A. Reineking

Effects of earthworms and organic litter distribution on plant performance and aphid reproduction

Human management practices and large detritivores such as earthworms incorporate plant litter into the soil, thereby forming a heterogeneous soil environment from which plant roots extract nutrients. In a greenhouse experiment we investigated effects of earthworms and spatial distribution of 15N-labelled grass litter on plants of different functional groups [Lolium perenne (grass), Plantago lanceolata (forb), Trifolium repens (legume)]. Earthworms enhanced shoot and root growth in L. perenne and P. lanceolata and N uptake from organic litter and soil in all plant species. Litter concentrated in a patch (compared with litter mixed homogeneously into the soil) increased shoot biomass and 15N uptake from the litter in L. perenne and enhanced root proliferation in P. lanceolata when earthworms were present. Growth of clover (T. repens) was rather independent of the presence of earthworms and organic litter distribution: nevertheless, clover took up more nitrogen in the presence of earthworms and exploited more 15N from the added litter than the other plant species. The magnitude of the effects of earthworms and organic litter distribution differed between the plant species, indicating different responses of plants with contrasting root morphology. Aphid (Myzus persicae) reproduction was reduced on P. lanceolata in the presence of earthworms. We suggest that earthworm activity may indirectly alter plant chemistry and hence defence mechanisms against herbivores.

Daily variation of the radon concentration indoors and outdoors and the influence of meteorological parameters

Series of continuous radon measurements in the open atmosphere and in a dwelling, including the parallel measurement of meteorological parameters, were performed over a period of several weeks. The radon concentration in indoor and outdoor air depends on meteorological conditions. In the open atmosphere the radon concentration varies between 1 and 100 Bq m-3, depending on weather conditions and time of day. During time periods of low turbulent air exchange (high pressure weather with clear night sky), especially in the night and early morning hours (night inversion layer), the diurnal variation of the radon concentration showed a pronounced maximum. Cloudy and windy weather conditions yield a small diurnal variation of the radon concentration. Indoors, the average level and the diurnal variation of the indoor radon concentration is also influenced by meteorological conditions. The measurements are consistent with a dependence of indoor radon concentrations on indoor-outdoor pressure differences.

Diurnal variation of the concentrations of radon and its short-lived daughters in the atmosphere near the ground

Abstract The continuous measurement of radon ( 222 Rn) and radon daughters (RaA( 218 Po), RaB( 214 Pb), RaC ( 214 Bi)) concentrations and meteorological parameters (temperature, wind velocity) is carried out simultaneously at different heights of the boundary layer near ground level (0.1, 1, 2 and 5 m above the ground) over a long time period with the aim of determining the change of the eddy diffusivity near ground level during a day under different weather conditions. The results show the great variation of the activity concentration of radon and radon daughters during a day (up to a factor of 20) depending on weather conditions. The temperature gradient appears to provide a good indication of which eddy diffusivity most closely represents the mixing strength in the atmosphere. The change of the equilibrium values between radon and its daughters during a day were used to calculate the diurnal variation of the eddy diffusivity.

The use of the natural radioactive noble gases radon and thoron as tracers for the study of turbulent exchange in the atmospheric boundary layer—Case study in and above a wheat field

The application of the radioactive noble gases radon (222Rn) and thoron (220Rn) as naturally occurring tracer elements for the measurement of turbulent transport in the atmosphere has been studied in a flat river valley in the vicinity of Gottingen. The measuring site was covered with a crop of wheat. The vertical distribution of radon and thoron was measured continuously over the complete vegetation cycle of the crop. A strong dependence of activity concentrations on meteorological conditions could be observed, yielding during up to 50-times higher night maxima of activity concentrations compared to the noon mimima. Eddy diffusivities were calculated for two height intervals inside and above the crop using a combination of thoron and radon data. A comparison with eddy diffusivities obtained above the crop from meteorological data yielded good agreement between both approaches. The tracer method showed, especially inside the crop, where meteorological methods fall short, the best results, caused by the large concentration gradient due to low vertical exchange.

An Online α-Impactor for Short-Lived Radon Daughters

A low-pressure cascade impactor was developed for continuous measurements of the size distributions of aerosol-attached radon and thoron decay products under environmental conditions. The emitted α-particles of the size fractionated activities are registered during air sampling with surface barrier detectors (active area = 2000 mm2) with an energy resolution < 6% (FWHM). The impactor consists of nine stages and back-up filters and operates at a flow rate of 5.1 m3 /h. The 50% cutoff diameters range between 65 and 15,530 nm. The detection limit for the short-lived radon daughters is ∼ 2 Bq/m3 for a sampling time of 1 h and a statistical error of 10%. To minimize energy losses of the ∼-particles and blow-off effects the sampling units are rotatable.