Metropolitan growth and the mobility and immobility of skilled and creative couples across the life course

The human capital and creative class hypotheses argue that the agglomeration of skilled and creative people is key to economic growth. Migration is assumed to play an important role in forming these agglomerations. However, the results of this study indicate that while younger cohorts of skilled and creative individuals are highly mobile, skilled and creative couples are highly immobile. This research hypothesizes that it is these relatively immobile skilled and creative couples that are behind the link between urban growth and concentrations of skill and creativity. Indeed, this analysis finds a strong empirical link between concentrations of skilled couples, but not creative class couples, and economic growth. Public policies designed to increase the size of the skilled population should be directed at retaining younger cohorts long enough for them to develop the local networks upon which spillover effects rely.     

Analysing Debris-Flow Impact Models, Based on a Small Scale Modelling Approach

The objective of this study is to analyse adaptable debris-flow impact models, which are very important for mitigation measurements and buildings using their sphere of influence. For this reason, 16 debris-flow experiments, on a small-scale modelling approach, were performed. Impact forces were measured with a force plate panel, consisting of 24 aluminium devices, coaxially mounted with resistance strain gauges. Flow velocities, flow heights as well as horizontal impact forces were sampled with a frequency of 2.4 kHz. Sub datasets of sampled raw force data were defined by applying an average median filter, a low-pass filter routine. Further, estimated peak pressure values as well as empirical coefficients of hydraulic impact models were compared, and the influence of signal processing is discussed.     

A Stream‐Based Methane Monitoring Approach for Evaluating Groundwater Impacts Associated with Unconventional Gas Development

Gaining streams can provide an integrated signal of relatively large groundwater capture areas. In contrast to the point‐specific nature of monitoring wells, gaining streams coalesce multiple flow paths. Impacts on groundwater quality from unconventional gas development may be evaluated at the watershed scale by the sampling of dissolved methane (CH₄) along such streams. This paper describes a method for using stream CH₄ concentrations, along with measurements of groundwater inflow and gas transfer velocity interpreted by 1‐D stream transport modeling, to determine groundwater methane fluxes. While dissolved ionic tracers remain in the stream for long distances, the persistence of methane is not well documented. To test this method and evaluate CH₄ persistence in a stream, a combined bromide (Br) and CH₄ tracer injection was conducted on Nine‐Mile Creek, a gaining stream in a gas development area in central Utah. A 35% gain in streamflow was determined from dilution of the Br tracer. The injected CH₄ resulted in a fivefold increase in stream CH₄ immediately below the injection site. CH₄ and δ¹³C_CH4 sampling showed it was not immediately lost to the atmosphere, but remained in the stream for more than 2000 m. A 1‐D stream transport model simulating the decline in CH₄ yielded an apparent gas transfer velocity of 4.5 m/d, describing the rate of loss to the atmosphere (possibly including some microbial consumption). The transport model was then calibrated to background stream CH₄ in Nine‐Mile Creek (prior to CH₄ injection) in order to evaluate groundwater CH₄ contributions. The total estimated CH₄ load discharging to the stream along the study reach was 190 g/d, although using geochemical fingerprinting to determine its source was beyond the scope of the current study. This demonstrates the utility of stream‐gas sampling as a reconnaissance tool for evaluating both natural and anthropogenic CH₄ leakage from gas reservoirs into groundwater and surface water.     

Gravity field contribution analysis of GOCE gravitational gradient components

A gravity field model is computed from the four accurate gravitational gradient components of GOCE (Gravity field and steady-state Ocean Circulation Explorer), combined with the analysis of the kinematic orbits, and some moderate constraint (or stabilization) in the polar areas where no observation from GOCE is available due to the orbit geometry. The normal matrix of each component is computed individually in order to study its contribution to the combined solution. The results show that the contribution of V_zz is the largest, with an average value of 32.74% of the total solution; the second and the third largest are V_zz and V_yy, with average values of 28.04% and 26.08%, respectively; the component V_xz contributes 11.81%. Validation with external data shows that each component has its characteristic value and that the information content of the component V_xz is not negligible and should be included for gravity field recovery. The orbit part as derived from high-low satellite-to-satellite tracking (SST-hl) to the GPS contributes mostly to the coefficients below degree and order (d/o) 20, and to non-zonal coefficients from d/o 20 to 80. The mean value of the contribution of the polar stabilization is the smallest with a value of 0.22%, nevertheless it is important. In addition to the contribution analysis in terms of the normal matrices, each individual component of the gradiometer has been combined with SST and polar stabilization, to give a set of single component gravity field models. These partially combined solutions are compared to the fully combined solution in terms of geoid differences. They show that the partially combined solution with V_zz is closest to the complete solution. Even closer is a combination with V_xx and V_yy. In addition to the GOCE-only solution, a GOCE-GRACE (Gravity Recovery And Climate Experiment) combined gravity field model is derived and the information content of GOCE and an available set of normal equations of GRACE are investigated. Results show that, as expected, GRACE dominates the solution below degree 90 and GOCE above degree 140.     

Evaluating legacy contaminants and emerging chemicals in marine environments using adverse outcome pathways and biological effects-directed analysis

Natural and synthetic chemicals are essential to our daily lives, food supplies, health care, industries and safe sanitation. At the same time protecting marine ecosystems and seafood resources from the adverse effects of chemical contaminants remains an important issue. Since the 1970s, monitoring of persistent, bioaccumulative and toxic (PBT) chemicals using analytical chemistry has provided important spatial and temporal trend data in three important contexts; relating to human health protection from seafood contamination, addressing threats to marine top predators and finally providing essential evidence to better protect the biodiversity of commercial and non-commercial marine species. A number of regional conventions have led to controls on certain PBT chemicals over several years (termed ‘legacy contaminants’; e.g. cadmium, lindane, polycyclic aromatic hydrocarbons [PAHs] and polychlorinated biphenyls [PCBs]). Analytical chemistry plays a key role in evaluating to what extent such regulatory steps have been effective in leading to reduced emissions of these legacy contaminants into marine environments. In parallel, the application of biomarkers (e.g. DNA adducts, CYP1A-EROD, vitellogenin) and bioassays integrated with analytical chemistry has strengthened the evidence base to support an ecosystem approach to manage marine pollution problems. In recent years, however, the increased sensitivity of analytical chemistry, toxicity alerts and wider environmental awareness has led to a focus on emerging chemical contaminants (defined as chemicals that have been detected in the environment, but which are currently not included in regulatory monitoring programmes and whose fate and biological impacts are poorly understood). It is also known that natural chemicals (e.g. algal biotoxins) may also pose a threat to marine species and seafood quality. Hence complex mixtures of legacy contaminants, emerging chemicals and natural biotoxins in marine ecosystems represent important scientific, economic and health challenges. In order to meet these challenges and pursue cost-effective scientific approaches that can provide evidence necessary to support policy needs (e.g. the European Marine Strategy Framework Directive), it is widely recognised that there is a need to (i) provide marine exposure assessments for priority contaminants using a range of validated models, passive samplers and biomarkers; (ii) integrate chemical monitoring data with biological effects data across spatial and temporal scales (including quality controls); and (iii) strengthen the evidence base to understand the relationship between exposure to complex chemical mixtures, biological and ecological impacts through integrated approaches and molecular data (e.g. genomics, proteomics and metabolomics). Additionally, we support the widely held view that (iv) that rather than increasing the analytical chemistry monitoring of large number of emerging contaminants, it will be important to target analytical chemistry towards key groups of chemicals of concern using effects-directed analysis. It is also important to evaluate to what extent existing biomarkers and bioassays can address various classes of emerging chemicals using the adverse outcome pathway (AOP) approach now being developed by the Organization for Economic Cooperation and Development (OECD) with respect to human toxicology and ecotoxicology.     

Variability of extreme precipitation in coastal river basins of the southern mexican Pacific region

Extreme wet and dry years (± 1 standard deviation, respectively), as well as the top 95 percentile (P95) of daily precipitation events, derived from tropical cyclone (TC) and nontropical cyclone (NTC) rainfall, were analyzed in coastal river basins in Southern Oaxaca, Mexico (Río Verde, Río Tehuantepec, and the Southern Coast). The study is based on daily precipitation records from 47 quality-controlled stations for the 1961 to 1990 period and TC data for the Eastern Tropical Pacific (EPAC). The aim of this study was to evaluate extreme (dry and wet) trends in the annual contribution of daily P95 precipitation events and to determine the relationship of summer precipitation with El Niño Southern Oscillation (ENSO) and the Pacifical Decadal Oscillation (PDO). A regionalization based on a rotated principal component analysis (PCA) was used to produce four precipitation regions in the coastal river basins. A significant negative correlation (significance at the 95% level) was only found with ONI in rainfall Region 3, nearest to the Gulf of Tehuantepec. Wet years, mainly linked to TC-derived P95 precipitation events, were associated with SST anomalies (≥?0.6°C) similar to weak La Niña and Neutral cool conditions, while dry years were associated with SST positive anomalies similar to Neutral warm conditions (≤?0.5°C). The largest contribution of extreme P95 precipitation derived from TCs to the annual precipitation was observed in Region 3. A significant upward trend in the contribution of TC-derived precipitation to the annual precipitation was found only in Region 1, low Río Verde.     

PERSPECTIVE ON CLIMATE CHANGE IN NORTH AMERICA DURING THE TWENTIETH CENTURY

The climate record from many parts of North America provides ample evidence of climate change. For specific elements such as temperature or precipitation, a substantial portion of these changes can be shown to be statistically significant; that is, they either reflect an unusual combination of events in a stationary process or they reflect a nonstationary process. The practical significance of a climate change, however, even when it can be shown to be statistically significant, cannot be assumed. Conversely, it is entirely possible to have a practically significant climate change without statistical significance, although this is less likely to occur.

The preponderance of evidence over recent years suggests that any notion regarding static climate regimes must be dismissed in favor of a dynamic system. The differential heating of our planet which results in a restless atmosphere can also yield a restless climate. Whether this dynamic climate system is merely a manifestation of natural variations or at least partly caused by changes in external influences, we cannot yet be certain. The fact that the climate has changed in North America during the 20th century, and in all likelihood will probably continue to do so in the future, should be considered in any decision-making process related to climate. [Key words: climatic change.]     

AGE ESTIMATES OF INLAND DUNES IN EAST-CENTRAL LOWER MICHIGAN USING SOILS DATA

Extensive deposits of eolian sand occur deep (>50 km) within the interior of east-central lower Michigan. These dunes are most common in the Saginaw lowland where they are parabolic, with limbs oriented northwesterly. Their presence on densely forested landscapes indicates that paleoenvironmental conditions differed sufficiently for dune formation to have occurred. In a previous study, Arbogast et al. (1997) illustrated that surface soils in the northwestern part of the Saginaw dune field were morphologically similar, consisting of weakly developed Spodosols (A/E/Bs/C horizonation). Thus, these dunes must have stabilized concurrently following regional mobilization of eolian sand. In this study, we present soils data from dunes in the southeastern part of the Saginaw dune field. Surface soils were analyzed at 19 sites in the Deford State Game Area in Tuscola County. Morphologically, the soils within the Deford area are similar (A/E/Bs/C horizonation), indicating that Deford dunes stabilized concurrently. Statistical (ANOVA, KW, factor analysis) comparison of Deford soils and soils to the northwest, however, reveals that significant developmental differences exist between the two areas, with Deford soils being better developed. Given that variables (climate, soil texture, pH) are more conducive for Spodosol development to the northwest, we conclude that Deford soils are older. Thus, Deford dunes must have stabilized prior to their counterparts to the northwest. [Key words: eolian processes, sand dunes, soils, Spodosols, Michigan.]     

INFLUENCE OF ENSO ON MAXIMUM,MINIMUM, AND MEAN TEMPERATURES IN THE SOUTHEAST UNITED STATES

The El Niño/Southern Oscillation (ENSO) phenomenon, in both its warm and cold states, has a pronounced influence on mean monthly temperature and precipitation in Southeast United States, particularly along the Gulf of Mexico coast. This paper examines the influence of ENSO warm and cold events on the average monthly maximum and minimum as well as mean temperatures at 88 stations across the Southeast during 1931–1994. Composite time series for the 24-month period from July prior to a warm- or cold-event year (year -1) to June following a warm- or cold-event year (year +1) are examined. In the months with the largest mean temperature departures, January and February of years +0 and +1, maximum and minimum temperature departures are of the same sign as the mean temperature departure. However, in much of the region south of Virginia, the maximum and minimum temperature departures are of opposite sign during the autumn of year +0 and spring of year +1. The role of cloud cover is examined in relation to the temperature response to ENSO. A decreased diurnal temperature range during the autumn of year +0 to the spring of year +1 occurred during warm events and is believed to be associated with increased cloud cover caused by an enhanced subtropical jet stream. [Key words: ENSO, temperature, cloud cover, Southeast United States.]     

A model for the demise of large, glacial Lake Ojibway, Ontario and Quebec

Large glacial lakes modulated the return of meltwater to the ocean during deglaciation, and their drainage may have initiated global climate change. Yet few records of their drainage come from observations within their basins. Sediment cores from nine lakes along a 240-km transect from northwestern Quebec to northeastern Ontario cover a portion of former Lake Ojibway and provide a stratigraphy of the terminal phase of this large glacial lake. Magnetic susceptibility, density, grain size, X-ray fluorescence chemistry and X-ray diffraction data were used to characterize stratigraphic changes within the basin. The basal sequence consists of till and rhythmites, with ice-proximal debris flows overlain by varves. The varves thin up-section and become unrecognizable, which indicates decreased deposition rates. This fine-grained sediment forms the matrix of a clay-pebble conglomerate. The clay-pebbles are ice-rafted debris (IRD). The IRD flux was probably constant, whereas the sedimentation rate of the finer-grained matrix decreased. The end of IRD marks the cessation of icebergs in the lake and is the best indication for drainage of the glacial lake. The conglomerate is capped by laminated to massive gray silt deposited after lake drainage and marks the transition to organic-rich, post-glacial lakes. Such sequences place drainage into the broader context of deglaciation.