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At least 433 records · Page 24Linked to original sources
USGS2008

Environmental chemical data for perishable sediments and soils collected in New Orleans, Louisiana, and along the Louisiana Delta following Hurricanes Katrina and Rita, 2005

In October 2005, nearly one month after Hurricanes Katrina and Rita, a team of scientists from the U.S. Geological Survey and the Missouri University of Science and Technology deployed to southern Louisiana to collect perishable environmental data resulting from the impacts of these storms. Perishable samples collected for this investigation are subject to destruction or ruin by removal, mixing, or natural decay; therefore, collection is time-critical following the depositional event. A total of 238 samples of sediment, soil, and vegetation were collected to characterize chemical quality. For this analysis, 157 of the 238 samples were used to characterize trace element, iron, total organic carbon, pesticide, and polychlorinated biphenyl concentrations of deposited sediment and associated shallow soils. In decreasing order, the largest variability in trace element concentration was detected for lead, vanadium, chromium, copper, arsenic, cadmium, and mercury. Lead was determined to be the trace element of most concern because of the large concentrations present in the samples ranging from 4.50 to 551 milligrams per kilogram (mg/kg). Sequential extraction analysis of lead indicate that 39.1 percent of the total lead concentration in post-hurricane sediment is associated with the iron-manganese oxide fraction. This fraction is considered extremely mobile under reducing environmental conditions, thereby making lead a potential health hazard. The presence of lead in post-hurricane sediments likely is from redistribution of pre-hurricane contaminated soils and sediments from Lake Pontchartrain and the flood control canals of New Orleans. Arsenic concentrations ranged from 0.84 to 49.1 mg/kg. Although Arsenic concentrations generally were small and consistent with other research results, all samples exceeded the U.S. Environmental Protection Agency’s Human Health Medium-Specific Screening Level of 0.39 mg/kg. Mercury concentrations ranged from 0.02 to 1.30 mg/kg. Comparing the mean mercury concentration present in post-hurricane samples with regional background data from the U.S. Geological Survey National Geochemical Dataset, indicates that mercury concentrations in post-hurricane sediment generally are larger. Sequential extraction analysis of 51 samples for arsenic indicate that 54.5 percent of the total arsenic concentration is contained in the extremely mobile iron-manganese oxide fraction. Pesticide and polychlorinated biphenyl Arochlor concentrations in post-hurricane samples were small. Prometon was the most frequently detected pesticide with concentrations ranging from 2.4 to 193 micrograms per kilogram (µg/kg). Methoxychlor was present in 22 samples with a concentration ranging from 3.5 to 3,510 µg/kg. Although methoxychlor had the largest detected pesticide concentration, it was well below the U.S. Environmental Protection Agency’s High-Priority Screening Level for residential soils. Arochlor congeners were not detected for any sample above the minimum detection level of 7.9 µg/kg.

Louisiana↗
USGS2018

Insights from long-term ungrazed and grazed watersheds in a salt desert Colorado Plateau ecosystem

Dryland ecosystems cover over 41% of the earth’s land surface, and living within these important ecosystems are approximately 2 billion people, a large proportion of whom are subsistence agropastoralists. Improper grazing in drylands can negatively impact ecosystem productivity, soil conservation, hydrologic processes, downstream water quantity and quality, and ultimately human health and economic well-being. Concerns regarding the degraded state of western US rangelands in the 1950s resulted in an interagency committee to study the effects of land use on runoff and erosion processes. In 1953, a federal research group established four paired watersheds in western Colorado to study the interaction of grazing by domestic livestock, runoff, and sediment yield. Exclusion of livestock from half of the watersheds dramatically reduced runoff and sediment yield after the first 10 yr—primarily due to changes in ground cover but not vegetation. Here, we report results of repeated soils and vegetation assessments of the experimental watersheds after more than 50 yr of grazing exclusion. Results show that many of the differences in soil conditions between grazed and ungrazed watersheds observed in the 1950s and 1960s were still present in 2004, despite reduced numbers of livestock: few differences in vegetation cover but large differences in biological soil crusts, soil stability, soil compaction, and soil biogeochemistry. There were differences among soil types in response to grazing history, especially soil lichen cover and soil organic matter, nitrogen, and sodium. Comparisons of ground cover measured in 2004 with those measured in 1953, 1966, and 1972 suggest much of the differences between grazed and ungrazed watersheds likely were driven by high sheep numbers during droughts in the 1950s. Persistence of these differences, despite large reductions in stocking rates , suggest the combination of overgrazing and drought may have pushed these salt desert ecosystems into a persistent, degraded ecological state.

Salt Desert Colorado Plateau Ecosystem↗
USGS2016

The geochemical atlas of Alaska, 2016

A rich legacy of geochemical data produced since the early 1960s covers the great expanse of Alaska; careful treatment of such data may provide significant and revealing geochemical maps that may be used for landscape geochemistry, mineral resource exploration, and geoenvironmental investigations over large areas. To maximize the spatial density and extent of data coverage for statewide mapping of element distributions, we compiled and integrated analyses of more than 175,000 sediment and soil samples from three major, separate sources: the U.S. Geological Survey, the National Uranium Resource Evaluation program, and the Alaska Division of Geological & Geophysical Surveys geochemical databases. Various types of heterogeneity and deficiencies in these data presented major challenges to our development of coherently integrated datasets for modeling and mapping of element distributions. Researchers from many different organizations and disparate scientific studies collected samples that were analyzed using highly variable methods throughout a time period of more than 50 years, during which many changes in analytical techniques were developed and applied. Despite these challenges, the U.S. Geological Survey has produced a new systematically integrated compilation of sediment and soil geochemical data with an average sample site density of approximately 1 locality per 10 square kilometers (km 2 ) for the entire State of Alaska, although density varies considerably among different areas. From that compilation, we have modeled and mapped the distributions of 68 elements, thus creating an updated geochemical atlas for the State.

Alaska↗
USGS2010

Movements of water, solutes, and stable isotopes in the unsaturated zones of two sand plains in the upper Midwest

Four month-long field experiments investigated movements of water and solutes through unsaturated sand plains near Princeton, Minnesota, and Oakes, North Dakota. Atrazine and bromide were applied to bare soils and soils planted with corn. The field plots were irrigated according to local farming practices. At the end of each experiment, unsaturated soils were analyzed for atrazine and bromide concentrations and oxygen and hydrogen isotope compositions of soil water. Most soil water was affected by evaporation but groundwater beneath the plots had no evaporative isotopic signature. Therefore most recharge consisted of water that was unaffected by evaporation. Sources of such water may have included snowmelt, prolonged or high-intensity rainfalls that were not interrupted by periods of drying, and water that moved through preferential flow paths. Preferential flow also was suggested by the detection of atrazine, deethylatrazine, and bromide in groundwater shortly after each application of irrigation water at Princeton and by isolated concentrations of atrazine and bromide in soil well below the main masses of chemicals at Oakes.

Minnesota, North Dakota↗
USGS2006

Trends of Abutment-Scour Prediction Equations Applied to 144 Field Sites in South Carolina

The U.S. Geological Survey conducted a study in cooperation with the Federal Highway Administration in which predicted abutment-scour depths computed with selected predictive equations were compared with field measurements of abutment-scour depth made at 144 bridges in South Carolina. The assessment used five equations published in the Fourth Edition of 'Evaluating Scour at Bridges,' (Hydraulic Engineering Circular 18), including the original Froehlich, the modified Froehlich, the Sturm, the Maryland, and the HIRE equations. An additional unpublished equation also was assessed. Comparisons between predicted and observed scour depths are intended to illustrate general trends and order-of-magnitude differences for the prediction equations. Field measurements were taken during non-flood conditions when the hydraulic conditions that caused the scour generally are unknown. The predicted scour depths are based on hydraulic conditions associated with the 100-year flow at all sites and the flood of record for 35 sites. Comparisons showed that predicted scour depths frequently overpredict observed scour and at times were excessive. The comparison also showed that underprediction occurred, but with less frequency. The performance of these equations indicates that they are poor predictors of abutment-scour depth in South Carolina, and it is probable that poor performance will occur when the equations are applied in other geographic regions. Extensive data and graphs used to compare predicted and observed scour depths in this study were compiled into spreadsheets and are included in digital format with this report. In addition to the equation-comparison data, Water-Surface Profile Model tube-velocity data, soil-boring data, and selected abutment-scour data are included in digital format with this report. The digital database was developed as a resource for future researchers and is especially valuable for evaluating the reasonableness of future equations that may be developed.

South Carolina↗
USGS2026

Assessing environmental drivers of denitrification in restored riverine floodplains

Restoration of impaired floodplains is an increasingly prevalent strategy for alleviating water quality concerns and reducing downstream flooding at watershed scales. Floodplains temporarily store water and slow flow velocity to promote sedimentation during overbank flooding and remove inorganic nitrogen from floodwater and groundwater via denitrification. Evaluating the impacts of different restoration strategies on denitrification can inform more strategic investments into floodplain modifications that improve water quality outcomes. Our research investigates how denitrification rates in floodplains respond to environmental factors that are actionable from an engineering perspective through design and water resources management. We seasonally measured soil denitrification enzyme activity and various environmental characteristics in 4 floodplains with different restoration design and management approaches at the confluence of the Wabash and Tippecanoe Rivers in Indiana, United States. Our results showed that denitrification rates in an agricultural floodplain were significantly lower than in restored floodplains with native vegetation. Certain soil conditions characteristic of floodplain wetlands were associated with higher denitrification, particularly elevated total nitrogen, moisture, silt, and organic matter contents. Vegetation species composition was correlated with denitrification rates. This link may reflect the direct effects of vegetation on soil conditions, such as supplying labile organic carbon, or indirect effects, such as vegetation acting as an indicator of hydrologic regime and land use. Denitrification seasonally varied, peaking in winter when nitrate supply from rivers draining agricultural watersheds in the region is also high. Substrate limitation of soil denitrification enzyme activity was most significant during the summer when overbank flooding, which replenishes soil nitrogen stocks, rarely occurs. Our findings indicate that denitrification capacity will likely be maximized in riverine floodplains that are restored as wetlands with diverse native vegetation and enhanced hydrologic connectivity. Such restoration activities promote higher denitrification rates via elevated moisture, fine sediment deposition, and soil organic matter.

Tippecanoe River, Wabash River↗
USGS1984

Rehabilitation materials from surface- coal mines in western U.S.A. III. Relations between elements in mine soil and uptake by plants.

Plant uptake of Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn from mine soils was assessed using alfalfa Medicago sativa, sainfoin Onobrychis viciaefolia, smooth brome Bromus inermis, crested wheatgrass Agropyron cristatum, slender wheatgrass A. trachycaulum and intermediate wheatgrass A. intermedium; mine soil (cover-soil and spoil material) samples were collected from rehabilitated areas of 11 western US surface-coal mines in North Dakota, Montana, Wyoming and Colorado. Correlations between metals in plants and DTPA-extractable metals from mine soils were generally not statistically significant and showed no consistent patterns for a single metal or for a single plant species. Metal uptake by plants, relative to amounts in DTPA extracts of mine soil, was positively related to mine soil organic matter content or negatively related to mine soil pH. DTPA-extractable metal levels were significantly correlated with mine soil pH and organic-matter content.-from Authors

Reclamation and Revegetation Research↗
USGS1996

Research-derived insights into surface geochemical hydrocarbon exploration

Research studies based on foreland basins (mainly in eastern Colorado) examined three surface geochemical exploration (SGE) methods as possible hydrocarbon (HC) exploration techniques. The first method, microbial soil surveying, has high potential as an exploration tool, especially hi development and enhanced recovery operations. Integrative adsorption, the second technique, is not effective as a quantitative SGE method because water, carbon dioxide, nitrous oxide, unsaturated hydrocarbons, and organic compounds are collected by the adsorbent (activated charcoal) much more strongly than covalently bonded microseeping Q-Cs thermogenic HCs. Qualitative comparisons (pattern recognition) of C8+ mass spectra cannot gauge HC gas microseepage that involves only the Q-Cs HCs. The third method, soil cakite surveying, also has no potential as an exploration tool. Soil calcite concentrations had patterns with pronounced areal contrasts, but these patterns had no geometric relationship to surface traces of established or potential production, that is, the patterns were random. Microscopic examination of thousands of soils revealed that soil calcite was an uncrystallized caliche coating soil particles. During its precipitation, caliche captures or occludes any gases, elements, or compounds in its immediate vicinity. Thus, increased signal intensity of some SGE methods should depend on increasing soil calcite concentrations. Analyses substantiate this hypothesis. Because soil calcite has no utility as a surface exploration tool, any surface method that depends on soil calcite has a diminished utility as an SGE tool. Isotopic analyses of soil calcites revealed carbonate carbon ??13C values of -4.0 to +2.07co (indicating a strong influence of atmospheric CO2) as opposed to expected values of-45 to -30%c if the carbonate carbon had originated from microbial oxidation of microseeping HC gases. These analyses confirm a surface origin for this soil calcite (caliche), which is not necessarily related to HC gas microseepage. This previously unappreciated pivotal role of caliche is hypothesized to contribute significantly to the poor and inconsistent results of some SGE methods.

AAPG Memoir↗
USGS2004

Mechanism and active variety of allelochemicals

This article summarizes allelochemicals' active variety, its potential causes and function mechanisms. Allelochemicals' activity varies with temperature, photoperiod, water and soils during natural processes, with its initial concentration, compound structure and mixed degree during functional processes, with plant accessions, tissues and maturity within-species, and with research techniques and operation processes. The prospective developmental aspects of allelopathy studies in the future are discussed. Future research should focus on: (1) to identify and purify allelochemicals more effectively, especially for agriculture, (2) the functions of allelopathy at the molecular structure level, (3) using allelopathy to explain plant species interactions, (4) allelopathy as a driving force of succession, and (5) the significance of allelopathy in the evolutionary processes.

Acta Botanica Sinica↗
USGS2019

Soil microbial communities and global change

Soils and soil microbial communities mediate the biogeochemical processes that underly ecosystem-level changes. This chapter examines why soils and soil microbial communities are important for understanding impacts and feedbacks to global change. It discusses the technological approaches and challenges that are at the frontiers of this research area. Global change impacts on microbial communities can be categorized as press or pulse disturbances. Global increases in atmospheric temperature are among the most profound and concerning long-term changes affecting human society. The chapter focuses on the examples from Western North America, where issues such as land cover change, wildfire, and permafrost thaw are some of the most observable global change impacts. Wildfire is a natural phenomenon that lies at the basis of the process of plant succession. Recovery and regrowth of vegetation after wildfire regenerates carbon and nutrient pools, such that long-term impacts on the ecosystems may be small.

Book chapter↗
USGS1974

The soil creep-curved tree fallacy

No evidence has been found in eastern deciduous forests to substantiate statements that curved tree trunks, downslope tilted tree trunks, and upslope trailing tree root systems are the result of soil creep. Curvature and tilting of trunks are described as geotropic and phototropic responses to physical and physiological conditions unrelated to soil creep. The occurrence of upslope trailing of roots has not been demonstrated.

Journal of Research of the U.S. Geological Survey↗
USGS2020

Comment on 'Kidron (2018): Biocrust research: A critical view on eight common hydrological‐related paradigms and dubious theses. Ecohydrology, e2061'

Kidron (2018) uses a straw man argument in an attempt to debunk eight putative hydrological‐related paradigms he believes to be “common among hydrologists, ecologists, or microbiologists that investigate biocrusts.” These paradigms relate to the roles of physical crusts and vascular plants in biocrust development, the major drivers (climate, porosity, hydrophobicity, and exopolysaccharides) of hydrology (infiltration and runoff), and the effect of mosses on hydrology and therefore vascular plants. We see two major problems with his arguments. First, they assume that the paradigms in question are generally accepted by biocrust researchers. Second, they are based on Kidron's (2018) world view of biocrusts, which has largely been informed by his own studies from a single, distinctly unique area of sand dunes at the Nizzana Research Site in the Negev Desert, Israel. This narrow focus and the selective use of published material disqualify his arguments. Our collective experience, based on more than 250 person years of biocrust research, and more than 700 scientific publications on biocrusts from all continents including Antarctica, indicates that, far from the straw man arguments proposed by Kidron (2018), there is no evidence to support the existence of a unifying theory that captures the global effects of biocrusts on hydrology. Our collective works demonstrate that, contrary to claims by Kidron (2018), the hydrological effects of biocrusts are strongly nuanced, varying with, but not limited to, differences in ecological context, landscape position, site condition, crust type and composition, climatic zone, soil texture and porosity, surface morphology, and spatial scale (reviewed in Weber, Büdel, & Belnap, 2016). Below, we critically analyse each of Kidron's (2018) paradigms, providing rigorous empirical evidence to show that none represent commonly held views among the biocrust research community.

Ecohydrology↗
USGS1987

Results of a workshop concerning ecological zonation in bottomland hardwoods

Under Section 404 of the Clean Water Act, the U.S. Environmental Protection Agency (EPA) has regulatory responsibilities concerning the discharge of dredged or fill material into the Nation's waters. In addition to its advisory role in the U.S. Army Corps of Engineers' permit program, EPA has a number of specific authorities, including formulation of the Section 404(b)(1) Guidelines, use of Section 404(c) to prohibit disposal at particular sites, and enforcement actions for unauthorized discharges. A number of recent court cases focus on the geographic scope of Section 404 jurisdiction in potential bottomland hardwood (BLH) wetlands and the nature of landclearing activities in these areas that require a permit under Section 404. Accordingly, EPA needs to establish the scientific basis for implementing its responsibilities under Section 404 in bottomland hardwoods. EPA is approaching this task through a series of workshops designed to provide current scientific information on bottomland hardwoods and to organize that information in a manner pertinent to key questions, including the following. What are the characteristics of bottomland hardwoods (in terms of hydrology, soils, vegetation, fish, wildlife, agricultural potential, and the like) and how can the functions (e.g., flood storage, water quality maintenance, detrital export) that they perform best be quantified? How do perturbations like landclearing, levee construction, and drainage impact the functions that bottomland hardwoods perform and how can these effects best be quantified? And finally, how significant are the impacts and how is their significance likely to change under various management scenarios? The first workshop in this series was held December 3-7, 1984, in St. Francisville, Louisiana. The workshop was attended by over 40 scientists and regulators (see ACKNOWLEDGMENTS section) and facilitated by the editors of this report under an Interagency Agreement between EPA and the U.S. Fish and Wildlife Service. The general objective of the workshop was to examine ways in which the structure and function of BLH ecosystems can be characterized and, in particular, to investigate the utility of a conceptual framework developed at a workshop held in Lake Lanier, Georgia, in 1980. In this framework, the transition from aquatic habitats to upland habitats through a BLH ecosystem is divided into six zones based on concomitant variation in the soil moisture regime and associated vegetation (Table 1). The zonation concept is of particular interest to EPA from at least two perspectives. The first is simply as a framework for organizing information. If the zones are discernible in the field, have recognizable characteristics, and perform identifiable functions, they might form a useful basis for tasks such as assessing the impacts of a particular site-specific activity. The second is the potential utility of the zonation concept in identifying the wetland portions of BLH communities. If the zones can be recognized in the field, and if one or more of them can be shown consistently to have wetland characteristics (i.e., perform functions, such as detrital export, often attributed to wetlands), while others do not, then the zones might have utility in identifying areas that fall under the jurisdiction of Section 404. The workshop itself was divided into two parts. The first was a series of papers in which authors described current research and data-synthesis activities in the context of the zonation concept. The second was a series of six workgroups in which participants discussed the zonation concept from the perspective of hydrology, soils, vegetation, fish, wildlife, and ecosystem processes. This report is a compilation of the written material from those workgroups, much of which was produced at the workshop. The formal papers presented in the first part of the workshop have been distributed to participants under separate cover, but are referenced in this report by citations such as: (Jones, workshop presentation).

Report↗
USGS2003

Changes in the chemistry of lakes and precipitation in high-elevation national parks in the western United States, 1985–1999

High-elevation lakes in the western United States are sensitive to atmospheric deposition of sulfur and nitrogen due to fast hydrologic flushing rates, short growing seasons, an abundance of exposed bedrock, and a lack of well-developed soils. This sensitivity is reflected in the dilute chemistry of the lakes, which was documented in the U.S. Environmental Protection Agency's Western Lake Survey of 1985. Sixty-nine lakes in seven national parks sampled during the 1985 survey were resampled during fall 1999 to investigate possible decadal-scale changes in lake chemistry. In most lakes, SO 4 concentrations were slightly lower in 1999 than in 1985, consistent with a regional decrease in precipitation SO 4 concentrations and in SO 2 emissions in the western United States. Nitrate concentrations also tended to be slightly lower in 1999 than in 1985, in contrast with generally stable or increasing inorganic N deposition in the west. Differences in alkalinity were variable among parks but were relatively consistent within each park. Possible effects of annual and seasonal-scale variations in precipitation amount on lake chemistry were evaluated based on climate data available for the parks and an analysis of climatic effects at two research watersheds with long-term records. Results suggest that rain prior to sampling in 1985 may have caused elevated NO 3 in some lakes due to direct runoff of precipitation and flushing of NO 3 from alpine soils, which may explain some of the decrease in NO 3 concentrations observed in survey lakes.

Water Resources Research↗
USGS1993

Selecting islands and shoals for conservation based on biological and aesthetic criteria

Consideration of biological quality has long been an important component of rating areas for conservation. Often these same areas are highly valued by people for aesthetic reasons, creating demands for housing and recreation that may conflict with protection plans for these habitats. Most methods of selecting land for conservation purposes use biological factors alone. For some land areas, analysis of aesthetic qualities is also important in describing the scenic value of undisturbed land. A method for prioritizing small islands and shoals based on both biological and visual quality factors is presented here. The study included 169 undeveloped islands and shoals a??0.8 ha in the Thousand Islands Region of the St. Lawrence River, New York. Criteria such as critical habitat for uncommon plant and animal species were considered together with visual quality and incorporated into a rating system that ranked the islands and shoals according to their priority for conservation management and protection from development. Biological factors were determined based on previous research and a field survey. Visual quality was determined by visual diagnostic criteria developed from public responses to photographs of a sample of islands. Variables such as elevation, soil depth, and type of plant community can be used to classify islands into different categories of visual quality but are unsuccessful in classifying islands into categories of overall biological quality.

Environmental Management↗
USGS2007

Luminescence ages for alluvial-fan deposits in Southern Death Valley: Implications for climate-driven sedimentation along a tectonically active mountain front

Controversy exists over whether alluvial-fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics. Knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause. Alluvial-fan deposits in Death Valley and throughout the arid southwestern United States have long been the subjects of study, but their ages have generally eluded researchers until recently. Most mapping efforts have recognized at least four major relative-age groupings (Q1 (oldest), Q2, Q3, and Q4 (youngest)), using observed changes in surface soils and morphology, relation to the drainage net, and development of desert pavement. Obtaining numerical age determinations for these morphologic stages has proven challenging. We report the first optically stimulated luminescence (OSL) ages for three of these four stages deposited within alluvial-fans along the tectonically active Black Mountains of Death Valley. Deposits showing distinct, remnant bar and swale topography (Q3b) have OSL ages from 7 to 4 ka., whereas those with moderate to poorly developed desert pavement and located farther above the active channel (Q3a) have OSL ages from 17 to 11 ka. Geomorphically older deposits with well-developed desert pavement (Q2d) have OSL ages ???25 ka. Using this OSL-based chronology, we note that alluvial-fan deposition along this tectonically active mountain front corresponds to both wet-to-dry and dry-to-wet climate changes recorded globally and regionally. These findings underscore the influence of climate change on alluvial fan deposition in arid and semi-arid regions. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS1999

Habitat invasibility and dominance by alien annual plants in the western Mojave Desert

Patterns of habitat invasibility and alien dominance, respectively measured as species richness and biomass of alien annual plants, were evaluated in association with four habitat factors at the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, USA. Habitat factors varied in levels of disturbance outside (high) and inside (low) the DTNA, and in levels of soil nutrients in washlet (high) and hummock (low) topographic positions, in Larrea -north (high), Larrea -south (medium), and interspace (low) microhabitats near creosote bushes ( Larrea tridentata ), and during 1995 when rainfall was 207% (high) and 1994 when rainfall was 52% (low) of the long-term average. Dominant alien plants included the annual grasses Bromus rubens , Bromus trinii , and Schismus spp., and the forb Erodium cicutarium . Species richness and dominance of alien annual plants were slightly higher where disturbance was high, and much higher where soil nutrients were high. B. rubens and B. trinii were most dominant in washlets and in the Larrea -north microhabitats during both years. These two species evolved in mesic ecosystems, and appeared to be particularly limited by soil nutrients at this site. Schismus spp. and E. cicutarium were also most dominant in washlets, but their dominance varied between interspaces in 1994 and the Larrea -south microhabitat in 1995. Monitoring to detect the invasion of new annual plants should focus on regions of high rainfall and nitrogen deposition and on washes and beneath-canopy microhabitats. The ecological range of each alien species should be evaluated separately, because their evolutionary origins may greatly affect their patterns of invasion and dominance in the Mojave Desert.

California↗
USGS1985

A procedure for estimating Bacillus cereus spores in soil and stream-sediment samples — A potential exploration technique

The presence of bacterial spores of the Bacillus cereus group in soils and stream sediments appears to be a sensitive indicator of several types of concealed mineral deposits, including vein-type gold deposits. The B. cereus assay is rapid, inexpensive, and inherently reproducible. The test, currently under investigation for its potential in mineral exploration, is recommended for use on a research basis. Among the aerobic spore-forming bacilli, only B. cereus and closely related strains produce an opaque zone in egg-yolk emulsion agar. This characteristic, also known as the Nagler of lecitho-vitellin reaction, has long been used to rapidly indentify and estimate presumptive B. cereus . The test is here adapted to permit rapid estimation of B. cereus spores in soil and stream-sediment samples. Relative standard deviation was 10.3% on counts obtained from two 40-replicate pour-plate determinations. As many as 40 samples per day can be processed. Enough procedural detail is included to permit investigation of the test in conventional geochemical laboratories using standard microbiological safety precautions.

Journal of Geochemical Exploration↗