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At least 325 records · Page 18Linked to original sources

Coastal vulnerability assessment of Golden Gate National Recreation Area to sea-level rise

A coastal vulnerability index (CVI) was used to map the relative vulnerability of the coast to future sea-level rise within the legislative boundary of Golden Gate National Recreation Area (GGNRA) in Northern California. The CVI ranks the following in terms of their physical contribution to sea-level rise-related coastal change: geomorphology, regional coastal slope, rate of relative sea-level rise, historical shoreline change rates, mean tidal range and mean significant wave height. The rankings for each input variable were combined, and an index value calculated for 1-minute grid cells covering the park. The CVI highlights those regions where the physical effects of sea-level rise might be the greatest. This approach combines the coastal system's susceptibility to change with its natural ability to adapt to changing environmental conditions, yielding a quantitative, although relative, measure of the park's natural vulnerability to the effects of sea-level rise. The CVI provides an objective technique for evaluation and long-term planning by scientists and park managers. The GGNRA coastlines consists of sand and gravel beaches, rock cliffs, sand dune cliffs, unconsolidated bluffs, and pocket beaches. The areas within GGNRA that are likely to be most vulnerable to sea-level rise are areas of unconsolidated sediment where shoreline erosion rates are high and wave energy is high.

Open-File Report↗

Applying portfolio theory to benefit endangered amphibians in coastal wetlands threatened by climate change, high uncertainty, and significant investment risk

The challenge of selecting strategies to adapt to climate change is complicated by the presence of irreducible uncertainties regarding future conditions. Decisions regarding long-term investments in conservation actions contain significant risk of failure due to these inherent uncertainties. To address this challenge, decision makers need an arsenal of sophisticated but practical tools to help guide spatial conservation strategies. Theory asserts that managing risks can be achieved by diversifying an investment portfolio to include assets – such as stocks and bonds – that respond inversely to one another under a given set of conditions. We demonstrate an approach for formalizing the diversification of conservation assets (land parcels) and actions (restoration, species reintroductions) by using correlation structure to quantify the degree of risk for any proposed management investment. We illustrate a framework for identifying future habitat refugia by integrating species distribution modeling, scenarios of climate change and sea level rise, and impacts to critical habitat. Using the plains coqui ( Eleutherodactylus juanariveroi ), an endangered amphibian known from only three small wetland populations on Puerto Rico’s coastal plains, we evaluate the distribution of potential refugia under two model parameterizations and four future sea-level rise scenarios. We then apply portfolio theory using two distinct objective functions and eight budget levels to inform investment strategies for mitigating risk and increasing species persistence probability. Models project scenario-specific declines in coastal freshwater wetlands from 2% to nearly 30% and concurrent expansions of transitional marsh and estuarine open water. Conditional on the scenario, island-wide species distribution is predicted to contract by 25% to 90%. Optimal portfolios under the first objective function – benefit maximization – emphasizes translocating frogs to existing protected areas rather than investing in the protection of new habitat. Alternatively, optimal strategies using the second objective function – a risk-benefit tradeoff framework – include significant investment to protect parcels for the purpose of reintroduction or establishing new populations. These findings suggest that leveraging existing protected areas for species persistence, while less costly, may contain excessive risk and could result in diminished conservation benefits. Although our modeling includes numerous assumptions and simplifications, we believe this framework provides useful inference for exploring resource dynamics and developing robust adaptation strategies using an approach that is generalizable to other conservation problems which are spatial or portfolio in nature and subject to unresolvable uncertainty.

Puerto Rico↗

Santa Barbara area coastal ecosystem vulnerability assessment

The Santa Barbara Area Coastal Ecosystem Vulnerability Assessment (SBA CEVA) is a multidisciplinary research project that investigates future changes to southern Santa Barbara County climate, beaches, watersheds, wetland habitats and beach ecosystems. The target audience is local land use planners and decision makers. The main objective is to provide information that assists the Cities of Santa Barbara, Carpinteria, and Goleta, the County of Santa Barbara, and UC Santa Barbara in climate adaptation planning with a clear focus on coastal ecosystems. Led by California Sea Grant, SBA CEVA was developed from the work of three of the state’s leading ecological and climatological research programs: UCSB’s Santa Barbara Coastal Long-Term Ecological Research (LTER) Program, the UCSD Scripps Institution of Oceanography (SIO) and their activities within the California and Nevada Applications Program Regional Integrated Science and Assessment (CNAP RISA), the California 4th Climate Assessment and the Southwest Climate Science Center Program, and USGS Coastal Storm Modeling System (CoSMoS)

California↗

Advances in morphodynamic modeling of coastal barriers: A review

As scientific understanding of barrier morphodynamics has improved, so has the ability to reproduce observed phenomena and predict future barrier states using mathematical models. To use existing models effectively and improve them, it is important to understand the current state of morphodynamic modeling and the progress that has been made in the field. This manuscript offers a review of the literature regarding advancements in morphodynamic modeling of coastal barrier systems and summarizes current modeling abilities and limitations. Broadly, this review covers both event-scale and long-term morphodynamics. Each of these sections begins with an overview of commonly modeled phenomena and processes, followed by a review of modeling developments. After summarizing the advancements toward the stated modeling goals, we identify research gaps and suggestions for future research under the broad categories of improving our abilities to acquire and access data, furthering our scientific understanding of relevant processes, and advancing our modeling frameworks and approaches.

Virginia↗

Discharge, suspended sediment, and salinity in the Gulf Intracoastal Waterway and adjacent surface waters in South-Central Louisiana, 1997–2008

Discharge, suspended sediment, and salinity data collected between 1997 and 2008 indicate that the Gulf Intracoastal Waterway (GIWW) is an important distributary of river water and suspended sediments to coastal wetlands in south-central coastal Louisiana. Following natural hydraulic gradients, the GIWW passively distributes freshwater and suspended sediments from the Atchafalaya River to areas at least 30 to 50 miles west and east, respectively, of Morgan City. The magnitude and reach of the discharge in the GIWW increase as stage of the Wax Lake Outlet at Calumet and Lower Atchafalaya River (LAR) at Morgan City increase. The magnitude and duration of discharge vary from year to year depending on the flow regime of the Atchafalaya River. Annual discharge of water in the GIWW was greater during years when stage of the LAR remained anomalously high throughout the year, compared with average and peak flood years. During years when Atchafalaya River flow is low, Bayou Boeuf, a waterway draining the Verret subbasin, becomes a major source of water maintaining the eastward flow in the GIWW. The GIWW is the only means of getting river water to some parts of coastal Louisiana. The length of time stage of the LAR at Morgan City exceeds a given height has increased from the 1940s to 2008. This shift has increased the length of time the GIWW functions as a predictable distributary of river water each year. Similar shifts in the future could be expected to increase the duration and amounts of river water reaching coastal Louisiana wetlands through the GIWW. Median suspended-sediment concentrations in the GIWW to the west of Morgan City were around 160 milligrams per liter (mg/L). In the GIWW east of Morgan City, median concentrations were 120–160 mg/L, except in Bayou Boeuf at Railroad Bridge in Amelia and the parts of the GIWW between Bayou Boeuf and the Houma Navigation Canal; median concentrations here were around 100 mg/L. River water penetrates much of the Louisiana coast, as demonstrated by the large year-to-year fluctuations in salinity regimes of intradistributary basins in response to differences in flow regimes of the Mississippi and the Atchafalaya Rivers. This occurs directly through inflow along the GIWW and through controlled diversions and indirectly by transport into basin interiors after mixing with the Gulf of Mexico. The GIWW plays an important role in moderating salinity in intradistributary basins; for example, salinity in surface waters just south of the GIWW between Bayou Boeuf and the Houma Navigation Canal remained low even during a year with prolonged low water (2000).

Louisiana↗

Salt marsh habitats and diamondback terrapins in a rapidly changing climate: A review

The impacts associated with global climate change (e.g., sea-level rise, tropical storms, and warming temperatures) are expected to alter predator–prey interactions, foundation species, and plant community structure in coastal ecosystems. While the complex dynamics of these habitats have been examined under future climate predictions, few ecosystem models incorporate influences from fauna, such as the diamondback terrapin, the only estuarine turtle native to North America. This review examines the impacts of climate change on diamondback terrapins ( Malaclemys terrapin ) and the role that terrapins play as higher trophic level predators and keystone species in driving the dynamics of these ecosystems. We also review the potential implications of changes to terrapin populations on coastal ecosystems as a conservation challenge and suggest solutions to advance our understanding of those complex systems. Because of their role as a keystone and area-sensitive species that helps maintain healthy coastal habitats by foraging on herbivorous periwinkle snails, alterations to terrapin life history from climate change are expected, which could have significant impacts to the conservation of coastal habitats. Life history alterations could occur due to individual stressors, such as warming temperatures altering terrapin sex ratios. However, because of the complexity of these coastal systems, these stressors could also act additively or synergistically. Inclusion of faunal taxa such as the diamondback terrapin in modeling efforts examining climate change impacts to coastal ecosystems would better represent the complexity of these habitats thereby providing a more comprehensive evaluation of the entire ecosystem, resulting in more effective conservation strategies.

Estuaries and Coasts↗

An introduction to the “Oceans and Society: Blue Planet” Initiative

We live on a blue planet, and Earth’s waters benefit many sectors of society. The future of our blue planet is increasingly reliant on the services delivered by marine, coastal and inland waters and on the advancement of effective, evidence-based decisions on sustainable development. “Oceans and Society: Blue Planet” (hereafter denoted as “GEO Blue Planet”) is an initiative of the Group on Earth Observations (GEO) that aims to ensure the sustained development and use of ocean and coastal observations for the benefit of society. GEO Blue Planet works to advance and exploit synergies among the many observational programmes devoted to ocean and coastal waters; to improve engagement with a variety of stakeholders for enhancing the timeliness, quality and range of information delivered; and to raise awareness of the societal benefits of ocean observations at the public and policy levels. This paper summarizes the role of GEO Blue Planet, current activities and considerations for future directions.

Journal of Operational Oceanography↗

Coupling centennial-scale shoreline change to sea-level rise and coastal morphology in the Gulf of Mexico using a Bayesian network

Predictions of coastal evolution driven by episodic and persistent processes associated with storms and relative sea-level rise (SLR) are required to test our understanding, evaluate our predictive capability, and to provide guidance for coastal management decisions. Previous work demonstrated that the spatial variability of long-term shoreline change can be predicted using observed SLR rates, tide range, wave height, coastal slope, and a characterization of the geomorphic setting. The shoreline is not suf- ficient to indicate which processes are important in causing shoreline change, such as overwash that depends on coastal dune elevations. Predicting dune height is intrinsically important to assess future storm vulnerability. Here, we enhance shoreline-change predictions by including dune height as a vari- able in a statistical modeling approach. Dune height can also be used as an input variable, but it does not improve the shoreline-change prediction skill. Dune-height input does help to reduce prediction uncer- tainty. That is, by including dune height, the prediction is more precise but not more accurate. Comparing hindcast evaluations, better predictive skill was found when predicting dune height (0.8) compared with shoreline change (0.6). The skill depends on the level of detail of the model and we identify an optimized model that has high skill and minimal overfitting. The predictive model can be implemented with a range of forecast scenarios, and we illustrate the impacts of a higher future sea-level. This scenario shows that the shoreline change becomes increasingly erosional and more uncertain. Predicted dune heights are lower and the dune height uncertainty decreases.

Earth's Future↗

Projection of wave conditions in response to climate change: A community approach to global and regional wave downscaling

Future changes in wind-wave climate have broad implications for coastal geomorphology and management. General circulation models (GCM) are now routinely used for assessing climatological parameters, but generally do not provide parameterizations of ocean wind-waves. To fill this information gap, a growing number of studies use GCM outputs to independently downscale wave conditions to global and regional levels. To consolidate these efforts and provide a robust picture of projected changes, we present strategies from the community-derived multi-model ensemble of wave climate projections (COWCLIP) and an overview of regional contributions. Results and strategies from one contributing regional study concerning changes along the eastern North Pacific coast are presented.

Conference Paper↗

The use of data-mining techniques for developing effective decisionsupport systems: A case study of simulating the effects ofclimate change on coastal salinity intrusion

Natural-resource managers and stakeholders face difficult challenges when managing interactions between natural and societal systems. Potential changes in climate could alter interactions between environmental and societal systems and adversely affect the availability of water resources in many coastal communities. The availability of freshwater in coastal streams can be threatened by saltwater intrusion. Even though the collective interests and computer skills of the community of managers, scientists and other stakeholders are quite varied, there is an overarching need for equal access by all to the scientific knowledge needed to make the best possible decisions. This paper describes a decision support system, PRISM-2, developed to evaluate salinity intrusion due to potential climate change along the South Carolina coast in southeastern USA. The decision support system is disseminated as a spreadsheet application and integrates the output of global circulation models, watershed models and salinity intrusion models with real-time databases for simulation, graphical user interfaces, and streaming displays of results. The results from PRISM-2 showed that a 31-cm and 62-cm increase in sea level reduced the daily availability of freshwater supply to a coastal municipal intake by 4% and 12% of the time, respectively. Future climate change projections by a global circulation model showed a seasonal change in salinity intrusion events from the summer to the fall for the majority of events.

South Carolina↗

On the use of wave parameterizations and a storm impact scaling model in National Weather Service Coastal Flood and decision support operations

National Weather Service (NWS) Weather Forecast Offices (WFO) are responsible for issuing coastal flood watches, warnings, advisories, and local statements to alert decision makers and the general public when rising water levels may lead to coastal impacts such as inundation, erosion, and wave battery. Both extratropical and tropical cyclones can generate the prerequisite rise in water level to set the stage for a coastal impact event. Forecasters use a variety of tools including computer model guidance and local studies to help predict the potential severity of coastal flooding. However, a key missing component has been the incorporation of the effects of waves in the prediction of total water level and the associated coastal impacts. Several recent studies have demonstrated the importance of incorporating wave action into the NWS coastal flood program. To follow up on these studies, this paper looks at the potential of applying recently developed empirical parameterizations of wave setup, swash, and runup to the NWS forecast process. Additionally, the wave parameterizations are incorporated into a storm impact scaling model that compares extreme water levels to beach elevation data to determine the mode of coastal change at predetermined “hotspots” of interest. Specifically, the storm impact model compares the approximate storm-induced still water level, which includes contributions from tides, storm surge, and wave setup, to dune crest elevation to determine inundation potential. The model also compares the combined effects of tides, storm surge, and the 2 % exceedance level for vertical wave runup (including both wave setup and swash) to dune toe and crest elevations to determine if erosion and/or ocean overwash may occur. The wave parameterizations and storm impact model are applied to two cases in 2009 that led to significant coastal impacts and unique forecast challenges in North Carolina: the extratropical “Nor'Ida” event during 11-14 November and the large swell event from distant Hurricane Bill on 22 August. The coastal impacts associated with Nor'Ida were due to the combined effects of surge, tide, and wave processes and led to an estimated 5.8 million dollars in damage. While the impacts from Hurricane Bill were not as severe as Nor'Ida, they were mainly associated with wave processes. Thus, this event exemplifies the importance of incorporating waves into the total water level and coastal impact prediction process. These examples set the stage for potential future applications including adaption to the more complex topography along the New England coast.

Conference Paper↗

Patterns and controls of mercury accumulation in sediments from three thermokarst lakes on the Arctic Coastal Plain of Alaska

The biogeochemical cycle of mercury will be influenced by climate change, particularly at higher latitudes. Investigations of historical mercury accumulation in lake sediments inform future predictions as to how climate change might affect mercury biogeochemistry; however, in regions with a paucity of data, such as the thermokarst-rich Arctic Coastal Plain of Alaska (ACP), the trajectory of mercury accumulation in lake sediments is particularly uncertain. Sediment cores from three thermokarst lakes on the ACP were analyzed to understand changes in, and drivers of, Hg accumulation over the past ~ 100 years. Mercury accumulation in two of the three lakes was variable and high over the past century (91.96 and 78.6 µg/m 2 /year), and largely controlled by sedimentation rate. Mercury accumulation in the third lake was lower (14.2 µg/m 2 /year), more temporally uniform, and was more strongly related to sediment Hg concentration than sedimentation rate. Sediment mercury concentrations were quantitatively related to measures of sediment composition and VRS-inferred chlorophyll a , and sedimentation rates were related to various catchment characteristics. These results were compared to data from 37 previously studied Arctic and Alaskan lakes. Results from the meta-analysis indicate that thermokarst lakes have significantly higher and more variable Hg accumulation rates than non-thermokarst lakes, suggesting that certain properties (e.g., thermal erosion, thaw slumping, low hydraulic conductivity) likely make lakes prone to high and variable Hg accumulation rates. Differences and high variability in Hg accumulation among high latitude lakes highlight the complexity of predicting future climate-related change impacts on mercury cycling in these environments.

Alaska↗

A pilot biodiversity inventory and monitoring protocol in support of coastal adaptation projects in tidal and nearshore subtidal habitats of Boston Harbor Islands

The Boston Harbor Islands National Recreation Area (BOHA) is at high risk to the impacts of sealevel rise (SLR) and erosion from coastal storms. In June 2021, the National Trust for Historic Preservation listed the islands as one of America’s 11 Most Endangered Historic Places due to climate change. BOHA partners have been working to find climate adaptive solutions to protect and sustain critical ecological and cultural resources on the islands. A range of coastal adaptation efforts are currently under consideration including increased shoreline armoring and nature-based adaptation solutions. Any action taken in the coastal zone will require an assessment of environmental and ecological communities that could potentially be impacted by disturbance caused by restoration or adaptation projects. The primary goals of the initial phase of this project were to: 1) synthesize occurrence and distribution records of biodiversity living in and using mixed coarse substrate habitats of the intertidal zone of the Boston Harbor Islands; and 2) identify and compile potential methods to develop a standard and repeatable monitoring protocol to track changes (natural or anthropogenic) in intertidal biodiversity over time and across locations; and 3) conduct preliminary site scoping of target islands to identify locations for collecting new baseline data. A biodiversity inventory list was compiled, showing a total of 451 unique species were observed in BOHA between 1861-2020. Of this list, 55 species (invertebrates: 47; algae: 8) were considered nonindigenous species; a watchlist was also developed to help BOHA partners identify potential future invaders that could colonize and impact intertidal communities due to ongoing climate change or disturbance events. Native species observed in BOHA were evaluated using existing conservation frameworks and climate vulnerability information to prioritize species at greatest risk from anthropogenic and environmental stressors for future actions. Lastly, site scoping activities during 2021 identified three types of sites for future intertidal monitoring initiatives: (1) sites with relatively high biodiversity and foundational species, (2) erosional sites near cultural areas of importance to NPS, and (3) sites with generic (common across islands) biodiversity. Overall results are anticipated to help the NPS and BOHA partners identify a suite of species and sites for future monitoring given anticipated adaptation projects and ongoing changes due to SLR, coastal storms and other stressors.

Massachusetts↗

Final report: A novel monitoring framework to assess intertidal biodiversity in mixed coarse substrate habitats across the Boston Harbor Islands

The Boston Harbor Islands National Recreation Area (BOHA) is at high risk to the impacts of sea-level rise (SLR) and erosion from coastal storms. In June 2021, the National Trust for Historic Preservation listed the islands as one of America’s 11 Most Endangered Historic Places due to climate change. BOHA partners have been working to find climate adaptive solutions to protect and sustain critical ecological and cultural resources on the islands. A range of coastal adaptation efforts are currently under consideration including increased shoreline armoring and nature-based adaptation solutions. Any action taken in the coastal zone will require an assessment of environmental and ecological communities that could potentially be impacted by disturbance caused by restoration or adaptation projects. The primary goals of the initial phase of this project were to: 1) synthesize occurrence and distribution records of biodiversity living in and using mixed coarse substrate habitats of the intertidal zone of the Boston Harbor Islands; and 2) identify and compile potential methods to develop a standard and repeatable monitoring protocol to track changes (natural or anthropogenic) in intertidal biodiversity over time and across locations; and 3) conduct preliminary site scoping of target islands to identify locations for collecting new baseline data. A biodiversity inventory list was compiled, showing a total of 451 unique species were observed in BOHA between 1861-2020. Of this list, 55 species (invertebrates: 47; algae: 8) were considered nonindigenous species; a watchlist was also developed to help BOHA partners identify potential future invaders that could colonize and impact intertidal communities due to ongoing climate change or disturbance events. Native species observed in BOHA were evaluated using existing conservation frameworks and climate vulnerability information to prioritize species at greatest risk from anthropogenic and environmental stressors for future actions. Lastly, site scoping activities during 2021 identified three types of sites for future intertidal monitoring initiatives: (1) sites with relatively high biodiversity and foundational species, (2) erosional sites near cultural areas of importance to NPS, and (3) sites with generic (common across islands) biodiversity. Overall results are anticipated to help the NPS and BOHA partners identify a suite of species and sites for future monitoring given anticipated adaptation projects and ongoing changes due to SLR, coastal storms and other stressors.

Massachusetts↗

Southeast

The Southeast includes vast expanses of coastal and inland low-lying areas, the southern portion of the Appalachian Mountains, numerous high-growth metropolitan areas, and large rural expanses. These beaches and bayous, fields and forests, and cities and small towns are all at risk from a changing climate. While some climate change impacts, such as sea level rise and extreme downpours, are being acutely felt now, others, like increasing exposure to dangerous high temperatures, humidity, and new local diseases, are expected to become more significant in the coming decades. While all regional residents and communities are potentially at risk for some impacts, some communities or populations are at greater risk due to their locations, services available to them, and economic situations. Observed warming since the mid-20th century has been uneven in the Southeast region, with average daily minimum temperatures increasing three times faster than average daily maximum temperatures. The number of extreme rainfall events is increasing. Climate model simulations of future conditions project increases in both temperature and extreme precipitation. Trends towards a more urbanized and denser Southeast are expected to continue, creating new climate vulnerabilities. Cities across the Southeast are experiencing more and longer summer heat waves. Vector-borne diseases pose a greater risk in cities than in rural areas because of higher population densities and other human factors, and the major urban centers in the Southeast are already impacted by poor air quality during warmer months. Increasing precipitation and extreme weather events will likely impact roads, freight rail, and passenger rail, which will likely have cascading effects across the region. Infrastructure related to drinking water and wastewater treatment also has the potential to be compromised by climate-related events. Increases in extreme rainfall events and high tide coastal floods due to future climate change will impact the quality of life of permanent residents as well as tourists visiting the low-lying and coastal regions of the Southeast. Sea level rise is contributing to increased coastal flooding in the Southeast, and high tide flooding already poses daily risks to businesses, neighborhoods, infrastructure, transportation, and ecosystems in the region. There have been numerous instances of intense rainfall events that have had devastating impacts on inland communities in recent years. The ecological resources that people depend on for livelihoods, protection, and well-being are increasingly at risk from the impacts of climate change. Sea level rise will result in the rapid conversion of coastal, terrestrial, and freshwater ecosystems to tidal saline habitats. Reductions in the frequency and intensity of cold winter temperature extremes are already allowing tropical and subtropical species to move northward and replace more temperate species. Warmer winter temperatures are also expected to facilitate the northward movement of problematic invasive species, which could transform natural systems north of their current distribution. In the future, rising temperatures and increases in the duration and intensity of drought are expected to increase wildfire occurrence and also reduce the effectiveness of prescribed fire practices. Many in rural communities are maintaining connections to traditional livelihoods and relying on natural resources that are inherently vulnerable to climate changes. Climate trends and possible climate futures show patterns that are already impacting—and are projected to further impact—rural sectors, from agriculture and forestry to human health and labor productivity. Future temperature increases are projected to pose challenges to human health. Increases in temperatures, water stress , freeze-free days, drought, and wildfire risks, together with changing conditions for invasive species and the movement of diseases, create a number of potential risks for existing agricultural systems. Rural communities tend to be more vulnerable to these changes due to factors such as demography, occupations, earnings, literacy, and poverty incidence. In fact, a recent economic study using a higher scenario (RCP8.5) suggests that the southern and midwestern populations are likely to suffer the largest losses from future climate changes in the United States. Climate change tends to compound existing vulnerabilities and exacerbate existing inequities. Already poor regions, including those found in the Southeast, are expected to continue incurring greater losses than elsewhere in the United States.

Report↗

Coastal vulnerability assessment of Assateague Island National Seashore (ASIS) to sea-level rise

A coastal vulnerability index (CVI, http://pubs.usgs.gov/of/2004/1020/html/cvi.htm) was used to map relative vulnerability of the coast to future sea-level rise within Assateague Island National Seashore (ASIS) in Maryland and Virginia. The CVI ranks the following in terms of their physical contribution to sea-level rise-related coastal change: geomorphology, regional coastal slope, rate of relative sea-level rise, shoreline change rates, mean tidal range and mean wave height. Rankings for each variable were combined and an index value calculated for 1-minute grid cells covering the park. The CVI highlights those regions where the physical effects of sea-level rise might be the greatest. This approach combines the coastal system's susceptibility to change with its natural ability to adapt to changing environmental conditions, yielding a quantitative, although relative, measure of the park's natural vulnerability to the effects of sea-level rise. The CVI provides an objective technique for evaluation and long-term planning by scientists and park managers. Assateague Island consists of stable and washover dominated portions of barrier beach backed by wetland and marsh. The areas within Assateague that are likely to be most vulnerable to sea-level rise are those with the highest occurrence of overwash and the highest rates of shoreline change.

Maryland, Virginia↗

Long-term assessments are critical to determining persistence and shoreline protection from oyster reef nature-based coastal defenses

Nature-based coastal defense using bivalve reefs provides a potentially self-sustaining approach for regions facing high coastal land loss, relative sea level rise and increasing frequency and intensity of storms. Success of such nature-based coastal defense depends on the reef-building species' life history, habitat requirements, and ability to thrive through short-term and longer-term environmental variation, yet few projects have reported on outcomes beyond the first few years. In coastal Louisiana, USA, Crassostrea virginica (oyster) is an ecosystem engineer, creating self-sustaining, vertically accreting reefs that also provide ecosystem services. Here, we examine the short (< 3 years) and medium (> 10 years) term outcomes of experimental reefs constructed in 2009 for nature-based coastal defense in a Louisiana, USA estuarine lake. Oyster reef density, demography, along with adjacent salt marsh, and shoreline movement were compared at six fringing shoreline reefs and paired reference sites over the first three years post-construction (2009–2011), and a decade later (2019–2020). Oyster density measured in 2019–2020 (< 60 ind m −2 ) was less than 10% of density measured during 2009–2011 (> 1000 ind m −2 ). This density difference largely reflected a lack of new recruits and small oysters (< 75 mm shell height) in later samples, with adult oyster densities similar between 2011, 2019 and 2020. Lack of smaller oysters in recent sampling likely reflected the impact of multiple extended low salinity events in this region in recent years, including the record-breaking low salinity in 2019. No differences in shoreline characteristics were detected in marsh vegetation, soil properties or nutrient concentrations between reef and reference sites during early and later years. Similarly, shoreline erosion at both reef and reference sites immediately post-construction, and 10 years later, was high (~1 m y −1 ) indicating a lack of shoreline protection from these reefs. These findings highlight the need to consider both current and future conditions, including the effect of extreme years, when implementing nature-based coastal defense. On the other hand, the persistence of reproductive-sized oysters on the reef 10 years post creation, indicate reef resilience and potential for reef development and shoreline benefits, should better site conditions return in future years. Determining restoration success within variable and dynamic environments requires frequent monitoring which is required to understand responses to short and longer-term environmental variation.

Louisiana↗

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles.

California↗