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At least 1,441 records · Page 80Linked to original sources
USGS2001

Carbon dioxide in magmas and implications for hydrothermal systems

This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems. Because some metals, including gold, can be more volatile in vapor phases than coexisting liquids, the presence of CO2 may indirectly aid the process of metallogenesis by inducing phase separation.

Mineralium Deposita↗
USGS2003

Concentrations of metals in feathers and blood of nestling Black-Crowned Night-Herons (Nycticorax nycticorax) in Chesapeake and Delaware Bays

Over the past decade, destruction and degradation of wetland habitat has contributed to the decline of wading bird colonies on the Atlantic Coast. In 1998, an initial assessment of the possible contribution of metal pollution to declining heron populations in Chesapeake and Delaware Bays was conducted. Study sites included two heronries in industrialized locations (Pea Patch Island, DE and Baltimore Harbor, MD), and a reference site (Holland Island) remotely located in the southern Chesapeake Bay. Concentrations of 19 metals, metalloids, and trace elements were examined in blood and breast feathers of 14-16 day old nestling black-crowned night-herons. Metal concentrations in blood were low and showed few site differences, though mercury was elevated at Pea Patch Island as compared to other sites. In feathers, metal concentrations appeared to be in the low to moderate range at all sites, though limited data exist for interpreting pollutant concentrations in feathers of nestling wading birds. Where differences were detected, concentrations at Pea Patch Island were consistently greater than those at Baltimore Harbor and Holland Island. Feathers collected at Pea Patch Island had significantly greater concentrations of aluminum, barium, iron, lead, magnesium, and manganese, but were generally found to be within the range of concentrations detected in other nestling birds, where that information was available. Based on these results, metal pollution does not appear to be an immediate threat to BCNH colonies at these two locations, though future monitoring of some elements (Pb, Mn, and Al) may be warranted.

Bulletin of Environmental Contamination and Toxico↗
USGS2009

Toxicity of sediment cores collected from the Ashtabula River in northeastern Ohio, USA, to the amphipod Hyalella azteca

This study was conducted to support a Natural Resource Damage Assessment and Restoration project associated with the Ashtabula River in Ohio. The objective of the study was to evaluate the chemistry and toxicity of 50 sediment samples obtained from five cores collected from the Ashtabula River (10 samples/core, with each 10-cm-diameter core collected to a total depth of about 150 cm). Effects of chemicals of potential concern (COPCs) measured in the sediment samples were evaluated by measuring whole-sediment chemistry and whole-sediment toxicity in the sediment samples (including polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], organochlorine pesticides, and metals). Effects on the amphipod Hyalella azteca at the end of a 28-day sediment toxicity test were determined by comparing survival or length of amphipods in individual sediment samples in the cores to the range of responses of amphipods exposed to selected reference sediments that were also collected from the cores. Mean survival or length of amphipods was below the lower limit of the reference envelope in 56% of the sediment samples. Concentrations of total PCBs alone in some samples or concentrations of total PAHs alone in other samples were likely high enough to have caused the reduced survival or length of amphipods (i.e., concentrations of PAHs or PCBs exceeded mechanistically based and empirically based sediment quality guidelines). While elevated concentrations of ammonia in pore water may have contributed to the reduced length of amphipods, it is unlikely that the reduced length was caused solely by elevated ammonia (i.e., concentrations of ammonia were not significantly correlated with the concentrations of PCBs or PAHs and concentrations of ammonia were elevated both in the reference sediments and in the test sediments). Results of this study show that PAHs, PCBs, and ammonia are the primary COPCs that are likely causing or substantially contributing to the toxicity to sediment-dwelling organisms. ?? 2009 US Government.

Archives of Environmental Contamination and Toxico↗
USGS2004

The occurrence of lysogenic bacteria and microbial aggregates in the lakes of the McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys of Antarctica form the coldest and driest ecosystem on Earth. Within this region there are a number of perennially ice-covered (3–6 m thick) lakes that support active microbial assemblages and have a paucity of metazoans. These lakes receive limited allochthonous input of carbon and nutrients, and primary productivity is limited to only 6 months per year owing to an absence of sunlight during the austral winters. In an effort to establish the role that bacteria and their associated viruses play in carbon and nutrient cycling in these lakes, indigenous bacteria, free bacteriophage, and lysogen abundances were determined. Total bacterial abundances (TDC) ranged from 3.80 × 10 4 to 2.58 × 10 7 cells mL −1 and virus-like particle (VLP) abundances ranged from 2.26 × 10 5 to 5.56 × 10 7 VLP mL −1 . VLP abundances were significantly correlated ( P < 0.05) with TDC, bacterial productivity (TdR), chlorophyll a (Chl a ), and soluble reactive phosphorus (SRP). Lysogenic bacteria, determined by induction with mitomycin C, made up between 2.0% and 62.5% of the total population of bacteria when using significant decreases and increases in TDC and VLP abundances, respectively, and 89.5% when using increases in VLP abundances as the sole criterion for a successful induction event. The contribution of viruses released from induced lysogens contributed <0.015% to the total viral production rate. Carbohydrate and protein based organic aggregates were abundant within the water column of the lakes and were heavily colonized by bacteria and VLPs. Alkaline phosphatase activity was detected within the matrix of the aggregates, implying phosphorus deficiency and consortial nutrient exchanges among microorganisms.

Microbial Ecology↗
USGS2020

What could explain δ13C signatures in biocrust cyanobacteria of drylands?

Dryland ecosystems are increasing in geographic extent and contribute greatly to interannual variability in global carbon dynamics. Disentangling interactions among dominant primary producers, including plants and autotrophic microbes, can help partition their contributions to dryland C dynamics. We measured the δ 13 C signatures of biological soil crust cyanobacteria and dominant plant species (C 3 and C 4 ) across a regional scale in the southwestern USA to determine if biocrust cyanobacteria were coupled to plant productivity (using plant-derived C mixotrophically), or independent of plant activity (and therefore purely autotrophic). Cyanobacterial assemblages located next to all C 3 plants and one C 4 species had consistently more negative δ 13 C (by 2‰) than the cyanobacteria collected from plant interspaces or adjacent to two C 4 Bouteloua grass species. The differences among cyanobacterial assemblages in δ 13 C could not be explained by cyanobacterial community composition, photosynthetic capacity, or any measured leaf or root characteristics (all slopes not different from zero). Thus, microsite differences in abiotic conditions near plants, rather than biotic interactions, remain a likely mechanism underlying the observed δ 13 C patterns to be tested experimentally.

New Mexico↗
USGS2001

Quantification of mine-drainage inflows to Little Cottonwood Creek, Utah, using a tracer-injection and synoptic-sampling study

Historic mining in Little Cottonwood Canyon in Utah has left behind many mine drainage tunnels that discharge water to Little Cottonwood Creek. To quantify the major sources of mine drainage to the stream, synoptic sampling was conducted during a tracer injection under low flow conditions (September 1998). There were distinct increases in discharge downstream from mine drainage and major tributary inflows that represented the total surface and subsurface contributions. The chemistry of stream water determined from synoptic sampling was controlled by the weathering of carbonate rocks and mine drainage inflows. Buffering by carbonate rocks maintained a high pH throughout the study reach. Most of the metal loading was from four surface-water inflows and three subsurface inflows. The main subsurface inflow was from a mine pool in the Wasatch Tunnel. Natural attenuation of all the metals resulted in the formation of colloidal solids, sorption of some metals, and accumulation onto the streambed. The deposition on the streambed could contribute to chronic toxicity for aquatic organisms. Information from the study will help to make decisions about environmental restoration.

Utah↗
USGS2012

Wildlife contact analysis: Emerging methods, questions, and challenges

Recent technological advances, such as proximity loggers, allow researchers to collect complete interaction histories, day and night, among sampled individuals over several months to years. Social network analyses are an obvious approach to analyzing interaction data because of their flexibility for fitting many different social structures as well as the ability to assess both direct contacts and indirect associations via intermediaries. For many network properties, however, it is not clear whether estimates based upon a sample of the network are reflective of the entire network. In wildlife applications, networks may be poorly sampled and boundary effects will be common. We present an alternative approach that utilizes a hierarchical modeling framework to assess the individual, dyadic, and environmental factors contributing to variation in the interaction rates and allows us to estimate the underlying process variation in each. In a disease control context, this approach will allow managers to focus efforts on those types of individuals and environments that contribute the most toward super-spreading events. We account for the sampling distribution of proximity loggers and the non-independence of contacts among groups by only using contact data within a group during days when the group membership of proximity loggers was known. This allows us to separate the two mechanisms responsible for a pair not contacting one another: they were not in the same group or they were in the same group but did not come within the specified contact distance. We illustrate our approach with an example dataset of female elk from northwestern Wyoming and conclude with a number of important future research directions.

Behavioral Ecology and Sociobiology↗
USGS2000

Chemical characteristics of urban stormwater sediments and implications for environmental management, Maricopa County, Arizona

Investigations of the chemical characteristics of urban stormwater sediments in the rapidly growing Phoenix metropolitan area of Maricopa County, Arizona, showed that the inorganic component of these sediments generally reflects geologic background values. Some concentrations of metals were above background values, especially cadmium, copper, lead, and zinc, indicating an anthropogenic contribution of these elements to the sediment chemistry. Concentrations, however, were not at levels that would require soil remediation according to guidelines of the U.S. Environmental Protection Agency. Arsenic concentrations generally were above recommended values for remediation at a few sites, but these concentrations seem to reflect geologic rather than anthropogenic factors. Several organochlorine compounds no longer in use were ubiquitous in the Phoenix area, although concentrations generally were low. Chlordane, DDT and its decay products DDE and DDD, dieldrin, toxaphene, and PCBs were found at almost all sites sampled, although some of the pesticides in which these compounds are found have been banned for almost 30 years. A few sites showed exceptionally high concentrations of organochlorine compounds. On the basis of published guidelines, urban stormwater sediments do not appear to constitute a major regional environmental problem with respect to the chemical characteristics investigated here. At individual sites, high concentrations of organic compounds - chlordane, dieldrin, PCBs, and toxaphene - may require some attention. The possible environmental hazard presented by low-level organochlorine contamination is not addressed in this paper; however, high levels of toxicity in urban sediments are difficult to explain. Sediment toxicity varied significantly with time, which indicates that these tests should be evaluated carefully before they are used for management decisions.Investigations of the chemical characteristics of urban stormwater sediments in the rapidly growing Phoenix metropolitan area of Maricopa County, Arizona, showed that the inorganic component of these sediments generally reflects geologic background values. Some concentrations of metals were above background values, especially cadmium, copper, lead, and zinc, indicating an anthropogenic contribution of these elements to the sediment chemistry. Concentrations, however, were not at levels that would require soil remediation according to guidelines of the U.S. Environmental Protection Agency. Arsenic concentrations generally were above recommended values for remediation at a few sites, but these concentrations seem to reflect geologic rather than anthropogenic factors. Several organochlorine compounds no longer in use were ubiquitous in the Phoenix area, although concentrations generally were low. Chlordane, DDT and its decay products DDE and DDD, dieldrin, toxaphene, and PCBs were found at almost all sites sampled, although some of the pesticides in which these compounds are found have been banned for almost 30 years. A few sites showed exceptionally high concentrations of organochlorine compounds. On the basis of published guidelines, urban stormwater sediments do not appear to constitute a major regional environmental problem with respect to the chemical characteristics investigated here. At individual sites, high concentrations of organic compounds - chlordane, dieldrin, PCBs, and toxaphene - may require some attention. The possible environmental hazard presented by low-level organochlorine contamination is not addressed in this paper; however, high levels of toxicity in urban sediments are difficult to explain. Sediment toxicity varied significantly with time, which indicates that these tests should be evaluated carefully before they are used for management decisions.

Environmental Management↗
USGS2004

Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Nestedness of faunal assemblages is a multiscale phenomenon, potentially influenced by a variety of factors. Prior small-scale studies have found freshwater fish species assemblages to be nested along stream courses as a result of either selective colonization or extinction. However, within-stream gradients in temperature and other factors are correlated with the distributions of many fish species and may also contribute to nestedness. At a regional level, strongly nested patterns would require a consistent set of structuring mechanisms across streams, and correlation among species' tolerances of the environmental factors that influence distribution. Thus, nestedness should be negatively associated with the spatial extent of the region analyzed and positively associated with elevational gradients (a correlate of temperature and other environmental factors). We examined these relationships for the freshwater fishes of Virginia. Regions were defined within a spatial hierarchy and included whole river drainages, portions of drainages within physiographic provinces, and smaller subdrainages. In most cases, nestedness was significantly stronger in regions of smaller spatial extent and in regions characterized by greater topographic relief. Analysis of hydrologic variability and patterns of faunal turnover provided no evidence that interannual colonization/extinction dynamics contributed to elevational differences in nestedness. These results suggest that, at regional scales, nestedness is influenced by interactions between biotic and abiotic factors, and that the strongest nestedness is likely to occur where a small number of organizational processes predominate, i.e., over small spatial extents and regions exhibiting strong environmental gradients. ?? Springer-Verlag 2004.

Oecologia↗
USGS2022

Summer/fall diet and macronutrient assimilation in an Arctic predator

Free-ranging predator diet estimation is commonly achieved by applying molecular-based tracers because direct observation is not logistically feasible or robust. However, tracers typically do not represent all dietary macronutrients, which likely obscures resource use as prey proximate composition varies and tissue consumption can be specific. For example, polar bears ( Ursus maritimus ) preferentially consume blubber, yet diets have been estimated using fatty acids based on prey blubber or stable isotopes of lipid-extracted prey muscle, neither of which represent both protein and lipid macronutrient contributions. Further, additional bias can be introduced because dietary fat is known to be flexibly routed beyond short-term energy production and storage. We address this problem by simultaneously accounting for protein and lipid assimilation using carbon and nitrogen isotope compositions of lipid-containing prey muscle and blubber to infer summer/fall diet composition and macronutrient proportions from Chukchi Sea polar bear guard hair ( n = 229) sampled each spring between 2008 and 2017. Inclusion of blubber (85–95% lipid by dry mass) expanded the isotope mixing space and improved separation among prey species. Ice-associated seals, including nutritionally dependent pups, were the primary prey in summer/fall diets with lower contributions by Pacific walruses ( Odobenus rosmarus ) and whales. Percent blubber estimates confirmed preferential selection of this tissue and represented the highest documented lipid assimilation for any animal species. Our results offer an improved understanding of summer/fall prey macronutrient usage by Chukchi Sea polar bears which likely coincides with a nutritional bottleneck as the sea ice minimum is approached.

Alaska↗
USGS2014

Abrupt climate-independent fire regime changes

Wildfires have played a determining role in distribution, composition and structure of many ecosystems worldwide and climatic changes are widely considered to be a major driver of future fire regime changes. However, forecasting future climatic change induced impacts on fire regimes will require a clearer understanding of other drivers of abrupt fire regime changes. Here, we focus on evidence from different environmental and temporal settings of fire regimes changes that are not directly attributed to climatic changes. We review key cases of these abrupt fire regime changes at different spatial and temporal scales, including those directly driven (i) by fauna, (ii) by invasive plant species, and (iii) by socio-economic and policy changes. All these drivers might generate non-linear effects of landscape changes in fuel structure; that is, they generate fuel changes that can cross thresholds of landscape continuity, and thus drastically change fire activity. Although climatic changes might contribute to some of these changes, there are also many instances that are not primarily linked to climatic shifts. Understanding the mechanism driving fire regime changes should contribute to our ability to better assess future fire regimes.

Ecosystems↗
USGS2023

Respiratory acclimation of tropical forest roots in response to in situ experimental warming and hurricane disturbance

Climate projections predict higher temperatures and more frequent hurricanes in the tropics. Tropical plants subjected to these stresses may respond by acclimating their physiology. We investigated tropical forest root respiration in response to in situ experimental warming and hurricane disturbance in eastern Puerto Rico. We measured mass-normalized root specific respiration, root biomass, and root traits at the Tropical Responses to Altered Climate Experiment (TRACE), where understory vegetation is warmed + 4 °C above ambient. Our measurements span 5 years, including before and after two major hurricanes, to quantify root contributions to ecosystem carbon fluxes. Experimental warming did not affect root specific respiration at a standard temperature of 25° (RSR 25 , mean = 3.89 nmol CO 2 g −1 s −1 ) or the temperature sensitivity of root respiration (Q 10 , mean = 1.75), but did result in decreased fine-root biomass, thereby decreasing area-based estimations of ecosystem-level root respiration in warmed plots by ~ 35%. RSR 25 of newer roots, which increased with increasing root nitrogen, showed greater rates 6 months after the hurricanes, but subsequently decreased after 12 months. Root specific respiration did not acclimate to higher temperatures, based on lack of adjustments in either Q 10 or RSR 25 in the warmed plots; however, decreased root biomass indicates the root contribution to soil carbon dioxide efflux was overall lower with warming. Lower root biomass may also limit nutrient and water uptake, having potential negative effects on carbon assimilation. Our results show that warming and hurricane disturbance have strong potential to affect tropical forest roots, as well as ecosystem carbon fluxes.

Ecosystems↗
USGS2025

Variation in soil organic carbon across a latitudinal chronosequence of mangrove poleward expansion

The critical carbon sink provided by coastal wetlands, known as blue carbon, can be affected by multiple aspects of climate change. One important example is warming-induced mangrove poleward expansion, which is shifting dominant plant cover across tropical–temperate transitional zones and altering ecosystem structure and function. We examined how mangrove expansion affects soil organic carbon (SOC) quantity and source, using measurements of SOC density and isotopic signatures (δ 13 C and δ 15 N) at 15 sites across Florida’s west coast (USA). The sampled sites represent examples of three expansion stages: a latitudinal chronosequence of mangrove expansion, spanning mature mangroves in the south, former ecotones at mid latitudes, and current ecotones in the north. Our analyses of soil core data indicate that mangrove expansion stage is a significant predictor of SOC density, δ 13 C, and δ 15 N, but not C:N ratio. Current ecotones exhibited significantly lower SOC density but higher δ 13 C, suggesting a greater contribution of preexisting C 4 salt marshes, while no difference was found between former ecotones and mature mangroves. SOC density, δ 13 C, and δ 15 N were found to vary with mangrove aboveground biomass, stage, and sedimentary setting along the latitudinal gradient. For all three mangrove expansion stages, SOC density decreased with depth, but δ 13 C showed no vertical trend, suggesting that mangroves contributed organic carbon to the entire 20-cm soil profile. The observed regional trend of SOC across mangrove expansion stages highlights the ecological impacts of warming-driven vegetation shifts in coastal wetlands, though further evidence is needed to determine the primary drivers and mechanisms, while also considering local and regional environmental factors.

Florida↗
USGS2006

The application of satellite differential SAR interferometry-derived ground displacements in hydrogeology

The application of satellite differential synthetic aperture radar (SAR) interferometry, principally coherent (InSAR) and to a lesser extent, persistent-scatterer (PSI) techniques to hydrogeologic studies has improved capabilities to map, monitor, analyze, and simulate groundwater flow, aquifer-system compaction and land subsidence. A number of investigations over the previous decade show how the spatially detailed images of ground displacements measured with InSAR have advanced hydrogeologic understanding, especially when a time series of images is used in conjunction with histories of changes in water levels and management practices. Important advances include: (1) identifying structural or lithostratigraphic boundaries (e.g. faults or transitional facies) of groundwater flow and deformation; (2) defining the material and hydraulic heterogeneity of deforming aquifer-systems; (3) estimating system properties (e.g. storage coefficients and hydraulic conductivities); and (4) constraining numerical models of groundwater flow, aquifer-system compaction, and land subsidence. As a component of an integrated approach to hydrogeologic monitoring and characterization of unconsolidated alluvial groundwater basins differential SAR interferometry contributes unique information that can facilitate improved management of groundwater resources. Future satellite SAR missions specifically designed for differential interferometry will enhance these contributions. ?? Springer-Verlag 2006.

Hydrogeology Journal↗
USGS2007

Application of environmental groundwater tracers at the Sulphur Bank Mercury Mine, California, USA

Boron, chloride, sulfate, ??D, ??18O, and 3H concentrations in surface water and groundwater samples from the Sulphur Bank Mercury Mine (SBMM), California, USA were used to examine geochemical processes and provide constraints on evaporation and groundwater flow. SBMM is an abandoned sulfur and mercury mine with an underlying hydrothermal system, adjacent to Clear Lake, California. Results for non-3H tracers (i.e., boron, chloride, sulfate, ??D, and ??18O) identify contributions from six water types at SBMM. Processes including evaporation, mixing, hydrothermal water input and possible isotopic exchange with hydrothermal gases are also discerned. Tritium data indicate that hydrothermal waters and other deep groundwaters are likely pre-bomb (before ???1952) in age while most other waters were recharged after ???1990. A boron-based steady-state reservoir model of the Herman Impoundment pit lake indicates that 71-79% of its input is from meteoric water with the remainder from hydrothermal contributions. Results for groundwater samples from six shallow wells over a 6-month period for ??D and ??18O suggests that water from Herman Impoundment is diluted another 3% to more than 40% by infiltrating meteoric water, as it leaves the site. Results for this investigation show that environmental tracers are an effective tool to understand the SBMM hydrogeologic regime. ?? Springer-Verlag 2007.

Hydrogeology Journal↗
USGS2020

The influence of snow cover, air temperature, and groundwater flow on the active-layer thermal regime of Arctic hillslopes drained by water tracks

Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A three-dimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate.

Alaska↗
USGS2007

Variation in northern bobwhite demography along two temporal scales

Quantification and understanding of demographic variation across intra- and inter-annual temporal scales can benefit from the development of theoretical models of evolution and applied conservation of species. We used long-term survey data for northern bobwhites (Colinus virginianus) collected at the northern and southern extent of its geographic range to develop matrix population models which would allow investigation of intra- and inter-annual patterns in bobwhite population dynamics. We first evaluated intra-annual patterns in the importance of a seasonal demographic rate to asymptotic population growth rate with prospective perturbation analysis (elasticity analysis). We then conducted retrospective analysis (life table response experiments) of inter-annual patterns in the contribution of observed changes in demography to the observed change in population growth rate. Survival in the earliest age class during the nonbreeding season had the greatest potential influence in both the northern and southern populations. Examination of inter-annual variation in demography indicated that variation in nonbreeding season survival in the earliest age class contributed the most to observed changes in population growth rate in the northern population. In contrast, changes in fertility in the earliest age class in the southern population had the greatest influence on changes in population growth rate. Prospective elasticity analyses highlight the similarities in bobwhite demography throughout different parts of its geographic range, while retrospective life table response experiments revealed important patterns in the temporal differences of bobwhite life history at the northern and southern extent of its geographic range. ?? 2007 The Society of Population Ecology and Springer.

Population Ecology↗
USGS2009

Spatially detailed quantification of metal loading for decision making: Metal mass loading to American fork and Mary Ellen Gulch, Utah

Effective remediation requires an understanding of the relative contributions of metals from all sources in a catchment, and that understanding must be based on a spatially detailed quantification of metal loading. A traditional approach to quantifying metal loading has been to measure discharge and chemistry at a catchment outlet. This approach can quantify annual loading and the temporal changes in load, but does not provide the needed spatial detail to evaluate specific sources, which is needed to support remediation decisions. A catchment or mass-loading approach provides spatial detail by combining tracer-injection and synoptic-sampling methods to quantify loading. Examples of studies in American Fork, Utah, and its tributary Mary Ellen Gulch illustrate this different approach. The mass-loading study in American Fork treated Mary Ellen Gulch as a single inflow. From that point of view, Mary Ellen Gulch was one of the greatest sources of Fe, Mn, Zn, and colloidal Pb loads to American Fork. But when Mary Ellen Gulch was evaluated in a separate catchment study, the detailed locations of metal loading were identified, and the extent of metal attenuation upstream from the mouth of Mary Ellen Gulch was quantified. The net, instantaneous load measured at the mouth of Mary Ellen Gulch for remediation planning would greatly underestimate the contributions of principal sources within the catchment. Extending the detailed sampling downstream from Mary Ellen Gulch indicated the possibility of diffuse groundwater inflow from Mary Ellen Gulch to American Fork. Comparing loads for Mary Ellen Gulch in the two studies indicates that metal loads could be substantially underestimated for planning purposes without the detailed catchment approach for the low-flow conditions in these studies. A mass-loading approach provides both the needed quantification of metal loading and the spatial detail to guide remediation decisions that would be the most effective in the catchments.

Mine Water and the Environment↗