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USGS2017

Perspectives on chemical oceanography in the 21st century: Participants of the COME ABOARD Meeting examine aspects of the field in the context of 40 years of DISCO

The questions that chemical oceanographers prioritize over the coming decades, and the methods we use to address these questions, will define our field's contribution to 21st century science. In recognition of this, the U.S. National Science Foundation and National Oceanic and Atmospheric Administration galvanized a community effort (the Chemical Oceanography MEeting: A BOttom-up Approach to Research Directions, or COME ABOARD) to synthesize bottom-up perspectives on selected areas of research in Chemical Oceanography. Representing only a small subset of the community, COME ABOARD participants did not attempt to identify targeted research directions for the field. Instead, we focused on how best to foster diverse research in Chemical Oceanography, placing emphasis on the following themes: strengthening our core chemical skillset; expanding our tools through collaboration with chemists, engineers, and computer scientists; considering new roles for large programs; enhancing interface research through interdisciplinary collaboration; and expanding ocean literacy by engaging with the public. For each theme, COME ABOARD participants reflected on the present state of Chemical Oceanography, where the community hopes to go and why, and actionable pathways to get there. A unifying concept among the discussions was that dissimilar funding structures and metrics of success may be required to accommodate the various levels of readiness and stages of knowledge development found throughout our community. In addition to the science, participants of the concurrent Dissertations Symposium in Chemical Oceanography (DISCO) XXV, a meeting of recent and forthcoming Ph.D. graduates in Chemical Oceanography, provided perspectives on how our field could show leadership in addressing long-standing diversity and early-career challenges that are pervasive throughout science. Here we summarize the COME ABOARD Meeting discussions, providing a synthesis of reflections and perspectives on the field.

Marine Chemistry↗

USGS2018

Benthic foraminifera from the Carnarvon Ramp reveal variability in Leeuwin Current activity (Western Australia) since the Pliocene

Benthic foraminiferal assemblages from a ~300 m deep core from an outer carbonate-ramp site off Western Australia (International Ocean Discovery Program Core U1460A) were examined to reconstruct the paleoceanographic evolution of the Carnarvon Ramp and the warm surficial Leeuwin Current (LC) for the last 3.54 Ma. Of the identified 179 benthic foraminiferal species, occurrences of the 15 most abundant taxa were assessed using Q-mode Cluster Analysis and Non-Metric Dimensional Scaling. Diversity, equitability, planktonic/benthic index, microhabitat preference, and sedimentary parameters such as lithology and sponge spicule content were analyzed to gather information about past intermediate- and surface-water circulation. Relative abundances of infaunal and epifaunal species were applied to indicate changes in organic-matter supply and oxygenation at the sea floor. Influence of upwelling was recognized by a high infaunal species ratio, with dominance by Uvigerina peregrina , Lagena annellatrachia and Trifarina bradyi . Epifaunal species such as Hanzawaia nipponica and Hyalinea florenceae gradually became more abundant around 1.14 Ma, indicating increased ventilation and establishment of the paleo-LC. A more substantial change was initiated by 0.91 Ma as marked by key species Spirorutilus carinatus and Rotorbinella sp. , together with increased faunal diversity, benthic foraminiferal accumulation rates, and evidence for suspension feeding sponges. With the LC flow suppressing upwelling, and better ventilated waters entering the shelf, the environment favored epifaunal agglutinates, rotalids, and miliolids, while buliminids decreased. Under high-flow conditions of the LC, sponge spicules and skeletal carbonate production reached an optimum at ~0.6 Ma before returning to modern conditions. Supported by these observations, we propose the following paleoceanographic evolution of the Carnarvon Ramp: During the late Pliocene to mid Pleistocene (3.54–0.91 Ma) conditions of deep-water upwelling from the Western Australian Current and Indian Ocean Gyre indicate the absence of the capping LC on the outer carbonate ramp. A transitional phase started in the mid Pleistocene (1.14–0.61 Ma). The paleo-LC triggered gradual oxygenation at the sediment-water interface, which coincided with an increase in carbonate sedimentation rates, and waning sea-surface productivity. During a third phase, mid Pleistocene to present (0.91–0 Ma), the LC’s intensity and flow rates peaked at ~0.6 Ma. Benthic foraminiferal accumulation rates reached a high, then decreased to present-day rates. For short periods, sea-surface productivity was moderately enhanced, likely due to fluctuating LC persistence or landward shift during glacial maxima.

Western Australia↗

USGS2011

Coastal habitat degradation and green sea turtle diets in Southeastern Brazil

To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear.

Vitoria↗

USGS2020

Vegetation responses to Quaternary volcanic and hydrothermal disturbances in the Northern Rocky Mountains and Greater Yellowstone Ecosystem (USA)

Volcanic and hydrothermal processes produce disturbances by diverse mechanisms and ecological responses are varied. New and published pollen records from the Northern Rocky Mountains and Greater Yellowstone Ecosystem document the response of vegetation to three different types of volcanic and hydrothermal disturbances: (1) Pleistocene rhyolite lava flows in the central Greater Yellowstone Ecosystem created infertile landscapes that have shaped vegetation since rhyolite emplacement. Nutrient-poor, well-drained soils that developed on these flows supported low-diversity grassland during late-glacial time and Pinus contorta forests in interglacial periods. (2) Ash layers from eruptions of Pacific Northwest stratovolcanoes are commonly preserved in lake-sediment records in the Northern Rocky Mountains, and associated pollen records show enhancement of steppe vegetation for years to decades. (3) Local hydrothermal explosions have resulted in vegetation changes in hydrothermal areas that indicate tree mortality following deposition of explosion debris, followed by recovery in years. Thus, the type and duration of the vegetation response to volcanic and hydrothermal disturbances are highly contextual and governed by the antecedent plant communities and the magnitude and mechanism of the volcanic or hydrothermal disturbance. Vegetation resilience varied between disturbances, ranging from enduring ecosystem parameter changes to short-lived state changes in resilient plant communities.

Idaho, Montana, Wyoming↗

USGS2022

Impact of climate change on mollusks and other invertebrate resources at the Dominican University of California archaeological site (CA-MRN-254), Marin County, California

We have identified and provided ecological interpretations of 30 taxa recovered at two shellmounds at the Dominican University of California archaeology site in Marin County, California (CA-MRN-254). A Q-mode cluster analysis was used to group the samples according to their faunal similarity. The clusters ranged from a diverse grouping of 100 samples with 27 taxa (Cluster A) to those with a more restricted assemblage (4–9 taxa in Clusters B to E). The Q-mode clusters were then used to interpret the variability in food resources utilized through the 1800 years of site occupation. During the Intermediate Middle Period (A.D.100-300), the inhabitants appeared to be selective in the marine taxa they used, evident by the presence of Cluster B and E assemblages. A diverse (Cluster A) assemblage was then utilized at the site at one or both of the shellmounds through the remainder of the occupancy period, including the Middle/Late Period Transition (A.D. 700–900) and Late Period Phase 1C (A.D. 900–1300), coincident with the extensive drought conditions of the Medieval Climatic Anomaly (MCA) in the San Francisco Bay area. These findings suggest the marine invertebrate resources utilized by the site occupants were not significantly affected by the persistent aridity associated with the MCA.

California↗

USGS2019

User needs for future Landsat missions

Landsat satellites have been operating since 1972, providing the longest continuous observation record of the Earth’s land surface. Over the past half century, the Landsat user community has grown exponentially, encompassing more diverse and evolving scientific research and operational uses. Understanding current and future user needs is crucial to informing the design of Landsat missions beyond Landsat 9. The U.S. Geological Survey (USGS) initiated a user needs collection process to document needs from U.S. Federal civil subject matter experts who rely on moderate-resolution land imaging data across a diverse range of scientific research and application domains. In total, 379 moderate-resolution land imaging user needs were collected through structured interviews. The findings indicate that, at present, users need continuity in Landsat capabilities with free and open data access. Improvements to future Landsat systems should include 10 m spatial resolution and at least weekly cloud-free observation frequency. Spectral enhancements should include the addition of red edge bands, and multiple, narrower visible, near infrared, shortwave infrared, and thermal infrared bands. Ideally, a variety of applications need continuous, full-spectrum coverage in 10 nm-wide bands spanning the visible to shortwave infrared (VSWIR) region (400–2500 nm) and 5 to 8 multispectral thermal infrared bands. Non-Federal (state, local, commercial, academic, and international) sources found similar results, but a more comprehensive comparison across these communities through a broader survey may provide additional insights. USGS-collected moderate-resolution land imaging user needs are an input to the Landsat 10 Architecture Study to develop and assess feasible Landsat 10 mission architectures.

Remote Sensing of Environment↗

USGS2023

High-frequency time series comparison of Sentinel-1 and Sentinel-2 for open and vegetated water across the United States (2017-2021)

Frequent observations of surface water at fine spatial scales will provide critical data to support the management of aquatic habitat, flood risk and water quality. Sentinel-1 and Sentinel-2 satellites can provide such observations, but algorithms are still needed that perform well across diverse climate and vegetation conditions. We developed surface inundation algorithms for Sentinel-1 and Sentinel-2, respectively, at 12 sites across the conterminous United States (CONUS), covering a total of >536,000 km 2 and representing diverse hydrologic and vegetation landscapes. Each scene in the 5-year (2017–2021) time series was classified into open water, vegetated water, and non-water at 20 m resolution using variables from Sentinel-1 and Sentinel-2, as well as variables derived from topographic and weather datasets. The Sentinel-1 algorithm was developed distinct from the Sentinel-2 model to explore if and where the two time series could potentially be integrated into a single high-frequency time series. Within each model, open water and vegetated water (vegetated palustrine, lacustrine, and riverine wetlands) classes were mapped. The models were validated using imagery from WorldView and PlanetScope. Classification accuracy for open water was high across the 5-year period, with an omission and commission error of only 3.1% and 0.9% for the Sentinel-1 algorithm and 3.1% and 0.5% for the Sentinel-2 algorithm, respectively. Vegetated water accuracy was lower, as expected given that the class represents mixed pixels. The Sentinel-2 algorithm showed higher accuracy (10.7% omission and 7.9% commission error) relative to the Sentinel-1 algorithm (28.4% omission and 16.0% commission error). Patterns over time in the proportion of area mapped as open or vegetated water by the Sentinel-1 and Sentinel-2 algorithms were charted and correlated for a subset of all 12 sites. Our results showed that the Sentinel-1 and Sentinel-2 algorithm open water time series can be integrated at all 12 sites to improve the temporal resolution, but sensor-specific differences, such as sensitivity to vegetation structure versus pixel color, complicate the data integration for mixed-pixel, vegetated water. The methods developed here provide inundation at 5-day (Sentinel-2 algorithm) and 12-day (Sentinel-1 algorithm) time steps to improve our understanding of the short- and long-term response of surface water to climate and land use drivers in different ecoregions.

continental United States↗

USGS2023

Quantification of wetland vegetation communities features with airborne AVIRIS-NG, UAVSAR, and UAV LiDAR data in Peace-Athabasca Delta

Arctic-boreal wetlands, important ecosystems for biodiversity and ecological services, are experiencing hydrological changes including permafrost thaw, earlier snowmelt, and increased wildfire susceptibility. These changes are affecting wetland productivity, species diversity, and biogeochemical cycles. However, given the diverse forms and structures of wetland vegetation communities, traditional wetland maps generated from lower spatial and spectral resolution satellite imagery lack community-level vegetation classification and miss spatially complex patterns. In this study, we built a cloud-based workflow to map wetland vegetation community of the Peace-Athabasca Delta (PAD), Canada, by leveraging high-resolution (5-m) airborne multi-sensor datasets, namely NASA's Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) and Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), and a historical LiDAR archive. Validation of our classifications using ground references indicates that classifications derived from AVIRIS-NG have higher accuracies (≥87.9%) than either UAVSAR (65.6%) or LiDAR (75.9%) for mapping wetland vegetation communities. We also show improved classification accuracy when combining information from multiple sensors. In particular, incorporating AVIRIS-NG and UAVSAR datasets substantially reduced omission errors of wet graminoid and wet shrub classes from 29.6% to 20.5% and from 10.8% to 7.5%, respectively. Combining AVIRIS-NG and LiDAR datasets further improves overall accuracy (+2.2%) for most classifications, especially emergent vegetation, wet graminoid, and wet shrub. The best performing model, using features derived from all three sensors, achieved an overall accuracy of 93.5%. The framework established here can be used to leverage extensive airborne AVIRIS-NG and UAVSAR datasets collected across Alaska and northwest Canada to understand the spatial distribution of Arctic-Boreal wetland vegetation communities.

Remote Sensing of Environment↗

USGS2017

Improved accuracy in quantitative laser-induced breakdown spectroscopy using sub-models

Accurate quantitative analysis of diverse geologic materials is one of the primary challenges faced by the Laser-Induced Breakdown Spectroscopy (LIBS)-based ChemCam instrument on the Mars Science Laboratory (MSL) rover. The SuperCam instrument on the Mars 2020 rover, as well as other LIBS instruments developed for geochemical analysis on Earth or other planets, will face the same challenge. Consequently, part of the ChemCam science team has focused on the development of improved multivariate analysis calibrations methods. Developing a single regression model capable of accurately determining the composition of very different target materials is difficult because the response of an element’s emission lines in LIBS spectra can vary with the concentration of other elements. We demonstrate a conceptually simple “sub-model” method for improving the accuracy of quantitative LIBS analysis of diverse target materials. The method is based on training several regression models on sets of targets with limited composition ranges and then “blending” these “sub-models” into a single final result. Tests of the sub-model method show improvement in test set root mean squared error of prediction (RMSEP) for almost all cases. The sub-model method, using partial least squares regression (PLS), is being used as part of the current ChemCam quantitative calibration, but the sub-model method is applicable to any multivariate regression method and may yield similar improvements.

Spectrochimica Acta Part B: Atomic Spectroscopy↗

USGS2016

Mercury risk to avian piscivores across western United States and Canada

The widespread distribution of mercury (Hg) threatens wildlife health, particularly piscivorous birds. Western North America is a diverse region that provides critical habitat to many piscivorous bird species, and also has a well-documented history of mercury contamination from legacy mining and atmospheric deposition. The diversity of landscapes in the west limits the distribution of avian piscivore species, complicating broad comparisons across the region. Mercury risk to avian piscivores was evaluated across the western United States and Canada using a suite of avian piscivore species representing a variety of foraging strategies that together occur broadly across the region. Prey fish Hg concentrations were size-adjusted to the preferred size class of the diet for each avian piscivore (Bald Eagle = 36 cm, Osprey = 30 cm, Common and Yellow-billed Loon = 15 cm, Western and Clark's Grebe = 6 cm, and Belted Kingfisher = 5 cm) across each species breeding range. Using a combination of field and lab-based studies on Hg effect in a variety of species, wet weight blood estimates were grouped into five relative risk categories including: background (< 0.5 μg/g), low (0.5–1 μg/g), moderate (1–2 μg/g), high (2–3 μg/g), and extra high (> 3 μg/g). These risk categories were used to estimate potential mercury risk to avian piscivores across the west at a 1 degree-by-1 degree grid cell resolution. Avian piscivores foraging on larger-sized fish generally were at a higher relative risk to Hg. Habitats with a relatively high risk included wetland complexes (e.g., prairie pothole in Saskatchewan), river deltas (e.g., San Francisco Bay, Puget Sound, Columbia River), and arid lands (Great Basin and central Arizona). These results indicate that more intensive avian piscivore sampling is needed across Western North America to generate a more robust assessment of exposure risk.

Science of the Total Environment↗

USGS2016

Spatial and temporal variability of contaminants within estuarine sediments and native Olympia oysters: A contrast between a developed and an undeveloped estuary

Chemical contaminants can be introduced into estuarine and marine ecosystems from a variety of sources including wastewater, agriculture and forestry practices, point and non-point discharges, runoff from industrial, municipal, and urban lands, accidental spills, and atmospheric deposition. The diversity of potential sources contributes to the likelihood of contaminated marine waters and sediments and increases the probability of uptake by marine organisms. Despite widespread recognition of direct and indirect pathways for contaminant deposition and organismal exposure in coastal systems, spatial and temporal variability in contaminant composition, deposition, and uptake patterns are still poorly known. We investigated these patterns for a suite of persistent legacy contaminants including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) and chemicals of emerging concern including pharmaceuticals within two Oregon coastal estuaries (Coos and Netarts Bays). In the more urbanized Coos Bay, native Olympia oyster ( Ostrea lurida ) tissue had approximately twice the number of PCB congeners at over seven times the total concentration, yet fewer PBDEs at one-tenth the concentration as compared to the more rural Netarts Bay. Different pharmaceutical suites were detected during each sampling season. Variability in contaminant types and concentrations across seasons and between species and media (organisms versus sediment) indicates the limitation of using indicator species and/or sampling annually to determine contaminant loads at a site or for specific species. The results indicate the prevalence of legacy contaminants and CECs in relatively undeveloped coastal environments highlighting the need to improve policy and management actions to reduce contaminant releases into estuarine and marine waters and to deal with legacy compounds that remain long after prohibition of use. Our results point to the need for better understanding of the ecological and human health risks of exposure to the diverse cocktail of pollutants and harmful compounds that will continue to leach from estuarine sediments over time.

Oregon↗

USGS2016

Mercury in western North America: A synthesis of environmental contamination, fluxes, bioaccumulation, and risk to fish and wildlife

Western North America is a region defined by extreme gradients in geomorphology and climate, which support a diverse array of ecological communities and natural resources. The region also has extreme gradients in mercury (Hg) contamination due to a broad distribution of inorganic Hg sources. These diverse Hg sources and a varied landscape create a unique and complex mosaic of ecological risk from Hg impairment associated with differential methylmercury (MeHg) production and bioaccumulation. Understanding the landscape-scale variation in the magnitude and relative importance of processes associated with Hg transport, methylation, and MeHg bioaccumulation requires a multidisciplinary synthesis that transcends small-scale variability. The Western North America Mercury Synthesis compiled, analyzed, and interpreted spatial and temporal patterns and drivers of Hg and MeHg in air, soil, vegetation, sediments, fish, and wildlife across western North America. This collaboration evaluated the potential risk from Hg to fish, and wildlife health, human exposure, and examined resource management activities that influenced the risk of Hg contamination. This paper integrates the key information presented across the individual papers that comprise the synthesis. The compiled information indicates that Hg contamination is widespread, but heterogeneous, across western North America. The storage and transport of inorganic Hg across landscape gradients are largely regulated by climate and land-cover factors such as plant productivity and precipitation. Importantly, there was a striking lack of concordance between pools and sources of inorganic Hg, and MeHg in aquatic food webs. Additionally, water management had a widespread influence on MeHg bioaccumulation in aquatic ecosystems, whereas mining impacts where relatively localized. These results highlight the decoupling of inorganic Hg sources with MeHg production and bioaccumulation. Together the findings indicate that developing efforts to control MeHg production in the West may be particularly beneficial for reducing food web exposure instead of efforts to simply control inorganic Hg sources.

Science of the Total Environment↗

USGS2018

Association between degradation of pharmaceuticals and endocrine-disrupting compounds and microbial communities along a treated wastewater effluent gradient in Lake Mead

The role of microbial communities in the degradation of trace organic contaminants in the environment is little understood. In this study, the biotransformation potential of 27 pharmaceuticals and endocrine-disrupting compounds was examined in parallel with a characterization of the native microbial community in water samples from four sites variously impacted by urban run-off and wastewater discharge in Lake Mead, Nevada and Arizona, USA. Samples included relatively pristine Colorado River water at the upper end of the lake, nearly pure tertiary-treated municipal wastewater entering via the Las Vegas Wash, and waters of mixed influence (Las Vegas Bay and Boulder Basin), which represented a gradient of treated wastewater effluent impact. Microbial diversity analysis based on 16S rRNA gene censuses revealed the community at this site to be distinct from the less urban-impacted locations, although all sites were similar in overall diversity and richness. Similarly, Biolog EcoPlate assays demonstrated that the microbial community at Las Vegas Wash was the most metabolically versatile and active. Organic contaminants added as a mixture to laboratory microcosms were more rapidly and completely degraded in the most wastewater-impacted sites (Las Vegas Wash and Las Vegas Bay), with the majority exhibiting shorter half-lives than at the other sites or in a bacteriostatic control. Although the reasons for enhanced degradation capacity in the wastewater-impacted sites remain to be established, these data are consistent with the acclimatization of native microorganisms (either through changes in community structure or metabolic regulation) to effluent-derived trace contaminants. This study suggests that in urban, wastewater-impacted watersheds, prior exposure to organic contaminants fundamentally alters the structure and function of microbial communities, which in turn translates into greater potential for the natural attenuation of these compounds compared to more pristine sites.

Arizona, Nevada↗

USGS2022

Stable isotopes provide insight into sources and cycling of N compounds in the Sacramento-San Joaquin Delta, California, USA

River deltas and their diverse array of aquatic environments are increasingly impacted by anthropogenic inputs of nitrogen (N). These inputs can alter the N biogeochemistry of these systems and promote undesirable phenomena including harmful algae blooms and invasive aquatic macrophytes. To examine N sources and biogeochemical processes in the Sacramento-San Joaquin Delta, a river delta located in central California, USA, that is fed primarily by the Sacramento River, we utilized a multi-tracer approach that measured N species concentrations and stable isotope values monthly from April 2011 to November 2012 in samples collected from the channelized mainstem of the Sacramento River, two channelized distributaries of the Sacramento River, and the Cache Slough Complex, a network of Sacramento River tributaries and shallow water wetland habitat. We found that the Sacramento River and its channelized distributaries received N primarily in the form of NH 4 + from treated wastewater effluent and that NH 4 + was lost rapidly while NO 3 − was gained more slowly during subsequent downstream transit, driven by an array of biogeochemical processes whose identities could be constrained via examination of stable isotope values. The Cache Slough Complex, which was characterized by lower net flows and higher water residence times than the Sacramento River and its distributaries, received variable inputs of low conductivity water elevated in NH 4 + from the Sacramento River and higher conductivity water elevated in NO 3 − from landward tributaries. Deviations from expected conservative mixing of these sources were spatially variable but broadly indicative of local inputs of treated wastewater effluent NO 3 − , conversion of Sacramento River NH 4 + to NO 3 − via nitrification, uptake of NH 4 + and NO 3 − by phytoplankton, and remineralization of organic N. These findings highlight both the diversity in N dynamics in anthropogenically impacted river delta environments and the utility of a multi-tracer approach in constraining these processes in such complex systems.

California↗

USGS2004

Reconstruction of the Upper Jurassic Morrison Formation extinct ecosystem - A synthesis

A synthesis of recent and previous studies of the Morrison Formation and related beds, in the context of a conceptual climatic/hydrologic framework, permits reconstruction of the Late Jurassic dinosaurian ecosystem throughout the Western Interior of the United States and Canada. Climate models and geologic evidence indicate that a dry climate persisted in the Western Interior during the Late Jurassic. Early and Middle Kimmeridgian eolian deposits and Late Kimmeridgian alkaline, saline wetland/lacustrine deposits demonstrate that dryness persisted throughout the Kimmeridgian. Tithonian-age coal reflects lower evaporation rates associated with a slight cooling trend, but not a significant climate change. With a subtropical high over the Paleo-Pacific Ocean and atmospheric circulation generally toward the east, moisture carried by prevailing winds "rained out" progressively eastward, leaving the continental interior-and the Morrison depositional basin-dry. Within the basin, high evaporation rates associated with the southerly paleolatitude and greenhouse effects added to the dryness. Consequently, the two main sources of water-groundwater and surface water-originated outside the basin, through recharge of regional aquifers and streams that originated in the western uplands. Precipitation that fell west of the basin recharged aquifers that underlay the basin and discharged in wetlands and lakes in the distal, low-lying part of the basin. Precipitation west of the basin also fed intermittent and scarce perennial streams that flowed eastward. The streams were probably "losing" streams in their upstream reaches, and contributed to a locally raised water table. Elsewhere in the basin, where the floodplain intersected the water table, small lakes dotted the landscape. Seasonal storms, perhaps in part from the Paleo-Gulf of Mexico, brought some precipitation directly to the basin, although it was also subjected to "rain out" en route. Thus, meteoric input to the basin was appreciably less than groundwater and surface water contributions. The terrestrial Morrison ecosystem, which can be likened to a savannah, expanded with the northward retreat of the Late Jurassic Western Interior Seaway. The ecosystem was a complex mosaic, the components of which shifted through time. Riparian environments probably were the most diverse parts of the ecosystem, where a multi-storeyed canopy supported a diverse fauna, from insects to dinosaurs. Equable conditions also existed in wetlands, lakes, and elsewhere on the floodplain when seasonal rainfall brought an herbaceous groundcover to life. Eolian environments and alkaline, saline wetlands were inhospitable to life.Large herbivorous dinosaurs were adapted to this semi-arid landscape. Their size was an adaptive asset based on considerations of food requirements associated with a low metabolism and was also an advantage for migration during drought. Some of the large sauropods were adapted to browsing the higher vegetation associated with riparian environments; others to grazing the herbaceous groundcover on the floodplain and charophytes in the wetlands. The extensive distal wetlands may, in fact, have been refugia for some of these herbivores during the dry season and droughts. Extended periods of drought account for some of the dinosaur death assemblages; yet, the ecosystem could also sustain the most unusual life forms that ever roamed the Earth. ?? 2004 Elsevier B.V. All rights reserved.

Sedimentary Geology↗

USGS2011

Geological effects and implications of the 2010 tsunami along the central coast of Chile

Geological effects of the 2010 Chilean tsunami were quantified at five near-field sites along a 200 km segment of coast located between the two zones of predominant fault slip. Field measurements, including topography, flow depths, flow directions, scour depths, and deposit thicknesses, provide insights into the processes and morphological changes associated with tsunami inundation and return flow. The superposition of downed trees recorded multiple strong onshore and alongshore flows that arrived at different times and from different directions. The most likely explanation for the diverse directions and timing of coastal inundation combines (1) variable fault rupture and asymmetrical slip displacement of the seafloor away from the epicenter with (2) resonant amplification of coastal edge waves. Other possible contributing factors include local interaction of incoming flow and return flow and delayed wave reflection by the southern coast of Peru. Coastal embayments amplified the maximum inundation distances at two sites (2.4 and 2.6 km, respectively). Tsunami vertical erosion included scour and planation of the land surface, inundation scour around the bases of trees, and channel incision from return flow. Sheets and wedges of sand and gravel were deposited at all of the sites. Locally derived boulders up to 1 m in diameter were transported as much as 400 m inland and deposited as fields of dispersed clasts. The presence of lobate bedforms at one site indicates that at least some of the late-stage sediment transport was as bed load and not as suspended load. Most of the tsunami deposits were less than 25 cm thick. Exceptions were thick deposits near open-ocean river mouths where sediment supply was abundant. Human alterations of the land surface at most of the sites provided opportunities to examine some tsunami effects that otherwise would not have been possible, including flow histories, boulder dispersion, and vegetation controls on deposit thickness.

Central Coast↗

USGS2013

Effects of canopy tree species on belowground biogeochemistry in a lowland wet tropical forest

Tropical rain forests are known for their high biological diversity, but the effects of plant diversity on important ecosystem processes in this biome remain unclear. Interspecies differences in both the demand for nutrients and in foliar and litter nutrient concentrations could drive variations in both the pool sizes and fluxes of important belowground resources, yet our understanding of the effects and importance of aboveground heterogeneity on belowground biogeochemistry is poor, especially in the species-rich forests of the wet tropics. To investigate the effects of individual tree species on belowground biogeochemical processes, we used both field and laboratory studies to examine how carbon (C), nitrogen (N), and phosphorus (P) cycles vary under nine different canopy tree species – including three legume and six non-legume species – that vary in foliar nutrient concentrations in a wet tropical forest in southwestern Costa Rica. We found significant differences in belowground C, N and P cycling under different canopy tree species: total C, N and P pools in standing litter varied by species, as did total soil and microbial C and N pools. Rates of soil extracellular acid phosphatase activity also varied significantly among species and functional groups, with higher rates of phosphatase activity under legumes. In addition, across all tree species, phosphatase activity was significantly positively correlated with litter N/P ratios, suggesting a tight coupling between relative N and P inputs and resource allocation to P acquisition. Overall, our results suggest the importance of aboveground plant community composition in promoting belowground biogeochemical heterogeneity at relatively small spatial scales.

Soil Biology and Biochemistry↗

USGS2022

The influence of soil development on the depth distribution and structure of soil microbial communities.

Although it has been shown that the interaction of climate and time shape the dynamics of soil organic matter (SOM) storage and preservation in soil, the role of soil microbial communities in this dynamic remains unclear. Microbial communities are present throughout soil profiles and likely play critical roles in SOM and nutrient cycling, however the influence of other factors such as soil development (i.e., age) and the composition SOM on microbial community variation with depth has yet to be quantified. Improving our understanding of the relationship between soil development, soil depth, and microbial communities may provide insight to the critical role they play in cycling and preservation of SOM, as well as more mechanistic predictions of the response of soil communities to change, such as landscape-scale changes in available moisture or temperature regimes. Here we compare soils spanning a soil age by climate gradient (i.e., climo-chronosequence) to better understand the mechanisms which influence soil microbial community structure and the molecular composition of SOM. While we observed little depth-dependence in metrics of microbial community structure (i.e., composition, diversity, dissimilarity) across the range of soil development under a wetter climate, we found significant depth-dependent changes in community metrics under a drier climate, which became more pronounced as soils became older. This shift in bacterial and archaeal community structure and diversity is most apparent below a clay-rich argillic horizon formed in the older, drier soils. The molecular composition of SOM as measured by high resolution mass spectrometry (i.e., FTICR MS) also exhibited similar shifts in composition with soil depth and age. Our results highlight how soil moisture shapes the interaction of soil development, SOM, and microbial community composition. Differences in the moisture regime between our two study sites drives differences in biogeochemical depth gradients and subsequent variation in soil microbes and SOM. This suggests that knowledge of not just the pedogenic trajectory of soil development, but also the spatial position relative to distinct pedogenic features, are important for explaining variations in the depth-dependencies of microbial communities and associated SOM.

California↗