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USGS2019

Observations on the range and nesting biology of the Mexican endemic rufous-capped brush-finch (Atlapetes Pileatus Pileatus)

The Rufous-capped Brush-finch ( Atlapetes pileatus ) is a species endemic to Mexico, whose breeding biology has received little attention. We studied two nests of the nominate subspecies from the mountains of southern Sonora. Nests were untidy, broad, open cups, placed in low, thick vegetation. Clutch size at one nest consisted of three immaculate white eggs. The second nest contained two Brush-finch nestlings and one cowbird ( Molothrus sp.) nestling. Both parents brought food to the nestlings, but delivered significantly more food to the cowbird nestling. Most of our observations of nest architecture, egg coloration, and adult behaviors are consistent with previous descriptions for Rufous-capped Brush-finch and other members of the genus Atlapetes . This is the first report of cowbird brood-parasitism on the Rufous-capped Brush-finch, as well as the first confirmed record of breeding by this species in Sonora.

Ornitología Neotropical↗

USGS2000

Environmental Setting and Effects on Water Quality in the Great and Little Miami River Basins, Ohio and Indiana

The Great and Little Miami River Basins drain approximately 7,354 square miles in southwestern Ohio and southeastern Indiana and are included in the more than 50 major river basins and aquifer systems selected for water-quality assessment as part of the U.S. Geological Survey's National Water-Quality Assessment Program. Principal streams include the Great and Little Miami Rivers in Ohio and the Whitewater River in Indiana. The Great and Little Miami River Basins are almost entirely within the Till Plains section of the Central Lowland physiographic province and have a humid continental climate, characterized by well-defined summer and winter seasons. With the exception of a few areas near the Ohio River, Pleistocene glacial deposits, which are predominantly till, overlie lower Paleozoic limestone, dolomite, and shale bedrock. The principal aquifer is a complex buried-valley system of sand and gravel aquifers capable of supporting sustained well yields exceeding 1,000 gallons per minute. Designated by the U.S. Environmental Protection Agency as a sole-source aquifer, the Buried-Valley Aquifer System is the principal source of drinking water for 1.6 million people in the basins and is the dominant source of water for southwestern Ohio. Water use in the Great and Little Miami River Basins averaged 745 million gallons per day in 1995. Of this amount, 48 percent was supplied by surface water (including the Ohio River) and 52 percent was supplied by ground water. Land-use and waste-management practices influence the quality of water found in streams and aquifers in the Great and Little Miami River Basins. Land use is approximately 79 percent agriculture, 13 percent urban (residential, industrial, and commercial), and 7 percent forest. An estimated 2.8 million people live in the Great and Little Miami River Basins; major urban areas include Cincinnati and Dayton, Ohio. Fertilizers and pesticides associated with agricultural activity, discharges from municipal and industrial wastewater-treatment and thermoelectric plants, urban runoff, and disposal of solid and hazardous wastes contribute contaminants to surface water and ground water throughout the study area. Surface water and ground water in the Great and Little Miami River Basins are classified as very hard, calcium-magnesiumbicarbonate waters. The major-ion composition and hardness of surface water and ground water reflect extensive contact with the carbonate-rich soils, glacial sediments, and limestone or dolomite bedrock. Dieldrin, endrin, endosulfan II, and lindane are the most commonly reported organochlorine pesticides in streams draining the Great and Little Miami River Basins. Peak concentrations of the herbicides atrazine and metolachlor in streams commonly are associated with post-application runoff events. Nitrate concentrations in surface water average 3 to 4 mg/L (milligrams per liter) in the larger streams and also show strong seasonal variations related to application periods and runoff events. Ambient iron concentrations in ground water pumped from aquifers in the Great and Little Miami River Basins often exceed the U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (300 micrograms per liter). Chloride concentrations are below aesthetic drinking-water guidelines (250 mg/L), except in ground water pumped from low-yielding Ordovician shale; chloride concentrations in sodium-chloriderich ground water pumped from the shale bedrock can exceed 1,000 mg/L. Some of the highest average nitrate concentrations in ground water in Ohio and Indiana are found in wells completed in the buried-valley aquifer; these concentrations typically are found in those parts of the sand and gravel aquifer that are not overlain by clay-rich till. Atrazine was the most commonly detected herbicide in private wells. Concentrations of volatile organic compounds in ground water generally were below Federal drinking-water standards, except near areas of known or suspected contamination. Evaluation of fish and macroinvertebrate community performance in streams and rivers draining the Great and Little Miami River Basins indicates that most streams meet basic aquatic-life-use criteria set by the Ohio Environmental Protection Agency for warmwater habitat. Stream reaches whose biological community performance meet aquatic-lifeuse criteria defined for exceptional warmwater habitat are found in Twin Creek, the Upper Great Miami River, the Little Miami River, and the Whitewater River Basins. Other streams have exhibited significant improvements in biological community performance (and water quality)'that are attributed primarily to reduced pollutant loadings from wastewater-treatment plants upgraded since 1972. Four hydrogeomorphic regions were delineated in the Great and Little Miami River Basins based on distinct and relatively homogeneous natural characteristics. Primary features used to delineate the hydrogeomorphic regions include bedrock geology, surficial geology, physiography, hydrology, soil types, and vegetation. These four regions Till Plains, Drift Plains/Unglaciated, Interlobate, and Fluvial are used in the Great and Little Miami River Basins study to assess the influence of natural features of the environmental setting on surface- and ground-water quality.

Indiana, Ohio↗

USGS2000

Water quality in the eastern Iowa basins, Iowa and Minnesota, 1996-98

The water quality in rivers and streams and in selected aquifers in eastern Iowa and part of southern Minnesota is described and illustrated. Major ions, nitrogen and other nutrients, and pesticides and some of their breakdown compounds were analyzed in both surface and ground water. Biological communities that included fish, invertebrates, and algae, were described in relation to stream water quality. Volatile organic compounds that originate from fuels, solvent, and industry were analyzed from ground-water samples. Agricultural and urban land-use effects on shallow ground-water compared and contrasted.

Iowa, Minnesota↗

USGS2005

A checklist of the aquatic invertebrates of the Delaware River Basin, 1990-2000

This paper details a compilation of aquatic-invertebrate taxa collected at 1,080 sites as part of 13 surface-water-quality studies completed by selected Federal, state, and local environmental agencies during 1990-2000, within the 32,893-km2 area of the Delaware River Basin. This checklist is intended to be a 'working list' of aquatic invertebrates that can be applied successfully to the calculation and interpretation of various biological estimators to determine the status of water quality and can be used as a foundation to document the current state of biodiversity. It is not intended as a comprehensive historical inventory of the literature or of private and public holdings. A total of 11 phyla comprising 20 classes, 46 orders, 196 families, 685 genera, and 835 species were recorded.

Data Series↗

USGS2009

Northern Prairie Wildlife Research Center

The Northern Prairie Wildlife Research Center (NPWRC) conducts integrated research to fulfill the Department of the Interior's responsibilities to the Nation's natural resources. Located on 600 acres along the James River Valley near Jamestown, North Dakota, the NPWRC develops and disseminates scientific information needed to understand, conserve, and wisely manage the Nation's biological resources. Research emphasis is primarily on midcontinental plant and animal species and ecosystems of the United States. During the center's 40-year history, its scientists have earned an international reputation for leadership and expertise on the biology of waterfowl and grassland birds, wetland ecology and classification, mammalian behavior and ecology, grassland ecosystems, and application of statistics and geographic information systems. To address current science challenges, NPWRC scientists collaborate with researchers from other U.S. Geological Survey centers and disciplines (Biology, Geography, Geology, and Water) and with biologists and managers in the Department of the Interior (DOI), other Federal agencies, State agencies, universities, and nongovernmental organizations. Expanding upon its scientific expertise and leadership, the NPWRC is moving in new directions, including invasive plant species, restoration of native habitats, carbon sequestration and marketing, and ungulate management on DOI lands.

Fact Sheet↗

USGS2008

Using Molecular Genetic Markers to Resolve a Subspecies Boundary: The Northern Boundary of the Southwestern Willow Flycatcher in the Four-Corner States

*Executive Summary* The northern boundary of the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) is currently approximated as running through southern Colorado and Utah, but the exact placement is uncertain because this subspecies shares a border with the more northern and non-endangered E. t. adastus. To help resolve this issue, we evaluated the geographic distribution of mitochondrial and nuclear DNA by sampling breeding sites across the four-corner states (Arizona, Colorado, New Mexico, and Utah). We found that breeding sites clustered into two major groups generally consistent with the currently designated boundary, with the exception of three sites situated along the current boundary. However, delineating a precise boundary that would separate the two subspecies is made difficult because (1) we found evidence for a region of intergradation along the boundary area, suggesting the boundary is not discreet, and (2) the boundary region is sparsely populated, with too few extant breeding populations to precisely locate a boundary. The boundary region encompasses an area where elevation changes markedly over relatively short distances, with low elevation deserts to the south and more mesic, higher elevation habitats to the north. We hypothesized that latitudinal and elevational differences and their concomitant ecological effects could form an ecological barrier that inhibited gene flow between the subspecies, forming the basis for the subspecies boundary. We modeled changes in geographic patterns of genetic markers as a function of latitude and elevation finding significant support for this relationship. The model was brought into a GIS environment to create multiple subspecies boundaries, with the strength of each predicted boundary evaluated on the basis of how much genetic variation it explained. The candidate boundary that accounted for the most genetic variation was situated generally near the currently recognized subspecies boundary, but should be more biologically meaningful because it incorporates the landscape features that may be driving separation of the subspecies. Even so, we caution that using any narrow boundary line as an indicator of subspecies identity could be misleading because biologically the boundary is a region of intergradation rather than a discrete line. Designating, a boundary ultimately becomes a regulatory and management decision based on how much of the genetic variation unique to a subspecies should be protected. We discuss how the results of this study can help guide this decision process by wildlife policy makers.

Open-File Report↗

USGS1995

Inventory of biological investigations related to stream water quality in the South Platte River basin, Colorado, Nebraska, and Wyoming, 1891-1994

An inventory of the biological investigations conducted in the South Platte River Basin from 1891 to 1994 was done as a part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program in the South Platte River Basin. To aid in the sampling design of the biological component of the South Platte NAWQA, sources of water-related studies were compiled from computerized literature searches of biological data bases and by contacting other Federal, State, and local agencies. Biological investigations were categorized by their location in either of two major physiographic provinces-the Southern Rocky Mountains or the Great Plains, or in the transition zone between the mountains and the plains. From this collection of 102 references, five general categories of biological investigations were identified: algae, invertebrates, fish, habitat characterization, and chemicals in organism tissue. The most abundant literature was on studies of invertebrate and fish communities. Invertebrate studies primarily were conducted in the mountain region. There was limited information on algae, invertebrates in the plains region, flood-plain vegetation in the mountains and transition zone, and chemicals in organism tissue.

Open-File Report↗

USGS2002

Water-quality assessment of the Great Salt Lake basins, Utah, Idaho, and Wyoming: Environmental setting and study design

The Great Salt Lake Basins, Utah, Idaho, and Wyoming is one of 51 study units in the United States where the status and trends of water quality, and the factors controlling water quality, are being studied by the National Water-Quality Assessment Program of the U.S. Geological Survey. The 14,500-square-mile Great Salt Lake Basins study unit encompasses three major river systems that enter Great Salt Lake: the Bear, the Weber, and the Utah Lake/Jordan River systems. The environmental setting of the study unit includes natural and human-related factors that potentially influence the physical, chemical, and/or biological quality of the surface- and ground-water resources. Surface- and ground-water components of the planned assessment activities are designed to evaluate the sources of natural and human-related factors that affect the water quality in the Great Salt Lake Basins study unit.

Idaho, Utah, Wyoming↗

USGS1988

Chemical quality, benthic organisms, and sedimentation in streams draining coal-mined lands in Raccoon Creek basin, Ohio, July 1984 through September 1986

The Ohio Department of Natural Resources, Division of Reclamation, plans widespread reclamation of abandoned coal mines in the Raccoon Creek basin in southeastern Ohio. Throughout Raccoon Creek basin, chemical, biological, and suspended-sediment data were collected from July 1984 through September 1986. Chemical and biological data collected at 17 sites indicate that the East Branch, Brushy Creek, Hewett Fork, and Little Raccoon Creek subbasins, including Flint Run, are affected by drainage from abandoned coal mines. In these basins, median pH values ranged from 2.6 to 5.1, median acidity values ranged from 20 to 1,040 mg/L (milligrams per liter) as CaCo 3 , and median alkalinity values ranged from 0 to 4 mg/L as CaCo 3 . Biological data indicate that these basins do not support diverse populations because of degraded water systems. Suspended-sediment yields of 70.7 tons per square mile per year at the headwaters of Raccoon Creek and 54.5 tons per square mile per year near the month of Raccoon Creek indicate that cumulative sedimentation from erosion of abandoned-mine lands is not excessive in the basin.

Ohio↗

USGS1992

Limnology of Big Lake, south-central Alaska, 1983-84

The limnological characteristics and trophic state of Big Lake in south-central Alaska were determined from the results of an intensive study during 1983-84. The study was begun in response to concern over the potential for eutrophication of Big Lake, which has experienced substantial residential development and recreational use because of its proximity to Anchorage. The east and west basins of the 1,213 square-hectometer lake were each visited 36 times during the 2-year study to obtain a wide variety of physical, chemical, and biological data. During 1984, an estimate was made of the lake's annual primary production. Big Lake was classified as oligotrophic on the basis of its annual mean values for total phosphorus (9.5 micrograms per liter), total nitrogen (209 micrograms per liter), chlorophyll-a (2.5 micrograms per liter), secchi-disc transparency (6.3 meters), and its mean daily integral primary production of 81.1 milligrams of carbon fixed per square meter. The lake was, however, uncharacteristic of oligotrophic lakes in that a severe dissolved-oxygen deficit developed within the hypolimnion during summer stratification and under winter ice cover. The summer dissolved-oxygen deficit resulted from the combination of strong and persistent thermal stratification, which developed within 1 week of the melting of the lake's ice cover in May, and the failure of the spring circulation to fully reaerate the hypolimnion. The autumn circulation did reaerate the entire water column, but the ensuing 6 months of ice and snow cover prevented atmospheric reaeration of the water column and led to development of the winter dissolved-oxygen deficit. The anoxic conditions that eventually developed near the lake bottom allowed the release of nutrients from the bottom sediments and facilitated ammonification reactions. These processes yielded hypolimnetic concentrations of nitrogen and phosphorus compounds, which were much larger than the oligotrophic concentrations measured within the epilimnion. An analysis of nitrogen-to-phosphorus ratios showed that nitrogen was the nutrient most likely to limit phytoplankton growth during the summer. Although mean chlorophyll-a concentrations were at oligotrophic levels, concentrations did peak at 46.5 micrograms per liter in the east basin. During each year and in both basins, the peak chlorophyll-a concentrations were measured within the hypolimnion because the euphotic zone commonly was deeper than the epilimnion during the summer. The annual integral primary production of Big Lake in 1984 was 29.6 grams of carbon fixed per square meter with about 90 percent of that produced during May through October. During this time period, the lake received 76 percent of its annual input of solar irradiance. Monthly integral primary production, in milligrams of carbon fixed per square meter, ranged from 1.5 in January to 7,050 in July. When compared with the range of annual integral primary production measured in 50 International Biological Program lakes throughout the world, Big Lake had a low value of annual integral primary production. The results of this study lend credence to the concerns about the potential eutrophication of Big Lake. Increases in the supply of oxygen-demanding materials to Big Lake could worsen the hypolimnetic dissolved-oxygen deficit and possibly shift the lake's trophic state toward mesotrophy or eutrophy.

Water Supply Paper↗

USGS1997

Kauai's endangered solitaires: Update on population status and distribution 1996

The puaioihi ( Myadestes palmeri ) and the kamao ( M. myadestinus ) are endangered solitaires endemic to Kauai in the Hawaiian Islands and now restricted to the Alakai Swamp. The puaiohi has been rare historically with population estimates declining since the first population surveys 1968-73. Puaiohi were believed to be on the verge of extinction with population estimates less than 35 birds since 1981. In 1995 intensive studies of the breeding biology and population status of the puaiohi began using mist netting, color banding, spot mapping, and surveys. Fifty active nests were discovered and 63-75 birds monitored at the Koaie study site. Seven survey expeditions in 1996 detected 55-70 more puaiohi from 6 of 8 main river drainages of four survey areas explored. Although still rare and vulnerable to extinction (145±19 individuals known), puaiohi are more widely distributed within the Alakai Swamp than previously believed. Our data from 1996 suggest previous surveys methods have underestimated the population size or that the population has increased since 1981. The kamao has not been confirmed since 1985, but unconfirmed reports were made from 1989-1996. We have not sighted kamao to date despite intensive search efforts. We infer from detection probabilities that the species in highly likely to be extinct.

Hawaii↗

USGS2013

Nitrate in watersheds: straight from soils to streams?

Human activities are rapidly increasing the global supply of reactive N and substantially altering the structure and hydrologic connectivity of managed ecosystems. There is long-standing recognition that N must be removed along hydrologic flowpaths from uplands to streams, yet it has proven difficult to assess the generality of this removal across ecosystem types, and whether these patterns are influenced by land-use change. To assess how well upland nitrate (NO 3 - ) loss is reflected in stream export, we gathered information from >50 watershed biogeochemical studies that reported nitrate concentrations ([NO 3 - ]) for stream water and for either upslope soil solution or groundwater NO 3 - to examine whether stream export of NO3- accurately reflects upland NO 3 - losses. In this dataset, soil solution and streamwater [NO 3 - ] were correlated across 40 undisturbed forest watersheds, with streamwater [NO 3 - ] typically half (median = 50%) soil solution [NO 3 - ]. A similar relationship was seen in 10 disturbed forest watersheds. However, for 12 watersheds with significant agricultural or urban development, the intercept and slope were both significantly higher than the relationship seen in forest watersheds. Differences in concentration between soil solution or groundwater and stream water may be attributed to biological uptake, microbial processes including denitrification, and/or preferential flow routing. The results of this synthesis are consistent with the hypotheses that undisturbed watersheds have a significant capacity to remove nitrate after it passes below the rooting zone and that land use changes tend to alter the efficiency or the length of watershed flowpaths, leading to reductions in nitrate removal and increased stream nitrate concentrations.

Journal of Geophysical Research G: Biogeosciences↗

USGS2014

Wind River subbasin restoration: U.S. Geological Survey annual report November 2012 through December 2013

Executive Summary The Wind River subbasin in southwest Washington State provides habitat for a population of wild Lower Columbia River steelhead Oncorhynchus mykiss . There have been no hatchery steelhead planted in the Wind River subbasin since 1994, and hatchery adults are estimated to be less than one percent of adults in any year (pers comm. Thomas Buehrens, Washington Department of Fish and Wilflife). We used Passive Integrated Transponder (PIT)-tagging and a series of instream PIT-tag interrogation systems (PTIS) to investigate life-histories, populations, and efficacy of habitat restoration actions for these steelhead. Data from our study, and companion work by Washington Department of Fish and Wildlife (WDFW), will contribute to Bonneville Power Administration’s (BPA) Research Monitoring and Evaluation (RM&E) Program Strategy of Fish Population Status Monitoring ( www.cbfish.org/ProgramStrategy.mvc/ViewProgramStrategySummary/1 ), specifically the sub-strategies of: 1) Assessing the Status and Trends of Diversity of Natural Origin Fish Populations and to uncertainties research regarding differing life histories of a wild steelhead population, 2) Assessing the Status and Trend of Adult Natural Origin Fish Populations, and 3) Monitoring and Evaluating the Effectiveness of Tributary Habitat Actions Relative to Environmental, Physical, or Biological Performance Objectives. During summer 2013, we PIT-tagged parr steelhead in headwater areas of the Wind River subbasin to investigate variable life-histories, specifically to compare fate of those juvenile steelhead that move downstream prior to smolting with those that remain in their natal areas until smolting. A series of instream PTISs monitored movement of these fish. Detections at the instream PTISs showed trends of parr emigration during summer and fall, in addition to the expected movement of parr and smolts in spring. Long-term monitoring of PIT-tagged fish over multiple years will provide information on contribution of various life-history strategies to smolt production and adult returns, as well as helping to identify factors influencing parr movement. Movements of PIT-tagged adult steelhead were tracked with our instream PTISs. These data have provided information on timing of adult movements to various parts of the watershed, which is allowing us to assess adult returns to tributary watersheds within the Wind River subbasin. Determination of adult use of tributary watersheds has provided data that will contribute to evaluating the efficacy of the removal of Hemlock Dam from Trout Creek. Hemlock Dam, located at rkm 2.0 of Trout Creek was removed in summer 2009 and had contributed to hydrologic impairment of Trout Creek. Evaluating restoration efforts is of interest to many managers and agencies so that funding and time are allocated for best results. The evaluation of various life-histories of Lower Columbia River steelhead within the Wind River subbasin will provide information to better track populations, and to direct habitat restoration and water allocation planning. Increasingly detailed Viable Salmonid Population information, such as that provided by PIT-tagging and instream PTISs networks like those we are building and operating in the Wind River subbasin, will provide data to inform policy and management, as life-history strategies and production bottlenecks are identified and understood.

Washington↗

USGS1975

Environmental problems in the coastal and wetlands ecosystems of Virginia Beach, Virginia

Many of the city of Virginia Beach's beach stabilization and sewage disposal problems are the result of an inadequate understanding of the physical and biological systems. Influenced by population and economic pressures, natural systems were artificially stabilized by engineering projects that had to be constantly maintained. These same pressures continue to prevail today in spite of a new environmental awareness; changes are occurring very slowly. Furthermore, the lack of adequate sewage disposal facilities and the continued urbanization of inappropriate areas are threatening Virginia Beach's attractiveness as a resort area.

North Carolina;Virginia↗

USGS2000

Water quality in the central Arizona basins, Arizona, 1995-98

The water quality in rivers and streams and in selected aquifers in central Arizona basins in Arizona is described and illustrated. Major ions, nitrogen and other nutrients, and pesticides and some of their breakdown compounds were analyzed in both surface and ground water. Biological communities that included fish, invertebrates, and algae, were described in relation to stream water quality. Volatile organic compounds that originate from fuels, solvents, and industry were analyzed from ground-water samples. Agricultural and urban land-use effects on shallow ground water are compared and contrasted.

Circular↗

USGS2001

Geology, hydrology, and water quality in the vicinity of a Brownfield redevelopment site in East Moline, Illinois

An investigation of the geology, hydrology, and water quality in the vicinity of a Brownfield redevelopment site in East Moline, Illinois, was designed to determine if metals and organic compounds detected in the fill deposits in this area posed a threat to the water resources. The hydrologic features of concern at the site are surface water at a pond and surrounding wetland, the Mississippi River, and an unnamed stream and ground water in the shallow aquifer. The shallow aquifer is composed of saturated fill, sand and gravel, and weathered bedrock. The overall direction of surface- and ground-water flow in the study area is toward the Mississippi River. In the eastern part of the pond and wetland, ground water discharges to surface water. In the western part of the pond and wetland, surface water recharges to ground water. Everyday during the period for which water-level data were available, between 4.7 ' 10-4 and 1.4 ' 10-1 cubic feet of water flowed across a 1 square foot area of aquifer. Variations in values for oxidation-reduction potential and specific conductance may be affected by heterogeneity in the chemical composition of the fill and unconsolidated deposits and the bedrock units. Chemical and biological processes are altering the chemistry of the water in the pond relative to its ground-water source. Concentrations of iron and manganese in water samples appear to be affected by the local geochemical environment in the aquifer. The data do not indicate that contaminants in the fill material are having a substantial adverse affect on surface- or ground-water quality in the study area.

Illinois↗

USGS2007

Comparisons of Water Quality and Biological Variables from Colorado River Shoreline Habitats in Grand Canyon, Arizona, under Steady and Fluctuating Discharges from Glen Canyon Dam

Glen Canyon Dam operations are known to affect mainstem Colorado River temperature and shoreline habitats for native fish. Options for ameliorating the impacts that operations have on young native fish include changing release volumes and/or changing the daily range of releases. Long-term alterations of operations that may produce a measurable biological response can be costly, particularly if the treatment involves reduced power generation. In September and October 2005, a series of two-week releases occurred that alternated between daily fluctuations that varied by 76 m3 s-1 and steady releases. The purpose of these short-term experiments was to study the effect of daily operations on water quality parameters and biotic constituents (phytoplankton, macroinvertebrates, and fishes) of associated shoreline habitats. Our results indicate that measured biological and physical parameters were, in general, unaffected by flow treatments. However, results should be interpreted cautiously as time within and between treatments was likely insufficient to affect measured parameters. These results lead to the recommendation that studies like this may be more amenable to laboratory experiments first and then applied to a large-scale setting, preferably for longer duration.

Open-File Report↗

USGS1982

Determination and analysis of bearing capacity of calcarenites off the Florida Keys

A specially designed instrument was used to determine the in situ bearing capacity at 12 sites in the carbonate sand seaward of the Florida Keys. The resulting data set not only represents unique information in such an environment, but also provided an opportunity to determine whether bearing capacity is controlled by any specific property of the calcarenites, or, conversely, whether the bearing-capacity value could be used as an index of a particular substrate characteristic. The in sltu measurements were made in several subenvironments in order to bracket the variability of sediment properties throughout the area. Samples were collected at each bearing-capacity test site and w .ere analyzed for selected geological and geotechnical properties, including texture, grain shapes, and biological constituents. No relationship was found between bearing capacity and any of the analyzed properties of the sediment. Although many salient characteristics of calcarenites exist, at the stress levels used in this study their influence is either masked owing to the complex interaction of properties that leads to a specific bearing-capacity value or, at least in these sediments, is absent.

Open-File Report↗