Upper Water Column Nitrous Oxide Distributions in the Northeast Subarctic Pacific Ocean

This is the first study to investigate the magnitude and distribution of N₂O concentrations along the Line P oceanographic transect in the Northeast (NE) subarctic Pacific Ocean. Concentrations of N₂O were measured from the surface to 600 m depth at five stations between 126°W and 145°W. Although nitrification within the mixed layer may produce some N₂O, we conclude that mixing and diffusion processes, which vertically transport N₂O upwards from below the mixed layer, are the primary sources of N₂O to the surface waters of the NE subarctic Pacific Ocean. Below the mixed layer, nitrification appears to be the dominant source of N₂O, and based on correlations of excess N₂O (ΔN₂O) versus apparent oxygen utilization and NO₃ ^? concentrations, we estimated that the N₂O yield from nitrification was approximately 0.028 to 0.040%. The longitudinal distributions of N₂O concentrations below the mixed layer were variable and we consider the potential role that different transiting water masses may play in contributing to this variability. Finally, we estimated that the regional average sea-to-air N₂O flux was 4.37 mol of N₂O km^?2 d^?1, a value which is approximately four times that of the global average seawater-to-air flux rate. Our N₂O yield estimates are within the range of those expected under oxic conditions, leading us to conclude that decreasing dissolved O₂ concentrations in the NE subarctic Pacific Ocean, and the water masses that influence this region, over the past 50 years have yet to produce a substantial increase in N₂O production. Given the expectation that dissolved O₂ concentrations in the subarctic Pacific Ocean will continue to decrease during this century, this study has provided an important baseline from which future studies will be able to track changes in seawater N₂O concentrations and fluxes to the atmosphere.

[Traduit par la rédaction] La présente étude est la première à s'intéresser à la valeur et à la distribution des concentrations de N₂O le long du transect océanographique de la ligne P dans le Pacifique Nord-Est subarctique. Les concentrations de N₂O ont été mesurées de la surface jusqu’à une profondeur de 600 m à cinq stations entre 126°O et 145°O. Bien que la nitrification à l'intérieur de la couche de mélange puisse produire du N₂O, nous concluons que le mélange et les processus de diffusion, qui transportent verticalement le N₂O vers le haut à partir d'en dessous de la couche de mélange, sont les sources principales de N₂O pour les eaux de surface du Pacifique Nord-Est subarctique. En dessous de la couche mélange, la nitrification semble être la principale source de N₂O, et d'après les corrélations de l'excès de N₂O (ΔN₂O) par rapport à l'utilisation apparente d'oxygène et aux concentrations de NO₃ ^?, nous avons estimé que le rendement en N₂O de la nitrification était approximativement de 0,028 à 0,040%. Les distributions longitudinales des concentrations de N₂O en dessous de la couche de mélange étaient variables et nous considérons le rôle possible que des différentes masses d'eau transitoires peuvent avoir à jouer dans cette variabilité. Finalement, nous avons estimé que la moyenne régionale du flux mer–air de N₂O était de 4,37 moles de N₂O km^?2 j^?1, une valeur qui est environ quatre fois celle du taux planétaire moyen du flux eau de mer–air. Nos estimations du rendement en N₂O sont de l'ordre de celles attendues dans des conditions oxyques, ce qui nous amène à conclure que la diminution des concentrations d'oxygène dissout dans le Pacifique Nord–Est subarctique, et dans les masses d'eau qui influencent cette région, au cours des cinquante dernières années ont encore à produire une augmentation substantielle de production de N₂O. Étant donné qu'on s'attend à ce que les concentrations d'oxygène dissout dans le Pacifique subarctique continuent à diminuer durant le présent siècle, cette étude a fourni une importante base de référence à partir de laquelle de futures études pourront suivre les changements dans les concentrations de N₂O dans l'eau de mer et dans ses flux vers l'atmosphère.     

OSL quartz age underestimation due to unstable signal components

When measuring samples from southern Peru, we discovered an age offset between feldspar infrared-stimulated luminescence (IRSL) and quartz optically stimulated luminescence (OSL) ages. This age offset was not only found in these particular samples but was also observed in samples from a range of geographical localities. Extensive analysis revealed that it is actually the quartz age that underestimates the true depositional age, and this is due to a very weak fast component combined with other thermally unstable OSL signal components. We discuss properties of these poorly behaving samples and how to detect such samples prior to the OSL single-aliquot regenerative-dose (SAR) measurement. Finally, existing approaches to improve equivalent dose (D_e) determination are discussed for samples from southern Peru.     

Changes in body condition and fatty acid composition of wild Mediterranean horse mackerel (Trachurus mediterraneus, Steindachner, 1868) associated to sea cage fish farms

Net-cage fish farms attract a great number of wild fishes, altering their behaviour and possibly their physiology. Wild Mediterranean horse mackerel (Trachurus mediterraneus), sampled from populations aggregated around two Mediterranean fish farms and from two natural control populations, were analyzed for differences in body condition, stomach content and fatty acid composition. Pellets used to feed caged fish in both farms were also analyzed to identify their relationship with the fatty acid composition of tissue of wild fish. T. mediterraneus aggregated around the farms throughout the year although large seasonal changes in abundance and biomass occurred. Wild fish aggregated at farms mainly ate food pellets while control fish fed principally on juvenile fish and cephalopods. Wild fish that fed around the cages had a significantly higher body fat content than the control fish (7.30+/-1.8% and 2.36+/-0.7%, respectively). The fatty acid composition also differed between farm-associated and control fish, principally because of the significantly increased levels of linoleic (C18:2omega6) and oleic (C18:1omega9) acids and decreased docosahexaenoic acid (C22:6omega3) in farm-associated fish. The increased condition of wild fish associated with farms could increase the spawning ability of coastal fish populations, if wild fish are protected from fishing while they are present at farms. The fatty acids compositions could also serve as biomarkers to infer the influence of a fish farm on the local fish community, helping to better describe the environmental impact of fish farming.     

Hydraulic testing of low-permeability formations: A case study in the granite of Cadalso de los Vidrios, Spain

In recent years, the study of low-permeability geological formations has undergone considerable development. This is mainly due to the use of natural geological barriers to confine waste disposals, preventing leaking water from bringing contaminants into contact with the biosphere and the groundwater resources.In that context, the Spanish Geological Survey (IGME, Spanish acronym), supported by the National Radioactive Waste Management Agency (ENRESA, Spanish acronym) and with the technical advice of the Swedish Nuclear Fuel and Waste Management Company (SKB) designed and built a Mobile Hydrogeological Unit (UMH, Spanish acronym) for low-permeability formations characterization, which has been operational since 1997 and has been used for different purposes. Among other possibilities, the UMH allows conducting: constant transient-state flow-rate injection tests, constant-head transient-state injection tests, pseudo-stationary state injection tests, pressure fall-off tests, slug tests and pulse tests.The main objectives of this article are to describe the hydraulic characterization methodology used by IGME to carry out hydraulic tests in low permeability environment, to compare different testing methods and to summarize the results that have been obtained when characterizing the leucogranites of Cadalso de los Vidrios in Spain.The study area presents an increasing interest for granite production inside the Community of Madrid. The petrological and structural characteristics of the granite rocks and the core-samples extracted from a 200 m deep borehole investigation are described. The packer tests are conducted with the Mobile Hydrogeological Unit.The tests are interpreted with the help of analytical solutions. The main software used is Hytool, an open source matlab toolbox that provides a library of analytical solutions and a set of routines to facilitate hydraulic tests interpretation.The results allow the elaboration of a comparative analysis of the applied hydraulic tests and to define the hydraulic conductivity optimum application interval most suited for each of the used methods.Hydraulic conductivity values obtained varies from 3.20·10^− 7 m/s, for the upper weathered layer, to 2.80·10^− 12 m/s, for the test section from 97.36 to 116.15 m depth.Finally, the hydraulic conductivity values obtained in this area are compared with other case studies of granite formations around the world.     

Property matters: Agricultural restructuring and changing landlord-tenant relationships in England

Little research has been conducted on the restructuring activities of tenant farmers in response to changing tenancy legislation and recent CAP reforms. This paper examines the geography of farm tenancy agreements in England since 1995 and presents some findings from postal and telephone surveys on the possible future business trajectories of tenant farmers and the changing nature of landlord-tenant relationships. A clear north-south divide is identified in terms of farm tenancy agreements and a complex array of different tenancy agreements is demonstrated. The relationships between landlords and tenants are changing and the increasing variety of agreements provides evidence of a more fluid (post-feudal) system of agricultural leases. Nevertheless, high levels of uncertainty and negativity characterise tenant farmers’ views on the impacts of CAP reforms. Crucially, the very identity of a tenant farmer is changing, towards an owner-occupier who rents additional land, and there is an urgent need for more detailed research on the ‘consequential geographies’ of farm property rights and the changing nature of landlord-tenant relationships.     

“It’s a gestalt experience”: Landscape values and development pressure in Hawke’s Bay, New Zealand

Demand for both primary residences and second homes in high-amenity areas has led to escalating property values and widespread development pressure in coastal New Zealand. We focus on a major development proposal at Ocean Beach, a greenfield coastal site in the Hawke’s Bay region, and seek to explain the opposition it has provoked. In so doing, we address three questions: first, what landscape values are articulated within the planning process; second, what is the anticipated impact of 1000 new dwellings on those values; and third, how does place attachment figure in the ensuing debates. We address these questions though a thematic analysis of data derived from official reports and proposals, planning submissions, and key informant interviews. We find Ocean Beach to be a place that offers a quintessential coastal experience, often linked to youthful memories. Additionally, the site is valued for its accessibility and wilderness qualities - perceptions heightened by awareness that areas of undeveloped coastline relatively close to population centres are increasingly scarce. We contend that such sites are doubly valuable: in a formal sense, as natural landscapes whose processes and forms receive regulatory protection; and in an informal sense, as sites that generate human meaning, including emotions such as nostalgia, freedom and belonging.     

Nuances of neighbourhood: Children’s perceptions of the space between home and school in Auckland, New Zealand

This paper examines primary school children’s experiences of travelling between home and school within three neighbourhoods. Our investigation is set in Auckland, New Zealand, where parental practices such as chauffeuring are commonplace, yet are increasingly recognised as limiting children’s physical fitness and environmental awareness. Drawing on children’s voices, writing and photographs, we investigate how children currently travel to school, how they would like to travel, and how their perspectives on neighbourhood space vary by age, socio-economic status and school location. Findings reveal that over half of the participants did not like the way they travelled to school. Most desire to travel independently within public space, but are limited in their ability to do so, given the fears and obstacles that prevail within their neighbourhoods. We contend that restricted use of public space diminishes children’s agency in inner suburbs. Our analysis reveals that children favour ‘active travel’ for many of the same reasons as health professionals and transport planners. We conclude that as long as children are seen as innocents in need of protection, they will have limited agency in travel decisions and highly contingent access to public space.     

Mid-Jurassic Tectonothermal Event Superposed on a Paleozoic Geological Record in the Acatlán Complex of Southern Mexico: Hotspot Activity During the Breakup of Pangea

U-Pb isotopic analyses of zircon from the lowest structural units of the Acatlán Complex of southern Mexico indicate that Paleozoic tectonothermal events are overprinted by mid-Jurassic (175±3 to 171±1 Ma), low pressure migmatization (5–6 kb), polyphase deformation, and intrusion of felsic and mafic magmas. Ensuing rapid cooling recorded by ⁴⁰Ar/³⁹Ar muscovite, biotite and K-feldspar ages is estimated to have taken place at 21±3°C/my at exhumation rates of 0.6 mm/yr. Such rapid exhumation requires a combination of erosion and tectonic unroofing that is recorded by top-to-the-west kinematic data. Synchronous tectonic unroofing is also recorded 100 km to the east in the adjacent Oaxaca terrane, where top-to-the-north, extensional shear zones occur in Paleozoic strata.This pattern of extension suggests tectonic unroofing in response to domal uplift (radius >100 km) like that associated with core complexes, slab windows, and hotspots. Most tectonic analyses for the Jurassic place the Acatlán Complex in the forearc region of an arc in Colombia lying 600–800 km inboard of the subduction zone, presumably in response to flat-slab subduction. Modern analogues suggest that flat-slab subduction reflects subduction of young buoyant oceanic lithosphere adjacent to either a mid-oceanic ridge, or a plume. Since core complexes are typical of arc-backarc regions, and slab windows generally produce metamorphic belts, the forearc setting and associated domal uplift suggest a plume to be the most likely cause of this Jurassic tectonothermal pulse in southern Mexico. This plume activity is synchronous with the opening of the Gulf of Mexico during the breakup of Pangea, to which it may have contributed.     

Aquifer Discharge Drives Microbial Community Change in Karst Estuaries

Karst estuaries are unique systems governed by freshwater inputs that flow directly to the sea through karst conduits and/or matrices. Because they are found at the interface between terrestrial and marine environments, they can act as sentinels to climate change and as indicators of aquifer health. The physical and geochemical gradients formed in karst estuaries are a direct result of the interactions between inland hydrological conditions and sea level. To examine the influence these gradients have on microbial communities in the water column and sediment of a karst estuary, we studied the spring-fed Double Keyhole Karst Estuary in west central Florida for a 2-year period. Four sites were monitored within this system starting at the Double Keyhole Spring Conduit extending 2 km west through the estuary toward the Gulf of Mexico. Water column and sediment samples were collected quarterly at all sites from September 2011 through September 2013. Archaeal, bacterial, and microbial eukaryote communities were analyzed using quantitative PCR and length-heterogeneity PCR. The biological communities were analyzed in the context of hydrological, physical, and geochemical parameters in order to determine which factor(s) governed the observed changes of microbial abundance and richness. The major finding of this study was that microbial community change in this karst estuary was primarily driven by the volume of aquifer discharge and associated physical gradients, and less by the geochemical fluctuations within the system.