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At least 415 records · Page 23Linked to original sources
USGS2025

2022 McKinney rain-on-wildfire event, dissolved oxygen sags, and a fish kill on the Klamath River, California

The longitudinal propagation of water-quality and ecological impairments in rivers during and after wildfires remain poorly understood. In Northern California, the 2022 McKinney Fire burned 243 km 2 of the Klamath National Forest, with 83% of the burned area classified as moderate to high severity. During the active wildfire, a high-intensity monsoonal rain event triggered sediment-laden flooding and runoff-initiated debris flows, causing extreme water-quality impairments and a 95 km fish kill zone along the main-stem Klamath River. This rain-on-wildfire event produced a flood wave that outpaced a sediment pulse, diminishing the dilution effect of the floodwaters. A network of high-frequency water-quality sensors recorded water-quality impairments that propagated 296 km downstream. Impairments at the nearest monitoring station, situated 71 km downstream from the fire perimeter, included dissolved oxygen sags to zero (anoxia) for 5.25 h, turbidity spikes exceeding 1000 FNU, a doubling of specific conductance from 175 to 415 µS/cm (at 25 °C), and pH anomalies of 0.5 units from 7.8 to 7.3. This novel rain-on-wildfire event triggered the first flush of fire-scar material during an active wildfire, resulting in water-quality impairments unprecedented in the historical monitoring data for the river spanning 2012 to 2022. This study provides new insights into the potential role of rain-on-wildfire events in generating extreme downstream water-quality and ecological impairments in a more fire-prone future.

California, Oregon↗
USGS2025

Using bioavailability modeling to refine copper treatments for zebra mussel control and better understanding risks to non-target species

Copper can be toxic to aquatic organisms at high concentrations and has been previously used successfully to control zebra mussels ( Dreissena polymorpha ). Because copper’s toxicity changes with water chemistry, using the same copper concentration in different waterbodies could yield different outcomes. We demonstrate how measuring water chemistry parameters and using the Biotic Ligand Model (BLM) and multiple linear regression (MLR) models can predict a suitable, site-specific copper concentration for management. We exposed zebra mussel adults and non-target organisms to varying concentrations of copper over 10 d in a mobile laboratory. We found that one non-target species, Daphnia magna , had a 50% chance of survival at 9.50 µg Cu/L (i.e., the 50% lethal concentration, LC 50 ), within our BLM-predicted range of 3.38–16.95 µg Cu/L LC 50 values. In the future, managers could make similar predictions and tailor their copper concentrations to their management goals. We also measured zebra mussel larvae mortality at copper concentrations ranging from 0 to 191 µg Cu/L. While those results were inconclusive, we present the results of this work as a foundation for future projects. Our study underscores the importance of developing site-specific copper concentration recommendations and demonstrates the potential utility of the BLM and MLR approaches for informing those recommendations.

Minnesota↗
USGS2025

Alternating movement strategies of a tropical raptor

The majority of raptor species reside in the tropics, yet very little is known about their movement ecology. However, quantifying movement behavior can provide otherwise elusive information on resource needs, habitat selection, and ecological constraints, which is important for understanding ecological patterns and the management of species of conservation concern. On the Island of Hawai‘i, Hawai‘i, USA, the endemic ‘Io, or Hawaiian Hawk ( Buteo solitarius ), is a species of conservation concern that little is known of their movement ecology, yet they are dependent on a fragmented and rapidly changing environment. We tracked 15 individuals for up to 18 months across a diverse landscape on the eastern side of the island. We found that all ‘Io occupied a relatively small geographic area, their place of residency, where they spent all or most of their time. However, 10 individuals also exhibited an alternative movement pattern, where individuals repeatedly commuted back and forth between their place of residency to another, geographically disjunct location. These commuter periods, which could last from 24–180 days, were characterized by frequent (9–259) movements, with individual trips lasting 4–77 h away from their place of residency and 12–47 h in between commuter trips. In most cases, individuals went to the same non-contiguous commuting destination, even across multiple commuting sessions, indicating high fidelity to commuting locations. The ‘Io is a forest adapted Buteo but occurs across a diverse landscape from forest to agriculture lands to urban areas. Habitat selection analysis indicated high individual variation among different birds, but generally a preference for forest patches at localized levels. The discovery of the alternative commuting strategy for many ‘Io represents a cryptic movement pattern in the species, demonstrating the power of small, long-lived Global Position System tracking devices to track movement and providing important insights into the ecology of a tropical island raptor.

Hawaii↗
USGS2025

Warming Alaskan rivers affect first-year growth in critical northern food fishes

Arctic and subarctic rivers are warming rapidly, with unknown consequences for migratory fishes and the human communities dependent on them. To date, few studies have provided a comprehensive assessment of possible climate change impacts on the hydrology and temperature of Arctic rivers at the regional scale, and even fewer have connected those changes to multiple fish species with input and guidance from Indigenous communities. We used climate, hydrologic, and fish-growth simulations of historical (1990–2021) and future (2034–2065) young-of-year (YOY) growth potential of Chinook salmon ( Oncorhynchus tshawytscha ) and Dolly Varden ( Salvelinus malma ) for seven river basins in the Arctic-Yukon-Kuskokwim (AYK) region of Alaska, USA and Yukon Territory, Canada. Historically, summer water temperatures of all river basins remained below thresholds regarded as deleterious for Chinook salmon (14.6 °C) and Dolly Varden (16 °C), even in the warmest years. However, by the mid-century, Chinook salmon growth was limited, with declines in the warmest years in most river basins. Conversely, Dolly Varden are expected to benefit, with a near-doubling in growth projections in all river basins. This suggests that there may be an increase in suitable habitat for Dolly Varden by mid-century. The results highlight species-specific consequences of climate change and can guide future research on refugia for these species of cultural and subsistence importance to Indigenous communities in the AYK region and throughout the Arctic.

Alaska↗
USGS2025

Diel and spatial variability in cyanobacterial composition, gene abundance, and toxin concentration: A pilot study

We designed a pilot field study to assess relations between sunlight, cyanobacteria, and cyanotoxins. In 2021, we collected day (07:00 h, 10:00 h, 13:00 h, 16:00 h) and night samples (19:00 h, 22:00 h, 01:00 h, 04:00 h) at two locations in Kabetogama Lake, MN, USA. One sample set was collected from the lakeward end of a boat dock and the other on the nearby shoreline. Cyanobacterial phylogenetic eDNA differences over 24 h (pseudo F = 2.0938, p = 0.127) were not significant. Copies of anatoxin ( anaC ) and microcystin ( mcyE ) synthetase genes varied significantly over the sampling times at the dock (Friedman Χ 2 = 15.01, df = 7, p = 0.036; Friedman Χ 2 = 19.22, df = 7, p = 0.008) and the shoreline (Friedman Χ 2 = 19.33, df = 7, p = 0.007; Friedman Χ 2 = 20.56, df = 7, p = 0.005), with the highest anaC counts occurring during the night for both sites. Additionally, the highest total and dissolved microcystin concentrations occurred at night. Despite the proximity of the sampling locations, cyanobacterial phylogenetic eDNA results indicate that the variability between sites (pseudo-F = 27.547, p = 0.001) were greater than temporal differences over 24 h (pseudo F = 2.0938, p = 0.127). Understanding the effect of diel and spatial variability may help researchers and resource managers make informed decisions about sampling and potential exposure.

Minnesota↗
USGS2025

Precipitation timing mediates life-stage and population-level associations with climate for an indicator species

Global climate change is contributing to declines in biodiversity, although changes vary across geographic regions and species. The iconic greater sage-grouse (Centrocercus urophasianus; sage-grouse) is central to conservation within the North American sagebrush ecosystem, yet its vulnerability to climate effects remains poorly understood. We used hierarchical models to explore weather and climatic influences on sage-grouse across nearly four decades, focusing first on pattern (population change), then process (demographic life stage). We quantified eight indicators of temperature and/or moisture conditions across time lags of 0–1.5 years leading up to current year breeding activities. Sage-grouse population growth tended to increase following above-average growing season precipitation. Precipitation or drought timing influenced whether process effects were positive or negative. More summer and/or fall moisture corresponded with increases in subsequent year brood and adult survival, while concurrent seasonal drought led to reductions in nest survival. Positive concurrent spring drought associations with adult and brood survival were largely outweighed by positive prior year moisture effects. Density-dependence and indirect effects of precipitation through vegetation and forage resource pathways likely contributed to nuanced responses across life stages. Our research improves mechanistic understanding of this indicator species’ sensitivity to climatic factors, while reinforcing the importance of large-scale conservation initiatives for sagebrush ecosystems.

Scientific Reports↗
USGS2025

Greenhouse gas emissions from ditches in oil palm plantations on tropical peatlands in Malaysia

Tropical peatlands, which store 20% of global peat carbon, are increasingly threatened by conversion to alternative land-uses such as oil palm plantations, pulp wood plantations, crop growth or other economic activities. This transformation involves peatland drainage, which lowers water tables, exposes peat to oxygen, and alters greenhouse gas (GHG) emissions: increasing carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) fluxes while reducing methane (CH 4 ) emissions from soils. However, drainage ditches created in the process may become significant sources of CH 4 due to anoxic conditions. This study quantified GHG fluxes from drainage ditches in Sarawak, Malaysia, through spatial sampling conducted during the daytime in the transitional period between the drier and wetter seasons using portable trace gas analyzers. Median fluxes were 0.19 g CH 4 m −2 d −1 , 17.1 g CO 2 m −2 d −1 , and − 0.12 mg N 2 O m −2 d −1 . Physical water parameters such as pH, oxygen concentration, temperature, and oxidation–reduction potential were found to be significant drivers of GHG fluxes. The median emissions from ditches in one hectare of land were 5.84 kg CO 2 ha −1 d −1 , 2.78 kg CH 4 as CO 2 eq ha −1 d −1 , and − 0.001 kg N 2 O as CO 2 eq ha −1 d −1 . These findings underscore the role of drainage ditches as CH 4 sources in tropical peatland agriculture, highlighting the need for further research into GHG management in these modified landscapes.

Scientific Reports↗
USGS2025

Cryptic life history diversity supports endangered species recovery in an ultra-urbanized landscape

Urban landscapes are often overlooked in conservation planning, allowing human activities to take precedence in ecosystem management. However, even heavily modified environments can support diverse species profiles, but continued expansion of the human footprint could transform these biodiversity hotspots into ecological traps that serve as hidden catalysts for demographic declines. In the backdrop of one of the world’s most urbanized landscapes-New York City, USA—is a federally endangered population of shortnose sturgeon ( Acipenser brevirostrum ) that has been quietly recovering for several decades despite many demographic threats. Here, we identify a unique behavioral phenotype of shortnose sturgeon that occupies habitats in New York Harbor in late spring and fall, likely using the area to optimize bioenergetic processes. As this study highlights, urbanized environments can be a nexus for cryptic phenotypic diversity which, if overlooked, can disrupt eco-evolutionary processes and contribute to population and species loss.

New York↗
USGS2025

Present-day vertical land motions (VLM) of the Chesapeake Bay region derived from robust network imaging of global navigation satellite system (GNSS) observations

The Chesapeake Bay region (defined as longitudes − 78° to -74° and latitudes 36.5° to 40°) experiences the highest rates of relative sea-level rise (RSLR) on the Atlantic Coast. Regional land subsidence influences RSLR, however quantified rates of vertical land motions (VLM) are inconsistent in published solutions. For 5 years from 2019 to 2023, new Global Navigation Satellite System (GNSS) campaign data were collected at over 60 sites across the Chesapeake Bay region annually. These data were processed and combined with continuous GNSS data (120 stations) from the region covering the same time-period using GAMIT-GLOBK to produce 3D velocities and their associated uncertainties. We use the Robust Network Imaging algorithm to interpolate GNSS-derived VLM to produce a new regional VLM solution of the Chesapeake Bay region. We find that land subsidence is ubiquitous throughout the region with rates varying from − 2.97 to -0.40 mm/yr. In major cities across the Chesapeake Bay region, VLM rates are − 1.1 ± 1.6 mm/yr (1-sigma) for Washington DC, -0.8 ± 1.4 mm/yr for Baltimore, MD, -2.4 ± 0.5 mm/yr for Ocean City, MD, and − 2.3 ± 1.0 mm/yr for Hampton, VA. When we compare our VLM rates with a geodetic-based solution from 1974, we observe meaningful shifts in the locations and rates of maximum subsidence. The results of this work underscore that regular monitoring of VLM and can be used to improve projections of relative sea-level changes as well as the associated coastal hazards for communities in the Chesapeake Bay region.

Delaware, Maryland, New Jeresy, Pennsylvania, Virg↗
USGS2026

Per- and polyfluoroalkyl substances in waters associated with oil and gas development in the Denver Basin

Use of per- and polyfluoroalkyl substances (PFAS) in the petroleum industry could be a cause for concern due to the large volumes of produced water (PW) generated during oil and gas extraction, the reuse of these wastes in water-stressed regions, and adverse health outcomes related to PFAS exposures. However, PW PFAS characterization is nearly absent in the literature, and hydraulic fracturing (HF) chemical disclosures often omit the identities of additives as proprietary. Here we evaluate PFAS in PW samples from three petroleum wells in the Denver Basin during their first year of production. Total concentrations of targeted PFAS (Σ 40 PFAS) were < 35 ng/L in PW samples, with short-chain PFAS like perfluorobutanoic acid persisting throughout the sampled duration. Analysis of freshwater inputs for hydraulic fracturing (Σ 40 PFAS ~ 113 ng/L) and mixed fracture fluid (Σ 40 PFAS ~ 69 ng/L) indicated much of the targeted PFAS content was derived from the input water, and not from HF additives, however samples subjected to oxidation indicated the presence of PFAS precursors that would not be detected by targeted analysis. This study highlights that while PFAS content is low in the studied PWs, the potential for redistribution of PFAS in the environment may be a consideration for reuse applications.

Colorado, Nebraska, Wyoming↗
USGS2026

Leveraging socioeconomic flows to inform shared, migratory species conservation

Migratory species, and the many cultural and economic values they provide, are declining worldwide. Previous research has quantified ecosystem service flows for single migratory species to provide valuable information on the dynamics of socio-ecological systems to inform cross-jurisdictional management. There are efficiencies in implementation to be gained from considering the dynamics of multiple species (e.g., ecological guilds) simultaneously. As proof of concept, this paper demonstrates how ecosystem service flows can be aggregated spatially for a group of three North American migratory species. We further present a flexible approach to estimating how conservation funding can be allocated equitably between regions of the migratory range. Results show that most benefits from these three migratory species are supported locally by habitat within each region, but net interregional flows exist, including a $33.1M annual subsidy from Mexico to the U.S. and Canada. Results also suggest that directing 18% of net conservation funding raised for these species in the U.S. and Canada toward conservation projects in Mexico would redress inequities in shared management responsibility. Considering the values provided by multiple species simultaneously has the potential to broaden coalitions and expedite negotiation of international agreements by providing a better shared understanding of the benefits to each party.

North America↗
USGS2025

American alligators (Alligator mississippiensis) as wetland ecosystem carbon stock regulators

Blue carbon refers to organic carbon sequestered by oceanic and coastal ecosystems. This stock has gained global attention as a high organic carbon repository relative to other ecosystems. Within blue carbon ecosystems, tidally influenced wetlands alone store a disproportionately higher amount of organic carbon than other blue carbon systems. North America harbors 42% of tidally influenced global wetland area, which has been identified as a critical carbon stock in the context of climate change mitigation. However, quantified associations between vertebrate biota and carbon sequestration within ecosystems are in their infancy and have been incidental, given that microbial trophic levels are thought to drive nutrient dynamics. Here, we assess the relationship between American alligator ( Alligator mississippiensis ) demography and tidally influenced wetland soil carbon stock among habitats at continental, biogeographically-relevant, and local scales. We used soil core profile data from the Smithsonian’s Coastal Carbon Network and filtered for continuous core profiles in tidally influenced wetland areas along the Gulf and Atlantic Coasts of the United States. Results indicate that American alligator presence is positively correlated with soil carbon stock across habitats within their native distribution. Further, American alligator demographic variables are positively correlated with soil carbon stock at local scales. These conclusions are concordant with previous findings that apex predators, through trophic cascade theory, play a key role in regulating soil carbon stock and that alligators are functional apex predators in carbon dynamics and a key commercialized natural resource.

Connecticut, Delaware, Florida, Georgia, Louisiana↗
USGS2025

Overwinter and prespawning movements by a vulnerable freshwater pelagophilic minnow

The decline of pelagophil minnows is related to river fragmentation across the southern Great Plains landscape. Because we know little about pelagophil movement patterns and timing, we aimed to quantify the movements of the vulnerable Arkansas River shiner (ARS) during the winter (November–March) and prespawning (April–June) seasons. We tagged 4233 ARS using visible implant elastomer, passive integrated transponder, or p-Chip micro-transponder tags in 2018–2020. We sampled to recapture tagged fish weekly during the winter and biweekly during the spring. Tagged fish exhibited a downstream movement bias and movement was weakly related to increasing temperature, discharge, and photoperiod during winter, however most of the variability was explained by a random individual effect. Larger individuals moved greater distances than smaller fish. Upstream movements by a migratory portion of the population appeared to begin around late February based on the presence of fish at previously unoccupied sites. However, the first long-distance (30-km) upstream movement by a tagged fish was documented in late May. We show evidence that some ARS may be resident fish at sites throughout winter and spring of multiple years. To conserve freshwater pelagophil minnows, our results indicate water management strategies improving river connectivity in late winter through the spawning season may benefit spawning by migratory individuals, whereas lateral connectivity might benefit the resident portion of the population. Research efforts under experimental flows could provide insight to improved recovery options.

Oklahoma↗
USGS2025

Nature-based solutions could offset coastal squeeze of tidal wetlands from sea-level rise on the U.S. Pacific coast

In this study, we explored the opportunities for tidal wetland landward migration in response to sea-level rise on the Pacific Coast of the United States. By employing a systematic spatial approach, we quantified the available space for wetland migration with sea-level rise across 61 estuarine drainage areas. Although many of the existing tidal wetlands are small patches, our analyses show that 63% of the estuaries lacked the landward migration space needed to replace current tidal wetland extent, thereby threatening a wide range of protected species and ecosystem services. Developed lands and steep topography represent common barriers to migration along the Pacific coast, especially in central and southern California. The available wetland migration space consists primarily of agriculture, pasture, and freshwater wetlands, with most of the area available for migration occurring in just a few watersheds. In most watersheds tidal wetland migration would only occur with human intervention or facilitation. The greatest amount of area available for wetland migration was in the San Francisco Bay-Delta and Columbia River estuaries, together accounting for 58% of all available migration space on the Pacific Coast. Nature-based solutions to reduce tidal wetland loss from sea-level rise can include restoration in suitable areas, removal of barriers to tidal wetland migration, and elevation building approaches. Tidal wetland restoration opportunities could increase area by 59%, underscoring it as a plausible approach to prevent tidal wetland loss in those estuaries and a viable Nature-based solution. 54% of estuaries building elevations of existing tidal wetlands may be the most feasible approach needed. Our analyses illustrate the importance of management efforts that use Nature-based approaches to prevent tidal wetland ecosystem and species loss over the coming decades from sea-level rise.

Pacific Coast↗
USGS2025

A novel method for estimating pathogen presence, prevalence, load, and dynamics at multiple scales

The use of quantitative real-time PCR (qPCR) to monitor pathogens is common; however, quantitative frameworks that consider the observation process, dynamics in pathogen presence, and pathogen load are lacking. This can be problematic in the early stages of disease progression, where low level detections may be treated as ‘inconclusive’ and excluded from analyses. Alternatively, a framework that accounts for imperfect detection would provide more robust inferences. To better estimate pathogen dynamics, we developed a hierarchical multi-scale dynamic occupancy hurdle model (MS-DOHM). The model used data gathered during sampling for Pseudogymnoascus destructans (Pd) , the causative agent of white-nose syndrome, a fungal disease that has cause severe declines in several species of hibernating bats in North America. The model allowed us to estimate initial occupancy, colonization, persistence and prevalence of Pd at bat hibernacula. Additionally, utilizing the relationship between cycle threshold and pathogen load, we estimated pathogen detectability and modeled expected colony and bat pathogen loads. To assess the ability of MS-DOHM to estimate pathogen dynamics, we compared MS-DOHM’s results to those of a dynamic occupancy model and naïve detection/non-detection. MS-DOHM’s estimates of site-level pathogen presence were up to 11.9% higher than estimates from the dynamic occupancy model and 35.7% higher than naïve occupancy. Including prevalence and load in our modeling framework resulted in estimates of pathogen arrival that were two to three years earlier compared to the dynamic occupancy and naïve detection/non-detection, respectively. Compared to naïve values, MS-DOHM predicted greater pathogen loads on colonies; however, we found no difference between model estimates and naïve values of prevalence. While the model predicted no declines in site-level prevalence, there were instances where pathogen load decreased in colonies that had been Pd positive for longer periods of time. Our findings demonstrate that accounting for pathogen load and prevalence at multiple scales changes our understanding of Pd dynamics, potentially allowing earlier conservation intervention. Additionally, we found that accounting for pathogen load and prevalence within hibernacula and among individuals resulted in a better fitting model with greater predictive ability.

Scientific Reports↗
USGS2025

Wave driven cross shore and alongshore transport reveal more extreme projections of shoreline change in island environments

Coastal erosion, intensified by sea level rise, poses significant threats to coastal communities in Hawaiʻi and similar island communities. This study projects long-term shoreline change on the Hawaiian Island of O‘ahu using the data-assimilated CoSMoS-COAST shoreline change model. CoSMoS-COAST models four key shoreline processes: (1) Alongshore transport, (2) Recession due to sea level rise, (3) Cross-shore transport due to waves, and (4) Residual processes represented by a linear trend term. This study marks the first application of CoSMoS-COAST for an oceanic equatorial island with narrow beaches and a dynamic wave climate. The model is informed with a novel combination of shoreline data derived from high-resolution imagery from Planet, Sentinel-2, and Landsat satellites, wave-climate hindcasts specific to Hawai‘i, and regional beach-slope surveys. On a dynamic northern Oʻahu beach, the model achieved a root mean square error of 9.4 m between observations and model output. CoSMoS-COAST predicts that 81% of O‘ahu’s sandy beach coastline could experience beach loss by 2100; with 39.8% of this loss happening by 2030. This represents an increase, 43.3%, in net landward shoreline change compared to previous erosion forecasts, for 0.3 m of sea level rise (2050). Additionally, dynamic processes such as cross-shore equilibrium processes and alongshore sediment transport, play a large contribution to gross shoreline change within the next decade, particularly on O ‘ahu’s north and west shores. In the long term, we find that recession due to sea level rise and residual processes dominate, but dynamic, wave-driven processes (longshore and cross-shore transport) still account for 34% of shoreline change between present and 2100. We assert dynamic, wave-driven processes are a crucial addition for accurate modeling of island sandy beach environments. These findings have implications for O‘ahu’s coastal planning and development, suggesting updates to shoreline policies that rely upon erosion forecasting, and highlights the importance of incorporating wave and alongshore transport in erosion models for other Pacific islands.

Hawaii↗
USGS2025

Movement patterns of invasive red swamp crayfish vary with sex and environmental factors

Invasive species disproportionately invade freshwater ecosystems, threatening biodiversity. Defining when, where, and why aquatic invasive species move can help inform management strategies, yet the movement ecology of some of the most pervasive invasive species remains unknown. Red swamp crayfish ( Procambarus clarkii ; RSC) are the most widespread invasive crayfish and negatively affect ecosystems worldwide. We employed high-dimensional acoustic telemetry to investigate the movement patterns of 24 individual RSC across three months in an invaded water body. We assessed the effects of various extrinsic factors, such as time of day, temperature, precipitation, and proximity to the water’s edge, along with intrinsic factors, such as sex, reproductive form, and size, at different scales, including movement steps, range distribution, and behavioral states. We found that movement patterns across all scales were overwhelmingly driven by sex and reproductive form. Furthermore, RSC showed increased overall activity at night and near the water’s edge. By establishing baseline movement patterns and identifying key contributing factors, these findings provide a foundation for the development of adaptive management strategies for controlling invasive RSC populations.

Michigan↗
USGS2025

Nature-based solutions extend the lifespan of a regional levee system under climate change

Nature-based solutions are receiving increasing attention as a cost-effective climate adaptation strategy. Horizontal levees are nature-based adaptation solutions that include a sloping wetland habitat buffer fronting a levee. They can offer a hybrid solution to reinforce traditional levees in estuarine areas—plants on the horizontal levee can provide wave attenuation benefits as well as habitat benefits, but how the design of horizontal levees influences risk of levee failure remains unquantified. We use a hydrodynamic model, XBeach non-hydrostatic (XB-NH), to assess the stability and sustainability of existing levees and determine how hybrid nature-based climate adaptation measures can reduce the risk of overtopping on levees in San Francisco Bay. We compare overtopping rates in the existing levee system and in a variety of nature-based adaptation scenarios using a range of widths and slopes of horizontal levees to assess how horizontal levees perform in reducing risk of flooding, both with present day conditions and sea level rise. We show that climate change will challenge existing levee flood defenses in San Francisco Bay and increase the risk of overtopping, and that the nature-based solution of horizontal levees can meaningfully reduce risk of overtopping while simultaneously supporting marsh habitat. Flood risk reduction and habitat provision are both maximized with more gradually sloping and wider horizontal levee designs. Results show that the risk of overtopping can be reduced by up to 30% with horizontal levees. This analysis provides insight into horizontal levee design considerations and a methodological approach to adapt levees to prepare for climate change in urban wave-exposed estuaries. We show that horizontal levees can support preparation for the projected impacts of sea level rise (SLR) while simultaneously providing new intertidal wetland habitat.

California↗