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USGS2016

GOES-derived fog and low cloud indices for coastal north and central California ecological analyses

Fog and low cloud cover (FLCC) changes the water, energy, and nutrient flux of coastal ecosystems. Easy-to-use FLCC data are needed to quantify the impacts of FLC on ecosystem dynamics during hot, dry Mediterranean climate summers. FLCC indices were generated from 26,000 hourly night and day FLCC maps derived from Geostationary Environmental Operational Satellite (GOES) data for June, July, August, and September, 1999- 2009 for coastal California, latitude 34.50°N, south of Monterey Bay, to latitude 41.95°N, north of Crescent City. Monthly FLCC average hours per day (h/d) range from < 2 to 18. Average FLCC over the ocean increases from north (9 h/d) to south (14 h/d) whereas FLCC over land is reversed. Over land, FLCC is highest where land juts into the prevailing NW winds and is lowest in the lee of major capes. FLCC advects furthest inland through low-lying NW ocean-facing valleys. At night hours of FLCC is higher more frequently on land than over the ocean. Interannual FLCC coefficient of variation shows long term geographic stability strongly associated with landform position. Contours delineating homogeneous zones of FLCC, derived from average decadal h/d FLCC, provide data to refine the commonly used term ‘fog belt.’ FLCC indices are available for download from the California Landscape Conservation Cooperative Climate Commons website. FLCC indices can be used to improve analyses of biogeographic and bioclimatic species distribution models, meteorological mechanisms driving FLCC patterns, ecohydrological investigations of evapotranspiration, solar energy feasibility studies, agricultural irrigation demand and viticultural ripening models.

Earth and Space Science↗

USGS2021

Evaluating natural experiments in ecology: Using synthetic controls in assessments of remotely sensed land treatments

Many important ecological phenomena occur on large spatial scales and/or are unplanned and thus do not easily fit within analytical frameworks that rely on randomization, replication, and interspersed a priori controls for statistical comparison. Analyses of such large‐scale, natural experiments are common in the health and econometrics literature, where techniques have been developed to derive insight from large, noisy observational data sets. Here, we apply a technique from this literature, synthetic control, to assess landscape change with remote sensing data. The basic data requirements for synthetic control include (1) a discrete set of treated and untreated units, (2) a known date of treatment intervention, and (3) time series response data that include both pre‐ and post‐treatment outcomes for all units. Synthetic control generates a response metric for treated units relative to a no‐action alternative based on prior relationships between treated and unexposed groups. Using simulations and a case study involving a large‐scale brush‐clearing management event, we show how synthetic control can intuitively infer treatment effect sizes from satellite data, even in the presence of confounding noise from climate anomalies, long‐term vegetation dynamics, or sensor errors. We find that accuracy depends on the number and quality of potential control units, highlighting the importance of selecting appropriate control populations. Although we consider the synthetic control approach in the context of natural experiments with remote sensing data, we expect the methodology to have wider utility in ecology, particularly for systems with large, complex, and poorly replicated experimental units.

Ecological Applications↗

USGS2017

Estimating thermal performance curves from repeated field observations

Estimating thermal performance of organisms is critical for understanding population distributions and dynamics and predicting responses to climate change. Typically, performance curves are estimated using laboratory studies to isolate temperature effects, but other abiotic and biotic factors influence temperature-performance relationships in nature reducing these models' predictive ability. We present a model for estimating thermal performance curves from repeated field observations that includes environmental and individual variation. We fit the model in a Bayesian framework using MCMC sampling, which allowed for estimation of unobserved latent growth while propagating uncertainty. Fitting the model to simulated data varying in sampling design and parameter values demonstrated that the parameter estimates were accurate, precise, and unbiased. Fitting the model to individual growth data from wild trout revealed high out-of-sample predictive ability relative to laboratory-derived models, which produced more biased predictions for field performance. The field-based estimates of thermal maxima were lower than those based on laboratory studies. Under warming temperature scenarios, field-derived performance models predicted stronger declines in body size than laboratory-derived models, suggesting that laboratory-based models may underestimate climate change effects. The presented model estimates true, realized field performance, avoiding assumptions required for applying laboratory-based models to field performance, which should improve estimates of performance under climate change and advance thermal ecology.

Ecology↗

USGS2020

High‐resolution dynamically downscaled rainfall and temperature projections for ecological life zones within Puerto Rico and for the U.S. Virgin Islands

The weather research and forecasting (WRF) model and a combination of the regional spectral model (RSM) and the Japanese Meteorological Agency Non‐Hydrostatic Model (NHM) were used to dynamically downscale selected CMIP5 global climate models to provide 2‐km projections with hourly model output for Puerto Rico and the U.S. Virgin Islands. Two 20‐year time slices were downscaled for historical (1986–2005) and future (2041–2060) periods following RCP8.5. Projected changes to mean and extreme temperature and precipitation were quantified for Holdridge life zones within Puerto Rico and for the U.S. Virgin Islands. The evaluation reveals a persistent cold bias for all islands in the U.S. Caribbean, a dry bias across Puerto Rico, and a wet bias on the windward side of mountains within the U.S. Virgin Islands. Despite these biases, model simulations show a robust drying pattern for all islands that is generally larger for Puerto Rico (25% annual rainfall reduction for some life zones) than the U.S. Virgin Islands (12% island average). The largest precipitation reductions are found during the more convectively active afternoon and evening hours. Within Puerto Rico, the model uncertainty increases for the wetter life zones, especially for precipitation. Across the life zones, both models project unprecedented maximum and minimum temperatures that may exceed 200 days annually above the historical baseline with only small changes to the frequency of extreme rainfall. By contrast, in the U.S. Virgin Islands, there is no consensus on the location of the largest drying relative to the windward and leeward side of the islands. However, the models project the largest increases in maximum temperature on the southern side of St. Croix and in higher elevations of St. Thomas and St. John.

Puerto Rico↗

USGS2017

Long-term spatial heterogeneity in mallard distribution in the Prairie pothole region

The Prairie Pothole Region (PPR) of north-central United States and south-central Canada supports greater than half of all breeding mallards ( Anas platyrhynchos ) annually counted in North America and is the focus of widespread conservation and research efforts. Allocation of conservation resources for this socioeconomically important population would benefit from an understanding of the nature of spatiotemporal variation in distribution of breeding mallards throughout the 850,000 km 2 landscape. We used mallard counts from the Waterfowl Breeding Population and Habitat Survey to test for spatial heterogeneity and identify high- and low-abundance regions of breeding mallards over a 50-year time series. We found strong annual spatial heterogeneity in all years: 90% of mallards counted annually were on an average of only 15% of surveyed segments. Using a local indicator of spatial autocorrelation, we found a relatively static distribution of low-count clusters in northern Montana, USA, and southern Alberta, Canada, and a dynamic distribution of high-count clusters throughout the study period. Distribution of high-count clusters shifted southeast from northwestern portions of the PPR in Alberta and western Saskatchewan, Canada, to North and South Dakota, USA, during the latter half of the study period. This spatial redistribution of core mallard breeding populations was likely driven by interactions between environmental variation that created favorable hydrological conditions for wetlands in the eastern PPR and dynamic land-use patterns related to upland cropping practices and government land-retirement programs. Our results highlight an opportunity for prioritizing relatively small regions within the PPR for allocation of wetland and grassland conservation for mallard populations. However, the extensive spatial heterogeneity in core distributions over our study period suggests such spatial prioritization will have to overcome challenges presented by dynamic land-use and climate patterns in the region, and thus merits additional monitoring and empirical research to anticipate future population distribution. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Wildlife Society Bulletin↗

USGS1997

The frequency and intensity of Atlantic hurricanes and their influence on the structure of south Florida mangrove communities

Hurricanes are formidable forces that wreak havoc on society and nature alike. Mangrove ecosystems are especially vulnerable because they thrive in the intertidal zone of tropical regions where hurricanes originate and are most frequent. Because mangroves are found at the land-sea interface where hurricanes are often most intense, these coastal forests are subject to damage from both high wind and surge. Mangroves are also an important habitat for many colonial and migratory birds and other wildlife, along with being nursery grounds for our fisheries. The fate of mangrove habitat as influenced by hurricanes may be threatened in the future under a global warming environment that might yield more intense storms than have been previously observed. Simulation models of hurricane abiotics and mangrove community dynamics have been developed to evaluate the effects of hurricanes on mangrove habitat across the South Florida landscape. Model applications show that hurricane frequency and intensity have varied spatially across Florida’s lower peninsula over the last century of record. Hindcast simulations of actual hurricane tracks and conditions seem to account for the structural composition of modernday mangrove forests across South Florida. A recurrence interval of major storms every 30 years over the last century is the major factor controlling mangrove ecosystem dynamics in South Florida. Some climate change models predict an increase in hurricane intensity over the next century that may further alter the structure and composition of our mangrove ecosystems. Model results of climate change scenarios indicate that future mangrove forests are likely to be diminished in stature and perhaps include a higher proportion of red mangroves. This modeling approach offers the ability to assess decadal and longer time scale changes in hurricane behavior and its effects on community structure and distribution of important plant associations such as the fate of mangrove habitat.

Florida↗

USGS2007

Dissolved organic carbon in Alaskan boreal forest: Sources, chemical characteristics, and biodegradability

The fate of terrestrially-derived dissolved organic carbon (DOC) is important to carbon (C) cycling in both terrestrial and aquatic environments, and recent evidence suggests that climate warming is influencing DOC dynamics in northern ecosystems. To understand what determines the fate of terrestrial DOC, it is essential to quantify the chemical nature and potential biodegradability of this DOC. We examined DOC chemical characteristics and biodegradability collected from soil pore waters and dominant vegetation species in four boreal black spruce forest sites in Alaska spanning a range of hydrologic regimes and permafrost extents (Well Drained, Moderately Well Drained, Poorly Drained, and Thermokarst Wetlands). DOC chemistry was characterized using fractionation, UV-Vis absorbance, and fluorescence measurements. Potential biodegradability was assessed by incubating the samples and measuring CO2 production over 1 month. Soil pore water DOC from all sites was dominated by hydrophobic acids and was highly aromatic, whereas the chemical composition of vegetation leachate DOC varied significantly with species. There was no seasonal variability in soil pore water DOC chemical characteristics or biodegradability; however, DOC collected from the Poorly Drained site was significantly less biodegradable than DOC from the other three sites (6% loss vs. 13-15% loss). The biodegradability of vegetation-derived DOC ranged from 10 to 90% loss, and was strongly correlated with hydrophilic DOC content. Vegetation such as Sphagnum moss and feathermosses yielded DOC that was quickly metabolized and respired. In contrast, the DOC leached from vegetation such as black spruce was moderately recalcitrant. Changes in DOC chemical characteristics that occurred during microbial metabolism of DOC were quantified using fractionation and fluorescence. The chemical characteristics and biodegradability of DOC in soil pore waters were most similar to the moderately recalcitrant vegetation leachates, and to the microbially altered DOC from all vegetation leachates.

Alaska↗

USGS2017

Meteorological drivers of hypolimnetic anoxia in a eutrophic, north temperate lake

Oxygen concentration is both an indicator and driver of water quality in lakes. Decreases in oxygen concentration leads to altered ecosystem function as well as harmful consequences for aquatic biota, such as fishes. The responses of oxygen dynamics in lakes to climate-related drivers, such as temperature and wind speed, are well documented for lake surface waters. However, much less is known about how the oxic environment of bottom waters, especially the timing and magnitude of anoxia in eutrophic lakes, responds to changes in climate drivers. Understanding how important ecosystem states, such as hypolimnetic anoxia, may respond to differing climate scenarios requires a model that couples physical-biological conditions and sufficiently captures the density stratification that leads to strong oxygen gradients. Here, we analyzed the effects of changes in three important meteorological drivers (air temperature, wind speed, and relative humidity) on hypolimnetic anoxia in a eutrophic, north temperate lake using the anoxic factor as an index that captures both the temporal and spatial extent of anoxia. Air temperature and relative humidity were found to have a positive correlation with anoxic factor, while wind speed had a negative correlation. Air temperature was found to have the greatest potential impact of the three drivers on the anoxic factor, followed by wind speed and then relative humidity. Across the scenarios of climate variability, variation in the simulated anoxic factor was primarily due to changes in the timing of onset and decay of stratification. Given the potential for future changes in climate, especially increases in air temperature, this study provides important insight into how these changes will alter lake water quality.

Ecological Modelling↗

USGS2013

Quantifying wetland–aquifer interactions in a humid subtropical climate region: An integrated approach

Wetlands are widely recognized as sentinels of global climate change. Long-term monitoring data combined with process-based modeling has the potential to shed light on key processes and how they change over time. This paper reports the development and application of a simple water balance model based on long-term climate, soil, vegetation and hydrological dynamics to quantify groundwater–surface water (GW–SW) interactions at the Norman landfill research site in Oklahoma, USA. Our integrated approach involved model evaluation by means of the following independent measurements: (a) groundwater inflow calculation using stable isotopes of oxygen and hydrogen ( 16 O, 18 O, 1 H, 2 H); (b) seepage flux measurements in the wetland hyporheic sediment; and (c) pan evaporation measurements on land and in the wetland. The integrated approach was useful for identifying the dominant hydrological processes at the site, including recharge and subsurface flows. Simulated recharge compared well with estimates obtained using isotope methods from previous studies and allowed us to identify specific annual signatures of this important process during the period of study (1997–2007). Similarly, observations of groundwater inflow and outflow rates to and from the wetland using seepage meters and isotope methods were found to be in good agreement with simulation results. Results indicate that subsurface flow components in the system are seasonal and readily respond to rainfall events. The wetland water balance is dominated by local groundwater inputs and regional groundwater flow contributes little to the overall water balance.

Oklahoma↗

USGS2022

A new indicator approach to reconstruct agricultural land use in Europe from sedimentary pollen assemblages

The reconstruction of human impact is pivotal in palaeoecological studies, as humans are among the most important drivers of Holocene vegetation and ecosystem change. Nevertheless, separating the anthropogenic footprint on vegetation dynamics from the impact of climate and other environmental factors (disturbances such as fire, erosion, floods, landslides, avalanches, volcanic eruptions) is a challenging and still largely open issue. For this purpose, palynologists mostly rely on cultural indicator pollen types and related indices that consist of sums or ratios of these pollen types. However, the high environmental and biogeographical specificity of cultural indicator plants hinders the application of the currently available indices to wide geographical settings. Furthermore, the achievable taxonomic resolution of cultural indicator pollen types may hamper their indicative capacity. In this study, we propose the agricultural land use probability (LUP) index, a novel approach to quantify human impact intensity on European ecosystems based on cultural indicator pollen types. From the ‘classic’ cultural indicators, we construct the LUP index by selecting those with the best indicator capacity based on bioindication criteria. We first train the LUP index using twenty palynological sequences along a broad environmental gradient, spanning from treeless alpine to subtropical mediterranean evergreen plant communities. We then validate the LUP index using independent pollen datasets and archaeological proxies. Finally, we discuss the suitability of the selected pollen types and the potential of the LUP index for quantifying Holocene human impact in Europe, concluding that careful application of the LUP index may significantly contribute to refining pollen-based land-use reconstructions.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2026

Enhancements to the USGS Landsat Level 2 surface temperature and emissivity product for Collection 3 reprocessing

The Landsat program provides the longest continuous global record of thermal infrared observations of the Earth's surface, underpinning critical applications in climate monitoring, water resources, ecosystem dynamics, urban heat analysis, and natural hazard assessment. The release of a global inventory of Landsat Collection 2 Level 2 surface temperature products by the U.S. Geological Survey (USGS) marked a major milestone in operational provision of Landsat thermal infrared analysis-ready data. Ongoing validations and community uses of Collection 2 have identified opportunities to further improve accuracy, uncertainty characterization, and emissivity correction across diverse atmospheric and surface conditions. In preparation for the planned Landsat Collection 3 reprocessing of the Landsat data record in the late 2020s, the USGS is implementing a coordinated set of enhancements to the Level 2 surface temperature products. These include revised emissivity estimation that leverages external datasets, improved atmospheric characterization and uncertainty propagation, expanded dynamic range for high temperature targets, consideration of split window atmospheric correction algorithm for Landsat 8 and 9, and decoupling of thermal infrared processing from visible to shortwave infrared constraints to enable surface temperature retrievals under low or no solar illumination conditions. These changes are designed to improve product quality and consistency across the Landsat record. Beyond near-term performance gains, the Collection 3 design establishes a scalable processing architecture to accommodate the expanded spectral and radiometric measurement capabilities of the forthcoming Landsat 10 mission. By preserving continuity across the Landsat 4–9 record while enabling future algorithm evolution, Landsat Collection 3 will provide a foundation for long-term, multi-decadal Earth system thermal infrared observations.

Remote Sensing of Environment↗

USGS2014

Temperature drives global patterns in forest biomass distribution in leaves, stems, and roots

Whether the fraction of total forest biomass distributed in roots, stems, or leaves varies systematically across geographic gradients remains unknown despite its importance for understanding forest ecology and modeling global carbon cycles. It has been hypothesized that plants should maintain proportionally more biomass in the organ that acquires the most limiting resource. Accordingly, we hypothesize greater biomass distribution in roots and less in stems and foliage in increasingly arid climates and in colder environments at high latitudes. Such a strategy would increase uptake of soil water in dry conditions and of soil nutrients in cold soils, where they are at low supply and are less mobile. We use a large global biomass dataset (>6,200 forests from 61 countries, across a 40 °C gradient in mean annual temperature) to address these questions. Climate metrics involving temperature were better predictors of biomass partitioning than those involving moisture availability, because, surprisingly, fractional distribution of biomass to roots or foliage was unrelated to aridity. In contrast, in increasingly cold climates, the proportion of total forest biomass in roots was greater and in foliage was smaller for both angiosperm and gymnosperm forests. These findings support hypotheses about adaptive strategies of forest trees to temperature and provide biogeographically explicit relationships to improve ecosystem and earth system models. They also will allow, for the first time to our knowledge, representations of root carbon pools that consider biogeographic differences, which are useful for quantifying whole-ecosystem carbon stocks and cycles and for assessing the impact of climate change on forest carbon dynamics.

Proceedings of the National Academy of Sciences of↗

USGS2007

The FORE-SCE model: a practical approach for projecting land cover change using scenario-based modeling

A wide variety of ecological applications require spatially explicit, historic, current, and projected land use and land cover data. The U.S. Land Cover Trends project is analyzing contemporary (1973–2000) land-cover change in the conterminous United States. The newly developed FORE-SCE model used Land Cover Trends data and theoretical, statistical, and deterministic modeling techniques to project future land cover change through 2020 for multiple plausible scenarios. Projected proportions of future land use were initially developed, and then sited on the lands with the highest potential for supporting that land use and land cover using a statistically based stochastic allocation procedure. Three scenarios of 2020 land cover were mapped for the western Great Plains in the US. The model provided realistic, high-resolution, scenario-based land-cover products suitable for multiple applications, including studies of climate and weather variability, carbon dynamics, and regional hydrology.

Journal of Land Use Science↗

USGS2021

Current distribution and abundance of Kohala forest birds in Hawai‘i

The Kohala volcano is home to the most spatially isolated population of Hawaiian forest birds on Hawai‘i Island and contains one of the few native bird populations in the state that has not been monitored since the original Hawai‘i Forest Bird Survey (HFBS) in 1979. We surveyed 143 stations across 13 transects in Pu‘u ‘O ‘Umi Natural Area Reserve on Kohala from February through April 2017 and compared our results to data from the 1979 HFBS conducted at 80 stations across three transects in the same location as our study site. We detected 2806 individuals of 15 species and measured relative abundance, relative occurrence, and density for seven species. We observed changes in species densities ranging from −8.4% (Hawai‘i ‘Elepaio, Chasiempis sandwichensis ) to +714% (‘I‘iwi, Drepanis coccinea ). Equivalence testing showed meaningful increases in population densities for all but one species, the Hawai‘i ‘Elepaio. The increases in population densities on Kohala are in stark contrast to the widespread declines in population densities of native species elsewhere in Hawai‘i. Relative occurrence was greater in 2017 than in 1979 for all species except Hawai‘i ‘Elepaios and House Finches ( Haemorhous mexicanus ), and relative abundance increased for all species except Hawai‘i ‘Elepaios, House Finches, and Melodious Laughing Thrushes ( Garrulax canorus ). We also documented the range expansion of Japanese Bush Warblers ( Cettia diphone ) in Kohala. Our results indicate that this spatially isolated avian community remains biologically diverse, and most population densities are increasing in the study area. Our results provide a framework for future surveys and a baseline for understanding possible changes in population and community dynamics as birds respond to climate change and avian disease on Kohala volcano.

Hawai'i↗

USGS2015

Arctic biodiversity: Increasing richness accompanies shrinking refugia for a cold-associated tundra fauna

As ancestral biodiversity responded dynamically to late-Quaternary climate changes, so are extant organisms responding to the warming trajectory of the Anthropocene. Ecological predictive modeling, statistical hypothesis tests, and genetic signatures of demographic change can provide a powerful integrated toolset for investigating these biodiversity responses to climate change, and relative resiliency across different communities. Within the biotic province of Beringia, we analyzed specimen localities and DNA sequences from 28 mammal species associated with boreal forest and Arctic tundra biomes to assess both historical distributional and evolutionary responses and then forecasted future changes based on statistical assessments of past and present trajectories, and quantified distributional and demographic changes in relation to major management regions within the study area. We addressed three sets of hypotheses associated with aspects of methodological, biological, and socio-political importance by asking (1) what is the consistency among implications of predicted changes based on the results of both ecological and evolutionary analyses; (2) what are the ecological and evolutionary implications of climate change considering either total regional diversity or distinct communities associated with major biomes; and (3) are there differences in management implications across regions? Our results indicate increasing Arctic richness through time that highlights a potential state shift across the Arctic landscape. However, within distinct ecological communities, we found a predicted decline in the range and effective population size of tundra species into several discrete refugial areas. Consistency in results based on a combination of both ecological and evolutionary approaches demonstrates increased statistical confidence by applying cross-discipline comparative analyses to conservation of biodiversity, particularly considering variable management regimes that seek to balance sustainable ecosystems with other anthropogenic values. Refugial areas for cold-adapted taxa appear to be persistent across both warm and cold climate phases and although fragmented, constitute vital regions for persistence of Arctic mammals.

Ecosphere↗

USGS2018

The geology and paleontology of Tule Springs Fossil Beds National Monument, Nevada

On December 19, 2014, Tule Springs Fossil Beds National Monument, located in the Las Vegas Valley of southern Nevada, was established by Congress as the 405th unit of the National Park Service to “conserve, protect, interpret, and enhance for the benefit of present and future generations the unique and nationally important paleontological, scientific, educational, and recreational resources and values of the land” (P.L. 113-291, sec. 3092). Vertebrate fossils have been known from the region for more than a century, and recent work has established the Tule Springs local fauna as one of the most significant Pleistocene vertebrate faunas in the American Southwest. The sedimentary sequence that entombs the fossils represents a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Work in Tule Springs Fossil Beds National Monument continues today through the efforts of scientists from the U.S. Geological Survey, National Park Service, and academic institutions across the country.

Nevada↗

USGS2018

The Las Vegas Formation

The Las Vegas Formation was established in 1965 to designate the distinctive light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada. In a coeval designation, the sediments were subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the literature. Use of the Las Vegas Formation name over the past half century has been hampered because of the lack of a robust definition and characterization of the entire lithostratigraphic sequence, its geographic distribution, and chronology. This study evaluates and describes deposits attributed to the Las Vegas Formation with detailed stratigraphy, sedimentology, and field relations. A large suite of radiocarbon and luminescence ages facilitates revision and temporal expansion of the geochronology. In all, we characterize 17 informal geologic units within the formation, each dating to a unique period of geologic time, with stratigraphically ascending members X, A, B, D, and E and attendant beds in members B, D, and E. The age of the Las Vegas Formation spans at least the middle Pleistocene to early Holocene (from approximately 573 to 8.53 kilo-annum [thousands of years before present]) and is related to past episodes of groundwater discharge in the Las Vegas Valley. The contextual information derived from this new framework is dually noteworthy because the sediments entomb one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represent a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Characterizing the nature of these important deposits stabilizes the nomenclature, promotes the continued use of the informal units within the formation, and facilitates studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern United States.

Nevada↗

USGS2019

Variability in shelf sedimentation in response to fluvial sediment supply and coastal erosion over the past 1,000 years in Monterey Bay, CA, United States

Continental shelf environments are uniquely situated to capture some of the most dynamic processes on Earth including climatic variability and anthropogenic modifications to coastal systems. Understanding how these processes have affected sediment delivery and accumulation on the shelf in the past may provide insight into potential changes in the future. To address this, we investigated shelf sedimentation within Monterey Bay, California. Sediment cores were collected from four locations throughout the bay to capture both the modern and late Holocene sedimentological record using grain size analysis, and sediment chronologies determined from 210 Pb, 137 Cs, and 14 C. From the grain size results we focused on the total percent sand, and established a Littoral Sand Fraction (LSF) index to assess sediment contribution from the littoral zone as a result coastal erosion. Grain size results from the multicores consistently showed an increase in sand over the past several decades (post 1970s). For the cores located within the bay proximal to three major rivers, the increase in sand corresponded to a general increase in the LSF over the same period. We attributed these trends to increased sediment contributions to the shelf due to accelerated coastal erosion in the region. This accelerated coastal erosion was likely the combined result of dam construction in the mid-twentieth century that limited fluvial supply to the coast, and a shift in climate toward wetter, stormier period. Applying these sediment characteristics back over the past ∼1,000 years we found that dry climatic periods resulted in deposits that were limited in total sand but enriched in littoral material suggesting elevated coastal erosion. During wet periods deposits were enriched in total sand but limited in littoral sand suggesting elevated fluvial supply and low erosion. Compared to the late Holocene record, the previous several decades represent a shift to a new regime, uncharacteristic of deposits over the past millennia, highlighting the impact humans have had on shelf sedimentation.

California↗