Functional Performance of Three Invasive <Emphasis Type="Italic">Marenzelleria</Emphasis> Species Under Contrasting Ecological Conditions Within the Baltic Sea

A 4-week laboratory experiment investigated the behaviour (survival and bioirrigation) and impact of the invasive polychaetes Marenzelleria viridis, M. neglecta and M. arctia on sediment-water solutes exchange, porewater chemistry, and Fe and P interactions in high-salinity sandy sediment (HSS) and low-salinity muddy sediment (LSM) from the Baltic Sea. M. viridis showed deep burrowing with efficient bioirrigation (11 L m^?2 day^?1) and high survival (71%) in HSS, while M. arctia exhibited shallow burrowing with high bioirrigation (12 L m^?2 day^?1) and survival (88%) in LSM. M. neglecta behaved poorly in both ecological settings (bioirrigation, 5–6 L m^?2 day^?1; survival, 21–44%). The deep M. viridis bioirrigation enhanced total microbial CO₂ (TCO₂) production in HSS by 175% with a net efflux of NH₄⁺ and PO₄^3?, at rates 3- to 27-fold higher than for the other species. Although the shallow and intense bioirrigation of M. arctia in LSM stimulated microbial TCO₂ production to some extent (61% enhancement), the nutrient fluxes close to zero indicate that it effectively prevented the P release. Porewater Fe:PO₄^3? ratios revealed that the oxidizing effect of M. arctia bioirrigation increased the PO₄^3? adsorption capacity of LSM twofold relative to defaunated controls while no buffering of PO₄^3? was detected in M. viridis HSS treatment. Therefore, the different behaviour of the three species in various environments and the sharp contrast between M. viridis and M. arctia effects on C, N and P cycling must be considered carefully when the ecological role of Marenzelleria species in the Baltic Sea is evaluated.     

Staying with the system: theoretical consistency and change in Danish geographical work on the Sahel

Scholars have studied the Sahel intensely since major droughts hit the region in the early 1970s. One of the most persistent of these in terms of both volume and time span is Anette Reenberg. In this paper we explore her studies of the Sahel published in peer-reviewed journals and their impact over the last three decades. Reenberg has had a remarkably stable theoretical agenda concerned with the importance of understanding the social and biophysical systems as one coupled human-environmental system. This agenda has influenced contemporary as well as subsequent Danish scholars publishing on the Sahel. Taking papers published in Geografisk Tidsskrift-Danish Journal of Geography as an example we show how scholars have moved from treating aspects of the Sahelian droughts according to the traditional natural-social science divide towards a much more coupled manner. This rise of the coupled human-environmental system framework in the journal may be attributed to Reenberg’s theoretical agenda as well as a new international stream of research joining the human and environmental sciences in an interdisciplinary effort. Hence, it is also shown how Reenberg’s theoretical agenda have influenced scholars trying to grasp contemporary global change. This is especially evident in the land science community.     

The Rhodes/HartRAO 2326-MHz radio continuum survey

We have made scanning observations with the HartRAO 26-m radio telescope to obtain a pencil-beam map of 67 per cent of the sky at 2326 MHz. This is the highest resolution and highest frequency radio continuum map of this type made of such a large area of sky.   In this paper we describe the observations and data reduction procedures used to produce the survey. The resulting map has an angular resolution (HPBW) of 20 arcmin, and the rms pointing accuracy is 1.2 arcmin. The rms noise fluctuations are less than 30-mK T _FB over the whole map. We estimate that the uncertainty in the temperature scale is less than 5 per cent, and that the error in the absolute zero level is better than 80-mK T _FB in any direction.   High-contrast half-tone images of the data with a model of the diffuse galactic background subtracted are presented. These images show many complex emission structures up to and beyond 50° latitude, and illustrate the quality of the data. Extracts from the survey data are available via FTP by arrangement with the authors.     

Adaptation to climate change impacts on urban storm water: a case study in Arvika, Sweden

Already today, the functionality of many sewer and storm water systems are not up to the required standards and consequently flooding problems are experienced in case of heavy storms. System upgrades are required, which are however complicated by the expected future increase in short-term rainfall intensities as a result of climate change. In this case study, focusing on the town of Arvika, Sweden, this issue is investigated in three main steps. In the first, extreme value analyses of 30-min rainfall from an ensemble of climate projections are carried out to estimate the future increase and generate a future design storm. In the second, the existing system’s response to both today’s and future design storms are simulated by a coarse sewer model setup (MOUSE) and a detailed coupled surface-sewer model setup (TSR). In the third and final step, system upgrades are designed and evaluated by both models. The results indicate an increase by 10–30 % of today’s short-term rainfall extremes by the end of the century. Upgrading the system to achieve a satisfactory performance for the future design storm would cost approximately twice as much as an upgrade based on today’s design storm.     

On the Gas Phase Reactions Between Volatile Biogenic Mercury Species and the Nitrate Radical

Tropospheric mercury is dominated by gas phase species. In this paper, the gas phase reactions between the nitrate radical and volatile biogenic mercury species have been investigated. An upper limit for the gas phase rate coefficient for reaction between elemental mercury and NO₃-radicals was determined to 4 × 10^–15 cm³ molecule^–1 s^–1 by using the fast flow-discharge technique. The reaction between dimethyl mercury and NO₃, previously shown to be rapid, has also been studied in the laboratory with respect to product distribution using FT-IR. The result from the product study is consistent with a transformation of dimethyl mercury into inorganic, divalent mercury. All carbon delivered as dimethyl mercury was transformed into formaldehyde, methanol and methyl peroxynitrate. Hg was observed as a minor (2%) product. By exclusion, HgO is proposed as the mercury-containing product. Thus, the reaction between dimethyl mercury and the nitrate radical is excluded as a source of monomethyl mercury species in the atmosphere.     

Estimation of the Lagrangian Velocity Structure Function Constant C0 by Large-Eddy Simulation

The inertial subrange Kolmogorov constant C ₀, which determines the effective turbulent diffusion in velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C ₀ by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian velocity structure function in the inertial subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C ₀ is C ₀=4.3±0.3 consistent with values found in the literature     

Bifurcation analysis of 3D ocean flows using a parallel fully-implicit ocean model

To understand the physics and dynamics of the ocean circulation, techniques of numerical bifurcation theory such as continuation methods have proved to be useful. Up to now these techniques have been applied to models with relatively few degrees of freedom such as multi-layer quasi-geostrophic and shallow-water models and relatively low-resolution (e.g., 4° horizontal resolution) primitive equation models. In this paper, we present a new approach in which continuation methods are combined with parallel numerical linear system solvers. With this implementation, we show that it is possible to compute steady states versus parameters (and perform fully implicit time integration) of primitive equation ocean models with up to a few million degrees of freedom.