An approach to assess land-cover trends in the conterminous United States (1973-2000)
No abstract available.
Conterminous United States↗
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Mesozoic and Cenozoic structural trends under southern Bering Sea shelf
Mesozoic rocks exposed near the tip of the Alaska Peninsula form an antiformal structure that flanks the southern side of Bristol Bay basin and that can be traced with geophysical data about 700 km offshore to the vicinity of the Pribilof Islands. Upper Jurassic sandstone and Upper Cretaceous mudstone dredged from the top and flanks of this structure near the islands confirm that Mesozoic rocks extend from the Alaska Peninsula to the Bering sea margin. The southern part of the Bering Sea Shelf is underlain by several large structural basins: St. George, Amak, and Bristol Bay basins. These filled basins encompass an offshore area of about 31,000 sq km; St. George basin contains more than 10 km of strata. Reflection profiles show that the surface of the offshore antiformal structures is an angular unconformity overlain by Cenozoic beds. This unconformity can be traced toward the axes of the adjacent subshelf basins where, as a disconformity, it parallels underlying and overlying strata. Dredge data suggest that the unconformity and disconformity may be as old as middle to Late Cretaceous. The downdip trace of the unconformity in Bristol Bay basin is underlain by reflectors paralleling the contact, a relation suggesting that the basin and perhaps other shelf basins may be underlain by ancient Mesozoic depocenters. The bulk of the thick sections in these basins is, however, thought to be mainly Cenozoic in age. Strata in the basins are cut by high-angle growth faults. The faults commonly offset the seafloor, which implies that basin subsidence and filling continue to the present. Shallow-water diatomaceous mudstone of Eocene and Oligocene age dredged from the continental slope near the Pribilof Islands indicates that collapse of the margin and outer shelf basins began by at least early Tertiary time. In Mesozoic time, the Bering margin between Siberia and the Alaska Peninsula (Beringian margin) may have been a zone of either oblique underthrusting or transform motion between the North American and Pacific lithosphere (Kula plate?). This motion may have rifted the edge of the North American plate, resulting in the formation of a series of elongate basins and ridges paralleling the plate edge. These hypothetical basins may have controlled the location and initial subsidence of Bristol Bay, Amak, and St. George basins. Formation of the Aleutian Island arc in late Mesozoic or earliest Tertiary time presumably terminated plate interaction along the Beringian margin. Sediment loading and subsequent subsidence of the remnant plate within the abyssal Bering Sea may have caused continuing collapse of the Beringian margin in latest Cretaceous and earliest Tertiary time.
AAPG Bulletin↗
Regional porosity trends of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity, with comparisons to formations of other basins
Sandstone porosity of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity decreases systematically as depth and thermal maturity increase over a wide range. Median porosity is about 25% where equivalent vitrinite reflectance (R o ) is slightly over 0.7% in the northern part of the study area (Clarke County, Mississippi). Median porosity is reduced to 8% where R o approaches 2.7% in the southern part of the study area (state waters of Mobile Bay). Porosity of the cemented, tight zone at the top of the Norphlet in downdip locations is roughly 10% lower than porosities of facies underlying the tight zone, but nevertheless is slightly above the norm for other sandstones at similar R o levels. Porosity of dune facies is consistently 2-5% higher than that of interdune facies, other factors being equal. Our data show 3-6% higher porosity in chlorite-dominated intervals relative to intervals where illite is the dominant clay mineral. Norphlet porosity has little or no correlation with position relative to the present-day hydrocarbon-water contact. Based on comparisons at similar R o levels, median (50th-percentile) Norphlet porosity exceeds porosities of "typical" sandstones in other basins by more than a factor of two throughout the study area. Even the lower (10th-percentile) Norphlet porosities are higher than median porosities of sandstones in general.
Alabama, Mississippi, Florida↗
Trends of litter decomposition and soil organic matter stocks across forested swamp environments of the southeastern US
A common idea in the discussion of soil carbon processes is that litter decomposition rates and soil carbon stocks are inversely related. To test this overall hypothesis, simultaneous studies were conducted of the relationship of environmental gradients to leaf and wood decomposition, buried cloth decomposition and percent soil organic matter in Taxodium distichum swamps across the Mississippi River Alluvial Valley (MRAV) and northern Gulf of Mexico (GOM) of the US. Decomposition of leaf tissue was 6.2 to 10.9 times faster than wood tissue. Both precipitation and flooding gradients were negatively related to leaf and wood litter decomposition rates based on models developed using Stepwise General Model Selection (MRAV vs. GOM, respectively). Cotton cloth should not be used as a proxy for plant litter without prior testing because cloth responded differently than plant litter to regional environmental gradients in T . distichum swamps. The overall hypothesis was supported in the MRAV because environments with higher precipitation (climate normal) had lower rates of decomposition and higher percent soil organic matter. In the MRAV, higher levels of percent soil organic matter were related to increased 30-year climate normals (30 year averages of precipitation and air temperature comprising southward increasing PrinComp1). Soil organic carbon % in inland vs. coastal T . distichum forests of the MRAV were comparable (range = 1.5% to 26.9% vs. 9.8 to 31.5%, respectively). GOM swamps had lower rates of litter decomposition in more flooded environments. Woody T . distichum detritus had a half-life of up to 300 years in the MRAV, which points to its likely role in the maintenance of inland “teal” soil organic carbon. This unique study can contribute to the discussion of approaches to maintain environments conducive to soil carbon stock maximization.
Arkansas, Florida, Illinois, Louisiana, Mississipp↗
Abundance trends and status of the Little Colorado River population of humpback chub
The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture-recapture-based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid-1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age-2 and older fish are age dependent but apparently not time dependent. Back-calculation of recruitment using the apparent 1990s population age structure implies periods of higher recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and Wildlife Service recovery criterion of stable abundance is not being met for this population. Also, there is a critical need to develop new abundance indexing and tagging methods so that early, reliable, and rapid estimates of humpback chub recruitment can be obtained to evaluate population responses to management actions designed to facilitate the restoration of Colorado River native fish communities. ?? Copyright by the American Fisheries Society 2006.
North American Journal of Fisheries Management↗
Now trending … Earthquake information
The U.S. Geological Survey Earthquake Hazards Program has overall successfully fulfilled its mission of providing timely earthquake information via web applications and other methods. Imagine a single month of earthquake data delivery, serving 3.6 billion total data requests, including 29 million pageviews by 7.1 million users, 606 million automated data feeds, and 45 million catalog downloads. Yet, some challenges and lapses in delivery have happened at critical times, including during the Ridgecrest earthquakes in 2019. We delve into the evolving demand for real‐time information as well as the technologies put in place to support the ever‐growing number of users in an increasingly mobile world.
Seismological Research Letters↗
Sampling-variance effects on detecting density dependence from temporal trends in natural populations
Monte Carlo simulations were conducted to evaluate robustness of four tests to detect density dependence, from series of population abundances, to the addition of sampling variance. Population abundances were generated from random walk, stochastic exponential growth, and density-dependent population models. Population abundance estimates were generated with sampling variances distributed as lognormal and constant coefficients of variation ( cv ) from 0.00 to 1.00. In general, when data were generated under a random walk, Type I error rates increased rapidly for Bulmer's R, Pollard et al.'s, and Dennis and Taper's tests with increasing magnitude of sampling variance for n > 5 yr and all values of process variation. Bulmer's R * test maintained a constant 5% Type I error rate for n > 5 yr and all magnitudes of sampling variance in the population abundance estimates. When abundances were generated from two stochastic exponential growth models ( R = 0.05 and R = 0.10), Type I errors again increased with increasing sampling variance; magnitude of Type I error rates were higher for the slower growing population. Therefore, sampling error inflated Type I error rates, invalidating the tests, for all except Bulmer's R * test. Comparable simulations for abundance estimates generated from a density-dependent growth rate model were conducted to estimate power of the tests. Type II error rates were influenced by the relationship of initial population size to carrying capacity ( K ), length of time series, as well as sampling error. Given the inflated Type I error rates for all but Bulmer's R *, power was overestimated for the remaining tests, resulting in density dependence being detected more often than it existed. Population abundances of natural populations are almost exclusively estimated rather than censused, assuring sampling error. Therefore, because these tests have been shown to be either invalid when only sampling variance occurs in the population abundances (Bulmer's R, Pollard et al.'s, and Dennis and Taper's tests) or lack power (Bulmer's R * test), little justification exists for use of such tests to support or refute the hypothesis of density dependence.
Ecological Monographs↗
New approaches to the analysis of population trends in land birds: Comment
James et al. (1996, Ecology 77:13-27) used data from the North American Breeding Bird Survey (BBS) to examine geographic variability in patterns of population change for 26 species of wood warblers. They emphasized the importance of evaluating nonlinear patterns of change in bird populations, proposed LOESS-based non-parametric and semi-parametric analyses of BBS data, and contrasted their results with other analyses, including those of Robbins et al. (1989, Proceedings of the National Academy of Sciences 86: 7658-7662) and Peterjohn et al. (1995, Pages 3-39 in T. E. Martin and D. M. Finch, eds. Ecology and management of Neotropical migratory birds: a synthesis and review of critical issues. Oxford University Press, New York.). In this note, we briefly comment on some of the issues that arose from their analysis of BBS data, suggest a few aspects of the survey that should inspire caution in analysts, and review the differences between the LOESS-based procedures and other procedures (e.g., Link and Sauer 1994). We strongly discourage the use of James et al.'s completely non-parametric procedure, which fails to account for observer effects. Our comparisons of estimators adds to the evidence already present in the literature of the bias associated with omitting observer information in analyses of BBS data. Bias resulting from change in observer abilities should be a consideration in any analysis of BBS data.
Ecology↗
Biodiversity in a changing climate: a synthesis of current and projected trends in the US
This paper provides a synthesis of the recent literature describing how global biodiversity is being affected by climate change and is projected to respond in the future. Current studies reinforce earlier findings of major climate-change-related impacts on biological systems and document new, more subtle after-effects. For example, many species are shifting their distributions and phenologies at faster rates than were recorded just a few years ago; however, responses are not uniform across species. Shifts have been idiosyncratic and in some cases counterintuitive, promoting new community compositions and altering biotic interactions. Although genetic diversity enhances species' potential to respond to variable conditions, climate change may outpace intrinsic adaptive capacities and increase the relative vulnerabilities of many organisms. Developing effective adaptation strategies for biodiversity conservation will not only require flexible decision-making and management approaches that account for uncertainties in climate projections and ecological responses but will also necessitate coordinated monitoring efforts.
Frontiers in Ecology and the Environment↗
Spatial trends in marsh sediment deposition within a microtidal creek system, Waccasassa Bay, Florida
Marsh surface deposition, suspended sediment concentrations, tidal hydrodynamics, and marsh surface characteristics were measured within a tidal creek system of a west-central Florida, microtidal, open marine Juncus roemerianus marsh to examine the depositional relationship between a creek system and the surrounding marsh during nonstorm conditions. Results suggest that short-term marsh deposition is highly episodic with deposition showing an inverse relationship with marsh surface inundation. Deposition was greatest at marsh sites adjacent to secondary creek segments over all examined timescales. Variations in hydroperiod, time–velocity asymmetry, vegetation density, and sediment availability could not explain the observed differences in short-term deposition.
Florida↗
Rates and trends of coastal change in california and the regional behavior of the beach and cliff system
The U.S. Geological Survey (USGS) recently completed an analysis of shoreline change and cliff retreat along the California coast. This is the first regional, systematic measurement of coastal change conducted for the West Coast. Long-term (-120 y) and short-term (-25 y) shoreline change rates were calculated for more than 750 km of coastline, and 70 year cliff-retreat rates were generated for 350 km of coast. Results show that 40% of California's beaches were eroding in the long term. This number increased to 66% in the short term, indicating that many beaches have shifted toward a state of chronic erosion. The statewide average net shoreline change rates for the long and short term were 0.2 m/y and -0.2 m/y, respectively. The long-term accretional signal is likely related to large coastal engineering projects in some parts of the state and to large fluxes of sediment from rivers in other areas. The cliff-retreat assessment yielded a statewide average of -0.3 m/y. It was found that Northern California has the highest overall retreat rates, which are influenced by erosion hot spots associated with large coastal landslides and slumps. The databases established as part of the shoreline change and cliff-retreat analyses were further investigated to examine the dynamics of the beach/cliff system. A correlation analysis identified a strong relationship between the geomorphology of the coast and the behavior of the beach/cliff system. Areas of high-relief coast show negative correlations, indicating that higher rates of cliff retreat correlate with lower rates of shoreline erosion. In contrast, low- to moderate-relief coasts show strong positive correlations, wherein areas of high shoreline change correspond to areas of high cliff retreat.
Journal of Coastal Research↗
Trends in late Maastrichtian calcareous nannofossil distribution patterns, Western North Atlantic margin
First and last occurrences of several Maastrichtian calcareous nannofossil species are shown to be diachronous across paleodepth and paleoenvironment using the graphic correlation method. Calcareous nannofossil assemblages examined from eleven cores from a deep- to shallow-water transect along the eastern United States Atlantic margin document that the first occurrence of Micula murus (Martini 1961) Bukry 1973 is diachronous, appearing 2.0 million years earlier in open ocean sites than in shallow marine sites. The first occurrence (FO) of Lithraphidites kennethii Perch-Nielsen 1984 is also nonsynchronous, appearing in the deep ocean before its FO in neritic waters. The last occurrence (LO) of L. praequadratus Roth 1978 is diachronous across paleodepth, going locally extinct first in deeper water. The LO of Watznaueria bybelliae Self-Trail 1999 is also diachronous, going locally extinct first in shallow-water settings. Ceratolithoides amplector Burnett 1997, C. pricei Burnett 1997, C. self-trailiae Burnett 1997, C. ultimus Burnett 1997, Cribrocorona gallica (Stradner 1963) Perch-Nielsen 1973. Micula praemurus (Bukry 1973) Stradner and Steinmetz 1984, Pseudomicula quadratus Perch-Nielsen et al. 1978, and Semihololithus spp. are present consistently in common to frequent abundances in ODP holes 1050C and 1052E on the Blake Nose, but they are rare or absent from neritic sections in Coastal Plain cores. It is apparent that these species flourished in an open ocean setting, suggesting that differences in assemblage abundance and diversity between deep ocean and nearshore areas were controlled by paleoceanographic factors. These species are not used for biostratigraphy, but may be useful indicators of open ocean conditions. The line of correlation (LOC) for nine Coastal Plain cores clearly defines the Cretaceous-Tertiary (K/T) boundary unconformity at the top of the Maastrichtian section (Peedee Formation) and the Campanian-Maastrichtian (C/M) unconformity at the base of the Maastrichtian section (Peedee/Donoho Creek formational contact). The K/T boundary unconformity is undulatory in nature; updip Maastrichtian sections have been stripped to a greater depth than the downdip sections. The uppermost Campanian, all of the lowermost Maastrichtian, and the basal upper Maastrichtian sediments are missing from the study area.
Micropaleontology↗
Origin and significance of postore dissolution collapse breccias cemented with calcite and barite at the Meikle gold deposit, Northern Carlin trend, Nevada
The final event in a complicated hydrothermal history at the Meikle gold deposit was gold deficient but caused extensive postore dissolution of carbonate, collapse brecciation, and precipitation of calcite and barite crystals in the resulting cavities. Although previously interpreted to be part of the Carlin -type hydrothermal system, crosscutting relationships and U-Th-Pb geochronology constrain this hydrothermal event to late Pliocene time (ca. 2 Ma), nearly 36 Ma after ore formation. Mineralogic, fluid inclusion, and stable isotope data indicate that postore hydrothermal fluids were reduced, H 2 S-rich, unevolved meteoric waters ((δ 18 O = -17‰) of low temperature (ca. 65°C). The δ 18 O values of barite and calcite indicate that these minerals were in isotopic equilibrium, requiring that barite SO 4 was derived from the oxidation of reduced sulfur; however, preexisting sulfides in breccia cavities were not oxidized. The δ 34 S (15‰) values of barite are higher than those of local bulk sulfide and supergene alunite indicating that SO 4 was not derived from supergene oxidation of local sulfide minerals. The 15 per mil δ 34 S value suggests that the H 2 S in the fluids may have been leached from sulfur-rich organic matter in the local carbonaceous sedimentary rocks. A reduced H 2 S-rich fluid is also supported by the bright cathodoluminescence of calcite which indicates that it is Mn rich and Fe poor. Calcite has a narrow range of δ 13 C values (0.3-1.8‰) that are indistinguishable from those of the host Bootstrap limestone, indicating that CO 2 in the fluid was from dissolution of the local limestone. These data suggest that dissolution and brecciation of the Bootstrap limestone occurred where H 2 S-rich fluids encountered more oxidizing fluids and formed sulfuric acid (H 2 SO 4 ). Intense fracturing in the mine area by previous structural and hydrothermal events probably provided conduits for the descent of oxidized surface water which mixed with the underlying H 2 S-rich waters to form the dissolving acid. The surface-derived fluid apparently contained sufficient oxygen to produce H 2 SO 4 from H 2 S but not enough to alter pyrite to Fe oxide. Although H 2 S is an important gold -transporting ligand, the temperature was too low to transport a significant amount of gold . The presence of analogous calcite - and barite -lined cavities in other Carlin -type deposits suggests that the generation (and oxidation) of H 2 S-rich meteoric waters was a common phenomenon in north-central Nevada . Previous sulfur isotope studies have also shown that the Paleozoic sedimentary rocks were the principal source of H 2 S in Devonian sedimentary exhalative-type, Jurassic intrusion-related, Eocene Carlin -type, and Miocene low-sulfidation gold deposits in the region. The similar sulfur source in all of these systems suggests that basin brines, magmatic fluids, and meteoric waters all evolved to be H 2 S-rich ore fluids by circulation through Paleozoic sedimentary rocks. Thus, although not directly related to gold mineralization, the recent hydrologic history of the deposit provides important clues to earlier ore-forming processes that were responsible for gold mineralization.
Nevada↗
Trends in Engineering Geologic and Related Mapping 1972–1983
Progress is reviewed that has been made during the period 1972-1982 in producing medium- and small-scale engineering geologic maps with a variety of content. Improved methods to obtain and present information are evolving. Standards concerning text and map content, soil and rock classification, and map symbols have been proposed. Application of geomorphological techniques in terrain evaluation has increased, as has the use of aerial photography and other remote sensing. Computers are being used to store, analyze, retrieve, and print both text and map information. Development of offshore resources, especially petroleum, has led to marked improvement and growth in marine engineering geology and geotechnology. Coordinated planning for societal needs has required broader scope and increased complexity of both engineering geologic and environmental geologic studies. Refs.
Bulletin of the Association of Engineering Geologi↗
Roadside bear viewing opportunities in Yellowstone National Park: characteristics, trends, and influence of whitebark pine
Opportunities for viewing grizzly bears ( Ursus arctos ) and American black bears ( U. americanus ) from roadways in Yellowstone National Park (YNP) have increased in recent years. Unlike the panhandling bears common prior to the 1970s, current viewing usually involves bears feeding on natural foods. We define roadside bear viewing opportunities that cause traffic congestion as ‘‘bear-jams.’’ We investigated characteristics of bear-jams and their frequency relative to whitebark pine ( Pinus albicaulis ) cone production, an important fall food for bears, during 1990–2004. We observed a difference in diel distribution of bear-jams between species ( x 2 =70.609, 4 df, P<0.001) with the occurrence of grizzly bear-jams being more crepuscular. We found evidence for decreasing distances between bears and roadways and increasing durations of bears-jams. The annual proportion of bear-jams for both species occurring after the week of 13–19 August were 3–4 times higher during poor cone crop years than good. We suggest that native foods found in road corridors may be especially important to some individual bears during years exhibiting poor whitebark pine crops. We discuss management implications of threats to whitebark pine and increasing habituation of bears to people.
Idaho, Montana, Wyoming↗
Historical trends in Chesapeake Bay dissolved oxygen based on benthic foraminifera from sediment cores
Environmentally sensitive benthic foraminifera (protists) from Chesapeake Bay were used as bioindicators to estimate the timing and degree of changes in dissolved oxygen (DO) over the past five centuries. Living foraminifers from 19 surface samples and fossil assemblages from 11 sediment cores dated by 210 Pb, 137 Cs, 14 C, and pollen stratigraphy were analyzed from the tidal portions of the Patuxent, Potomac, and Choptank Rivers and the main channel of the Chesapeake Bay. Ammonia parkinsoniana , a facultative anaerobe tolerant of periodic anoxic conditions, comprises an average of 74% of modern Chesapeake foraminiferal assemblages (DO-0.47 and 1.72 ml l −1 ) compared to 0% to 15% of assemblages collected in the 1960s. Paleoecological analyses show that A. parkinsoniana was absent prior to the late 17th century, increased to 10–25% relative frequency between approximately 1670–1720 and 1810–1900, and became the dominant (60–90%) benthic formaniferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests of A. parkinsoniana occur in all cores (10–20% of Ammonia ), suggesting unprecedented stressful benthic conditions. These cores indicate that prior to the late 17th century, there was limited oxygen depletion. During the past 200 years, decadal scale variability in oxygen depletion has occurred, as dysoxic (DO=0.1–1.0 ml l −1 ), perhaps short-term anoxic (DO<0.1 ml l −1 ) conditions developed. The most extensive (spatially and temporally) anoxic conditions were reached during the 1970s. Over decadal timescales, DO variability seems to be linked closely to climatological factors influencing river discharge; the unprecedented anoxia since the early 1970s is attributed mainly to high freshwater flow and to an increase in nutrient concentrations from the watershed.
Maryland, Virginia↗