Water-soluble gases as partitioning tracers to investigate the pore volume-transmissivity correlation in a fracture

Hydraulically equivalent fractures may show striking differences when a gas-migration experiment is performed because of the different correlations between transmissivity, pore volume and entry pressure. We numerically simulate gas migration between injection and extraction boreholes in a parallel plate fracture with a heterogeneous fault gouge, in a rough-walled fracture filled with homogeneous material, and in a rough-walled empty fracture. The parallel plate model and the empty model clearly show the existence of preferential paths; for high variance of the transmissivity field, gas flow takes place only in few discrete channels separated by water-saturated regions. In contrast, in the fracture filled with homogeneous fault gouge, the gas saturation is continuous and more uniformly distributed. It appears a fundamental issue to be able to discriminate in situ among conceptual models that can yield such a different gas-saturation distribution. As in practice, the saturation distribution cannot be directly observed, tracer experiments are performed to characterize a fracture. For these reasons, we simulate the transport of tracers, which are added to the gas phase as soon as quasi-steady saturation distribution and extraction rate are achieved, and we compare the breakthrough curves obtained assuming different models. Our numerical simulations suggest that discrimination among the models on the basis of single-tracer tests is unlikely. A better tool to investigate fracture properties is provided by a gas-tracer test, in which a cocktail of gases with different water solubility is employed. These gases behave as partitioning tracers and allow us to estimate the gas saturation in the fracture. Indeed, by comparison of the residence-time distributions of different gases, we are able to compute a streamline effective saturation, which is an excellent estimate of fracture saturation. In addition, the streamline effective saturation curve contains information that is useful to identify the conceptual model that more likely applies to the fracture.     

Influence of micro-organisms on the dissolution of metallic platinum emitted by automobile catalytic converters

Platinum emitted by automotive catalyst converters mainly exists in the metallic form, which is not bioavailable. Several investigations showed that finely dispersed metallic platinum is dissolved in organic matrices to a significantly high degree [1,2]. In an exclusion experiment, observations were made as to whether the transformation of Pt(0) and other platinum compounds is mainly of a chemical nature or is influenced by micro-organisms. A previous experiment [2], concerning the interaction of several platinum compounds with a clay-like humic soil was repeated under sterile conditions to rule out the influence of micro-organisms. During the time of interaction (3–60 d), no significant differences were observed between the sterile and non-sterile modes. Thus, the dissolution of metallic platinum into soluble species, observed previously within this time period [2], seems to be mainly of a chemical nature. On leave from Liaoning University, Department of Chemistry, 110036 Shenyang, PR China     

The development of sun compass orientation in young homing pigeons

Summary A series of clock-shift experiments with young homing pigeons of various ages was performed to determine at what age they normally learn sun compass orientation. The response of untrained pigeons to shifting of their internal clock seems to depend on their age. When the clock-shifted birds were tested at an age of 11 weeks and younger, their departure bearings did not differ significantly from those of controls (Fig. 1, diagrams on the right); in tests with birds 12 weeks and older the characteristic deviation indicating the use of the sun compass was observed (Figs. 2 and 3). Birds that had participated in a short training program, however, used the sun compass at 8 weeks, the earliest age tested (Fig. 1, diagrams on the left). These findings show that the time of development of the sun compass strongly depends on flying experience. Within the first months of a bird's life, it seems to take place after the bird has been confronted with the need to orient, either spontaneously during extended exercise flights around its loft or imposed by training releases.The departure bearings of the very young, inexperienced birds that did not rely on the sun compass, however, were already oriented homeward. This indicates that the ability to navigate develops independently of the sun compass, before the sun compass is learned.Dedicated to Prof. Dr. F.W. Merkel for his 70th birthday     

Vibrational signals in the tremble dance of the honeybee,Apis mellifera

Summary The tremble dance is a behavior sometimes performed by honeybee foragers returning to the hive. The biological significance of this behavior was unclear until Seeley (1992) demonstrated that tremble dances occur mainly when a colony's nectar influx is so high that the foragers must undertake lenghty searches in order to find food storers to unload their nectar. He suggested that tremble dancing has the effect of stimulating additional bees to function as food-storers, thereby raising the colony's capacity for processing nectar. Here I describe vibrational signals emitted by the tremble dancers. Simulation experiments with artificial tremble dance sounds revealed that these sounds inhibited dancing and reduced recruitment to feeding sites. The results suggest that the tremble dance is a negative feedback system counterbalancing the positive feedback of recruitment by waggle dances. Thus, the tremble dance seems to affect not only the colony's nectar processing rate, but also its nectar intake rate.     

A spatially explicit and quantitative vulnerability assessment of ecosystem service change in Europe

Environmental change alters ecosystem functioning and may put the provision of services to human at risk. This paper presents a spatially explicit and quantitative assessment of the corresponding vulnerability for Europe, using a new framework designed to answer multidisciplinary policy relevant questions about the vulnerability of the human-environment system to global change. Scenarios were constructed for a range of possible changes in socio-economic trends, land uses and climate. These scenarios were used as inputs in a range of ecosystem models in order to assess the response of ecosystem function as well as the changes in the services they provide. The framework was used to relate the impacts of changing ecosystem service provision for four sectors in relation to each other, and to combine them with a simple, but generic index for societal adaptive capacity. By allowing analysis of different sectors, regions and development pathways, the vulnerability assessment provides a basis for discussion between stakeholders and policymakers about sustainable management of Europe’s natural resources. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Development of marginal emission factors for N losses from agricultural soils with the DNDC–CAPRI meta-model

The article discusses marginal emission factors for N losses from agricultural soils, with rape and wheat as examples, and presents results for EU15 as high-resolution maps and aggregated to Member State level. The results are generated by linking the economic model for the agricultural sector CAPRI (Common Agricultural Policy Regional Impact) with spatial down-scaling, and a statistical meta-model for the bio-physical model DNDC (DeNitrification–DeComposition). For a given agro-economic scenario, CAPRI supplies for each crop the crop share, yield and fertilizer application rate spatially downscaled to clusters of 1 km × 1 km grid cells. The results from CAPRI are processed by a meta-model of DNDC to estimate the local greenhouse gas emissions from the soil. DNDC is a dynamic process-oriented model, which estimates trace gas fluxes and nutrient turnover in agricultural soils. The fit of the regressions is typically very good (0.95R² for the majority of the regressions), and all coefficients are significant at 99% probability. The meta-model allows a seamless integration between the economic and the bio-physical models, offering additional benefit such as the site-specific calibration of the bio-physical model ensuring the match between simulated and observed yield at the grid-level.The meta-model is used to calculate marginal emission factors for a 1 kg ha⁻¹ increase of mineral N and manure fertilizer rates for rape and wheat, at different levels of fertilization. They show that for Western European farming practice, only a small fraction of extra nitrogen fertilizer would go into increased yields: most of it would be emitted to the environment. The largest spatial variability is observed for N₂O emissions. The derivation of marginal emission factors is just one of the many possible uses for the linked regionalized agro-economic and soil chemistry model, which exploits to a large extent both geo-referenced and regionally available statistical information at European scale.     

Agency and structure: a grounded theory approach to explain land-use change in the Mindo and western foothills of Pichincha,Ecuador

ABSTRACT

Although life and land decisions are individual, driven by perceptions of reality, they reflect broader social processes. This research aims to understand relevant land-use change processes and the context within which land-use change occurs in the study area. For this, we employ grounded theory techniques and procedures to analyze narratives and life history interviews. Based on these narratives, we re-construct past land-use changes. Additionally, we identify structural conditions that drive change, several dimensions of change, including cultural-cognitive dimensions, and future discourses. The identified structural conditions motivate changes in concepts, actions, and practices, in land-use, and institutions, eventually leading to generational changes. Further research is needed to examine how the so-called structural conditions producing change varies in different settings and contexts. These findings can provide insight into certain patterns and knowledge that may contribute to community planning, policy design, and the conception of sustainable solutions with more grounded knowledge.