Transmissivity of solar radiation through crowns of single urban trees—application for outdoor thermal comfort modelling

Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the transmissivity of total and direct solar radiation through crowns of single street trees in Göteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (T_mrt). Measured values of transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance.     

Integrated geophysical and geochemical study on AMD generation at the Haveri Au–Cu mine tailings,SW Finland

The Haveri tailings area contains 1.5 Mt of sulfide-bearing waste from the Au–Cu mine that operated during 1942–1961. Geophysical and geochemical methods were used to evaluate and characterize the generation of acid mine drainage (AMD). Correlations were examined among the electrical resistivity tomography (ERT) data, the total sulfide content and concentrations of sulfide-bound metals (Cu, Co, Fe, Mn, Ni, Pb and Zn) of tailings samples, and the resistivity and geochemistry of surface water. The resulting geophysical–geochemical model defines an area in the vadose tailings, where a low resistivity anomaly (<10 Ohm m) is correlated with the highest sulfide content, extensive sulfide oxidation and low pH (average 3.1). The physical and geochemical conditions, resulting from the oxidation of the sulfide minerals, suggest that the low resistivity anomaly is associated with acidic and metal-rich porewater (i.e., AMD). The lower resistivity values in the saturated zone of the central impoundment suggest the formation of a plume of AMD. The natural subsoil layer (silt and clay) and the bedrock surface below the tailings area were well mapped from the ERT data. The detected fracture zones of the bedrock that could work as leakage pathways for AMD were consistent with previous geological studies. The integrated methodology of the study offers a promising approach to fast and reliable monitoring of areas of potential AMD generation and its subsurface movement over large areas (ca. 9 ha). This methodology could be helpful in planning drill core sampling locations for geochemical and mineralogical analysis, groundwater sampling, and choosing and monitoring remedial programs.     

Forest Beliefs in an Urbanizing World: Views on and Usage of Forest Areas Among Persons with and Without a Migration Biography in Germany and Sweden

Previous studies have shown that environmental values of inhabitants of urban areas differ to some extent from those of people living in rural contexts. In the light of increasing urbanization, it is sometimes argued that these differences are becoming even greater, as people are becoming more and more alienated from nature. In the context of a larger survey study on beliefs about forests and forest management among the general public in Germany and Sweden, the influences of people’s migration biographies on their patterns of forest usage, their environmental concerns about forests, and the expectations and values they ascribe to forests are explored. While previous findings on differences between urban and rural populations are confirmed, we also find variation within these groups depending on their history of moving between the two spatial categories. This study thus adds a dynamic aspect to the discussion on the urban–rural perspective on beliefs about forests.     

Constraints on the Palaeoproterozoic tectono-metamorphic evolution of the Lewisian Gneiss Complex,NW Scotland: Implications for Nuna assembly

Despite extensive investigation, the tectono-thermal evolution of the Archean crust in the Lewisian Gneiss Complex in NW Scotland (LGC) is debated. Most U–Pb zircon geochronological and metamorphic studies have focused on rocks from the central region of the mainland LGC, where granulite facies assemblages associated with the oldest (Badcallian) tectono-metamorphic event at c. 2.75 Ga are overprinted by younger amphibolite facies assemblages related to the Inverian (c. 2.5 Ga) and subsequent Laxfordian (c. 1.9–1.65 Ga) tectono-thermal events. In the southern and northern regions of the mainland LGC, deformation and metamorphism associated with the Laxfordian event are pervasive, although the timing and conditions are poorly constrained. Here, we present new field, petrographic and structural data, U–Pb zircon and titanite geochronology and phase equilibrium modelling of amphibolite samples from the northern and southern regions. Our field observations show that in both regions, pre-Laxfordian structures are significantly reworked by steep NW-striking fabrics that are themselves pervasively overprinted by co-axial deformation and amphibolite facies metamorphism related to the Laxfordian event. In situ U–Pb titanite geochronology yields Laxfordian ages of 1853 ± 20 Ma in the southern region (P = 6–8 kbar and T = 640–690°C) and 1750 ± 20 Ma and 1776 ± 10 Ma in the northern region (P = 6–7.5 kbar and T = 740–760°C). While U–Pb dating of zircon rims from felsic gneisses in the central region shows a dominant Inverian metamorphic overprint at c. 2500 Ma, zircon rims in felsic gneisses from the northern and southern regions commonly yield Laxfordian dates as young as c. 1800 Ma. Combined, the results support the idea that, during the Palaeoproterozoic, the central region of the LGC acted as low-strain domain, in which intense deformation and metamorphism were restricted to crustal-scale shear zones. By contrast, in the southern and northern regions, early (c. 1.85 Ga) and late (c. 1.75 Ga) Laxfordian deformation and fluid-mediated metamorphism were much more pervasive and at higher P–T conditions than previously proposed. The diachronous Laxfordian evolution of the southern and northern regions indicate that they reflect early and late snapshots of collisional to transpressional tectonics in the mainland LGC. The long-lasting Laxfordian evolution documents the collision of the Rae and North Atlantic cratons during the Palaeoproterozoic amalgamation of the supercontinent Nuna, with implications for the palaeogeographic configuration of NW Scotland during Palaeoproterozoic Nuna.     

Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools

Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30‐ to 50‐year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple‐lines‐of‐evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (S _t > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m.     

Intra-City Variation in Urban Morphology and Turbulence Structure in Helsinki, Finland

Most atmospheric boundary-layer theories are developed over vegetative surfaces and their applicability at urban sites is questionable. Here, we study the intra-city variation of turbulence characteristics and the applicability of boundary-layer theory using building-morphology data across Helsinki, and eddy-covariance data from three sites: two in central Helsinki (400 m apart) and one 4 km away from the city centre. The multi-site measurements enable the analysis of the horizontal scales at which quantities that characterize turbulent transport vary: (i) Roughness characteristics vary at a 10-m scale, and morphometric estimation of surface-roughness characteristics is shown to perform better than the often used rule-of-thumb estimates (average departures from the logarithmic wind profile are 14 and 44 %, respectively). (ii) The drag coefficient varies at a 100-m scale, and we provide an updated parametrization of the drag coefficient as a function of z/z _H (the ratio of the measurement height to the mean building height). (iii) The transport efficiency of heat, water vapour and CO₂ is shown to be weaker the more heterogeneous the site is, in terms of sources and sinks, and strong scalar dissimilarity is observed at all sites. (iv) Atmospheric stability varies markedly even within 4 km across the city: the median difference in nocturnal sensible heat fluxes between the three sites was over 50W m^?2. Furthermore, (v) normalized power spectra and cospectra do not vary between sites, and they follow roughly the canonical theory as developed over vegetated terrain.     

The New Consort Gold Mine,Barberton greenstone belt,South Africa: orogenic gold mineralization in a condensed metamorphic profile

The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to, the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary rocks of the overlying c. 3,260–3,230 Ma Fig Tree Group. This contact, locally referred to as the Consort Bar, formed during ductile D₁ imbrication of the metavolcanosedimentary sequence and predates the main stage of the gold mineralization. The imbricate stack is situated in the immediate hanging wall of the basal granitoid–greenstone contact along the northern margin of the greenstone belt. It is characterized by a condensed metamorphic profile in which the metamorphic grade increases from upper greenschist facies conditions (510–530°C, 4 kbar) in rocks of the Fig Tree Group to upper amphibolite facies grades (600–700°C, 6–8 kbar) in the basal Onverwacht Group. Detailed structural and petrological investigations indicate that the Consort Bar represents a major structural break, which is largely responsible for the telescoping of metamorphic isograds within the structural sequence. Two stages of mineralization can be distinguished. Loellingite, pyrrhotite, and a calc–silicate alteration assemblage characterize an early high-T mineralization event, which is restricted to upper amphibolite facies rocks of the Onverwacht Group. This early mineralization may correlate with the local D₁ deformation. The second and main stage of gold mineralization was associated with renewed ductile shearing during D₂. The D₂ deformation resulted in the reactivation of earlier structures, and the formation of a NNW trending, steeply dipping shear zone system, the Shires Shear Zone, which separates two regional SE plunging D₁ synclines. The mineralized shear zones are intruded by abundant syn-kinematic pegmatite dykes that have previously been dated at c. 3040 Ma. Petrological and geothermobarometric data on ore and alteration assemblages indicate that the main stage of gold mineralization, which affected a crustal profile of ca. 1.5 km, was characterized by increasing temperatures (c. 520 to 600°C) with increasing structural depth. Sulfide assemblages in the ore bodies change progressively with metamorphic grade, ranging from arsenopyrite + pyrite + pyrrhotite in the structurally highest to arsenopyrite + pyrrhotite + chalcopyrite + loellingite in the structurally deepest part of the mine. The main stage of gold mineralization was broadly syn-peak metamorphic with respect to the Fig Tree Group, but postdates the peak of metamorphism in upper amphibolite facies rocks of the structurally underlying Onverwacht Group. This indicates that the mineralization coincided with the juxtaposition of the two units. As the footwall rocks were already on their retrograde path, metamorphic devolatilisation reactions within the greenstone sequence can be ruled out as the source of the mineralizing fluids.     

A comparison of helicopter-borne electromagnetics in frequency- and time-domain at the Cuxhaven valley in Northern Germany

Two different airborne electromagnetic methods were applied in the same area: the frequency-domain helicopter-borne electromagnetic (HEM) system operated by the Federal Institute for Geosciences and Natural Resources, Germany, and the time-domain SkyTEM system of the HydroGeophysics Group at the University of Aarhus, Denmark. For verification of and comparison with the airborne methods, ground-based transient electromagnetics and 2-D resistivity surveying were carried out. The target of investigation was the Cuxhaven valley in Northern Germany, which is a significant local groundwater reservoir. The course of this buried valley was revealed by drillings and the shape was determined by reflection seismics at several cross sections.We applied electrical and electromagnetic methods to investigate the structure of the valley filling consisting of gravel, sand, silt and clay. The HEM survey clearly outlines a shallow conductor at about 20m depth and a deeper conductor below 40m depth inside the valley. This is confirmed by 2-D resistivity surveying and a drilling. The thickness of the deeper conductor, however, is not revealed due to the limited investigation depth of the HEM system. The SkyTEM survey does not resolve the shallow conductor, but it outlines the thickness of the deeper clay layer inside the valley and reveals a conductive layer at about 180m depth outside the valley. The SkyTEM results are very consistent with ground-based transient electromagnetic soundings.Airborne electromagnetic surveying in general has the advantage of fast resistivity mapping with high lateral resolution. The HEM system is cost-efficient and fast, but the more expensive and slower SkyTEM system provides a higher depth of investigation. Ground-based geophysical surveys are often more accurate, but they are definitively slower than airborne surveys. It depends on targets of interest, time, budget, and manpower available by which a method or combination of methods will be chosen. A combination of different methods is useful to obtain a detailed understanding of the subsurface resistivity distribution.     

Particle trapping in stratified estuaries: Application to observations

Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability of scaling parameters and the response of ETM phenomena to a range of river flow (U _r ) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current amplitude (U_T), represented by low values of the Supply number S_r.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly, scaling variables and data are combined to express ETM properties in terms of the friction velocity (U_*),U _r , andU _T , allowing a considerable simplification of the parameters used to describe ETM.     

Processes of high-T fluid–rock interaction during gold mineralization in carbonate-bearing metasediments: the Navachab gold deposit,Namibia

The Navachab gold deposit in the Damara belt of central Namibia is hosted by a near-vertical sequence of amphibolite facies shelf-type metasediments, including marble, calc-silicate rock, and biotite schist. Petrologic and geochemical data were collected in the ore, alteration halos, and the wall rock to evaluate transport of elements and interaction between the wall rock and the mineralizing fluid. The semi-massive sulfide lenses and quartz–sulfide veins are characterized by a complex polymetallic ore assemblage, comprising pyrrhotite, chalcopyrite, sphalerite, and arsenopyrite, native bismuth, gold, bismuthinite, and bismuth tellurides. Mass balance calculations indicate the addition of up to several orders of magnitude of Au, Bi, As, Ag, and Cu. The mineralized zones also record up to eightfold higher Mn and Fe concentrations. The semi-massive sulfide lenses are situated in the banded calc-silicate rock. Petrologic and textural data indicate that they represent hydraulic breccias that contain up to 50 vol.% ore minerals, and that are dominated by a high-temperature (T) alteration assemblage of garnet–clinopyroxene–K-feldspar–quartz. The quartz–sulfide veins crosscut all lithological units. Their thickness and mineralogy is strongly controlled by the composition and rheological behavior of the wall rocks. In the biotite schist and calc-silicate rock, they are up to several decimeters thick and quartz-rich, whereas in the marble, the same veins are only a few millimeters thick and dominated by sulfides. The associated alteration halos comprise (1) an actinolite–quartz alteration in the biotite schist, (2) a garnet–clinopyroxene–K-feldspar–quartz alteration in the marble and calc-silicate rock, and (3) a garnet–biotite alteration that is recorded in all rock types except the marble. The hydrothermal overprint was associated with large-scale carbonate dissolution and a dramatic increase in CO₂ in the ore fluid. Decarbonation of wall rocks, as well as a low REE content of the ore fluid resulted in the mobilization of the REE, and the decoupling of the LREE from the HREE. The alteration halos not only parallel the mineralized zones, but may also follow up single layers away from the mineralization. Alteration is far more pronounced facing upward, indicating that the rocks were steep when veining occurred. The petrologic and geochemical data indicate that the actinolite–quartz– and garnet–clinopyroxene–K-feldspar–quartz alterations formed in equilibrium with a fluid (super-) saturated in Si, and were mainly controlled by the composition of the wall rocks. In contrast, the garnet–biotite alteration formed by interaction with a fluid undersaturated in Si, and was mainly controlled by the fluid composition. This points to major differences in fluid–rock ratios and changes in fluid composition during alteration. The alteration systematics and geometry of the hydrothermal vein system are consistent with cyclic fluctuations in fluid pressure during fault valve action. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.