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At least 775 records · Page 43Linked to original sources
USGS2023

Multi-decadal erosion rates from glacierized watersheds on Mount Baker, Washington, USA, reveal topographic, climatic, and lithologic controls on sediment yields

Understanding land surface change in and sediment export out of proglacial landscapes is critical for understanding geohazard and flood risks over engineering timescales and characterizing landscape evolution over geomorphic timescales. We used automated Structure from Motion software to process historical aerial photographs and, with modern lidar data, generated a high-resolution DEM time series with coverage over 10 glacierized watersheds on Mount Baker, Washington, USA for the time period between 1947 and 2015. We measured basin-wide sediment yields and sediment redistribution on hillslopes and in stream channels. Slopes within most measured erosion sites are above theoretical and observed debris-flow thresholds. We observed significant erosion of hillslopes and limited deposition on hillslopes and in stream channels. Sediment delivery ratios during time periods with net erosion averaged 0.73. We determined, consistent with previous field observations, that debris flows originating from moraines are a primary erosion mechanism in proglacial zones on Mount Baker. Time series measurements indicate that temporal variability in erosion rates is associated with climate oscillations, with higher erosion rates during cooler-wetter periods. Basin-wide sediment yield is positively correlated with lithology (r 2 = 0.54), hillslope angle (r 2 = 0.52), drainage area (r 2 = 0.82), and negatively correlated with stream channel slope (r 2 = 0.67). Topographic differences between high and low yielding basins indicate that spatial variability in erosion on Mount Baker is sensitive to Pleistocene and Holocene glacial and volcanic activity. Specific sediment yields in six basins averaged 4600 ton/km 2 /yr, consistent with global measurements in glacierized catchments. Specific sediment yield decreased with increasing basin area, with total loads in the downstream main stem Nooksack River estimated between 480 and 820 ton/km 2 /yr. Proglacial sediment yields account for between 18 and 32 % of total sediment load in the main stem Nooksack River and exceed contributions by bluff and terrace erosion, which account for between 8 and 13 % of total load. Our findings indicate that erosion in glacierized basins is sensitive to decadal climate oscillations and that high proglacial sediment yields provide an important contribution to river systems downstream, particularly in catchments where upland topography and lithology is favorable.

Washington↗
USGS2013

Short-term variability of 7 Be atmospheric deposition and watershed response in a Pacific coastal stream, Monterey Bay, California, USA

Beryllium-7 is a powerful and commonly used tracer for environmental processes such as watershed sediment provenance, soil erosion, fluvial and nearshore sediment cycling, and atmospheric fallout. However, few studies have quantified temporal or spatial variability of 7 Be accumulation from atmospheric fallout, and parameters that would better define the uses and limitations of this geochemical tracer. We investigated the abundance and variability of 7 Be in atmospheric deposition in both rain events and dry periods, and in stream surface-water samples collected over a ten-month interval at sites near northern Monterey Bay (37°N, 122°W) on the central California coast, a region characterized by a rainy winters, dry summers, and small mountainous streams with flashy hydrology. The range of 7 Be activity in rainwater samples from the main sampling site was 1.3–4.4 Bq L −1 , with a mean (±standard deviation) of 2.2 ± 0.9 Bq L −1 , and a volume-weighted average of 2.0 Bq L −1 . The range of wet atmospheric deposition was 18–188 Bq m −2 per rain event, with a mean of 72 ± 53 Bq m −2 . Dry deposition fluxes of 7 Be ranged from less than 0.01 up to 0.45 Bq m −2 d −1 , with an estimated dry season deposition of 7 Bq m −2 month −1 . Annualized 7 Be atmospheric deposition was approximately 1900 Bq m −2 yr −1 , with most deposition via rainwater (>95%) and little via dry deposition. Overall, these activities and deposition fluxes are similar to values found in other coastal locations with comparable latitude and Mediterranean-type climate. Particulate 7 Be values in the surface water of the San Lorenzo River in Santa Cruz, California, ranged from <0.01 Bq g −1 to 0.6 Bq g −1 , with a median activity of 0.26 Bq g −1 . A large storm event in January 2010 characterized by prolonged flooding resulted in the entrainment of 7 Be-depleted sediment, presumably from substantial erosion in the watershed. There were too few particulate 7 Be data over the storm to accurately model a 7 Be load, but the results suggest enhanced watershed export of 7 Be from small, mountainous river systems compared to other watershed types.

California↗
USGS2019

Assessment of larval fish assemblages and nursery habitat in the St. Clair River delta

The St. Clair River delta, part of the St. Clair-Detroit River System (SCDRS), is the most fished coastal wetland area in the Laurentian Great Lakes and provides nursery habitat for a variety of fish species; however, few large-scale surveys of larval fish have been performed within the delta since the 1980s. Larval fish, zooplankton, and aquatic plants were sampled at 20 sites from May through July in 2010 and 2011 to characterize shallow channel and backwater delta habitats used by fish. The larval fish assemblage was sampled using active and passive gears (conical nets and light traps) and was dominated by Cyprinidae, Catostomidae, and Gobiidae. The microzooplankton assemblage was composed of rotifers, copepod nauplii, and Dreissena spp. veligers, while the macrozooplankton assemblage was composed of mostly cyclopoids and harpacticoids in May and cladocerans later in the season. Scirpus spp. dominated the plant assemblage in June and was replaced by Chara spp. in July. Seasonal compositional shifts were evident for larval fish, zooplankton, and plant assemblages, and greater densities of microzooplankton and cladocerans were typically found in backwater areas. Assemblage compositions were comparable to those in historical surveys but invasive Gobiidae and Dreissena spp. veligers now represent substantial proportions of the larval fish and zooplankton assemblages, respectively. Due to the high connectivity and advective nature of the SCDRS, understanding the larval fish assemblage dynamics of the delta can help inform estimates of system productivity.

Michigan↗
USGS2025

Freshwater gastropod (Mollusca: Gastropoda) assemblages, habitat, and the first detection of an invasive gastropod species in two large, dreissenid-influenced, connecting rivers

Native freshwater gastropods are a highly diverse and imperiled group of mollusks in North America and are influenced by a growing number of problematic invasive species. Consequently, there has been an increased need for understanding aquatic gastropod assemblages throughout North America to implement conservation and management strategies. In the Laurentian Great Lakes, gastropod surveys have been sparse, and most surveys have focused on invasive species. To investigate gastropod assemblages in two large connecting rivers of the Great Lakes, the Detroit and St. Clair rivers, benthic surveys were conducted in 2019 and 2021. Sites in the Detroit River (n = 56) and the St. Clair River (n = 51) were surveyed using petite PONAR grabs from which gastropod shells were identified and quantified to family or a group of two combined families. In both the Detroit and St. Clair rivers, the gastropod family Pleuroceridae (37 % and 56 % total composition, respectively) and combined families Amnicolidae + Hydrobiidae (42 % and 23 % total composition, respectively) contributed the most to overall gastropod composition. Invasive Potamopyrgus antipodarum shells were identified at 4 (7 %) Detroit River sites and 10 (20 %) St. Clair River sites and represent the first documented occurrence in the Detroit River. Although this study was limited to quantifying densities based on shells and cannot assume live-collected snail densities, these results provide a baseline knowledge of the gastropod assemblages and habitat use in these two large river systems which can be used to implement conservation and management strategies.

Detroit River, St. Clair River↗
USGS2025

Detroit River becoming a crucible for boundary organization experimentation

The Detroit River has a long history of human use and abuse, resulting in public outcry over water pollution and resource degradation. This public outcry helped catalyze the enactment of many laws and the Canada-U.S. Great Lakes Water Quality Agreement which led to enhanced research, monitoring, and water pollution control. As pollution from industries and municipal wastewater treatment plants came under control and progress was made in management of single species, the focus shifted to a more comprehensive ecosystem approach that accounted for all the sources of pollution and targeted restoring ecosystem health with resilience. Over time, the Detroit River became a “proving ground” or crucible for experimenting with boundary organizations to overcome geographical, political, institutional, and disciplinary boundaries and strengthen science-policy-management linkages for ecosystem-based management. This study identified 15 boundary organizations functioning in the Detroit River watershed and evaluated two case studies – St. Clair-Detroit River System Initiative and State of the Strait Conferences. Key lessons learned from this study include: 1) establishing boundary organizations, promoting cooperative learning, and building capacity for boundary-spanning are essential for use of an ecosystem approach; 2) boundary spanning requires specific skills, experience, and improved linkages between research and practice; 3) the 15 boundary organizations provide a unique opportunity to collaborate in a community of practice to share knowledge, foster cooperative learning, enhance problem-solving, build trust, and demonstrate leadership; and 4) continued actionable science, investment in capacity building, and cooperative learning are essential to meet long-term goals of sustainability.

Detroit River↗
USGS2020

Lava–water interaction and hydrothermal activity within the 2014–2015 Holuhraun Lava Flow Field, Iceland

Lava that erupted during the 2014–2015 Holuhraun eruption in Iceland flowed into a proglacial river system, resulting in aqueous cooling of the lava and an ephemeral hydrothermal system. We carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time, using thermocouple measurements and data-logging sensors. The heat loss rate from advection through this hydrothermal system in August 2015 was ~5.5 × 10 8 W; since eruption, aqueous cooling likely accounted for ~1% of the total heat loss from the lava. This estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface, and thus is a lower bound. Near the terminus of the flow, advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow. Our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava–water interactions more generally. We also provide detailed methods for simple, low-cost monitoring of similar instances in the future.

Holuhraun Lava Flow Field↗
USGS2013

A step decrease in sediment concentration in a highly modified tidal river delta following the 1983 El Niño floods

Anthropogenic activities in watersheds can have profound effects on sediment transport through river systems to estuaries. Disturbance in a watershed combined with alterations to the hydro-climatologic regime may result in changes to the sediment flux, and exacerbate the impacts of extreme events (such as large-magnitude floods) on sediment transport. In the San Francisco Estuary, suspended sediment has been declining over the past 30 years as a result of declining sediment supply, contributing to dramatic changes in the ecology and geomorphology of the estuary. However, the decline has not been gradual. Recent observations of an abrupt decrease in suspended sediments in the San Francisco Bay have been explained by a model that suggests that the step change has occurred due to exceedance of a sediment regulation threshold that triggered the change from a sediment transport regime to a supply-limited system. We investigated structural changes in the historical record of total suspended solids (TSS) concentration measured in the upper estuary to verify the model predictions. TSS in the upper estuary exhibited an abrupt step decrease in 1983 corresponding to the record-high winter and summer flows from the 1982 to 1983 El Niño event. After this step change, TSS concentrations had a significant declining trend despite subsequent near-record high flows. The abrupt change in TSS followed by the declining trend provides evidence for the hypothesis of sediment supply limitation in the San Francisco Estuary.

California↗
USGS2014

Pluvial lakes in the Great Basin of the western United States: a view from the outcrop

Paleo-lakes in the western United States provide geomorphic and hydrologic records of climate and drainage-basin change at multiple time scales extending back to the Miocene. Recent reviews and studies of paleo-lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the Great Basin. In this review, emphasis is placed on equally important studies of lake history during the past ∼30 years that were derived from outcrop exposures and geomorphology, in some cases combined with cores. Outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate. Outcrops and landforms can yield direct evidence of lake level, facies changes that record details of lake-level fluctuations, and geologic events such as catastrophic floods, drainage-basin changes, and isostatic rebound. Cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level, water temperature and chemistry, and ecological conditions in the surrounding landscape. However, proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess, and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core. The best evidence for documenting absolute lake-level changes lies within the shore, nearshore, and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell. We review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors. Lake-level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial-scale details of fluctuations during the late Pleistocene and Holocene. Outcrop studies have documented the integration histories of several important drainage basins, including the Humboldt, Amargosa, Owens, and Mojave river systems, that have evolved since the Miocene within the active tectonic setting of the Great Basin; these histories have influenced lake levels in terminal basins. Many pre-late Pleistocene lakes in the western Great Basin were significantly larger and record wetter conditions than the youngest lakes. Outcrop-based lake-level data provide important checks on core-based proxy interpretations; we discuss four such comparisons. In some cases, such as for Lakes Owens and Manix, outcrop and core data synthesis yields stronger and more complete records; in other cases, such as for Bonneville and Lahontan, conflicts point toward reconsideration of confounding factors in interpretation of core-based proxies.

Great Basin↗
USGS2007

Sources and temporal dynamics of arsenic in a New Jersey watershed, USA

We examined potential sources and the temporal dynamics of arsenic (As) in the slightly alkaline waters of the Wallkill River, northwestern New Jersey, where violations of water-quality standards have occurred. The study design included synoptic sampling of stream water and bed sediments in tributaries and the mainstem, hyporheic-zone/ground water on the mainstem, and seasonal and diurnal sampling of water at selected mainstem sites. The river valley is bordered by gneiss and granite highlands and shale lowlands and underlain by glacial deposits over faulted dolomites and the Franklin Marble. Ore bodies in the Marble, which have been mined for rare Zn ore minerals, also contain As minerals. Tributaries, which drain predominantly forested and agricultural land, contributed relatively little As to the river. The highest concentrations of As (up to 34 μg/L) emanated from the outlet of man-made Lake Mohawk at the river's headwaters; these inputs varied substantially with season—high during warm months, low during cold months, apparently because of biological activity in the lake. Dissolved As concentrations were lower (3.3 μg/L) in river water than those in ground water discharging into the riverbed (22 μg/L) near the now-closed Franklin Mine. High total As concentrations (100–190 mg/kg) on the < 0.63 μm fraction of bed sediments near the mine apparently result from sorption of the As in the ground-water discharge as well as from the As minerals in the streambed. As concentrations in river water were diluted during high stream flow in fall, winter and spring, and concentrated during low flow in summer. In unfiltered samples from a wetlands site, diurnal cycles in trace-element concentrations occurred; As concentrations appeared to peak during late afternoon as pH increased, but Fe, Mn, and Zn concentrations peaked shortly after midnight. The temporal variability of As and its presence at elevated concentrations in ground water and sediments as well as streamwater demonstrate the importance of (1) sampling a variety of media and (2) determining the time scales of As variability to fully characterize its passage through a river system.

New Jersey↗
USGS2023

Understanding ecological response to physical characteristics in side channels of a large floodplain-river ecosystem

Side channels in large floodplain rivers serve a variety of important ecological roles, particularly in reaches where habitat conditions have been degraded or diminished. We developed hypotheses regarding side channel ecological structure whereby we expected species richness of young-of-year fishes to generally be higher in shallower, more physically heterogeneous side channels with lower velocities, with differences based on reproductive guild. We also hypothesized species richness of adult fishes to be higher in side channels with greater heterogeneity that could support diverse foraging resources and provide refugia during extreme flow conditions. To test these hypotheses, we used a 28-year fish community dataset from the Upper Mississippi and Illinois Rivers. Across six study reaches, we assessed metrics of side channel physical size, heterogeneity, and connectivity that were hypothesized to explain variance of fish community response, while accounting for site-level factors across 52 side channels using multilevel models. We then used these side channel-level characteristics in a K-means cluster analysis to classify 1126 side channels across 32 reaches of the river system. Our results indicated that the relative explanatory contributions of physical metrics varied by response variable, providing varying evidence in support of our hypotheses, and indicating that different forms of heterogeneity matter in different ways. Side channel-level factors were more explanatory of fish community responses in side channels of upstream reaches compared to downstream reaches and percent wet forest was the most explanatory side channel-level factor of fish community responses across all models. Our classification of side channels indicated strong spatial contrasts in the abundance and diversity of side channels across reaches. Scaling up to understand how the diversity and abundance of different types of side channels contributes to landscape-scale ecological functions and processes would be useful for establishing targets for reach-scale physical heterogeneity.

Upper Mississippi River and Illinois River↗
USGS2007

Chapter 8 Tool for monitoring hydrophilic contaminants in water: polar organic chemical integrative sampler (POCIS)

The development of the polar organic chemical integrative sampler (POCIS) provides environmental scientists and policy makers a tool for assessing the presence and potential impacts of the hydrophilic component of these organic contaminants. The POCIS provides a means for determining the time-weighted average (TWA) concentrations of targeted chemicals that can be used in risk assessments to determine the biological impact of hydrophilic organic compounds (HpOCs) on the health of the impacted ecosystem. Field studies have shown that the POCIS has advantages over traditional sampling methods in sequestering and concentrating ultra-trace to trace levels of chemicals over time resulting in increased method sensitivity, ability to detect chemicals with a relatively short residence time or variable concentrations in the water, and simplicity in use. POCIS extracts can be tested using bioassays and can be used in organism dosing experiments for determining toxicological significance of the complex mixture of chemicals sampled. The POCIS has been successfully used worldwide under various field conditions ranging from stagnant ponds to shallow creeks to major river systems in both fresh and brackish water.

Comprehensive Analytical Chemistry↗
USGS2000

Beryllium-7 as a tracer of short-term sediment deposition and resuspension in the Fox River Wisconsin

Short-term (∼monthly) sediment deposition and resuspension rates of surficial bed sediments in two PCB-laden impoundments on the Fox River, WI, were determined in the summer and fall of 1998 using 7 Be, a naturally occurring radioisotope produced in the atmosphere. Decay-corrected activities and inventories of 7 Be were measured in bed sediment and in suspended particles. Beryllium-7 activities generally decreased with depth in the top 5−10 cm of sediments and ranged from undetectable to ∼0.9 pCi cm - 3 . Inventories of 7 Be, calculated from the sum of activities from all depths, ranged from 0.87 to 3.74 pCi cm - 2 , and the values covaried between sites likely reflecting a common atmospheric input signal. Activities of 7 Be did not correlate directly with rainfall. Partitioning the 7 Be flux into “new” and “residual” components indicated that net deposition was occurring most of the time during the summer. Net erosion, however, was observed at the upstream site from the final collection in the fall. This erosion event was estimated to have removed 0.10 g (cm of sediment) - 2 , corresponding to ∼0.5 cm of sediment depth, and ∼6−10 kg of polychlorinated biphenyls (PCBs) over the whole deposit. Short-term accumulation rates were up to ∼130 times higher than the long-term rates calculated from 137 Cs profiles, suggesting an extremely dynamic sediment transport environment, even within an impounded river system.

Environmental Science & Technology↗
USGS2004

Biotransformation of tributyltin to tin in freshwater river-bed sediments contaminated by an organotin release

The largest documented release of organotin compounds to a freshwater river system in the United States occurred in early 2000 in central South Carolina. The release consisted of an unknown volume of various organotin compounds such tetrabutyltin (TTBT), tributyltin (TBT), tetraoctyltin (TTOT), and trioctyl tin (TOT) and resulted in a massive fish kill and the permanent closures of a municipal wastewater treatment plant and a local city's only drinking-water intake. Initial sampling events in 2000 and 2001 indicated that concentrations of the ecologically toxic TTBT and TBT were each greater than 10 000 ??g/kg in surface-water bed sediments in depositional areas, such as lakes and beaver ponds downstream of the release. Bed-sediment samples collected between 2001 and 2003, however, revealed a substantial decrease in bed-sediment organotin concentrations and an increase in concentrations of degradation intermediate compounds. For example, in bed sediments of a representative beaver pond located about 1.6 km downstream of the release, total organotin concentrations [the sum of TTBT, TBT, and the TBT degradation intermediates dibutyltin (DBT) and monobutyltin (MBT)] decreased from 38 670 to 298 ??g/kg. In Crystal Lake, a large lake about 0.4 km downstream from the beaver pond, total organotin concentrations decreased from 28 300 to less than 5 ??g/kg during the same time period. Moreover, bed-sediment inorganic tin concentrations increased from pre-release levels of less than 800 to 32 700 ??g/kg during this time. These field data suggest that the released organotin compounds, such as TBT, are being transformed into inorganic tin by bed-sediment microbial processes. Microcosms were created in the laboratory that contained bed sediment from the two sites and were amended with tributyltin (as tributyltin chloride) under an ambient air headspace and sacrificially analyzed periodically for TBT, the biodegradation intermediates DBT and MBT, and tin. TBT concentrations decreased faster [half-life (t1/2) = 28 d] in the organic-rich sediments (21.5%) that characterized the beaver pond as compared to the slower (t1/2 = 78 d) degradation rate in the sandy, organic-poor, sediments (0.43%) of Crystal Lake. Moreover, the concentration of inorganic tin increased in microcosms containing bed sediments from both locations. These field and laboratory results suggest that biotransformation of the released organotins, in particular the ecologically detrimental TBT, does occur in this fresh surface-water system impacted with high concentrations of neat organotin compounds.

Environmental Science & Technology↗
USGS2006

New insights into Arctic paleogeography and tectonics from U-Pb detrital zircon geochronology

To test existing models for the formation of the Amerasian Basin, detrital zircon suites from 12 samples of Triassic sandstone from the circum-Arctic region were dated by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS). The northern Verkhoyansk (NE Russia) has Permo-Carboniferous (265-320 Ma) and Cambro-Silurian (410-505 Ma) zircon populations derived via river systems from the active Baikal Mountain region along the southern Siberian craton. Chukotka, Wrangel Island (Russia), and the Lisburne Hills (western Alaska) also have Permo-Carboniferous (280-330 Ma) and late Precambrian-Silurian (420-580 Ma) zircons in addition to Permo-Triassic (235-265 Ma), Devonian (340-390 Ma), and late Precambrian (1000-1300 Ma) zircons. These ages suggest at least partial derivation from the Taimyr, Siberian Trap, and/ or east Urals regions of Arctic Russia. The northerly derived Ivishak Formation (Sadlerochit Mountains, Alaska) and Pat Bay Formation (Sverdrup Basin, Canada) are dominated by Cambrian-latest Precambrian (500-600 Ma) and 445-490 Ma zircons. Permo-Carboniferous and Permo-Triassic zircons are absent. The Bjorne Formation (Sverdrup Basin), derived from the south, differs from other samples studied with mostly 1130-1240 Ma and older Precambrian zircons in addition to 430-470 Ma zircons. The most popular tectonic model for the origin of the Amerasian Basin involves counterclockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic margin. The detrital zircon data suggest that the Chukotka part of the microplate originated closer to the Taimyr and Verkhoyansk, east of the Polar Urals of Russia, and not from the Canadian Arctic. Copyright 2006 by the American Geophysical Union.

Tectonics↗
USGS2008

Seasonal and spatial variability in dissolved organic matter quantity and composition from the Yukon River basin, Alaska

[1] The seasonal and spatial variability of dissolved organic matter (DOM) quantity and chemical composition were investigated in the Yukon River basin of Alaska, United States, and northwestern Canada. Dissolved organic carbon (DOC), chromophoric DOM (CDOM), and dissolved lignin phenols were measured across a range of source waters and the seasonal hydrograph. Strong relationships were determined between CDOM and both DOC and lignin phenols, highlighting the potential for deriving detailed spatial and temporal distributions of DOM composition from CDOM monitoring. Maximum concentrations of measured parameters were observed during the spring flush, when DOM had a remarkably high content of aromatic vascular plant material derived from surface soil and litter layers. A larger portion of riverine DOM was attributed to vascular plant sources than previously believed by utilizing representative vegetation leachates and a soil pore water as end‐members. In combination with recent studies highlighting export of young, labile DOM during the spring flush in northern high‐latitude river systems, our results suggest riverine DOM is less degraded and more labile than previously thought with clear ramifications for its biomineralization or photo‐oxidation in marine environments.

Global Biogeochemical Cycles↗
USGS2018

Ecological changes in the nannoplankton community across a shelf transect during the onset of the Paleocene-Eocene Thermal Maximum

Warming and other environmental changes during the Paleocene‐Eocene thermal maximum (PETM) led to profound shifts in the composition and structure of nannoplankton assemblages. Here we analyze the nature of these changes in expanded records from the Cambridge‐Dorchester and Mattawoman Creek‐Billingsley Road cores in Maryland. These cores comprise part of a transect of five paleoshelf cores from Maryland and New Jersey. We integrate multivariate analysis of assemblage data with proxy data to revise understanding of the paleoecological affinities of key species. In particular, Discoaster and Fasciculithus are interpreted as thermophiles without adaptation to particular nutrient levels, while Hornibrookina is considered an opportunist adapted to highly variable nearshore environments. Together the cores show consistent margin‐wide changes across the onset of the PETM, including a pulse of preevent warming, possibly combined with lower salinity, high seasonality, or increased turbidity. The event itself was characterized by continued warming and eutrophication across the paleoshelf. The Maryland sites experienced higher environmental variability as a result of their proximity to large river systems.

Paleoceanography and Paleoclimatology↗
USGS2022

The influence of drying on the aeolian transport of river-sourced sand

Transgression and regression of water levels (stages) have impacted the evolution of aeolian landforms and sedimentary deposits throughout geologic history. We studied this phenomenon over a five-day period of reduced flow on the Colorado River in Grand Canyon National Park, AZ, USA, in March 2021. These transient low flows exposed river-channel sand deposits to the air, causing progressive desiccation (drying) and thereby making these deposits susceptible to aeolian transport. We measured aeolian threshold friction velocities ( u *t ) for sand saltation and PM10 dust emissions, as well as other characteristics, on a subaerially exposed sandbar and downwind aeolian dunefield during each day of the low river flow. The sandbar transitioned from supply-limited to transport-limited aeolian sediment transport conditions during the regression in river water stage. A possible tipping point between the two transport conditions occurred approximately 48 hours after the drop in river flow. The empirically measured u *t decreased as the sandbar sediment dried with increased subaerial exposure time. Theoretical estimates and empirical measurements of u *t corresponded closely on the aeolian dunefield and on the sandbar when it was drier during the third and fourth day of the experiment. Eighty-seven percent of the variability in u *t was explained by empirical models that provide practical estimates of aeolian transport potential of subaerial river sediment deposits using monitoring data that are commonly available in this and other river systems. The work provides theoretical insight into the response of aeolian processes to sediment supply changes driven by periods of anthropogenic activity, drought, and climate change.

Arizona↗
USGS2025

High resolution mapping of submerged sediment size and suitable salmon spawning habitat using topo-bathymetric Lidar in the Santiam Basin, Oregon

The distribution of river-bed grain sizes plays a foundational role in river morphology and ecology. River-bed grain size is a key driver of channel form and process, and has first order effects on aquatic macroinvertebrate assemblages, fish nesting, and biogeochemical processes. Despite this importance, tools to spatially quantify grain-size distributions, particularly submerged grain-size distributions, are lacking. Efforts to address this knowledge gap include developing optical and sonographic tools, however, these approaches have limitations, especially in shallow rivers and over large spatial extents. This study quantifies submerged grain size at high resolution (1 m 2 ) across 260 km of geomorphically diverse river corridors in the Santiam River Basin, Oregon, by pairing bathymetric Lidar point clouds with georeferenced pebble counts. Results suggest that derivatives of Lidar point clouds are able to accurately estimate measured median grain size across seven of the eight river reaches investigated, including reaches above and below high-head dams. Spatial analysis of predicted grain-sizes in the context of Chinook salmon spawning habitat suggests that suitable size sediment patches in the upper, unregulated reaches the study basin is typically small and unorganized. In contrast, the larger rivers downstream of high-head dams typically have larger areas of suitable spawning gravels. This method may be useful for quantification of fish and macroinvertebrates habitats, surface grain-size metrics for sediment transport models, and monitoring of natural and anthropogenic changes in river systems.

Oregon↗