Detection of a significant change in the solar diameter

Drift-time measurements of the solar diameter made at Izaña and Locarno in 1990–1992 show a significant increase of the observed angular semidiameter when compared to results obtained at the same two sites in 1981. The observed increase of 0.4 is not due to a systematic (or long-term) variation, but seems to reflect a more complicated behaviour with time: As both series of measurements were made around a maximum of the 11-year cycle, it seems that a variation in phase with solar activity (in the sense of the Secchi-Rosa law) can be ruled out.     

A SF6 tracer study of horizontal mixing in Lake Constance

Horizontal mixing processes in the hypolimnion of the western part of Lake Constance are studied by measuring the dispersion of a sulfur hexafluoride (SF₆) tracer plume. Only 1 liter gaseous SF₆ (STP) was released at a central hypolimnic depth of 60 m in August 1990. Over a period of 3 months the horizontal dispersion of the tracer plume was measured by 19 surveys using a new, vertically integrating sampling device. The observed horizontal dispersion is marked by strong storm-induced stirring events. Nevertheless mean turbulent diffusion coefficients for the whole period can be computed. They rise about linear from 0.7 10⁵ cm²/s to 3.0 10⁵ cm²/s with the distance from the western end of the lake. For the hypolimnion of Überlingersee, a sill-separated basin in the western part of Lake Constance, a simple budget model gives an exchange time of 67 ± 6 days with the main basin (Obersee).     

Reproductive characteristics of invasive gammarids in the Rhine-Main-Danube catchment, South Germany

The gammarid composition at 25 sites in the rivers Danube, Main and the southern reaches of the Rhine were studied during the years 2002–2004. Dikerogammarus villosus and Echinogammarus ischnus were the most frequent species prevailing at 17 sites. Sympatric occurrence of D. villosus and E. ischnus was observed at 12 sites. Dikerogammarus haemobaphes was recorded at 7 sites; this species prevailed in the Danube, west of the Weltenburger Enge and in the Isar mouth where it co-existed with native species (Gammarus pulex and/or G. roeseli) at 6 sites. Dikerogammarus bispinosus and E. berilloni were found at only 1 site, where they co-existed with D. villosus and E. ischnus, and with D. villosus and native species, respectively. Investigation of reproductive characteristics at 3 sites showed that females of D. villosus and D. haemobaphes produced the biggest clutches with more than 100 eggs. Females of E. ischnus produced much smaller clutches (10–35 eggs on an average), but very big eggs. Clutch sizes and egg volumes of D. bispinosus and E. berilloni resembled those of native species. Our results suggest that the most successful invaders (D. villosus, D. haemobaphes and E. ischnus) display reproductive traits that facilitate their success. Both Dikerogammarus sp. allocate energy into production of many but small eggs, thus maximizing offspring number, while E. ischnus allocates its energy into production of fewer but large eggs which could be beneficial at sites where food is scarce.     

Coalbed methane in the Ruhr Basin, Germany: a renewable energy resource?

Around the globe underground hard coal mining leads to a release of methane into the atmosphere. About 7% of the global annual methane emissions originate from coal mining. In the year 2002, 16 countries used coal gas to generate heat and electricity. In many cases, the exact size of coalbed methane reservoirs is not identified. The possibility of a long-term gas production and its profitability at single sites are unknown. To clarify these points, the processes of gas generation as well as the gas-in-place volume have to be determined. Both issues are tackled here for the Ruhr basin. Within this basin, coal gas samples were taken at 13 gas production sites, spread over three samplings within 14 months. There were virtually no changes in the concentrations of gas components at single sites within this period. The isotope composition of methane (δ¹³C-methane: −40.0 to −57.3‰ vs. PDB) revealed that the produced methane is a mixture of gases of thermogenic and microbial origin. The microbial contribution of methane seems to be more pronounced at sites of active and especially abandoned coal mining than at unmined places. Ethane and propane are of thermogenic origin, with ethane's isotopic composition tending to heavier values (richer in ¹³C) with time. This time-dependent phenomenon is interpreted as being caused by desorption. In addition, living methanogenic archaea were detected in mine water samples from depths down to 1200 m.