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At least 1,081 records · Page 60Linked to original sources
USGS2010

Convergent radial dispersion: A Laplace transform solution for aquifer tracer testing

A Laplace transform solution was obtained for the injection of a tracer in a well situated in a homogeneous aquifer where steady, horizontal, radially convergent flow has been established due to pumping at a second well. The standard advection-dispersion equation for mass transfer was used as the controlling equation. For boundary conditions, mass balances that account for mixing of the tracer with the fluid residing in the injection and pumped wells were used. The derived solution, which can be adapted for either resident or flux-averaged concentration, is of practical use only for the pumped well. This problem is of interest because it is easily applied to field determination of aquifer dispersivity and effective porosity. Breakthrough curves were obtained by numerical inversion of the Laplace transform solution. It was found that tracer mixing with fluid in the pumped and injection wells, especially in low-porosity aquifers, may have a significant influence on the shape of the tracer breakthrough curves.

Water Resources Research↗
USGS1991

Radiocarbon test of earthquake magnitude at the Cascadia subduction zone

The Cascadia subduction zone, which extends along the northern Pacific coast of North America, might produce earthquakes of magnitude 8 or 9 ('great' earthquakes) even though it has not done so during the past 200 years of European observation 1–7 . Much of the evidence for past Cascadia earthquakes comes from former meadows and forests that became tidal mudflats owing to abrupt tectonic subsidence in the past 5,000 years 2,3,6,7 . If due to a great earthquake, such subsidence should have extended along more than 100 km of the coast 2 . Here we investigate the extent of coastal subsidence that might have been caused by a single earthquake, through high-precision radiocarbon dating of coastal trees that abruptly subsided into the intertidal zone. The ages leave the great-earthquake hypothesis intact by limiting to a few decades the discordance, if any, in the most recent subsidence of two areas 55 km apart along the Washington coast. This subsidence probably occurred about 300 years ago.

California, Oregon, Washington↗
USGS2008

Effects of disturbance on germination and seedling establishment in a coastal prairie grassland: A test of the competitive release hypothesis

1. We evaluated the responses of native grassland sods to a variety of types of disturbance in order to assess hypotheses about the competitive effects of established vegetation on seed germination and seedling establishment. In particular, we consider whether germination is more responsive to the magnitude and duration of vegetation removal (competitive release) or to individual disturbance types (specific effects). 2. Field-collected sods of coastal tallgrass prairie were subjected to no manipulation, cutting with clippings left, cutting with clippings removed (hayed), burning, and complete destruction of established vegetation under greenhouse conditions. The emergence and fate of seedlings, as well as light penetration through the canopy, were followed for a period of 4.5 months. 3. Total seedling emergence increased from cut to control, hayed, burned and plants-removed treatments. Several periods of increased seedling emergence suggested responses to both light penetration and seasonal change. 4. Species richness was lowest in cut sods and highest in sods that had plants removed or were burned. Rarefaction analysis showed that these differences were largely those expected from differences in seedling number, except for the cut treatment, which produced fewer species per seedling than other treatments. 5. Indicator species analysis and ordination methods revealed that seedling community composition overlapped strongly across all treatments, although the area of ordination space did increase with increasing numbers of seedlings. 6. Overall, most of the effects of disturbance could be explained by cumulative light penetration to the soil surface, an indicator of total competitive release, although a few specific effects could be found (particularly for the cutting treatment). Thus, these results generally support the competitive release hypothesis.

Journal of Ecology↗
USGS2011

Testing a high-resolution satellite interpretation technique for crop area monitoring in developing countries

District-level crop area (CA) is a highly uncertain term in food production equations, which are used to allocate food aid and implement appropriate food security initiatives. Remote sensing studies typically overestimate CA and production, as subsistence plots are exaggerated at coarser resolution, which leads to overoptimistic food reports. In this study, medium-resolution (MR) Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images were manually classified for Niger and corrected using CA estimates derived from high-resolution (HR) sample image, topographic and socioeconomic data. A logistic model with smoothing splines was used to compute the block-average (0.1°) probability of an area being cropped. Livelihood zones and elevation explained 75% of the deviance in CA, while MR did not add explanatory power. The model overestimates CA when compared to the national inventory, possibly because of temporal changes in intercropping and the exclusion of some staple crops in the national inventory.

International Journal of Remote Sensing↗
USGS2010

Re-analysis of a banding study to test the effects of an experimental increase in bag limits of mourning doves

In 1966-1971, eastern US states with hunting seasons on mourning doves (Zenaida macroura) participated in a study designed to estimate the effects of bag limit increases on population survival rates. More than 400 000 adult and juvenile birds were banded and released during this period, and subsequent harvest and return of bands, together with total harvest estimates from mail and telephone surveys of hunters, provided the database for analysis. The original analysis used an ANOVA framework, and resulted in inferences of no effect of bag limit increase on population parameters (Hayne 1975). We used a logistic regression analysis to infer that the bag limit increase did not cause a biologically significant increase in harvest rate and thus the experiment could not provide any insight into the relationship between harvest and annual survival rates. Harvest rate estimates of breeding populations from geographical subregions were used as covariates in a Program MARK analysis and revealed an association between annual survival and harvest rates, although this relationship is potentially confounded by a latitudinal gradient in survival rates of dove populations. We discuss methodological problems encountered in the analysis of these data, and provide recommendations for future studies of the relationship between harvest and annual survival rates of mourning dove populations.

Journal of Applied Statistics↗
USGS2012

Field-based evaluations of horizontal flat-plate fish screens, II: Testing of a unique off-stream channel device - The Farmers Screen

Screens are installed at water diversion sites to reduce entrainment of fish. Recently, the Farmers Irrigation District (Oregon) developed a unique flat-plate screen (the “Farmers Screen”) that operates passively and may offer reduced installation and operating costs. To evaluate the effectiveness of this screen on fish, we conducted two separate field experiments. First, juvenile coho salmon Oncorhynchus kisutch were released over a working version of this screen under a range of inflows (0.02–0.42 m 3 /s) and diversion flows (0.02–0.34 m 3 /s) at different water depths. Mean approach velocities ranged from 0 to 5 cm/s and sweeping velocities ranged from 36 to 178 cm/s. Water depths over the screen surface ranged from 1 to 25 cm and were directly related to inflow. Passage of fish over the screen under these conditions did not severely injure them or cause delayed mortality, and no fish were observed becoming impinged on the screen surface. Second, juvenile coho salmon and steelhead O. mykiss were released at the upstream end of a 34-m flume and allowed to volitionally move downstream and pass over a 3.5-m section of the Farmers Screen to determine whether fish would refuse to pass over the screen after encountering its leading edge. For coho salmon, 75–95% of the fish passed over the screen within 5 min and 82–98% passed within 20 min, depending on hydraulic conditions. For steelhead, 47–90% of the fish passed over the screen within 5 min and 79–95% passed within 20 min. Our results indicate that when operated within its design criteria, the Farmers Screen provides safe and efficient downstream passage of juvenile salmonids under a variety of hydraulic conditions.

North American Journal of Fisheries Management↗
USGS2016

Design and testing of a mesocosm-scale habitat for culturing the endangered Devils Hole Pupfish

aptive propagation of desert spring fishes, whether for conservation or research, is often difficult, given the unique and often challenging environments these fish utilize in nature. High temperatures, low dissolved oxygen, minimal water flow, and highly variable lighting are some conditions a researcher might need to recreate to simulate their natural environments. Here we describe a mesocosm-scale habitat created to maintain hybrid Devils Hole × Ash Meadows Amargosa Pupfish ( Cyprinodon diabolis × C. nevadensis mionectes ) under conditions similar to those found in Devils Hole, Nevada. This 13,000-L system utilized flow control and natural processes to maintain these conditions rather than utilizing complex and expensive automation. We designed a rotating solar collector to control natural sunlight, a biological reactor to consume oxygen while buffering water quality, and a reverse-daylight photosynthesis sump system to stabilize nighttime pH and swings in dissolved oxygen levels. This system successfully controlled many desired parameters and helped inform development of a larger, more permanent desert fish conservation facility at the U.S. Fish and Wildlife Service’s Ash Meadows National Wildlife Refuge, Nevada. For others who need to raise fish from unique habitats, many components of the scalable and modular design of this system can be adapted at reasonable cost.

North American Journal of Aquaculture↗
USGS2016

Contrasts between channels and backwaters in a large, floodplain river: Testing our understanding of nutrient cycling, phytoplankton abundance, and suspended solids dynamics

In floodplain rivers, variability in hydraulic connectivity interacts with biogeochemistry to determine the distribution of suspended and dissolved substances. Nutrient, chlorophyll a , and suspended solids data spanning longitudinal (5 study reaches across 1300 river km), lateral (main channel and backwaters), and temporal (1994–2011) gradients in the Upper Mississippi River (UMR) were used to examine the extent to which observed differences between the main channel and backwaters were consistent with expectations based on current understanding of biogeochemical processes in large rivers. For N and P, the results largely conformed to expectations. N concentrations were greater in the main channel than in the backwaters in 82 to 96% of the observations across river reaches. Maximum TP concentrations generally occurred in backwaters during summer, when backwater TP often exceeded that of the main channel. Flux of P from sediments may be a substantial source of water-column P in UMR backwaters in summer. The data for suspended solids and chlorophyll a suggest that some refinements are needed of our understanding of ecosystem processes in large rivers. During low-discharge conditions, concentrations of inorganic suspended solids often were greater in backwaters than in the main channel, suggesting the importance of sediment resuspension. Chlorophyll a concentrations were usually greater in backwaters than in the main channel, but exceptions indicate that phytoplankton abundance in the main channel of the UMR can sometimes be greater than is typically expected for large rivers.

Freshwater Science↗
USGS1988

Asynchronous hatching and food limitation: A test of Lack's hypothesis

Lack's (1954, 1968) hypothesis that asynchronous hatching of altricial birds is an adaptive response to unpredictable food shortages during the breeding season was examined in the highly granivorous Zebra Finch ( Poephila guttata ). I compared growth and survival of nestlings in asynchronous and artificially created synchronous broods reared under food-limited and food-abundant conditions in an aviary. I also examined the role of parental experience on survival and growth of nestlings. There was no differential mortality of Zebra Finch nestlings due to either asynchrony or food abundance. Young in abundant food treatments grew more rapidly, however, than those in food-restricted treatments. Heaviest Zebra Finch nestlings in a brood grew more quickly than their lightest siblings when food was limited, supporting Lack's hypothesis. Further, differential survival of light and heavy siblings occurred when food was abundant, suggesting that asynchronous hatching can be maladaptive under some ecological conditions. Nestlings reared by inexperienced parents suffered greater mortality and slower growth when food was abundant than nestlings raised by experienced parents. Prefledging mass was correlated with size at adulthood

The Auk↗
USGS2015

Now hiring! Empirically testing a three-step intervention to increase faculty gender diversity in STEM

Workforce homogeneity limits creativity, discovery, and job satisfaction; nonetheless, the vast majority of university faculty in science, technology, engineering, and mathematics (STEM) fields are men. We conducted a randomized and controlled three-step faculty search intervention based in self-determination theory aimed at increasing the number of women faculty in STEM at one US university where increasing diversity had historically proved elusive. Results show that the numbers of women candidates considered for and offered tenure-track positions were significantly higher in the intervention groups compared with those in controls. Searches in the intervention were 6.3 times more likely to make an offer to a woman candidate, and women who were made an offer were 5.8 times more likely to accept the offer from an intervention search. Although the focus was on increasing women faculty within STEM, the intervention can be adapted to other scientific and academic communities to advance diversity along any dimension.

BioScience↗
USGS2003

Initial river test of a monostatic RiverSonde streamflow measurement system

A field experiment was conducted on May 7-8, 2002 using a CODAR RiverSonde UHF radar system at Vernalis, California on the San Joaquin River. The monostatic radar configuration on one bank of the river, with the antennas looking both upriver and downriver, provided very high-quality data. Estimates of both along-river and cross-river surface current were generated using several models, including one based on normal-mode analysis. Along-river surface velocities ranged from about 0.6 m/s at the river banks to about 1.0 m/s near the middle of the river. Average cross-river surface velocities were 0.02 m/s or less.

California↗
USGS2008

Monitoring on-orbit stability of Terra MODIS and Landsat 7 ETM+ reflective solar bands using Railroad Valley Playa, Nevada (RVPN) test site

The Moderate Resolution Imaging Spectroradiometer (MODIS) Proto-Flight Model (PFM), launched on December 18, 1999, aboard NASA's Earth Observing System (EOS) Terra satellite has 20 reflective solar bands (RSB) with wavelengths ranging from 0.41 to 2.1 mum over a wide field of view (plusmn55deg). The Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensor was launched on April 15, 1999, and has six spectral bands located in the visible and shortwave infrared (SWIR) part of the electromagnetic spectrum (0.4 - 2.5 mum). The ETM+ belongs to the family of Thematic Mapper sensors flown on previous Landsat missions. In this study, over 75 cloud-free nadir near-simultaneous images over Railroad Valley Playa, Nevada (RVPN) were chosen covering entire missions of both sensors. RVPN (38.5degN and 115.7degW), located between the cities of Ely and Tonopah, Nevada, USA, is a high reflectance site with very high spatial, spectral, and temporal uniformity. It is referenced to the Worldwide Reference System-2 (WRS-2) with path 40 and row 33. Homogeneous regions of interest (ROI) were chosen and cross-calibration was performed using an image statistics approach to monitor the long-term stability of the two sensors.

Nevada↗
USGS2026

Testing the efficacy of industrial mitigation measures for caribou in the Arctic

1. Mitigation measures are commonly employed to reduce the negative effects of industrial development on wildlife but are not often evaluated for their efficacy. For example, oil fields in the Arctic typically incorporate design features intended to increase permeability for migratory, barren-ground caribou ( Rangifer tarandus) , even though there is limited empirical evidence of the effectiveness of some of these features. 2. Given expected increases in energy development in the North American Arctic, we examined whether two mitigation measures commonly used for migratory caribou, elevating pipelines and separating roads and pipelines, were effective at increasing the probability caribou would cross infrastructure. 3. We conducted our investigation on adult female caribou in the Central Arctic Herd of Alaska during summer, analyzing movement data from telemetry collars (2015-2020) in conjunction with spatial data on oil field infrastructure. To evaluate whether caribou would cross infrastructure as a function of the mitigation measures, we employed a generalized additive modeling framework capable of detecting non-linear and threshold responses. 4. We found that caribou were more likely to cross a pipeline when the nearest pipeline was elevated (≥1.9-m), a result that supports current mitigation recommendations. We also found that caribou were more likely to cross both a road and pipeline when they were directly adjacent to one another, as opposed to being spatially separated, a result that contradicts recommended mitigation strategies. 5. Synthesis and applications . As new energy projects are designed and implemented in environments around the globe, it is important to ensure that mitigation efforts for wildlife are scientifically validated for their efficacy. In the North American Arctic, such efforts will be critical for minimizing the impacts of expanding industrial development on migratory caribou and on the human communities that rely on them for subsistence.

Alaska↗