Managing land-use effects on Northland dune lakes: lessons from the past

The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation.     

The HI halo of spiral galaxies

A deep H I survey with the VLA of the spiral galaxy NGC 2403 has revealed the existence of a thick, low density layer of neutral gas surrounding the thin ‘cold’ disk. This layer has a mean rotation velocity 25–50 km s^-1 lower than that of the disk and a 10–20 km s^-1inflow towards the centre of the galaxy. In the central parts there are velocity differences from rotation of up to 150 km s^-1.Chandra observations of NGC 2403 show a diffuse, hot X-ray emitting gas component with a temperature of a few 10⁶ K. These results point at galactic fountain type of flows between disk and halo. ‘Halo’ gas with similar characteristics has also been observed in other spiral galaxies(e.g. NGC 6946, NGC 891). Such gas is probably similar to the IVCs and to some of the HVCs of the Milky Way.     

Diurnal photometric conditions at Teide observatory and long-term solar irradiance variations

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively.     

Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review

An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.