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At least 379 records · Page 21Linked to original sources
USGS2011

Diel biogeochemical processes in terrestrial waters

Many biogeochemical processes in rivers and lakes respond to the solar photocycle and produce persistent patterns of measureable phenomena that exhibit a day–night, or 24-h, cycle. Despite a large body of recent literature, the mechanisms responsible for these diel fluctuations are widely debated, with a growing consensus that combinations of physical, chemical, and biological processes are involved. These processes include streamflow variation, photosynthesis and respiration, plant assimilation, and reactions involving photochemistry, adsorption and desorption, and mineral precipitation and dissolution. Diel changes in streamflow and water properties such as temperature, pH, and dissolved oxygen concentration have been widely recognized, and recently, diel studies have focused more widely by considering other constituents such as dissolved and particulate trace metals, metalloids, rare earth elements, mercury, organic matter, dissolved inorganic carbon (DIC), and nutrients. The details of many diel processes are being studied using stable isotopes, which also can exhibit diel cycles in response to microbial metabolism, photosynthesis and respiration, or changes in phase, speciation, or redox state. In addition, secondary effects that diel cycles might have, for example, on biota or in the hyporheic zone are beginning to be considered. This special issue is composed primarily of papers presented at the topical session “Diurnal Biogeochemical Processes in Rivers, Lakes, and Shallow Groundwater” held at the annual meeting of the Geological Society of America in October 2009 in Portland, Oregon. This session was organized because many of the growing number of diel studies have addressed just a small part of the full range of diel cycling phenomena found in rivers and lakes. This limited focus is understandable because (1) fundamental aspects of many diel processes are poorly understood and require detailed study, (2) the interests and expertise of individual scientists typically do not encompass the wide diversity and range of processes that produce diel cycles, and (3) the logistics of making field measurements for 24-h periods has limited recognition and understanding of these important cycles. Thus, the topical session brought together hydrologists, biologists, geochemists, and ecologists to discuss field studies, laboratory experiments, theoretical modeling, and measurement techniques related to diel cycling. Hopefully with the cross-disciplinary synergy developed at the session as well as by this special issue, a more comprehensive understanding of the interrelationships between the diel processes will be developed. Needless to say, understanding diel processes is critical for regulatory agencies and the greater scientific community. And perhaps more importantly, expanded knowledge of biogeochemical cycling may lead to better predictions of how aquatic ecosystems might react to changing conditions of contaminant loading, eutrophication, climate change, drought, industrialization, development, and other variables.

Chemical Geology↗
USGS2013

Groundwater-quality data in the Santa Barbara study unit, 2011: Results from the California GAMA Program

Groundwater quality in the 48-square-mile Santa Barbara study unit was investigated by the U.S. Geological Survey (USGS) from January to February 2011, as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program’s Priority Basin Project (PBP). The GAMA-PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001 and is being conducted in collaboration with the SWRCB and Lawrence Livermore National Laboratory (LLNL). The Santa Barbara study unit was the thirty-fourth study unit to be sampled as part of the GAMA-PBP. The GAMA Santa Barbara study was designed to provide a spatially unbiased assessment of untreated-groundwater quality in the primary aquifer system, and to facilitate statistically consistent comparisons of untreated-groundwater quality throughout California. The primary aquifer system is defined as those parts of the aquifers corresponding to the perforation intervals of wells listed in the California Department of Public Health (CDPH) database for the Santa Barbara study unit. Groundwater quality in the primary aquifer system may differ from the quality in the shallower or deeper water-bearing zones; shallow groundwater may be more vulnerable to surficial contamination. In the Santa Barbara study unit located in Santa Barbara and Ventura Counties, groundwater samples were collected from 24 wells. Eighteen of the wells were selected by using a spatially distributed, randomized grid-based method to provide statistical representation of the study unit (grid wells), and six wells were selected to aid in evaluation of water-quality issues (understanding wells). The groundwater samples were analyzed for organic constituents (volatile organic compounds [VOCs], pesticides and pesticide degradates, and pharmaceutical compounds); constituents of special interest (perchlorate and N-nitrosodimethylamine [NDMA]); naturally occurring inorganic constituents (trace elements, nutrients, major and minor ions, silica, total dissolved solids [TDS], alkalinity, and arsenic, chromium, and iron species); and radioactive constituents (radon-222 and gross alpha and gross beta radioactivity). Naturally occurring isotopes (stable isotopes of hydrogen and oxygen in water, stables isotopes of inorganic carbon and boron dissolved in water, isotope ratios of dissolved strontium, tritium activities, and carbon-14 abundances) and dissolved noble gases also were measured to help identify the sources and ages of the sampled groundwater. In total, 281 constituents and water-quality indicators were measured. Three types of quality-control samples (blanks, replicates, and matrix spikes) were collected at up to 12 percent of the wells in the Santa Barbara study unit, and the results for these samples were used to evaluate the quality of the data for the groundwater samples. Blanks rarely contained detectable concentrations of any constituent, suggesting that contamination from sample collection procedures was not a significant source of bias in the data for the groundwater samples. Replicate samples generally were within the limits of acceptable analytical reproducibility. Matrix-spike recoveries were within the acceptable range (70 to 130 percent) for approximately 82 percent of the compounds. This study did not attempt to evaluate the quality of water delivered to consumers; after withdrawal from the ground, untreated groundwater typically is treated, disinfected, and (or) blended with other waters to maintain water quality. Regulatory benchmarks apply to water that is served to the consumer, not to untreated groundwater. However, to provide some context for the results, concentrations of constituents measured in the untreated groundwater were compared with regulatory and non-regulatory health-based benchmarks established by the U.S. Environmental Protection Agency (USEPA) and CDPH and to non-regulatory benchmarks established for aesthetic concerns by CDPH. Comparisons between data collected for this study and benchmarks for drinking water are for illustrative purposes only and are not indicative of compliance or non-compliance with those benchmarks. All organic constituents and most inorganic constituents that were detected in groundwater samples from the 18 grid wells in the Santa Barbara study unit were detected at concentrations less than drinking-water benchmarks. Of the 220 organic and special-interest constituents sampled for at the 18 grid wells, 13 were detected in groundwater samples; concentrations of all detected constituents were less than regulatory and non-regulatory health-based benchmarks. In total, VOCs were detected in 61 percent of the 18 grid wells sampled, pesticides and pesticide degradates were detected in 11 percent, and perchlorate was detected in 67 percent. Polar pesticides and their degradates, pharmaceutical compounds, and NDMA were not detected in any of the grid wells sampled in the Santa Barbara study unit. Eighteen grid wells were sampled for trace elements, major and minor ions, nutrients, and radioactive constituents; most detected concentrations were less than health-based benchmarks. Exceptions are one detection of boron greater than the CDPH notification level (NL-CA) of 1,000 micrograms per liter (μg/L) and one detection of fluoride greater than the CDPH maximum contaminant level (MCL-CA) of 2 milligrams per liter (mg/L). Results for constituents with non-regulatory benchmarks set for aesthetic concerns from the grid wells showed that iron concentrations greater than the CDPH secondary maximum contaminant level (SMCL-CA) of 300 μg/L were detected in three grid wells. Manganese concentrations greater than the SMCL-CA of 50 μg/L were detected in seven grid wells. Chloride was detected at a concentration greater than the SMCL-CA recommended benchmark of 250 mg/L in four grid wells. Sulfate concentrations greater than the SMCL-CA recommended benchmark of 250 mg/L were measured in eight grid wells, and the concentration in one of these wells was also greater than the SMCL-CA upper benchmark of 500 mg/L. TDS concentrations greater than the SMCL-CA recommended benchmark of 500 mg/L were measured in 17 grid wells, and concentrations in six of these wells were also greater than the SMCL-CA upper benchmark of 1,000 mg/L.

California↗
USGS2017

Physical characteristics of the lower San Joaquin River, California, in relation to white sturgeon spawning habitat, 2011–14

The U.S. Fish and Wildlife Service confirmed that white sturgeon ( Acipenser transmontanus ) recently spawned in the lower San Joaquin River, California. Decreases in the San Francisco Bay estuary white sturgeon population have led to an increased effort to understand their migration behavior and habitat preferences. The preferred spawning habitat of other white sturgeon (for example, those in the Columbia and Klamath Rivers) is thought to be areas that have high water velocity, deep pools, and coarse bed material. Coarse bed material (pebbles and cobbles), in particular, is important for the survival of white sturgeon eggs and larvae. Knowledge of the physical characteristics of the lower San Joaquin River can be used to preserve sturgeon spawning habitat and lead to management decisions that could help increase the San Francisco Bay estuary white sturgeon population. Between 2011 and 2014, the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, assessed selected reaches and tributaries of the lower river in relation to sturgeon spawning habitat by (1) describing selected spawning reaches in terms of habitat-related physical characteristics (such as water depth and velocity, channel slope, and bed material) of the lower San Joaquin River between its confluences with the Stanislaus and Merced Rivers, (2) describing variations in these physical characteristics during wet and dry years, and (3) identifying potential reasons for these variations. The lower San Joaquin River was divided into five study reaches. Although data were collected from all study reaches, three subreaches where the USFWS collected viable eggs at multiple sites in 2011–12 from Orestimba Creek to Sturgeon Bend were of special interest. Water depth and velocity were measured using two different approaches—channel cross sections and longitudinal profiles—and data were collected using an acoustic Doppler current profiler. During the first year of data collection (water year 2011), runoff was greatest, and gaged streamflow, measured as discharge, peaked at 875 cubic meters per second in the lower San Joaquin River. Also during that year, water velocity was generally between 0.6 and 0.9 meters per second, and depth was typically between 2.5 and 4.5 meters, but water depth exceeded 6 meters in several pools. Water year 2011 was classified as a “ wet ” year. Later water years were classified as either “ dry ” (water year 2012) or “ critical ” (water years 2013 and 2014). During the drier years, water was shallower, and velocities were slower. The streambed aggraded in several areas during the study. At Sturgeon Bend, for example, which had the deepest pool measured in 2011 (maximum depth was 14 meters), about 8 meters of sediment was deposited by 2014. The bed of the lower San Joaquin River was predominately sand, except in areas downstream from the mouth of Del Puerto Creek. A large amount of sand, gravel, and cobble was deposited at the mouth of Del Puerto Creek, and in the 9.5 kilometers downstream from the mouth of Del Puerto Creek, we encountered several gravel bars and patches of gravel-size (8–64 millimeters) bed material. Del Puerto and Orestimba Creeks drain from the Coast Ranges on the west side of the river. Only small quantities of gravel-size bed material were observed in the reach downstream from Orestimba Creek, indicating Orestimba Creek does not deliver much coarse sediment to the lower San Joaquin River. Del Puerto Creek appeared to be the primary source of gravels suitable for white sturgeon spawning in the lower San Joaquin River, and thus, it is important for the long-term spawning success of sturgeon in the San Joaquin River.

California↗
USGS2017

Food abundance, prey morphology, and diet specialization influence individual sea otter tool use

Sea otters are well-known tool users, employing objects such as rocks or shells to break open invertebrate prey. We used a series of generalized linear mixed effect models to examine observational data on prey capture and tool use from 211 tagged individuals from 5 geographically defined study areas throughout the sea otter’s range in California. Our best supported model was able to explain 75% of the variation in the frequency of tool use by individual sea otters with only ecological and demographic variables. In one study area, where sea otter food resources were abundant, all individuals had similar diets focusing on preferred prey items and used tools at low to moderate frequencies (4–38% of prey captures). In the remaining areas, where sea otters were food-limited, individuals specialized on different subsets of the available prey and had a wider range of average tool-use frequency (0–98% of prey captures). The prevalence of difficult-to-access prey in individual diets was a major predictor of tool use and increased the likelihood of using tools on prey that were not difficult to access as well. Age, sex, and feeding habitat also contributed to the probability of tool use but to a smaller extent. We developed a conceptual model illustrating how food abundance, the prevalence of difficult-to-access prey, and individual diet specialization interacted to determine the likelihood that individual sea otters would use tools and considered the model’s relevance to other tool-using species.

Behavioral Ecology↗
USGS2007

Mercury and drought along the lower Carson River, Nevada: II. Snowy egret and black-crowned night-heron reproduction on Lahontan Reservoir, 1997-2006

Mercury concentrations in the floodplain of the Carson River Basin in northwestern Nevada are some of the highest ever reported in a natural system. Thus, a portion of the basin including Lahontan Reservoir was placed on the U.S. Environmental Protection Agency’s Natural Priorities List for research and cleanup. Preliminary studies indicated that reproduction in piscivorous birds may be at risk. Therefore, a 10-year study (1997–2006) was conducted to evaluate reproduction of snowy egrets ( Egretta thula ) and black-crowned night-herons ( Nycticorax nycticorax ) nesting on Gull Island in Lahontan Reservoir. Special attention was given to the annual flow of the Carson River, the resultant fluctuation of this irrigation reservoir, and the annual exposure of snowy egrets and night-herons to methylmercury (MeHg). The dynamic character of the river due to flooding and drought (drought effect) influenced snowy egret and night-heron reproduction more so than did MeHg contamination of eggs. During an extended drought (2000–2004) in the middle of the study, snowy egret nests containing eggs with concentrations of MeHg (measured as total mercury [THg] ∼ 100% MeHg) ≥0.80 μg THg/g, ww, all failed, but in 1997 and 2006 (wet years with general flooding), substantial numbers of young were produced (but fewer than at nests where eggs contained <0.80 μg/g). Thus, a variable reproductive threshold of tolerance to MeHg may be associated with habitat quality (food type and abundance). Clearly, drought was the most important factor affecting snowy egret annual productivity. In contrast to snowy egrets, night-herons generally had fewer nests meeting the 0.80 μg THg/g criterion, and those above the criterion were less sensitive to mercury than were snowy egrets. Furthermore, night-herons appeared more tolerant of drought conditions than snowy egrets because they nested earlier, selected more protected nesting sites, and had a more generalist diet that provided additional food options including terrestrial organisms, which also reduced exposure to MeHg. A putative biological effect threshold of 2.0 μg THg/g in whole blood for young of both species was evaluated, which was frequently exceeded, but with no evidence, while still in the colony, of an association with direct mortality. An evaluation of physiological associations with blood residues and post-fledging survival will be presented in future reports in this series.

Ecotoxicology↗
USGS2002

Processes of lithosphere evolution: New evidence on the structure of the continental crust and uppermost mantle

We discuss the structure of the continental lithosphere, its physical properties, and the mechanisms that formed and modified it since the early Archean. The structure of the upper mantle and the crust is derived primarily from global and regional seismic tomography studies of Eurasia and from global and regional data on seismic anisotropy. These data as documented in the papers of this special issue of Tectonophysics are used to illustrate the role of different tectonic processes in the lithospheric evolution since Archean to present. These include, but are not limited to, cratonization, terrane accretion and collision, continental rifting (both passive and active), subduction, and lithospheric basal erosion due to a relative motion of cratonic keels and the convective mantle.

Tectonophysics↗
USGS2022

Monitoring the movements of juvenile Pacific Lamprey (Entosphenus tridentatus) in the Yakima River, Washington, using acoustic telemetry, 2019–20

Anthropogenic barriers to main-stem and tributary passage are one of the primary threats associated with declining populations of Pacific Lamprey ( Entosphenus tridentatus ) in the Columbia River Basin. Juvenile lamprey are of special interest because their downstream migration to the ocean may be affected by barriers such as dams or water diversions. Telemetry studies that describe the movement and passage of juvenile lamprey have not been possible until the recent development of a micro-transmitter specifically for use in juvenile lamprey and eels. Through a collaborative research approach, we used these prototype transmitters and acoustic monitoring arrays installed for a juvenile salmon ( Oncorhynchus spp.) migration study to evaluate juvenile lamprey movements in the Yakima River (river kilometer 179 to the river mouth) in 2019 and 2020. We tagged and released 152 juvenile lamprey from April 30 to June 5, 2019, and on June 9, 2020. Lamprey were released 6.9 kilometers (km) upstream from Wapato Dam, 1.2 km upstream from Prosser Dam, and into the canal and tailrace at Prosser Dam. Most tagged lamprey did not initiate downstream movements within the 18 days of tag life, as evidenced by our detections of lamprey in the highest numbers at the first monitoring site downstream from their release site, with limited or no detections at sites farther downstream. There was no evidence of missed detections (lamprey detected at a downstream site without corresponding detections upstream). Overall detections of tagged lamprey were low: 27.0 percent in 2019 and 48.0 percent in 2020. River flows were less than the 10-year average during the monitoring period and water temperatures were variable. Lamprey arrived at detections sites predominantly during periods of darkness (85.3–96.6 percent) following daytime releases. Travel rates through the study area ranged from 0.2 to 45.3 kilometers per day, and lamprey generally remained at each detection station for less than about 20 minutes. Groups of lamprey released together generally had similar travel rates with a small number of fish that moved more quickly or slowly than the remainder of the group. In addition to monitoring the migration and behavior of juvenile lamprey, we also assessed some assumptions of survival models (determining downstream drift of purposely killed fish and empirically measuring transmitter operating life) to benefit future evaluations focused on migration survival of juvenile lamprey.

Washington↗
USGS1956

Engineering geology of the Nenana-Rex area, Alaska

A geological examination of the Nenana-Rex area, Alaska, was made during August, 1954 by a Geological Survey party consisting of Reuben Kachadoorian, geologist, and Lloyd Plafker, field assistant. The area examined lies in parts of the Fairbanks A-4, A-5, B-4, B-5, C-4 and C-5 quadrangles (fig. 1). A preliminary highway route and the Alaska Railroad cross the area mapped. The preliminary highway route, surveyed in the summer of by the Alaska Road Commission, is a segment of a proposed road from Fairbanks to McKinley Park (pl. 1). The area was mapped with special emphasis placed upon geologic factors that would affect construction of the new highway. This report is a result of the studies along the highway and railroad routes, and describes only those areas that are of immediate importance in planning and construction of the highway (pl. 1).

Alaska↗
USGS2005

The fishes of Wilson's Creek National Battlefield, Missouri, 2003

An inventory of fishes of Wilson's Creek National Battlefield was conducted at eight sites on three streams, two springs, a pond, and within a cave. Fish were sampled using conventional electrofishing equipment during July 2003. Approximately 325 fish were collected and identified from five of the eight sampling sites. A total of 30 species of fish was collected from the eight sampling sites. The number of species collected at the sampling sites ranged from 0 to 23. Many of the 'most commonly' collected fish species are typical of Ozark streams. A preliminary expected species list incorrectly listed 12 species because of incorrect species range or habitat requirements. A thirteenth species (the Ozark cavefish, Amblyopsis rosae) is listed as 'unexpected.' However, this designation is uncertain because Ozark cavefish have been reported from several caves and springs in Greene County. Upon revising the list of expected species, the inventory yielded 30 of the 53 species (57 percent). Ten of the 30 fish species collected in this inventory previously had not been collected at Wilson's Creek National Battlefield. However, eight species collected in one or more of the two previous inventories were not collected in this effort. It is unknown if any change in environmental conditions has occurred that is responsible for the absence of these species. Although none of the species collected in this study are federally-listed threatened or endangered species, five species collected at Wilson's Creek National Battlefield may be of special interest to National Park Service managers and others because they are endemic to the Ozark Plateaus. The duskystripe shiner (Luxilus pilsbryi), Ozark bass (Ambloplites constellatus), Ozark chub (Erimystax harryi), and stippled darter (Etheostoma punctulatum) are common and found throughout much of the Ozark Plateaus. However, the Ozark sculpin (Cottus hypselurus) has a more limited range and more specific habitat requirements.

Scientific Investigations Report↗
USGS1957

Geology and ground-water resources of Galveston County, Texas

Galveston County, on the Texas gulf coast, is underlain by alternating beds of sand and clay. These sand and clay strata crop out in belts that roughly parallel the coastline and dip gently southeastward at an angle gre? +,er than the slope of the land, thereby creating artesian aquifers. The formations that yield potable water to wells are the Lissie formation, the "Alta Loma" sand and other sands of the Beaumont clay, and beach and dune sands of Recent aie. Most of the potable water is obtained on the mainland of Galveston County. The water from most wells on Galveston Island is highly mineralized. Before 1948, water for all public use and nearly all industrial use was derived from wells. Most ground water now used in the county is pumped from areas around Alta Loma and Texas City. The average daily pumpage in these areas increased from 6 million gallons in 1938 to 17.8 million gallons in 1940 and reached a peak of about 34 million gallons in 1945. Between 1945 and 1948 the rate of pumpage was nearly constant, but in 1948 surface water was diverted from the Brazos River to supply some of the Texas City industries and, as a result, the use of ground water was reduced about 30 percent. Water levels declined in county wells as the pumpage increased during the years prior to 1948. Since water from the Brazos River has been utilized the levels have risen in many wells and tended to become constant in others. Subsidence of the land in a large part of the county, particularly in the Texas City area, is attributed to the excessive withdrawal of ground water. Salt-water encroachment has been a problem in the county for many years. Salt water was present in the lower part of the "Alta Loma" sand in the Alta Loma and Texas City areas and throughout that sand on Galveston Island when the first wells were drilled. Encroachment from either below or downdip took place with the lowering of artesian pressure in the aquifer in the vicinity of Alta Loma and Texas City. Pumping tests reveal that the average coefficient of transmissibility of the "Alta Loma" sand is 102,000 at Alta Loma and 153,000 at Texas City. The coefficients- of transmissibility of sands in the upper part of the Beaumont clay around Texas City average 27,300. Surface water from the Brazos River, used for the irrigation of rice since 1942, was made available in 1948 to industries in Texas City as a substitute for ground water. The water from the Brazos River is variable in quality, but probably can be utilized on a somewhat larger scale than at present. Much additional ground water could be obtained from both the "Alta Loma" sand and the upper part of the Beaumont clay, especially in the northern and western parts of the county. Before large developments of supplies are planned, however, these areas should be explored by test drilling. The problems of well spacing and pumping rates should be thoroughly studied in order to determine the maximum development permitted by the ground-water supply. Current observations should be continued with special emphasis on the progress of salt-water encroachment.

Water Supply Paper↗
USGS2020

Red imported fire ants reduce invertebrate abundance, richness, and diversity in Gopher Tortoise burrows

Gopher Tortoise ( Gopherus polyphemus ) burrows support diverse commensal invertebrate communities that may be of special conservation interest. We investigated the impact of red imported fire ants ( Solenopsis invicta ) on the invertebrate burrow community at 10 study sites in southern Mississippi, sampling burrows (1998–2000) before and after bait treatments to reduce fire ant populations. We sampled invertebrates using an ant bait attractant for ants and burrow vacuums for the broader invertebrate community and calculated fire ant abundance, invertebrate abundance, species richness, and species diversity. Fire ant abundance in gopher tortoise burrows was reduced by >98% in treated sites. There was a positive treatment effect on invertebrate abundance, diversity, and species richness from burrow vacuum sampling which was not observed in ant sampling from burrow baits. Management of fire ants around burrows may benefit both threatened gopher tortoises by reducing potential fire ant predation on hatchlings, as well as the diverse burrow invertebrate community. Fire-ant management may also benefit other species utilizing tortoise burrows, such as the endangered Dusky Gopher Frog and Schaus swallowtail butterfly. This has implications for more effective biodiversity conservation via targeted control of the invasive fire ant at gopher tortoise burrows.

Mississippi↗
USGS2019

Southern sea otter (Enhydra lutris nereis) population biology at Big Sur and Monterey, California --Investigating the consequences of resource abundance and anthropogenic stressors for sea otter recovery

The range of the southern sea otter ( Enhydra lutris nereis ) spans most of the central California coast from Half Moon Bay to Gaviota. Some coastal areas within this range are heavily developed and highly impacted by humans, while other areas are wild and largely pristine. Determining the relative importance of food resource abundance, environmental conditions, and anthropogenic increases in pathogens and pollutants to population change in sea otters is critical to understanding limitations to population growth. To investigate the causal links between the sluggish population growth of sea otters in central California and factors that could be driving variation in survival and reproduction, we designed a study to compare two distinct subpopulations—one in an area of low human impact (Big Sur) and one in an area of high human impact (Monterey). Between 2008 and 2011, the U.S. Geological Survey and collaborators conducted a telemetry-based study of sea otters at these two locations. The results of this study were not consistent with the hypothesis that sea otters adjacent to human population centers (Monterey) experience higher exposure to pollutants and pathogens than those in lower impacted areas (Big Sur). In fact, based on serological analysis, female sea otters from Big Sur showed higher exposure rates to Toxoplasma gondii than did female otters from Monterey, while domoic acid exposure appeared to be similar at both sites. Gene expression (specifically transcription) analysis did not indicate any consistent differences between the two populations that would have suggested a response to pathogen or toxin exposure, although there were temporal changes in gene transcription for sea otters at Big Sur following potential exposure to run-off from wildfires that occurred during the study. Together, these metrics suggest that variation in exposure to environmental stressors occurred, but patterns were not clearly attributable to differences in human population densities or land-use patterns. When compared to Monterey, sea otters in Big Sur spent more time feeding, had a higher degree of dietary specialization, were in poorer body condition, and had lower survival rates (both pups and adults). Together, these metrics suggest that otters at Big Sur had greater nutritional stress, consistent with lower per-capita resource abundance. Overall, study results indicate that density-dependent population regulation, mediated by per-capita resource abundance, is the most significant factor currently limiting population growth in the center part of the range. Additionally, spatial and temporal variation in environmental and anthropogenic stressors also can affect sea otter health, although patterns of variation are complex and are not simply a function of proximity to human populations. We also found that exposure to environmental stressors (either natural or anthropogenic in origin) often is associated with resource limitation. Finally, our results indicate that sea otter populations are structured at relatively small spatial scales, and the processes that regulate population abundance (including density-dependent resource abundance) also occur at these smaller, more local scales.

California↗
USGS1982

Guidelines for determining flood flow frequency: Bulletin #17B of the Hydrology Subcommittee

In December 1967, Bulletin No. 15, "A Uniform Technique for Determining Flood Flow Frequencies," was issued by the Hydrology Committee of the Water Resources Council. The report recommended use of the Pearson Type III distribution with log transformation of the data (log-Pearson Type III distribution) as a base method for flood flow frequency studies. As pointed out in that report, further studies were needed covering various aspects of flow frequency determinations. In March 1976, Bulletin 17, "Guidelines for Determining Flood Flow Frequency" was issued by the Water Resources Council. The guide was an extension and update of Bulletin No. 15. It provided a more complete guide for flood flow frequency analysis incorporating currently accepted technical methods with sufficient detail to promote uniform application. It was limited to defining flood potentials in terms of peak discharge and exceedance probability at locations where a systematic record of peak flood flows is available. The recommended set of procedures was selected from those used or described in the literature prior to 1976, based on studies conducted for this purpose at the Center for Research in Water Resources of the University of Texas at Austin (summarized in Appendix 14) and on studies by the Work Group on Flood Flow Frequency. The "Guidelines" were revised and reissued in June 1977 as Bulletin 17A. Bulletin 17B is the latest effort to improve and expand upon the earlier publications. Bulletin 17B provides revised procedures for weighting a station skew value with the results from a generalized skew study, detecting and treating outliers, making two station comparisons, and computing confidence limits about a frequency curve. The Work Group that prepared this revision did not address the suitability of the original distribution or the generalized skew map. Major problems are encountered when developing guides for flood flow frequency determinations. There is no procedure or set of procedures that can be adopted which, when rigidly applied to the available data, will accurately define the flood potential of any given watershed. Statistical analysis alone will not resolve all flood frequency problems. As discussed in subsequent sections of this guide, elements of risk and uncertainty are inherent in any flood frequency analysis. User decisions must be based on properly applied procedures and proper interpretation of results considering risk and uncertainty. Therefore, the judgment of a professional experienced in hydrologic analysis will enhance the usefulness of a flood frequency analysis and promote appropriate application. It is possible to standarize many elements of flood frequency analysis. This guide describes each major element of the process of defining the flood potential at a specific location in terms of peak discharge and exceedance probability. Use is confined to stations where available records are adequate to warrant statistical analysis of the data. Special situations may require other approaches. In those cases where the procedures of this guide are not followed, deviations must be supported by appropriate study and accompanied by a comparison of results using the recommended procedures. As a further means of achieving consistency and improving results, the Work Group recommends that studies be coordinated when more than one analyst is working currently on data for the same location. This recommendation holds particularly when defining exceedance probabilities for rare events, where this guide allows more latitude. Flood records are limited. As more years of record become available at each location, the determination of flood potential may change. Thus, an estimate may be outdated a few years after it is made. Additional flood data alone may be sufficient reason for a fresh assessment of the flood potential. When making a new assessment, the analyst should incorporate in his study a review of earlier estimates. Where differences appear, they should be acknowledged and explained.

Bulletin↗
USGS2023

Coevolution with host fishes shapes parasitic life histories in a group of freshwater mussels (Unionidae: Quadrulini)

Ecological interactions among species often lead to parasitic lineages coevolving with host resources, which is often suggested as the primary driver of parasite diversification. Freshwater mussels are bivalves that possess a parasitic life cycle requiring larval encystment on freshwater vertebrates to complete metamorphosis. The North American freshwater mussel tribe Quadrulini has a suite of life history adaptations including highly specialized patterns of host use, infection strategies, and variable larval morphologies. However, the evolution of life histories has yet to be explored using phylogenetic comparative methods. In this study, we use a holistic approach incorporating biogeographical, ecological, molecular, and morphological datasets to reconstruct the evolution of Quadrulini. Comparative phylogenetic analyses suggested the diversification of Quadrulini has been driven, at least in part, by codiversification with their primary host fishes in Ictaluridae. Major diversification events in both ictalurids and quadrulines were estimated to have occurred in the Mississippi River basin throughout the Miocene. Life history characteristics associated with parasitism were supported to have coevolved with host repertories, supporting the hypothesis that ecological interactions with host fishes have shaped the evolution of highly specialized traits in this group. Our findings demonstrate the importance of ecological interactions with host resources in shaping the evolutionary history of freshwater mussels.

Bulletin of the Society of Systematic Biologists↗
USGS1972

An Analysis of the Population Dynamics of Selected Avian Species--With Special References to Changes During the Modern Pesticide Era

The impact of pesticides on the mortality rates and recruitment rates of nongame birds during the last 25 years was evaluated by studying the population dynamics of 16 species. A mathematical model showing the relations between population parameters that yielded stable populations was developed. The information needed for the model included (1) mortality rate schedule (obtained from recoveries of banded birds), (2) recruitment rates, and (3) the age of sexual maturity. The rate of recruitment necessary for a stable population and/or the annual rate of change (increase or decrease) in population levels were estimated. Population parameters were compared to determine whether changes had occurred between time periods (i.e., 1925-45 vs. 1946-65). The great horned owl, red-shouldered hawk, sparrow hawk, osprey, barn owl, Cooper's hawk, red-tailed hawk, great blue heron, blackcrowned night heron, brown pelican, barn swallow, chimney swift, blue jay, blackcapped chickadee, cardinal, and robin were subjected to this analysis. No increase in postfledging mortality rates in any of the species was detected during the last 25 years (since 1945). Since there was no evidence of increased mortality rates it was concluded that accelerated declines in several of the species studied resulted from lowered reproductive success. Mortality rates were found to have decreased in the Cooper's hawk, sparrow hawk, great blue heron, and brown pelican and this was associated with a decrease in shooting pressure. Evidence of lower recruitment rates was found in the brown pelican, osprey, Cooper's hawk, red-shouldered hawk, and sparrow hawk. No changes in recruitment rates were noted in the red-tailed hawk, great horned owl, great blue heron, or barn owl. Information on recruitment rates was not available for comparison with the other species although rates of recruitment essential for a stable population were estimated. This work will provide the basis for making comparisons in future studies. No change in recruitment rates was apparent among species feeding primarily on mammals. Species exhibiting a lowered reproductive success since 1945 were those whose major food items consisted of fish, reptiles, amphibians, or birds. Lowered reproductive success was accompanied by a decrease in eggshell thickness. Other investigators have reported that sparrow hawks and mallard ducks fed a diet of DDE and dieldrin have produced thin eggshells under laboratory conditions, and exhibited a lower, reproductive success. Many of the bird species that have declined are those that consume food in which chlorinated hydrocarbon pesticides have been concentrated through a series of transfers along food chains. The chlorinated hydrocarbon pesticides are believed responsible.

Wildlife Research Report↗
USGS2021

Age‐ and sex‐related dietary specialization facilitate seasonal resource partitioning in a migratory shorebird

Dietary specialization is common in animals and has important implications for individual fitness, inter‐ and intraspecific competition, and the adaptive potential of a species. Diet composition can be influenced by age‐ and sex‐related factors including an individual's morphology, social status, and acquired skills; however, specialization may only be necessary when competition is intensified by high population densities or increased energetic demands. To better understand the role of age‐ and sex‐related dietary specialization in facilitating seasonal resource partitioning, we inferred the contribution of biofilm, microphytobenthos, and benthic invertebrates to the diets of western sandpipers ( Calidris mauri ) from different demographic groups during mid‐winter (January/February) and at the onset of the breeding migration (April) using stable isotope mixing models. Western sandpipers are sexually dimorphic with females having significantly greater body mass and bill length than males. Diet composition differed between seasons and among demographic groups. In winter, prey consumption was similar among demographic groups, but, in spring, diet composition differed with bill length and body mass explaining 31% of the total variation in diet composition. Epifaunal invertebrates made up a greater proportion of the diet in males which had lesser mass and shorter bills than females. Consumption of Polychaeta increased with increasing bill length and was greatest in adult females. In contrast, consumption of microphytobenthos, thought to be an important food source for migrating sandpipers, increased with decreasing bill length and was greatest in juvenile males. Our results provide the first evidence that age‐ and sex‐related dietary specialization in western sandpipers facilitate seasonal resource partitioning that could reduce competition during spring at the onset of the breeding migration. Our study underscores the importance of examining resource partitioning throughout the annual cycle to inform fitness and demographic models and facilitate conservation efforts.

Ecology and Evolution↗
USGS2014

Metamorphosis alters contaminants and chemical tracers in insects: implications for food webs

Insects are integral to most freshwater and terrestrial food webs, but due to their accumulation of environmental pollutants they are also contaminant vectors that threaten reproduction, development, and survival of consumers. Metamorphosis from larvae to adult can cause large chemical changes in insects, altering contaminant concentrations and fractionation of chemical tracers used to establish contaminant biomagnification in food webs, but no framework exists for predicting and managing these effects. We analyzed data from 39 studies of 68 analytes (stable isotopes and contaminants), and found that metamorphosis effects varied greatly. δ 15 N, widely used to estimate relative trophic position in biomagnification studies, was enriched by 1‰ during metamorphosis, while δ 13 C used to estimate diet, was similar in larvae and adults. Metals and polycyclic aromatic hydrocarbons (PAHs) were predominantly lost during metamorphosis leading to 2 to 125-fold higher larval concentrations and higher exposure risks for predators of larvae compared to predators of adults. In contrast, manufactured organic contaminants (such as polychlorinated biphenyls) were retained and concentrated in adults, causing up to 3-fold higher adult concentrations and higher exposure risks to predators of adult insects. Both food web studies and contaminant management and mitigation strategies need to consider how metamorphosis affects the movement of materials between habitats and ecosystems, with special regard for aquatic-terrestrial linkages.

Environmental Science & Technology↗
USGS2024

Adaptive resource management: Achieving functional eradication of invasive snakes to benefit avian conservation

Natural resource management often co-occurs with considerable uncertainty. One approach to mitigating uncertainty is through adaptive resource management (ARM), a specialized form of structured decision-making that modifies management decisions or actions through monitoring and implementation. Here, we present a case study on the attempted eradication of an invasive brown treesnake ( Boiga irregularis ) in a 5-ha enclosure on Guam with uncertainty in approach. We applied an ARM process across three field phases of snake removal and evaluated whether (1) eradication was achievable and (2) eradication was necessary to achieve an avian response. Field phases included the application of aerial toxic baits, toxicant baiting large mouse and birds, trapping with live mouse and bird lures and hand capture. We found that each removal technique improved control by either removing many individuals or targeting a subset of individuals that resisted prior control approaches. Although the effort did not result in eradication, the evaluation of identified indicators allowed for timely adjustments to removal using the ARM process. The snake removal efforts yielded an avian response in the treatment area after integrating live birds as snake lures, suggesting functional eradication of snakes may be possible. We also, however, observed a release of invasive rodents following snake control, with birds being more sensitive to the presence of snakes than rodents. Synthesis and applications . We suggest that using adaptive resource management to evaluate each phase of action in relation to established goals allowed us to measure outcomes and was successful in eliminating uncertainty in the application of control tools for wildlife conservation. We were able to create a documented and successful approach towards removing snakes inside a snake-exclusion barrier by following the ARM process.

Journal of Applied Ecology↗