwater systems, and replacement of terrestrial forests with tidal wetlands. Wetland soils accumulate carbon (C) at faster rates than terrestrial soils, implying that sea level rise may lead to enhanced carbon accumulation. Here, we show that carbon stored in tree biomass greatly exceeds carbon stored in adjacent marsh soils so that marsh migration reduces total carbon stocks by ~50% in less than 100 years. Continued marsh soil carbon accumulation may eventually offset forest carbon loss, but we estimate that the time for replacement is similar to estimates of marsh survival (i.e., centuries), which suggests that forest C may never be replaced. These findings reveal a critical C source not included in coastal C budgets driven by migrating ecosystems and rapidly shifting allocations between carbon stored in soils and biomass.

58 GEOSCIENCES↗