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At least 811 records · Page 45Linked to original sources
USGS2010

Effects of temperature on silicate weathering: Solute fluxes and chemical weathering in a temperate rain forest watershed, Jamieson Creek, British Columbia

Chemical weathering of silicate minerals has long been known as a sink for atmospheric CO 2 , and feedbacks between weathering and climate are believed to affect global climate. While warmer temperatures are believed to increase rates of weathering, weathering in cool climates can be accelerated by increased mineral exposure due to mechanical weathering by ice. In this study, chemical weathering of silicate minerals is investigated in a small temperate watershed. The Jamieson Creek watershed is covered by mature coniferous forest and receives high annual precipitation (4000 mm), mostly in the form of rainfall, and is underlain by quartz diorite bedrock and glacial till. Analysis of pore water concentration gradients indicates that weathering in hydraulically unsaturated ablation till is dominated by dissolution of plagioclase and hornblende. However, a watershed scale solute mass balance indicates high relative fluxes of K and Ca, indicating preferential leaching of these solutes possibly from the relatively unweathered lodgement till. Weathering rates for plagioclase and hornblende calculated from a watershed scale solute mass balance are similar in magnitude to rates determined using pore water concentration gradients. When compared to the Rio Icacos basin in Puerto Rico, a pristine tropical watershed with similar annual precipitation and bedrock, but with dissimilar regolith properties, fluxes of weathering products in stream discharge from the warmer site are 1.8 to 16.2-fold higher, respectively, and regolith profile-averaged plagioclase weathering rates are 3.8 to 9.0-fold higher. This suggests that the Arrhenius effect, which predicts a 3.5- to 9-fold increase in the dissolution rate of plagioclase as temperature is increased from 3.4° to 22 °C, may explain the greater weathering fluxes and rates at the Rio Icacos site. However, more modest differences in K and Ca fluxes between the two sites are attributed to accelerated leaching of those solutes from glacial till at Jamieson Creek. Our findings suggest that under conditions of high rainfall and favorable topography, weathering rates of silicate minerals in warm tropical systems will tend to be higher than in cool temperate systems, even if the temperate system is has been perturbed by an episode of glaciation that deposits regolith high in fresh mineral surface area.

British Columbia↗
USGS2024

Tire-derived contaminants 6PPD and 6PPD-Q: Analysis, sample handling, and reconnaissance of United States stream exposures

The environmental ubiquity of tire and road wear particles (TRWP) underscores the need to understand the occurrence, persistence, and environmental effects of tire-related chemicals in aquatic ecosystems. One such chemical is 6PPD-quinone (6PPD-Q), a transformation product of the tire antioxidant 6PPD. In urban stormwater runoff 6PPD-Q can exceed acute toxicity thresholds for several salmonid species and is being implicated in significant coho salmon losses in the Pacific Northwest. There is a critical need to understand the prevalence of 6PPD-Q across watersheds to identify habitats heavily affected by TRWPs. We conducted a reconnaissance of 6PPD and 6PPD-Q in surface waters across the United States from sites (N = 94) with varying land use (urban, agricultural, and forested) and streamflow to better understand stream exposures. A rapid, low-volume direct-inject, liquid chromatography mass spectrometry method was developed for the quantitation of 6PPD-Q and screening for 6PPD. Laboratory holding times, bottle material, headspace, and filter materials were investigated to inform best practices for 6PPD-Q sampling and analysis. Glass bottles with PTFE-lined caps minimized sorption and borosilicate glass fiber filters provided the highest recovery. 6PPD-Q was stable for at least 5 months in pure laboratory solutions and for 75 days at 5 °C with minimal headspace in the investigated surface water and stormwaters. Results also indicated samples can be frozen to extend holding times. 6PPD was not detected in any of the 526 analyzed samples and there were no detections of 6PPD-Q at agricultural or forested sites. 6PPD-Q was frequently detected in stormwater (57%, N = 90) and from urban impacted sites (45%, N = 276) with concentrations ranging from 0.002 to 0.29 μg/L. The highest concentrations, above the lethal level for coho salmon, occurred during stormwater runoff events. This highlights the importance of capturing episodic runoff events in urban areas near ecologically relevant habitat or nursery grounds for sensitive species.

Chemosphere↗
USGS2005

Mineralogy and geochemistry of a Late Permian coal in the Dafang Coalfield, Guizhou, China: Influence from siliceous and iron-rich calcic hydrothermal fluids

This paper describes the influence of siliceous and iron-rich calcic low-temperature hydrothermal fluids (LTHF) on the mineralogy and geochemistry of the Late Permian No. 11 Coal (anthracitic, Rr =2.85%) in the Dafang Coalfield in northwestern Guizhou Province, China. The No. 11 Coal has high contents of vein ankerite (10.2 vol.%) and vein quartz (11.4 vol.%), with formation temperatures of 85 and 180 ??C, respectively, indicating that vein ankerite and vein quartz were derived from low-temperature calcic and siliceous hydrothermal fluids in two epigenetic episodes. The vein quartz appears to have formed earlier than vein ankerite did, and at least three distinct stages of ankerite formation with different Ca/Sr and Fe/Mn ratios were observed. The two types of mineral veins are sources of different suites of major and trace metals. Scanning electron microscope and sequential extraction studies show that, in addition to Fe, Mg, and Ca, vein ankerite is the dominant source of Mn, Cu, Ni, Pb, and Zn in the coal, and the contents of these five elements are as high as 0.09% and 74.0, 33.6, 185, and 289 ??g/g, respectively. In contrast, vein quartz is the main carrier mineral for platinum-group elements (PGEs) Pd, Pt, and Ir in the coal, and the contents of Pd, Pt, and Ir are 1.57, 0.15, and 0.007 ??g/g, respectively. Sequential extraction showed a high PGE content in the silicate fraction, up to 10.4 ??g/g Pd, 1.23 ??g/g Pt, and 0.05 ??g/g Ir, respectively. It is concluded that the formation of ankerite and quartz and the anomalous enrichment of trace elements in the No. 11 Coal in the Dafang Coalfield, Guizhou, result from the influx of calcic and siliceous low-temperature hydrothermal fluids. ?? 2004 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2004

A conceptual model for river water and sediment dispersal in the Santa Barbara Channel, California

The ephemeral Santa Clara River delivers large amounts of freshwater and sediment to the eastern Santa Barbara Channel during brief, episodic discharge events. This discharge into the channel was characterized here with shipboard measurements during floods of 1997 and 1998. Within approximately 1-km of the river mouth, the river discharge quickly stratifies into a freshened, turbid surface plume and a bottom nephloid layer. Observations immediately off the Santa Clara River mouth on a peak day of river discharge revealed that sediment rapidly settled from the freshened surface waters, as suspended sediment in the freshened surface plume contained only ???6% of the sediment mass expected if the sediment mixed conservatively. On the two subsequent days the reduction of sediment mass in the surface plume continued at ???50% per day. These observations suggest that river sediment undergoes rapid initial settling within ???1-km of the river mouth, followed by somewhat slower rates of settling. Although we did not measure sedimentation or bottom boundary layer processes, our mass balance results suggest that almost all of the river sediment either escapes along or deposits upon the inner shelf seabed.

Continental Shelf Research↗
USGS2007

The impact of floods and storms on the acoustic reflectivity of the inner continental shelf: A modeling assessment

Flood deposition and storm reworking of sediments on the inner shelf can change the mixture of grain sizes on the seabed and thus its porosity, bulk density, bulk compressional velocity and reflectivity. Whether these changes are significant enough to be detectable by repeat sub-bottom sonar surveys, however, is uncertain. Here the question is addressed through numerical modeling. Episodic flooding of a large versus small river over the course of a century are modeled with HYDROTREND using the drainage basin characteristics of the Po and Pescara Rivers (respectively). A similarly long stochastic record of storms offshore of both rivers is simulated from the statistics of a long-term mooring recording of waves in the western Adriatic Sea. These time series are then input to the stratigraphic model SEDFLUX2D , which simulates flood deposition and storm reworking on the inner shelf beyond the river mouths. Finally, annual changes in seabed reflectivity across these shelf regions are computed from bulk densities output by SEDFLUX2D and compressional sound speeds computed from mean seafloor grain size using the analytical model of Buckingham [1997. Theory of acoustic attenuation, dispersion, and pulse propagation in unconsolidated granular materials including marine sediments. Journal of the Acoustical Society of America 102, 2579–2596; 1998. Theory of compressional and shear waves in fluidlike marine sediments. Journal of the Acoustical Society of America 103, 288–299; 2000. Wave propagation, stress relaxation, and grain-tograin shearing in saturated, unconsolidated marine sediments. Journal of the Acoustical Society of America 108, 2796–2815]. The modeling predicts reflectivities that change from <12 dB for sands on the innermost shelf to >9 dB for muds farther offshore, values that agree with reflectivity measurements for these sediment types. On local scales of ∼100 m, however, maximum changes in reflectivity are <0.5 dB. So are most annual changes in reflectivity over all water depths modeled (i.e., 0–35 m). Given that signal differences need to be ⩾2–3 dB to be resolved, the results suggest that grain-size induced changes in reflectivity caused by floods and storms will rarely be detectable by most current sub-bottom sonars.

Continental Shelf Research↗
USGS2007

River plume patterns and dynamics within the Southern California Bight

Stormwater river plumes are important vectors of marine contaminants and pathogens in the Southern California Bight. Here we report the results of a multi-institution investigation of the river plumes across eight major river systems of southern California. We use in situ water samples from multi-day cruises in combination with MODIS satellite remote sensing, buoy meteorological observations, drifters, and HF radar current measurements to evaluate the dispersal patterns and dynamics of the freshwater plumes. River discharge was exceptionally episodic, and the majority of storm discharge occurred in a few hours. The combined plume observing techniques revealed that plumes commonly detach from the coast and turn to the left, which is the opposite direction of Coriolis influence. Although initial offshore velocity of the buoyant plumes was ∼50 cm/s and was influenced by river discharge inertia (i.e., the direct momentum of the river flux) and buoyancy, subsequent advection of the plumes was largely observed in an alongshore direction and dominated by local winds. Due to the multiple day upwelling wind conditions that commonly follow discharge events, plumes were observed to flow from their respective river mouths to down-coast waters at rates of 20–40 km/d. Lastly, we note that suspended-sediment concentration and beam-attenuation were poorly correlated with plume salinity across and within the sampled plumes (mean r 2 =0.12 and 0.25, respectively), while colored dissolved organic matter (CDOM) fluorescence was well correlated (mean r 2 =0.56), suggesting that CDOM may serve as a good tracer of the discharged freshwater in subsequent remote sensing and monitoring efforts of plumes.

California↗
USGS2009

Calibration of an estuarine sediment transport model to sediment fluxes as an intermediate step for simulation of geomorphic evolution

Modeling geomorphic evolution in estuaries is necessary to model the fate of legacy contaminants in the bed sediment and the effect of climate change, watershed alterations, sea level rise, construction projects, and restoration efforts. Coupled hydrodynamic and sediment transport models used for this purpose typically are calibrated to water level, currents, and/or suspended-sediment concentrations. However, small errors in these tidal-timescale models can accumulate to cause major errors in geomorphic evolution, which may not be obvious. Here we present an intermediate step towards simulating decadal-timescale geomorphic change: calibration to estimated sediment fluxes (mass/time) at two cross-sections within an estuary. Accurate representation of sediment fluxes gives confidence in representation of sediment supply to and from the estuary during those periods. Several years of sediment flux data are available for the landward and seaward boundaries of Suisun Bay, California, the landward-most embayment of San Francisco Bay. Sediment flux observations suggest that episodic freshwater flows export sediment from Suisun Bay, while gravitational circulation during the dry season imports sediment from seaward sources. The Regional Oceanic Modeling System (ROMS), a three-dimensional coupled hydrodynamic/sediment transport model, was adapted for Suisun Bay, for the purposes of hindcasting 19th and 20th century bathymetric change, and simulating geomorphic response to sea level rise and climatic variability in the 21st century. The sediment transport parameters were calibrated using the sediment flux data from 1997 (a relatively wet year) and 2004 (a relatively dry year). The remaining years of data (1998, 2002, 2003) were used for validation. The model represents the inter-annual and annual sediment flux variability, while net sediment import/export is accurately modeled for three of the five years. The use of sediment flux data for calibrating an estuarine geomorphic model guarantees that modeled geomorphic evolution will not exceed the actual supply of sediment from the watershed and seaward sources during the calibration period. Decadal trends in sediment supply (and therefore fluxes) can accumulate to alter decadal geomorphic change. Therefore, simulations of future geomorphic evolution are bolstered by this intermediate calibration step.

Continental Shelf Research↗
USGS2019

Sediment and organic carbon transport and deposition driven by internal tides along Monterey Canyon, offshore California

Submarine canyons provide globally important conduits for sediment and organic carbon transport into the deep-sea. Using a novel dataset from Monterey Canyon, offshore central California, that includes an extensive array of water column sampling devices, we address how fine-grained sediment and organic carbon are transported, mixed, fractionated, and buried along a submarine canyon. Anderson-type sediment traps were deployed 10 to 300 meters above the seafloor on moorings anchored between 278–1849 m water depths along the axial channel of Monterey Canyon during three consecutive 6-month deployments (2015–2017). Tidal currents within the canyon suspended and transported fine-grained sediment and organic carbon that were captured in sediment traps, which show apparent patterns and composition of sediment and organic carbon transport along the canyon. High sediment accumulation rates in traps increased up-canyon and near the seafloor with fine-scale (<1 cm) layering that was increasingly distinctive in CT scans. There was no along-canyon trend in the organic carbon composition (percent modern carbon and isotopic signatures) among trap locations, suggesting mixing. Organic carbon content (weight percent total organic carbon) and excess 210Pb activities (dpm/g) increased down-canyon, reflecting reduced flux of sediment and organic carbon into traps. Differing organic carbon signatures in traps compared with previous measurements of seabed deposits along Monterey Canyon suggest that canyon deposits may not reflect organic carbon available to organisms and transported through the canyon with internal tides. Organic carbon burial efficiency estimates from comparing core and trap samples are low (~26% or much less), suggesting that the modern upper Monterey Canyon may not be an effective sink for carbon in biogeochemical and CO2 cycling. Organic carbon isotopic signatures appear more marine in traps that sample from the water column than in cores that sample seafloor deposits, likely owing to the influence of sediment density flow events on deposits and preferential consumption of relatively fresh marine organic carbon on the seafloor that was largely prevented in preserved traps. Along-canyon sediment and organic carbon transport by internal tides likely occurs in many modern global submarine canyons, but canyon deposits and remaining organic carbon appear to preferentially reflect episodic sediment density flow events unrelated to internal tides. This study provides a quantified example and conceptual schematic for internal-tide-related sediment and organic carbon transport, mixing, and burial trends along a submarine canyon that are likely to have common global aspects.

California↗
USGS2014

Investigating the importance of sediment resuspension in Alexandrium fundyense cyst population dynamics in the Gulf of Maine

Cysts of Alexandrium fundyense , a dinoflagellate that causes toxic algal blooms in the Gulf of Maine, spend the winter as dormant cells in the upper layer of bottom sediment or the bottom nepheloid layer and germinate in spring to initiate new blooms. Erosion measurements were made on sediment cores collected at seven stations in the Gulf of Maine in the autumn of 2011 to explore if resuspension (by waves and currents) could change the distribution of over-wintering cysts from patterns observed in the previous autumn; or if resuspension could contribute cysts to the water column during spring when cysts are viable. The mass of sediment eroded from the core surface at 0.4 Pa ranged from 0.05 kg m −2 near Grand Manan Island, to 0.35 kg m −2 in northern Wilkinson Basin. The depth of sediment eroded ranged from about 0.05 mm at a station with sandy sediment at 70 m water depth on the western Maine shelf, to about 1.2 mm in clayey–silt sediment at 250 m water depth in northern Wilkinson Basin. The sediment erodibility measurements were used in a sediment-transport model forced with modeled waves and currents for the period October 1, 2010 to May 31, 2011 to predict resuspension and bed erosion. The simulated spatial distribution and variation of bottom shear stress was controlled by the strength of the semi-diurnal tidal currents, which decrease from east to west along the Maine coast, and oscillatory wave-induced currents, which are strongest in shallow water. Simulations showed occasional sediment resuspension along the central and western Maine coast associated with storms, steady resuspension on the eastern Maine shelf and in the Bay of Fundy associated with tidal currents, no resuspension in northern Wilkinson Basin, and very small resuspension in western Jordan Basin. The sediment response in the model depended primarily on the profile of sediment erodibility, strength and time history of bottom stress, consolidation time scale, and the current in the water column. Based on analysis of wave data from offshore buoys from 1996 to 2012, the number of wave events inducing a bottom shear stress large enough to resuspend sediment at 80 m ranged from 0 to 2 in spring (April and May) and 0 to 10 in winter (October through March). Wave-induced resuspension is unlikely in water greater than about 100 m deep. The observations and model results suggest that a millimeter or so of sediment and associated cysts may be mobilized in both winter and spring, and that the frequency of resuspension will vary interannually. Depending on cyst concentration in the sediment and the vertical distribution in the water column, these events could result in a concentration in the water column of at least 10 4 cysts m −3 . In some years, resuspension events could episodically introduce cysts into the water column in spring, where germination is likely to be facilitated at the time of bloom formation. An assessment of the quantitative effects of cyst resuspension on bloom dynamics in any particular year requires more detailed investigation.

Bay Of Fundy;Grand Manan Island;Gulf Of Maine;Jord↗
USGS2013

Current research issues related to post-wildfire runoff and erosion processes

Research into post-wildfire effects began in the United States more than 70 years ago and only later extended to other parts of the world. Post-wildfire responses are typically transient, episodic, variable in space and time, dependent on thresholds, and involve multiple processes measured by different methods. These characteristics tend to hinder research progress, but the large empirical knowledge base amassed in different regions of the world suggests that it should now be possible to synthesize the data and make a substantial improvement in the understanding of post-wildfire runoff and erosion response. Thus, it is important to identify and prioritize the research issues related to post-wildfire runoff and erosion. Priority research issues are the need to: (1) organize and synthesize similarities and differences in post-wildfire responses between different fire-prone regions of the world in order to determine common patterns and generalities that can explain cause and effect relations; (2) identify and quantify functional relations between metrics of fire effects and soil hydraulic properties that will better represent the dynamic and transient conditions after a wildfire; (3) determine the interaction between burned landscapes and temporally and spatially variable meso-scale precipitation, which is often the primary driver of post-wildfire runoff and erosion responses; (4) determine functional relations between precipitation, basin morphology, runoff connectivity, contributing area, surface roughness, depression storage, and soil characteristics required to predict the timing, magnitudes, and duration of floods and debris flows from ungaged burned basins; and (5) develop standard measurement methods that will ensure the collection of uniform and comparable runoff and erosion data. Resolution of these issues will help to improve conceptual and computer models of post-wildfire runoff and erosion processes.

Earth-Science Reviews↗
USGS2019

Igneous rocks in the Fish Creek Mountains and environs, Battle Mountain area, north-central Nevada: A microcosm of Cenozoic igneous activity in the northern Great Basin, Basin and Range Province, USA

The Great Basin of the western United States, the northern component of the Basin and Range Province, is a region of Cenozoic lithospheric extension with multiple periods and types of igneous activity. The composition and volume of Cenozoic magmas reflect a complex interaction between mantle-derived magmas and highly diverse crust, where both mantle sources and magmatic processes were modulated by tectonic environment. The Fish Creek Mountains in north-central Nevada underwent multiple igneous events ranging from ca. 40 Ma to 1 Ma that span all of the complex Cenozoic tectono-magmatic episodes of the Great Basin. The Fish Creek Mountains, therefore, is an ideal location to evaluate the different sources and processes involved in magma generation. Many plutons were emplaced in the region between about 40 and 38 Ma, several of which host base and precious metal deposits. Between 36 and 33 Ma, lava fields and calderas of the 37–19 Ma Ignimbrite Flare-up were emplaced. Both these and the preceding plutons resulted from southwestward rollback of the Farallon plate beneath North America during by far the most voluminous phase of Cenozoic magmatism. The lavas range from rare basalt and basaltic andesite to andesite, dacite, and rhyolite, have continental arc-like incompatible element patterns, and high initial 87 Sr/ 86 Sr and low εNd that require a metasomatized lithospheric mantle source combined with minor crustal component. Ignimbrites of the 34.4 Ma Cove Mine (trachydacite to rhyolite) and 34.0 Ma Caetano calderas (rhyolite to high-silica rhyolite) are abundantly porphyritic, include hydrous phases, were largely derived from partial melts of crustal rocks, but likely include 20–30% of a mantle-derived component. Igneous activity ceased in the region as the rollback-arc migrated to the southwest, but at 24.9 Ma a new caldera formed in the southern Fish Creek Mountains that was filled by ignimbrites of the Fish Creek Mountains Tuff. Intracaldera rhyolite ignimbrites range from aphyric, pumice-rich deposits at the base to progressively more quartz-feldspar phyric ignimbrites at higher levels; all flow units lack hydrous phases. No contemporaneous mafic or intermediate igneous activity accompanied caldera formation, but initial 87 Sr/ 86 Sr values in the Fish Creek Mountains tuffs are lower than in the Caetano Tuff, suggesting a greater mantle contribution to the 24.9 Ma ignimbrites. After another hiatus in igneous activity, the region was intruded and overlain by basalt to rhyolite dykes and lavas of the northern Nevada rift between 16.8 and 15.1 Ma. The primarily tholeiitic igneous suite is of the same age, chemistry, and isotopic composition as the Grande Ronde Formation of the Columbia River flood basalts, and evolved members (trachydacite and rhyolite) are crustally contaminated. The youngest northern Nevada rift lava is an alkali olivine basalt with isotopic affinity to basalts of the eastern Snake River Plain. After 10 Ma of quiescence, the region was locally covered by mafic lava flows with high-alumina olivine tholeiite compositions, represented by the 5.4 Ma Pumpernickel Valley flows. Their mid-ocean ridge-like incompatible element compositions indicate a depleted mantle source for the lavas, but radiogenic isotopic compositions indicate that the lavas of this region include a significant contribution from a mafic to ultramafic, high- 87 Sr/ 86 Sr source. The final igneous event in the Fish Creek Mountains region, the 4.0 to 1.0 Ma Buffalo Valley volcanic field, includes flows and spatter cones of transitional to alkalic basalt that are divided into two geochemical groups with identical isotopic compositions. They represent variable, low percent partial melts of the asthenosphere at different depths, yielding different rare earth element characteristics. Similar to the Lunar Crater volcanic field, the Buffalo Valley rocks represent a rare case where the lithosphere in the central Great Basin is now thin enough to allow melting of the underlying asthenosphere. Cenozoic magmatism in the northern Great Basin exhibits several transitions in magma sources and tectonic setting with time. Magmatism began as pre-extension, subduction-related, primarily lithospherically-derived magmas emplaced on/in tectonically-thickened crust. The onset of extension was partially driven by impingement of the Yellowstone plume that resulted in emplacement of rift-related volcanic and intrusive rocks in the northern Nevada rift, followed by the eruption of extension-related HAOT lavas along the northwest margin of the Great Basin. Finally, lithospheric thinning allowed for partial melting of the asthenosphere and eruption of alkaline basaltic lavas.

Nevada↗
USGS2021

Detrital zircon record of magmatism and sediment dispersal across the North American Cordilleran arc system (28-48°N)

As zircon U-Pb geochronology has become a leading method in sediment provenance studies and basin analysis over the past 20 years, the volume of detrital zircon data made available in published literature has enabled researchers to go beyond source-to-sink provenance studies to explore increasingly complex geologic problems. In this review, we utilize the growing body of detrital zircon data acquired from Jurassic-Paleocene forearc and foreland basin strata of the North American Cordillera to investigate the Mesozoic to earliest Cenozoic evolution of the arc and its associated basins between 28°N and 48°N. Our compilation includes 830 detrital zircon samples (101,898 individual ages) from 70 studies published between 2000 and 2020. For comparative purposes, we also compile 1307 igneous zircon U-Pb ages that characterize the magmatic history of the arc. We place primary emphasis on detrital zircon ages between 251 and 56 Ma that we infer to be uniquely derived from magmatic sources in the arc. Informed by existing knowledge of magmatic, structural, and sedimentological processes that acted on the orogen, we investigate spatial and temporal trends in these “arc-derived zircon” to establish a detrital record of arc magmatism, investigate source-to-sink relationships between the arc and adjacent basins, and discuss controls on sediment dispersal across the orogen. Our review shows that compilations of detrital zircon data from the Cordilleran forearc and foreland basin systems are excellent proxies for arc magmatism because the basins are enriched in arc-derived zircon and compilations provide space- and time-integrated records of crystallization ages. The compiled detrital zircon data support a history of continuous arc magmatism throughout Mesozoic and earliest Cenozoic time, characterized by low-volume magmatism from Triassic-Early Jurassic time (~251–174 Ma) and episodic higher-volume magmatism from Middle Jurassic-Late Cretaceous time (~174–66 Ma). These trends elucidate the initiation and timing of magmatic events at the orogen-scale and corroborate our understanding of cyclic arc behavior. Detrital zircon distributions are spatially and temporally variable both within and across basins, which we discuss relative to topographic development of the orogen and attendant responses of sediment dispersal systems. Detrital zircon distributions in the forearc signal rapid transfer of sediment from the arc to basins dominantly via fluvial processes. In contrast, detrital zircon distributions across the foreland reflect the presence of topographic barriers in the hinterland region of the arc that effectively isolated parts of the foreland. The presence of hinterland topography in turn highlights the important role of ash-fall events in delivering arc-derived zircon to the foreland, underscoring the need to consider ash-fall processes in paleodrainage reconstructions. These broad regional trends, and in general the close linkage between orogenic process and sediment dispersal, emerge from our compilation because it averages out much of the local variability observed in studies of more limited geographic or temporal extent.

North American Cordilleran arc system↗
USGS2009

Simulating the recovery of suspended sediment transport and river-bed stability in response to dam removal on the Elwha River, Washington

U.S. Department of the Interior is planning to remove two high dams (30 and 60 m) from the Elwha River, which will allow the river to erode sediment deposits in the reservoirs, and ultimately restore the river ecosystem. Fluvial sediment transport and deposition paradoxically represent ecological disturbance and restoration. A one-dimensional, movable boundary sediment-transport model was applied at a daily time step to simulate changes in river-bed elevations and particle-size distributions and concentrations of suspended sediment. The simulations included a three-year dam removal period and a four-year recovery period. Simulated concentrations of suspended sediment recover rapidly during the recovery period. Simulated bed elevation and particle-size distributions are stable for much of the river during the recovery period, but high flows periodically disturb the river bed, causing changes in river-bed elevation and particle-size distribution, especially during autumn, when summer/autumn chinook salmon are incubating in redds. Although the river bed will become increasingly stable after dam removal, episodic high flows will interrupt recovery trends. Productivity and diversity of the ecosystem may be lower because of excess sediment immediately after dam removal but should increase during recovery above current levels as the river. Monitoring of the recovery of the Elwha River ecosystem can target ecologically significant physical parameters indicating the transition from a sediment transport-limited state to a supply-limited state.

Ecological Engineering↗
USGS2009

Impacts of acidification on macroinvertebrate communities in streams of the western Adirondack Mountains, New York, USA

Limited stream chemistry and macroinvertebrate data indicate that acidic deposition has adversely affected benthic macroinvertebrate assemblages in numerous headwater streams of the western Adirondack Mountains of New York. No studies, however, have quantified the effects that acidic deposition and acidification may have had on resident fish and macroinvertebrate communities in streams of the region. As part of the Western Adirondack Stream Survey, water chemistry from 200 streams was sampled five times and macroinvertebrate communities were surveyed once from a subset of 36 streams in the Oswegatchie and Black River Basins during 2003-2005 and evaluated to: (a) document the effects that chronic and episodic acidification have on macroinvertebrate communities across the region, (b) define the relations between acidification and the health of affected species assemblages, and (c) assess indicators and thresholds of biological effects. Concentrations of inorganic Al in 66% of the 200 streams periodically reached concentrations toxic to acid-tolerant biota. A new acid biological assessment profile (acidBAP) index for macroinvertebrates, derived from percent mayfly richness and percent acid-tolerant taxa, was strongly correlated (R2 values range from 0.58 to 0.76) with concentrations of inorganic Al, pH, ANC, and base cation surplus (BCS). The BCS and acidBAP index helped remove confounding influences of natural organic acidity and to redefine acidification-effect thresholds and biological-impact categories. AcidBAP scores indicated that macroinvertebrate communities were moderately or severely impacted by acidification in 44-56% of 36 study streams, however, additional data from randomly selected streams is needed to accurately estimate the true percentage of streams in which macroinvertebrate communities are adversely affected in this, or other, regions. As biologically relevant measures of impacts caused by acidification, both BCS and acidBAP may be useful indicators of ecosystem effects and potential recovery at the local and regional scale.

Ecological Indicators↗
USGS2024

A model for evaluation of sediment exposure and burial for freshwater mussels from heavy particle sedimentation

Freshwater mussels (Bivalvia: Unionida) are an ecologically important faunal group. Excessive sediments, both in suspended and deposited formats, are believed to have negative effects on survival of freshwater mussels. However, there is a lack of quantitative tools for assessing the impact of abrupt and excessive sedimentation on freshwater mussel habitats. This gap in knowledge poses challenges for construction planning that necessitates evaluating sedimentation effects on mussels. In this paper, we present a simple Lagrangian particle tracking (LPT) model designed to investigate the downstream distances from the sediment release point where mussels may face risks of sediment exposure and burial during episodic sedimentation events. We validated the model in predicting the deposition of sands ranging from 125 to 625 &#x3BC; m "> 625μm in diameter within an open channel. Subsequently, we applied the LPT model to a representative stretch of mussel habitats in the lower Osage River, Missouri, USA. Implementing the LPT model using computational fluid dynamics analysis of river hydrodynamics, we investigated the downstream distances impacted by a hypothetical sedimentation event. The results indicate that the mussels within tens and hundreds of meters may be at risk of burial under low and high flow conditions, respectively. Mussels within hundreds and potentially thousands of meters may be at risks of sediment exposure under low and high flow conditions, respectively. The impacted distance is highly dependent on the sediment diameters and flow conditions. These results contribute valuable insights into the potential impacts of sedimentation on freshwater mussel habitats, aiding in informed decision-making for construction projects near these critical aquatic ecosystems.

Ecological Modelling↗
USGS2005

Nutrient contributions to the Santa Barbara Channel, California, from the ephemeral Santa Clara River

The Santa Clara River delivers nutrient rich runoff to the eastern Santa Barbara Channel during brief (???1-3 day) episodic events. Using both river and oceanographic measurements, we evaluate river loading and dispersal of dissolved macronutrients (silicate, inorganic N and P) and comment on the biological implications of these nutrient contributions. Both river and ocean observations suggest that river nutrient concentrations are inversely related to river flow rates. Land use is suggested to influence these concentrations, since runoff from a subwatershed with substantial agriculture and urban areas had much higher nitrate than runoff from a wooded subwatershed. During runoff events, river nutrients were observed to conservatively mix into the buoyant, surface plume immediately seaward of the Santa Clara River mouth. Dispersal of these river nutrients extended 10s of km into the channel. Growth of phytoplankton and nutrient uptake was low during our observations (1-3 days following runoff), presumably due to the very low light levels resulting from high turbidity. However, nutrient quality of runoff (Si:N:P = 16:5:1) was found to be significantly different than upwelling inputs (13:10:1), which may influence different algal responses once sediments settle. Evaluation of total river nitrate loads suggests that most of the annual river nutrient fluxes to the ocean occur during the brief winter flooding events. Wet winters (such as El Nin??o) contribute nutrients at rates approximately an order-of-magnitude greater than "average" winters. Although total river nitrate delivery is considerably less than that supplied by upwelling, the timing and location of these types of events are very different, with river discharge (upwelling) occurring predominantly in the winter (summer) and in the eastern (western) channel. ?? 2004 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗
USGS2022

Ocean connectivity drives trophic support for consumers in an intermittently closed coastal lagoon

Estuarine food webs are complex, as marine, freshwater, and terrestrial inputs combine and contribute variable amounts of organic material. Seasonal fluctuations in precipitation amplify the dynamism inherent to estuarine food webs, particularly in lagoonal estuaries, which can be seasonally closed and disconnected from the ocean in low-runoff periods (bar-built lagoons). Despite their abundance along coastlines in Mediterranean climates, the organic matter sources fueling bar-built lagoon food webs are poorly understood, particularly with respect to seasonal hydrologic variability, episodic marine connections, and internal nutrient cycling. In this study, we evaluate the food web of a bar-built lagoon with respect to seasonal differences in lagoon water quality, the sources of organic matter which support consumers, and the trophic ecology of resident fishes. Observed water quality conditions reflected biogeochemical processes associated with salinity-driven stratification and high lagoon residence times and were associated with strong seasonal differences in the contribution of different organic matter sources to lagoon consumers. A variety of organic matter sources supported consumers; marine inputs were important to lagoon food webs in spring when the lagoon was open, while summer food webs were largely driven by phytoplankton which was likely fueled by internal nutrient cycling. Fish diets were largely comprised of crustaceans and fish eggs, with clearly defined trophic niches in spring but high overlap in summer. This study demonstrates that the seasonal changes in bar-built lagoon food webs are largely dependent on ocean connectivity and internal cycling within the lagoon, rather than watershed processes as is typical for many estuaries.

California↗
USGS2026

VegET evapotranspiration for Africa: Continental-scale simulation, multi-product evaluation, and drought assessment

Study region Continental Africa, encompassing diverse climatic zones—tropical, arid, and temperate—and spanning major transboundary river basins such as the Nile, Niger, Congo, Volta, and Zambezi River Basins. The region exhibits pronounced hydroclimatic gradients and heterogeneous land use systems ranging from rainfed croplands and rangelands to dense tropical forests and irrigated schemes. Study focus Actual evapotranspiration (ETa) is a central component of the terrestrial water balance, governing the redistribution of water and energy between the land surface and the atmosphere. Accurate estimation of ETa at continental scale is critical for hydrological monitoring, water resource management, and climate adaptation, as well as for quantifying water, energy, and carbon fluxes that underpin sustainable development. In this study, we applied the agro-hydrologic VegET v2 model to simulate a new, high-resolution, continental-scale ETa dataset for Africa (2000–2021). The model results were benchmarked against four widely used remote sensing-based products—MODIS16 v6.1, SSEBop v6.1, WaPOR v3, and GLEAM v4.1a—across major climate zones, land use types, and River Basins, providing a comprehensive multi-product evaluation of evapotranspiration dynamics across the continent. New hydrological insights for the region Validation against eddy covariance flux tower observations at eight representative sites confirmed that VegET v2 accurately reproduces the seasonal dynamics of observed ETa, achieving a correlation (r) of 0.8 and an RMSE of 25 mm month⁻¹ —accuracy that is comparable to or higher than accuracies of satellite-based products MODIS16, SSEBop, and GLEAM. This study represents one of the first Africa-wide hydrological simulations of ETa, extending the VegET model beyond basin-scale applications. Intercomparisons reveal that VegET aligns closely with MODIS16, SSEBop, and GLEAM in humid and tropical regions (r = 0.80–0.90; RMSE < 20 mm month⁻¹), while greater discrepancies appear in arid and semi-arid zones, where WaPOR tends to overestimate ETa (RMSE ≥ 28 mm month⁻¹). Despite these differences, VegET effectively captures spatial and temporal ETa variability across rainfed croplands, forests, and savannas, supporting its utility in regional water balance assessments, water accounting, and drought monitoring. A key application of VegET v2 is the Evapotranspiration Deficit Index (ETDI), derived by integrating VegET-based ETa with potential evapotranspiration (PET) to quantify water stress. ETDI successfully captured major drought episodes across Africa, including persistent Sahelian and southern African dry spells, the 2020–2021 winter drought in the Maghreb, and the 2018–2019 austral summer drought in southern Africa, while identifying positive anomalies over central Africa indicative of recurrent wetness. These results underscore VegET’s capability as a hydrologically consistent, operational tool for continental ETa monitoring and drought assessment, offering support for basin-scale water balance studies, food security planning, and climate resilience across Africa’s diverse hydrological environments.

Journal of Hydrology: Regional Studies↗