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At least 955 records · Page 53Linked to original sources
USGS2020

Understanding effects of small dams on benthic metabolism and primary production in temperate forested streams

Dams can alter the chemical and physical conditions of downstream environments by increasing stream temperatures, altering nutrient limitation, reducing flow variability, and reducing fine sediment deposition. However, little is known about how fundamental stream ecosystem processes like productivity and respiration respond to dams. Nutrient diffusing substrates were installed in three dam streams and three control streams to evaluate the effect of dams on benthic gross primary productivity (GPP), respiration (R), and chlorophyll α production. Dam streams were an average of 5.6 °C warmer than control streams but GPP, R and chlorophyll α were not different between control and dam streams. Phosphorus enrichment increased heterotrophic R relative to controls (~1.8×) but not autotrophic GPP, R or chlorophyll α. Stream nutrient concentrations and nutrient limitation of heterotrophic R were similar in dam and control streams, suggesting that the dams had limited effects on nutrient transport downstream. Autotrophic GPP, R and chlorophyll α were limited by light and varied within and across streams, potentially masking our ability to detect differences caused solely by dams. Dams may alter stream ecosystem function but consideration of other factors associated with and independent of dams is critical for predicting ecosystem responses to dams.

Fundamental and Applied Limnology↗
USGS1998

Bacterial oxidation of dibromomethane and methyl bromide in natural waters and enrichment cultures

Bacterial oxidation of 14 CH 2 Br 2 and 14 CH 3 Br was measured in freshwater, estuarine, seawater, and hypersaline-alkaline samples. In general, bacteria from the various sites oxidized similar amounts of 14 CH 2 Br 2 and comparatively less 14 CH 3 Br. Bacterial oxidation of 14 CH 3 Br was rapid in freshwater samples compared to bacterial oxidation of 14 CH 3 Br in more saline waters. Freshwater was also the only site in which methyl fluoride-sensitive bacteria (e.g., methanotrophs or nitrifiers) governed brominated methane oxidation. Half-life calculations indicated that bacterial oxidation of CH 2 Br 2 was potentially significant in all of the waters tested. In contrast, only in freshwater was bacterial oxidation of CH 3 Br as fast as chemical removal. The values calculated for more saline sites suggested that bacterial oxidation of CH 3 Br was relatively slow compared to chemical and physical loss mechanisms. However, enrichment cultures demonstrated that bacteria in seawater can rapidly oxidize brominated methanes. Two distinct cultures of nonmethanotrophic methylotrophs were recovered; one of these cultures was able to utilize CH 2 Br 2 as a sole carbon source, and the other was able to utilize CH 3 Br as a sole carbon source.

California↗
USGS1962

Hornblendes formed during progressive metamorphism of amphibolites, northwest Adirondack Mountains, New York

Hornblendes in amphibolite interlayers in the paragneiss of the northwest Adirondack Mountains undergo systematic changes in color, composition, and density during progressive metamorphism from almandine- amphibolite to hornblende -granulite facies. In contrast, indices of refraction of the hornblendes remain about constant. In the almandine- amphibolite facies the amphibolite layers have the bulk composition of a saturated basalt and consist of bluish-green hornblende , andesine, and quartz. As these layers are traced into the hornblende -granulite facies, their composition undergoes a progressive change to that of an olivine basalt with brownish-green hornblende , clinopyroxene and orthopyroxene, and calcic andesine as major constituents. Compositional changes in the hornblendes with increasing grade of metamorphism include increases in Ti, Na, K, Cr, V, and Sc. Decreases occur in the amounts of Mn, Zn, OH + F + Cl, and in the ratios Fe 2 O 3 /FeO and Fe/Mg. Density of the hornblendes increases from 3.260 to 3.278 with the increasing grade of metamorphism . These changes in the hornblendes with increasing T and P, although well denned, are less pronounced than those measured in biotites and garnets of the enclosing paragneiss. Large variations in the physical and chemical properties of hornblendes in metamafic rocks reconstituted above the epidote- amphibolite facies appear to be induced principally by critical changes in the bulk composition of the total rock, and not by the regional gradients in T, P, or by changes in kind, or composition, of the coexisting minerals.

New York↗
USGS1968

On the maintenance of anomalous fluid pressures: I. thick sedimentary sequences

Various physical and chemical processes may be envisioned which will cause anomalous pressures on an underground fluid. In order to consider the maintenance of anomalous pressure, it is necessary to consider the problem as one of nonsteady fluid flow. The time rate of pressure change and maintenance depends upon the hydrodynamics of flow through porous media and the particular boundary conditions. This paper presents a series of general solutions to hydrodynamic models which are germane to the problem of creating and maintaining excess-fluid pressures in a thick sedimentary sequence. The creation and maintenance of fluid pressures approaching lithostatic pressure through a process of continuous sedimentation was evaluated. Our results indicate that a sedimentation rate of 500 m/10 6 yr (reasonable for the Gulf Coast) will create fluid pressures approaching lithostatic in a sedimentary column that has a hydraulic conductivity of 10 -8 cm sec -1 , or lower. It is apparent that the creation of anomalous pressure and its maintenance depends, to a large degree, upon the hydraulic conductivity and, to a lesser extent, upon the specific storage of clay layers within the system. © 1968, The Geological Society of America, Inc.

Geological Society of America Bulletin↗
USGS1971

Contrasting behavior of P, Ti, and Nb in a differentiated high-alumina olivine tholeiite and a calc-alkaline andesitic suite

Crystallization differentiation in a low-K 2 O, high-Al 2 O 3 olivine tholeiite (Hat Creek, California) yields segregation veins of basaltic andesite composition, and residual, interstitial glasses of dacite and rhyolite composition. P, Ti, and probably Nb, are progressively enriched in segregation veins and residual dacitic glass by crystallization of olivine, plagioclase, augite, and magnetite. P and Ti are depleted in residual rhyolitic glass by crystallization of magnetite, ilmenite, and apatite. By contrast, in a typical orogenic calc-alkaline suite (from Mount Jefferson, Oregon), P, Ti, and Nb are depleted with increasing K and Si. The most likely minerals capable of producing decreasing P, Ti, and Nb with increasing K are apatite, Fe-Ti oxides, amphibole, biotite, and sphene. There is no direct evidence of these minerals in Mount Jefferson basalt and andesite but they are present in calc-alkaline gabbro and tonalite and may occur at a shallow (crustal) depth beneath Mount Jefferson. Alternatively, mixing of dacite-rhyolite with basalt-andesite may account for the Mount Jefferson trend. By physical and chemical analogy with segregation veins and residual interstitial glasses, basaltic andesite and dacite-rhyolite magmas may segregate from complementary rock at depth, and mix during ascent to the surface.

California, Oregon↗
USGS1983

Relationship of two lacustrine ostracode species to solute composition and salinity: Implications for paleohydrochemistry ( Limnocythere sappaensis/staplini)

Nonmarine ostracode species are indicative of the physical and chemical nature of lacustrine environments. Although salinity has traditionally been regarded as one of the more important parameters that affect the occurrence patterns of lacustrine ostracodes, examination of the solute composition and salinities of the lakes where Limnocythere sappaensis and L. staplini live reveals that solute composition and not salinity is the most critical factor that controls their occurrence. The occurrence of these taxa in the modern world is mutually exclusive. L. sappaensis lives in water that is enriched in Na + -HCO 3 − - and depleted in Ca 2+ . L. staplini lives in water that is enriched in various combinations of Na + -Mg 2+ -Ca 2+ - -Cl − and is depleted in HCO 3 . These solute compositions are the product of the mineral fractionation processes described by Eugster and Hardie. The positive correlation between these two species occurrences and the mineralogic fractionation processes suggests that these taxa may be used as reliable paleohydrochemical indicators. Studies in progress dealing with other ostracode taxa suggest that saline lacustrine ostracodes can provide a precise method for reconstructing paleohydrochemistry.

Geology↗
USGS2011

Utah's geologic and geomorphic analogs to Mars—An overview for planetary exploration

Utah offers spectacular geologic features and valuable analog environments and processes for Mars studies. Horizontal strata of the Colorado Plateau are analogous to Mars because the overprint of plate tectonics is minimal, yet the effects of strong ground motion from earthquakes or impacts are preserved in the sedimentary record. The close proximity of analog environments and lack of vegetative cover are advantages for field and remote-sensing studies. Dry, desert climate and modern wind processes of Utah are comparable to Mars and its current surface. Analogs in Utah include eolian, sabkha and saline bodies, glacial, lacustrine, spring, alluvial, fluvial, delta, and outflow channel depositional environments, as well as volcanic landforms and impact craters. Analogous secondary processes producing modification features include: diagenetic concretions, weathering and soils, sinkholes, sapping, knobs and pinnacles, crusts and varnish, and patterned grounds. Utah's physical and chemical environments are analogous to conditions on Mars where water existed and could support microorganisms. The development of Mars includes: ancient and modern depositional records, burial and diagenesis, uplift and tectonic alteration, and modern sculpting or weathering of the surface exposures. Recent satellite images are providing unprecedented details that rival the outcrop scale. Analogs in Utah are prime field localities that can be utilized in planning future robotic and human missions to Mars, and for teaching the next generation of planetary explorers.

Utah↗
USGS2006

Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona

The Grand Falls basalt lava flow in northern Arizona was emplaced in late Pleistocene time. It flowed 10 km from its vent area to the Little Colorado River, where it cascaded into and filled a 65-m-deep canyon to form the Grand Falls lava dam. Lava continued ???25 km downstream and ???1 km onto the far rim beyond where the canyon was filled. Subsequent fluvial sedimentation filled the reservoir behind the dam, and eventually the river established a channel along the margin of the lava flow to the site where water falls back into the pre-eruption canyon. The ca. 150 ka age of the Grand Falls flow provided by whole-rock K-Ar analysis in the 1970s is inconsistent with the preservation of centimeter-scale flow-top features on the surface of the flow and the near absence of physical and chemical weathering on the flow downstream of the falls. The buried Little Colorado River channel and the present-day channel are at nearly the same elevation, indicating that very little, if any, regional downcutting has occurred since emplacement of the flow. Newly applied dating techniques better define the age of the lava dam. Infrared-stimulated luminescence dating of silty mudstone baked by the lava yielded an age of 19.6 ?? 1.2 ka. Samples from three noneroded or slightly eroded outcrops at the top of the lava flow yielded 3He cosmogenic ages of 16 ?? 1 ka, 17 ?? 1 ka, and 20 ?? 1 ka. A mean age of 8 ?? 19 ka was obtained from averaging four samples using the 40Ar/39Ar step-heating method. Finally, paleomagnetic directions in lava samples from two sites at Grand Falls and one at the vent area are nearly identical and match the curve of magnetic secular variation at ca. 15 ka, 19 ka, 23 ka, and 28 ka. We conclude that the Grand Falls flow was emplaced at ca. 20 ka. ?? 2006 Geological Society of America.

Geological Society of America Bulletin↗
USGS2015

Ignimbrites to batholiths: integrating perspectives from geological, geophysical, and geochronological data

Multistage histories of incremental accumulation, fractionation, and solidification during construction of large subvolcanic magma bodies that remained sufficiently liquid to erupt are recorded by Tertiary ignimbrites, source calderas, and granitoid intrusions associated with large gravity lows at the Southern Rocky Mountain volcanic field (SRMVF). Geophysical data combined with geological constraints and comparisons with tilted plutons and magmatic-arc sections elsewhere are consistent with the presence of vertically extensive (>20 km) intermediate to silicic batholiths (with intrusive:extrusive ratios of 10:1 or greater) beneath the major SRMVF volcanic loci (Sawatch, San Juan, Questa-Latir). Isotopic data require involvement of voluminous mantle-derived mafic magmas on a scale equal to or greater than that of the intermediate to silicic volcanic and plutonic rocks. Early waxing-stage intrusions (35–30 Ma) that fed intermediate-composition central volcanoes of the San Juan locus are more widespread than the geophysically defined batholith; these likely heated and processed the crust, preparatory for ignimbrite volcanism (32–27 Ma) and large-scale upper-crustal batholith growth. Age and compositional similarities indicate that SRMVF ignimbrites and granitic intrusions are closely related, but the extent to which the plutons record remnants of former magma reservoirs that lost melt to volcanic eruptions has been controversial. Published Ar/Ar-feldspar and U-Pb-zircon ages for plutons spatially associated with ignimbrite calderas document final crystallization of granitoid intrusions at times indistinguishable from the tuff to ages several million years younger. These ages also show that SRMVF caldera-related intrusions cooled and solidified soon after zircon crystallization, as magma supply waned. Some researchers interpret these results as recording pluton assembly in small increments that crystallized rapidly, leading to temporal disconnects between ignimbrite eruption and intrusion growth. Alternatively, crystallization ages of the granitic rocks are here inferred to record late solidification, after protracted open-system evolution involving voluminous mantle input, lengthy residence (10 5 –10 6 yr) as near-solidus crystal mush, and intermittent separation of liquid to supply volcanic eruptions. The compositions of the least-evolved ignimbrite magmas tend to merge with those of caldera-related plutons, suggesting that the plutons record nonerupted parts of long-lived cogenetic magmatic systems, variably modified prior to final solidification. Precambrian-source zircons are scarce in caldera plutons, in contrast to their abundance in some peripheral waning-stage intrusions of the SRMVF, implying dissolution of inherited crustal zircon during lengthy magma assembly for the ignimbrite eruptions and construction of a subvolcanic batholith. Broad age spans of zircons (to several million years) from individual samples of some ignimbrites and intrusions, commonly averaged and interpreted as “intrusion-emplacement age,” alternatively provide an incomplete record of intermittent crystallization during protracted incremental magma-body assembly, with final solidification only when the system began to wane. Analyses of whole zircons cannot resolve late stages of crystal growth, and early growth in a long-lived magmatic system may be poorly recorded due to periods of zircon dissolution. Overall, construction of a batholith can take longer than recorded by zircon-crystallization ages, while the time interval for separation and shallow assembly of eruptible magma may be much shorter. Magma-supply estimates (from ages and volcano-plutonic volumes) yield focused intrusion-assembly rates sufficient to generate ignimbrite-scale volumes of eruptible magma, based on published thermal models. Mid-Tertiary processes of batholith assembly associated with the SRMVF caused drastic chemical and physical reconstruction of the entire lithosphere, probably accompanied by asthenospheric input.

Colorado, New Mexico↗
USGS2025

Evaluating sediment transport and metal sorption in the San Juan River watershed

The physical and chemical characteristics of sediment influence the transport of metals in rivers. The San Juan River and its tributaries are located in the Four Corners Region in the southwestern United States and the watershed contains a wide variety of potential metal sources. Comparisons of past and present sediment data provide insight into the effects of seasonality and storm events on the transport of sediment within a watershed. Comparisons suggest finer (<0.63 µm) sediment particles increase at a greater rate during intense storm events than coarser sediment particles. These fine, clay-sized sediments have a greater potential for metal sorption. Statistical analyses compared upper and lower portions of the San Juan River. Results show that total elemental concentration decreases in sediments (1785.15 μ g l −1 ) and that concentrations increase in the aqueous phase (2063.08 μ g l −1 ) downstream in the San Juan River. Analyses using geochemical and scanning electron microscopy with energy dispersive spectroscopy suggest that sediment clay particles are the most likely constituent to transport metals in the San Juan River. Metal transport is further aided by metal oxide coatings that develop on the surfaces of larger particles. Increases in aggregation of fine-grained particles in the downstream portions of the San Juan River are also likely to bind elements within sediments, which can act as both a source and sink for metals in the lower watershed. CEC , geochemistry , PSD

Arizona, Colorado, New Mexico, Utah↗
USGS2003

Distinguishing palagonitized from pedogenically-altered basaltic Hawaiian tephra: Mineralogical and geochemical criteria

Palagonitization is a common, but imperfectly defined process that greatly modifies the physical and chemical properties of glassy basaltic tephra deposited in subaquatic/subglacial environments on Earth and perhaps Mars. It also results in textures and mineralogies that are distinct from other forms of (mainly pedogenic) low temperature alteration. Specifically, the process of palagonitization (1) initially results in the formation of 'palaginitized glass', a quasi- or nano-crystalline, rind-like material that contains smectite, as well as lesser amounts of other clays (e.g. serpentine), and (2) eventually results in consolidation of tephra, mediated through the accretion of palagonitized glass and later- formed authigenic cements. Conversely, pedogenic weathering of glassy basaltic tephra is characterized by disaggregation of tephra, and formation of a wide range of pedogenic products, including layer silicates (although not primarily smectite), short-range-order aluminosilicates and oxyhydroxides, whose composition reflects the intensity of the weathering environment. These mineralogical and textural properties can be readily recognized through a variety of techniques including electron microscopy/microprobe analysis, reflectance spectroscopy, X-ray diffraction and soil chemistry. Analyses of samples collected from the summit regions of Kilauea and Mauna Kea volcanoes on the island of Hawaii are presented here in order to illustrate differences between palagonitization and pedogenic weathering of glassy basaltic tephra. In the young Hawaiian tephras studied, palagonitization has occurred in response to hydrothermal activity shortly after deposition. Although some, non-hydrothermally affected tephras may eventually become palagonitized, those that have been strongly desilicated by intense pedogenic weathering will probably never become palagonitized.

Geological Society Special Publication↗
USGS2017

A diatom voucher flora from selected southeast rivers (USA)

This flora is intended to serve as an image voucher for samples analyzed for the U.S. Geological Survey Southeast Stream Quality Assessment (SESQA). The SESQA study included measurement of watershed and water quality parameters to determine the factors that have the greatest potential to alter biotic condition. Algal samples were collected at 108 sites in 2014, from streams representing gradients in chemical and physical alteration across the southeast region. More than 375 taxa were identified during analysis for species composition and abundance. This manuscript documents the flora with light micrographs of specimens representative of their morphologic range. We define “voucher flora” as images of specimens and the names applied to those specimens for a given project. Taxonomic vouchers from federal programs have generally not been made public, yet they are a salient element of a well-documented species dataset, particularly for long-term studies. This study is part of a broader effort to improve and encourage taxonomic consistency in federal, state and local programs by accessible identification resources and inter-lab comparisons.

Phytotaxa↗
USGS2009

Lead in the environment

Anthropogenic uses of lead have probably altered its availability and environmental distribution more than any other toxic element. Consequently, lead concentrations in many living organisms may be approaching thresholds of toxicity for the adverse effects of lead. Such thresholds are difficult to define, as they vary with the chemical and physical form of lead, exposure regime, other elements present and also vary both within and between species. The technological capability to accurately quantify low lead concentrations has increased over the last decade, and physiological and behavioral effects have been measured in wildlife with tissue lead concentrations below those previously considered safe for humans.s.236 Consequently. lead criteria for the protection of wildlife and human health are frequently under review, and 'thresholds' of lead toxicity are being reconsidered. Proposed lead criteria for the protection of natural resources have been reviewed by Eisler. Uptake of lead by plants is limited by its generally low availability in soils and sediments, and toxicity may be limited by storage mechanisms and its apparently limited translocation within most plants. Lead does not generally accumulate within the foliar parts of plants, which limits its transfer to higher trophic levels. Although lead may concentrate in plant and animal tissues, no evidence of biomagnification exists. Acid deposition onto surface waters and soils with low buffering capacity may influence the availability of lead for uptake by plants and animals, and this may merit investigation at susceptible sites. The biological significance of chronic low-level lead exposure to wildlife is sometimes difficult to quantify. Animals living in urban environments or near point sources of lead emission are inevitably subject to greater exposure to lead and enhanced risk of lead poisoning. Increasingly strict controls on lead emissions in many countries have reduced exposure to lead from some sources. and the .reduction of lead in gasoline has resulted in lower tissue lead concentrations in humans and wildlife from many, particularly urban, locations. However, it has been suggested that increasing use of organic lead compounds as catalysts for the production of plastics and as wood preservatives and biocides could adversely affect wildlife. The most significant source of direct wildlife mortality from lead is spent gunshot and fishing sinkers. Elevated mortality from shot ingestion in avian species resulted in the introduction of nontoxic (steel) shot zones along certain flyways in the United States in the mid-1970s and a total ban on the use of lead for waterfowl and coot hunting nationwide by 1992. Several other countries are now following suit and have either banned or are in the process of restricting the use of lead shot for waterfowl hunting. In the United States it has been estimated that since the 1986 hunting season. when the use of nontoxic shot became widespread. over 6 million ducks have not been lost to lead poisoning. Raptors, especially eagles, have also apparently benefited. although lead poisoning from ingestion of bullet fragments remains a problem for the critically threatened California condor. Quantifying reductions in lead mortality rates would be difficult since eagle populations throughout North America are rapidly recovering from other anthropogenic perturbations, especially organochlorine pesticides.

Book chapter↗
USGS1983

delta18O variations in the Halimeda of Virgin Islands sands: evidence of cool water in the northeast Caribbean, late Holocene

Halimeda segments from carbonate sands on the Virgin Islands platform have delta 18 O versus PDB isotopic values ranging from -0.3% to -1.3% (x = -0.9%). Modern Halimeda segments from the same area have a measured delta 18 O ranging from -2.0% to -2.5% PDB (x = -2.15%), and the carbonate skeleton appears to have formed in isotopic equilibrium with the oceanic waters on the platform. Biologic and geochemical data indicate that the sand deposits have accumulated under physical and chemical conditions similar to the modern shelf environment. 14 C data suggest that the sand was deposited over an approximate 5800-year span, centering about 4000 years B.P. The average isotopic difference of 1.25% between the Holocene and modern carbonate indicates that the late Holocene Halimeda lived in waters approximately 4 degrees cooler than the present.

Virgin Islands↗
USGS1987

Mineralogy and petrology of the Cretaceous- Tertiary boundary clay bed and adjacent clay-rich rocks, Raton Basin, New Mexico and Colorado.

The Cretaceous-Tertiary (K-T) boundary is preserved in a sequence of coal-bearing, fluvial rocks in the lower part of the Raton Formation (Late Cretaceous and Paleocene) at several sites in the east-central part of the Raton Basin. The K-T boundary occurs at the top of a kaolinitic claystone layer, commonly referred to as the "boundary clay layer," in an interval of coal and carbonaceous shale. The boundary is defined by the disappearance of certain fossil-pollen taxa. The boundary clay layer also contains shocked quartz grains and abundance anomalies of iridium, chromium, and other elements. Each of these characteristics support the hypothesis of an asteroid impact at the end of the Cretaceous. Small goyazite spheres were also found in the boundary clay bed; however, their origin is uncertain. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and thin-section petrography have shown that the boundary clay bed exhibits unique mineralogic and petrologic characteristics not possessed by other clay-rich beds in coal-bearing rocks of the Raton Basin. The boundary clay bed is composed primarily of well-crystallized kaolinite but also contains subordinate, randomly interstratified, mixed-layer illite/smectite, both of which appear to have been formed by the alteration of vitreous material in a coal-swamp environment. The bulk mineralogy of the boundary clay bed is similar to that of other kaolinite-rich clay beds (tonsteins) that altered in coal swamps from airfall volcanic ash. The alteration process and diagenetic products of the host material in the boundary clay bed, however, differed from those of the tonsteins, resulting in a unique petrographic fabric. The boundary clay bed is characterized by an overall imbricate fabric that may reflect an original vitreous material that included shards, bubbles, and spheres. The original fallout material of the boundary clay bed first altered to "cabbage-like" microspherules, indicating a halloysite or allophane precursor, and then to well-crystallized kaolinite; the well-crystallized kaolinite is the diagenetic stable phase for these rocks at their maximum burial conditions. In comparison, the vitreous components of the tonsteins were altered directly to coarse vermicular and platey kaolinite. Alteration of the original fallout material in the boundary bed was probably rapid, leading to hydrated, disordered, fine-grained clay minerals that formed into curled spherical or tubular shapes. The factors that produced these unique fabrics in the boundary clay bed existed at all K-T sites in the Raton Basin and were much different from those that formed the coarse platey and vermicular fabrics of ordinary tonsteins. The distinctive character of the boundary clay may be due to the unique nature and chemistry of the fallout material and (or) physical or chemical conditions existing shortly after its deposition.

Journal of Sedimentary Petrology↗
USGS2015

The effect of UV-C exposure on larval survival of the dreissenid quagga mussel

The rapid spread of quagga mussels ( Dreissena rostriformis bugensis ) has lead to their invasion of Lake Mead, Nevada, the largest reservoir in North America and partially responsible for providing water to millions of people in the southwest. Current strategies for mitigating the growth and spread of quagga mussels primarily include physical and chemical means of removing adults within water treatment, delivery, and hydropower facilities. In the present study, germicidal ultraviolet light (UV-C) was used to target the larval stage of wild-caught quagga mussel. The lethal effect of UV-C was evaluated at four different doses, 0.0, 13.1, 26.2, and 79.6 mJ/cm 2 . Tested doses were determined based on results from preliminary trials. The results demonstrate that germicidal UV-C is effective in controlling the free-swimming life history stages of larval quagga mussels.

Nevada↗
USGS2024

The anatomy of a drought in the upper San Francisco Estuary: Water quality and lower-trophic responses to multi-year droughts

Multi-year droughts are important and impactful features of California’s Mediterranean climate and can fundamentally affect the water quality and the ecosystem response of the San Francisco Estuary (Estuary) and the Sacramento-San Joaquin Delta (Delta). This study assesses data collected by long-term monitoring programs over the past 46 years (1975-2021) to evaluate how water quality in the Estuary changes during multi-year droughts. We found that multi-year droughts alter multiple physical and chemical parameters in the Estuary, increasing water temperature, salinity, water clarity, and nutrient levels. This trend was consistent across regions and seasons, with few exceptions. Increases in these parameters during droughts are likely caused by reduced Delta inflows that intensified in each successive dry year because of reduced precipitation and reservoir releases. Droughts did not substantially effect on tidal velocities within the Estuary, which remained mostly consistent across wet and dry periods. Trends in chlorophyll concentrations during droughts were more nuanced with higher concentrations occurring in the South-Central Delta region and during the winter and spring. Together, these results paint a picture of drought in the Estuary as warm, clear, high in nutrients, with patchy phytoplankton blooms (as indexed by chlorophyll), all of which have implications for higher trophic levels. Considering that droughts are expected to increase in frequency and intensity in California with climate change, it is imperative to understand the effects of multi-year droughts on the water quality conditions of the Estuary when making water management decisions.

California↗
USGS1962

Comparative toxicity of 3-trifluormethyl-4-nitrophenol (TFM) to larval lampreys and eleven species of fishes

The tolerances of larval lampreys, rainbow trout, and 10 species of warmwater fishes to 3-trifluormethyl-4-nitrophenol (TFM), a selective lamprey larvicide, were determined in three dilution waters of different physical and chemical characteristics. Differential toxic effects of the chemical to larval lampreys and test fishes varied broadly with the species of fish. Smallmouth bass and other centrarchids were most tolerant of the chemical; walleye, yellow perch, bullheads, and white suckers were most susceptible. The toxicity of TFM to both lampreys and fishes diminished as the conductivity and alkalinity of the dilution water increased. The differential action of the chemical was retained in all waters, however.

Transactions of the American Fisheries Society↗