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At least 919 records · Page 51Linked to original sources
USGS2001

The importance of competition in regulating plant species abundance along a salinity gradient

Current theories differ in their predictions concerning the effects of interspecific interactions on species growth and distribution along environmental gradients. In this study, we examined the influence of competition on species composition across a salinity gradient. This work involved three common fresh and brackish marsh species. The three species, Spartina patens, Sagittaria lancifolia, and Panicum hemitomon, differ in salt tolerances but are commonly found in overlapping zones across coastal marsh gradients in the southeastern United States. Plants were grown in a greenhouse under four salinity treatments (0, 2, 4, and 8 g/kg), in monocultures and in three‐species mixtures. Data from the monocultures and mixtures were used to examine the importance of competition in regulating community composition and species' growth. Results for individual species were significantly different when grown in monoculture vs. the three‐species mixture. While with increasing salinity community dominance shifted toward the most salt‐tolerant species, Spartina patens, competition was found to alter community composition equally over all salinities. However, the responses of individual species demonstrated a very different pattern; the relative importance of competition in influencing individual growth differed substantially depending on the salinity tolerances of species. These results support the contention that, as abiotic stress increases, competition becomes less of a limiting factor in regulating the abundance of a species. However, the role of competition at the community level is the sum of the individual species' responses and may or may not vary with the level of abiotic stress.

Ecology↗
USGS2010

Do competitors modulate rare plant response to precipitation change?

Ecologists increasingly suspect that climate change will directly impact species physiology, demography, and phenology, but also indirectly affect these measures via changes to the surrounding community. Unfortunately, few studies examine both the direct and indirect pathways of impact. Doing so is important because altered competitive pressures can reduce or magnify the direct responses of a focal species to climate change. Here, we examine the effects of changing rainfall on three rare annual plant species in the presence and absence of competition on the California Channel Islands. We used rain-out shelters and hand watering to exclude and augment early, late, and season-long rainfall, spanning the wide range of precipitation change forecast for the region. In the absence of competition, droughts reduced the population growth rates of two of three focal annuals, while increased rainfall was only sometimes beneficial, As compared to the focal species, the dominant competitors were more sensitive to the precipitation treatments, benefiting from increased season-long precipitation and harmed by droughts. Importantly, the response of two of three competitors to the precipitation treatments tended to be positively correlated with those of the focal annuals. Although this leads to the expectation that increased competition will counter the direct benefits of favorable conditions, such indirect effects of precipitation change proved weak to nonexistent in our experiment. Competitors had little influence on the precipitation response of two focal species, due to their low sensitivity to competition and highly variable precipitation responses. Competition did affect how our third focal species responded to precipitation change, but this effect only approached significance, and whether it truly resulted from competitor response to precipitation change was unclear. Our work suggests that even when competitors respond to climate change, these responses may have little effect on the focal species. Ultimately, the strength of the indirect effect depends on how strongly climate change alters competition, and how sensitive focal species are to changes in competition. ?? 2010 by the Ecological Society of America.

Ecology↗
USGS2009

Reproductive health of bass in the potomac, USA, drainage: Part 1. exploring the effects of proximity to wastewater treatment plant discharge

Intersex (specifically, testicular oocytes) has been observed in male smallmouth bass (SMB; Micropterus dolomieu ) and other centrarchids in the South Branch of the Potomac River, USA, and forks of the Shenandoah River, USA, during the past five years. This condition often is associated with exposure to estrogenic endocrine‐disrupting chemicals in some fish species, but such chemicals and their sources have yet to be identified in the Potomac. In an attempt to better understand the plausible causes of this condition, we investigated the reproductive health of bass sampled up‐ and downstream of wastewater treatment plant (WWTP) effluent point sources on the Potomac River in Maryland, USA. Smallmouth bass were sampled from the Conococheague Creek and the Monocacy River, and largemouth bass (LMB; Micropterus salmoides ) were collected near the Blue Plains WWTP on the mainstem of the Potomac River. Chemical analyses of compounds captured in passive samplers at these locations also were conducted. A high prevalence of intersex (82–100%) was identified in male SMB at all sites regardless of collection area. A lower prevalence of intersex (23%) was identified in male LMB collected at the Blue Plains site. When up‐ and downstream fish were compared, significant differences were noted only in fish from the Conococheague. Differences included condition factor, gonadosomatic index, plasma vitellogenin concentration, and estrogen to testosterone ratio. In general, chemicals associated with waste‐water effluent, storm‐water runoff, and agriculture were more prevalent at the downstream sampling sites. An exception was atrazine and its associated metabolites, which were present in greater concentrations at the upstream sites. It appears that proximity to effluent from WWTPs may influence the reproductive health of bass in the Potomac watershed, but inputs from other sources likely contribute to the widespread, high incidence of testicular oocytes.

Environmental Toxicology and Chemistry↗
USGS2009

Hydrologic characterization of desert soils with varying degrees of pedogenesis: 1. field experiments evaluating plant-relevant soil water behavior

To assess the eff ect of pedogenesis on the soil moisture dynamics infl uencing the character and quality of ecological habitat, we conducted infi ltration and redistribution experiments on three alluvial deposits in the Mojave National Preserve: (i) recently deposited active wash sediments, (ii) a soil of early Holocene age, and (iii) a highly developed soil of late Pleistocene age. At each, we ponded water in a 1-m-diameter infi ltration ring for 2.3 h and monitored soil water content and matric pressure during and atier infi ltration, using probes and electrical resistivity imaging (ERI). Infi ltration and downward fl ow rates were greater in younger material, favoring deep-rooted species. Deep-rooted species tend to colonize the margins of washes, where they are unaff ected by sediment transport that inhibits colonization. The ERI results support important generalizations, for example that shallower than 0.5 m, infi ltrated water persists longer in highly developed soil, favoring shallow-rooted species. Soil moisture data for the two youngest soils suggested that saturation overshoot, which may have signifi cant but unexplored hydroecologic and pedogenic eff ects, occurred at the horizontally advancing weting front. Spatial heterogeneity of soil properties generally increased with pedogenic development. Evidence suggested that some early-stage developmental processes may promote uniformity; the intermediate- age soil appeared to have the least heterogeneity in terms of textural variation with depth, and also the least anisotropy. Lateral heterogeneity was pronounced in older soil, having a multitude of eff ects on the distribution and retention of soil water, and may facilitate certain water-conserving strategies of plants over what would be possible in a laterally homogeneous soil. ?? Soil Science Society of America.

California↗
USGS1977

Interactions of nutrients, plant growth and herbivory in a mangrove ecosystem

The effect of nutrient enrichment of red mangroves ( Rhizophora mangle ) was studied by comparing two mangrove—covered islands in the Indian River at Ft. Pierce, Florida, USA, one (high nutrient) with and one (low nutrient) without a breeding colony of pelicans and egrets. Repeated measurements taken on > 100 tagged branches in each area revealed higher growth rates at the high nutrient site. Trees at the high nutrient site showed greater additions of (1) leaves; (2) reproductive parts; (3) new lateral branches; and (4) larger increments to existing stems. Growth in the fertilized stand also began earlier in the year and had a second maximum not shared by the low nutrient area. Both leaves and fruits at the high nutrient site were richer in nitrogen. More striking than the effects on plant growth, however, was the proportionately much greater stimulation of herbivory by insects in response to nutrient enrichment. Larvae of the five lepidopteran species that we observed feeding on buds or leaves were either more abundant or only present in the high nutrient area, as was the scolytid beetle that infested seedlings before they dropped from the parent tree. This difference in herbivory between sites disappeared when the birds seasonally migrated away from their nesting areas at the high nutrient site. This observation and the demonstration that the mangrove skipper Phocides pigmalion attains a higher growth efficiency on high nutrient leaves are both consistent with the hypothesis that increased nutritive value of vegetation (correlated with the increased concentration of nitrogen) is responsible for the 4x greater losses to herbivores in the high nutrient. Implications for environmental management and in more complex communities are discussed.

Florida↗
USGS2007

Aquatic Communities and Selected Water Chemistry in St. Vrain Creek near the City of Longmont, Colorado, Wastewater-Treatment Plant, 2005 and 2006

In 2005, the U.S. Geological Survey and the City of Longmont, Colo., began a study to document chemical characteristics of St. Vrain Creek that had previously been unavailable either due to high cost of analysis or lack of analytical capability. Stream samples were collected at seven sites on St. Vrain Creek during the spring of 2005 and 2006 for analysis of wastewater compounds. A Lagrangian-sampling design was followed during each sampling event, and time-of-travel studies were conducted just prior to each sampling event to determine appropriate sampling times for the synoptic. In addition, semipermeable membrane devices, passive samplers that concentrate hydrophobic organic chemicals, were installed at six sites during the spring of 2005 and 2006 for approximately 4 weeks. After retrieval, contaminant residues concentrated in the semipermeable membrane devices were recovered and used in a toxicity assay that provided a screen for aryl hydrocarbon receptor type compounds, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, and furans. In addition, the U.S. Geological Survey summarized information on macroinvertebrate and fish communities known from St. Vrain Creek dating back to the early 1900s in order to assess their utility in evaluating wastewater-treatment plant upgrades and habitat improvement projects. Unfortunately, because of inconsistencies in data collection these data cannot be used as intended; however, they are useful for understanding to some degree gross patterns in fish species distribution, but less so for macroinvertebrates.

Data Series↗
USGS2004

Overview--Development of a geodatabase and conceptual model of the hydrogeologic units beneath Air Force Plant 4 and Naval Air Station-Joint Reserve Base Carswell Field, Fort Worth, Texas

Air Force Plant 4 (AFP4) and adjacent Naval Air Station-Joint Reserve Base Carswell Field (NAS–JRB) at Fort Worth, Tex., constitute a contractor-owned, government-operated facility that has been in operation since 1942. Contaminants from the 3,600-acre facility, primarily volatile organic compounds (VOCs) and metals, have entered the ground-water-flow system through leakage from waste-disposal sites and from manufacturing processes. Environmental data collected at AFP4 and NAS–JRB during 1993–2002 created the need for consolidation of the data into a comprehensive temporal and spatial geodatabase. The U.S. Geological Survey (USGS), in cooperation with the U.S. Air Force Aeronautical Systems Center Environmental Management Directorate, developed a comprehensive geodatabase of temporal and spatial environmental data associated with the hydrogeologic units beneath the facility. A three-dimensional conceptual model of the hydrogeologic units integrally linked to the geodatabase was designed concurrently. Three hydrogeologic units—from land surface downward, the alluvial aquifer, the GoodlandWalnut confining unit, and the Paluxy aquifer—compose the subsurface of interest at AFP4 and NAS–JRB. The alluvial aquifer consists primarily of clay and silt with sand and gravel channel deposits that might be interconnected or interfingered. The Goodland-Walnut confining unit directly underlies the alluvial aquifer and consists of limestone, marl, shale, and clay. The Paluxy aquifer is composed of dense mudstone and fine- to coarse-grained sandstone

Texas↗
USGS2015

Contaminant removal by wastewater treatment plants in the Stillaguamish River Basin, Washington

Human activities in most areas of the developed world typically release nutrients, pharmaceuticals, personal care products, pesticides, and other contaminants into the environment, many of which reach freshwater ecosystems. In urbanized areas, wastewater treatment plants (WWTPs) are critical facilities for collecting and reducing the amounts of wastewater contaminants (WWCs) that ultimately discharge to rivers, coastal areas, and groundwater. Most WWTPs use multiple methods to remove contaminants from wastewater. These include physical methods to remove solid materials (primary treatment), biological and chemical methods to remove most organic matter (secondary treatment), advanced methods to reduce the concentrations of various contaminants such as nitrogen, phosphorus and (or) synthetic organic compounds (tertiary treatment), and disinfection prior to discharge (Metcalf and Eddy, Inc., 1979). This study examined the extent to which 114 organic WWCs were removed by each of three WWTPs, prior to discharge to freshwater and marine ecosystems, in a rapidly developing area in northwestern Washington State. Removal percentages for each WWC were estimated by comparing the concentrations measured in the WWTP influents with those measured in the effluents. The investigation was carried out in the 700-mi 2 Stillaguamish River Basin, the fifth largest watershed that discharges to Puget Sound (fig. 1).

Washington↗
USGS2003

Near field receiving water monitoring of trace metals in clams (Macoma balthica) and sediments near the Palo Alto water quality control plant in south San Francisco Bay, California: 2002

This report presents trace element concentrations analyzed on samples of fine-grained sediments and clams (Macoma balthica) collected from a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report serves as a continuation of the Near Field Receiving Water Monitoring Study, which was started in 1994. The data for 2002, herein, are interpreted within that context. Metal concentrations in both sediments and clam tissue samples have been within the range of values produced by seasonal variability. However, copper and zinc, display continued decreases. Copper in sediment was observed to drop below the ERL (Effects Range-Low) concentration for the third consecutive year and zinc concentrations never exceeded the ERL. Yearly average concentrations of copper, zinc and silver in Macoma balthica for 2002 are some of the lowest recorded since monitoring began in 1975. Mercury and selenium concentrations in sediments and clams at Palo Alto were similar concentrations observed elsewhere in the San Francisco Bay.

California↗
USGS2004

Near field receiving water monitoring of trace metals in clams (macoma balthica) and sediments near the Palo Alto Water Quality Control Plant in South San Francisco Bay, California: 2000

Trace element concentrations were analyzed on samples of fine-grained sediments and clams (Macoma balthica) collected from a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report serves as a continuation of the Near Field Receiving Water Monitoring Study, which was started in 1994. The data for 2003, herein, are interpreted within that context. Metal concentrations in both sediments and clam tissue samples have been within the range of values produced by seasonal variability; however, copper and zinc, display continued decreases over the last decade. In 2003, copper in sediment was observed to drop below the ERL (Effects Range-Low) concentration for the third consecutive year and zinc concentrations never exceeded the ERL. Yearly average concentrations of copper, zinc and silver in Macoma balthica for 2003 are some of the lowest recorded since monitoring began in 1975. Mercury and selenium concentrations in sediments and clams at Palo Alto were similar to concentrations observed elsewhere in the San Francisco Bay.

California↗
USGS2005

Geodatabase of environmental information for Air Force Plant 4 and Naval Air Station-Joint Reserve Base Carswell Field, Fort Worth, Texas, 1990-2004

Air Force Plant 4 (AFP4) and adjacent Naval Air Station-Joint Reserve Base (NAS-JRB) at Fort Worth, Tex., constitute a government-owned, contractor-operated (GOCO) facility that has been in operation since 1942. Contaminants from the facility, primarily volatile organic compounds (VOCs) and metals, have entered the groundwater-flow system through leakage from waste-disposal sites (landfills and pits) and from manufacturing processes (U.S. Air Force, Aeronautical Systems Center, 1995). The U.S. Geological Survey (USGS), in cooperation with the U.S. Air Force (USAF), Aeronautical Systems Center, Environmental Management Directorate (ASC/ENVR), developed a comprehensive database (or geodatabase) of temporal and spatial environmental information associated with the geology, hydrology, and water quality at AFP4 and NAS-JRB. The database of this report provides information about the AFP4 and NAS-JRB study area including sample location names, identification numbers, locations, historical dates, and various measured hydrologic data. This database does not include every sample location at the site, but is limited to an aggregation of selected digital and hardcopy data of the USAF, USGS, and various consultants who have previously or are currently working at the site.

Texas↗
USGS2006

Aquifer-test data for wells H-1, H-2A, H-2B, H-2C, and H-3 at the Waste Isolation Pilot Plant, southeastern New Mexico

A series of aquifer tests was performed by the U.S. Geological Survey on geologic units of Permian age at the Waste Isolation Pilot Plant site between February 1979 and July 1980 in wells H-1, H-2 complex (H-2A, H-2B, and H-2C), and H-3. The tested geologic units included the Magenta Dolomite and Culebra Dolomite Members of the Rustler Formation, and the contact zone between the Rustler and Salado Formations. Selected information on the tested formations, test dates, pre-test static water levels, test configurations, and raw data collected during these tests are tabulated in this report.

Open-File Report↗
USGS2006

Near-Field Receiving Water Monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California: 2005

Trace elements in sediment and the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity and benthic, macroinvertebrate community structure are reported for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January to December 2005, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2005 were consistent with results observed since 1990. Copper and zinc concentrations in sediment and bivalve tissue displayed a continued decrease over the last decade. In 2005, Cu concentrations were at or below the effects range-low (ERL) concentration (34 µg/g) for the entire year, the first time this has been observed. Also, zinc concentrations never exceeded the ERL (150 µg/g). Yearly average concentrations of copper, zinc and silver in Macoma petalum for 2005 were some of the lowest recorded since monitoring for metals began in 1975. The concentrations of mercury and selenium in sediments, during April and January 2004, respectively, were the highest values observed for these elements during this study. Later in 2005, concentrations decreased to historic levels. The increase in mercury and selenium in 2004 was not a permanent trend and concentrations of these elements in sediments and clams at Palo Alto remain similar to concentrations observed elsewhere in the San Francisco Bay. Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with with reduced concentrations of metals in the sediment and in the tissues of the biosentinal clam Macoma petalum from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis , a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. For the first time since its invasion in 1986, the non-indigenous filter-feeding bivalve Corbula ( Potamocorbula ) amurensis has shown up in small but persistent numbers in the benthic community.

California↗
USGS2006

Vascular Plant and Vertebrate Inventory of Montezuma Castle National Monument

Executive Summary We summarize past inventory efforts for vascular plants and vertebrates at Montezuma Castle National Monument (NM) in Arizona. We used data from previous research to compile complete species lists for the monument and to assess inventory completeness. There have been 784 species recorded at Montezuma Castle NM, of which 85 (11%) are non-native. In each taxon-specific chapter we highlight areas of resources that contributed to species richness or unique species for the monument. Of particular importance are Montezuma Well and Beaver and Wet Beaver creeks and the surrounding riparian vegetation, which are responsible for the monument having one of the highest numbers of bird species in the Sonoran Desert Network of park units. Beaver Creek is also home to populations of federally-listed fish species of concern. Other important resources include the cliffs along the creeks and around Montezuma Well (for cliff and cave roosting bats). Based on the review of past studies, we believe the inventory for most taxa is nearly complete, though some rare or elusive species will be added with additional survey effort. We recommend additional inventory, monitoring and research studies.

Open-File Report↗
USGS2007

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California--2006

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January 2006 to December 2006, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto's Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2006 were consistent with results observed since 1990. Most notably, copper and silver concentrations in sediment and clam tissue increased in the last year but the values remain well within range of past data. Other metals such as chromium, nickel, vanadium, and zinc remained relatively constant throughout the year except for maximum values generally occurring in winter months (January-March). Mercury levels in sediment and clam tissue were some of the lowest seen on record. Conversely, selenium concentrations reached a maximum level but soon returned to baseline levels. In all, metal concentrations in sediments and tissue remain within past findings. There are no obvious directional trends (increasing or decreasing). Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam M. petalum from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species (Ampelisca abdita and Streblospio benedicti) that brood their young and live on the surface of the sediment in tubes, have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis, a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment, has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. For the first time since its invasion in 1986, the non-indigenous filter-feeding clam Corbula (Potamocorbula) amurensis has shown up in small, but persistent, numbers in the benthic community.

California↗
USGS2008

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California: 2007

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January 2007 to December 2007, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2007 remained consistent with results observed since 1990. Most notably, copper and silver concentrations in sediment and clam tissue are elevated for the second consecutive year, but the values remain well within the range of past findings. Other metals such as chromium, nickel, vanadium, and zinc remained relatively constant throughout the year except for maximum values that generally occur in winter months (January-March). Mercury levels in sediment and clam tissue were some of the lowest seen on record. Last year’s elevated selenium levels appear to be transient, and selenium concentrations have returned to background levels. Overall, metal concentrations in sediments and tissue remain within past findings. Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes, have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis , a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment, has shown a concurrent increase in dominance and is now showing signs of population stability. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics.

California↗
USGS2008

Design and Operation of a Borehole Straddle Packer for Ground-Water Sampling and Hydraulic Testing of Discrete Intervals at U.S. Air Force Plant 6, Marietta, Georgia

A borehole straddle packer was developed and tested by the U.S. Geological Survey to characterize the vertical distribution of contaminants, head, and hydraulic properties in open-borehole wells as part of an ongoing investigation of ground-water contamination at U.S. Air Force Plant 6 (AFP6) in Marietta, Georgia. To better understand contaminant fate and transport in a crystalline bedrock setting and to support remedial activities at AFP6, numerous wells have been constructed that include long open-hole intervals in the crystalline bedrock. These wells can include several discontinuities that produce water, which may contain contaminants. Because of the complexity of ground-water flow and contaminant movement in the crystalline bedrock, it is important to characterize the hydraulic and water-quality characteristics of discrete intervals in these wells. The straddle packer facilitates ground-water sampling and hydraulic testing of discrete intervals, and delivery of fluids including tracer suites and remedial agents into these discontinuities. The straddle packer consists of two inflatable packers, a dual-pump system, a pressure-sensing system, and an aqueous injection system. Tests were conducted to assess the accuracy of the pressure-sensing systems, and water samples were collected for analysis of volatile organic compound (VOCs) concentrations. Pressure-transducer readings matched computed water-column height, with a coefficient of determination of greater than 0.99. The straddle packer incorporates both an air-driven piston pump and a variable-frequency, electronic, submersible pump. Only slight differences were observed between VOC concentrations in samples collected using the two different types of sampling pumps during two sampling events in July and August 2005. A test conducted to assess the effect of stagnation on VOC concentrations in water trapped in the system's pump-tubing reel showed that concentrations were not affected. A comparison was conducted to assess differences between three water-sampling methods - collecting samples from the well by pumping a packer-isolated zone using a submersible pump, by using a grab sampler, and by using a passive diffusion sampler. Concentrations of tetrachloroethylene, trichloroethylene and 1,2-dichloropropane were greatest for samples collected using the submersible pump in the packed-isolated interval, suggesting that the straddle packer yielded the least dilute sample.

Georgia↗