Lake In Northeastern Germany Research Articles

A gynandromorphic specimen of Oecetis ochracea (Curtis, 1825) from Germany (Trichoptera: Leptoceridae)

A gynandromorphous individual of caddisfly Oecetis ochracea (Curtis, 1825) is described and imaged by scanning electron microscopy. The animal was collected from a lake in Northeastern Germany in 2001. The appearances of abnormality were visible at the head, wings and the posterior abdominal segments.

Methanogenic Pathway and Archaeal Community Structure in the Sediment of Eutrophic Lake Dagow: Effect of Temperature

Methanogenic degradation of organic matter is an important microbial process in lake sediments. Temperature may affect not only the rate but also the pathway of CH4 production by changing the activity and the abundance of individual microorganisms. Therefore, we studied the function and structure of a methanogenic community in anoxic sediment of Lake Dagow, a eutrophic lake in north-eastern Germany. Incubation of sediment samples (in situ 7.5 degrees C) at increasing temperatures (4, 10, 15, 25, 30 degrees C) resulted in increasing production rates of CH4 and CO2 and in increasing steady-state concentrations of H2. Thermodynamic conditions for H2/CO2 -dependent methanogenesis were only exergonic at 25 and 30 degrees C. Inhibition of methanogenesis with chloroform resulted in the accumulation of methanogenic precursors, i.e., acetate, propionate, and isobutyrate. Mass balance calculations indicated that less CH4 was formed via H2 at 4 degrees C than at 30 degrees C. Conversion of 14CO2 to 14CH4 also showed that H2/CO2 -dependent methanogenesis contributed less to total CH4 production at 4 degrees C than at 30 degrees C. [2-14 C]Acetate turnover rates at 4 degrees C accounted for a higher percentage of total CH4 production than at 30 degrees C. Collectively, these results showed a higher contribution of H2-dependent methanogenesis and a lower contribution of acetate-dependent methanogenesis at high versus low temperature. The archaeal community was characterized by cloning, sequencing, and phylogenetic analysis of the 16S rRNA genes retrieved from the sediment. Sequences were affiliated with Methanosaetaceae, Methanomicrobiaceae, and three deeply branching euryarchaeotal clusters, i.e., group III, Rice cluster V, and a novel euryarchaeotal cluster, the LDS cluster. Terminal restriction fragment length polymorphism (T-RFLP) analysis showed that 16S rRNA genes affiliated to Methanosaetaceae (20-30%), Methanomicrobiaceae (35-55%), and group III (10-25%) contributed most to the archaeal community. Incubation of the sediment at different temperatures (4-30 degrees C) did not result in a systematic change of the archaeal community composition, indicating that change of temperature primarily affected the activity rather than the structure of the methanogenic community.

Bacterial activities in shallow lakes – a comparison between extremely acidic and alkaline eutrophic hard water lakes

Bacterial abundance and activity were investigated by DAPI-staining and 3H-thymidine incorporation method in samples from a very shallow, hypertrophic hard water lake and from acidic mining lakes in north-eastern Germany. Bacterial cell numbers in the acidic lakes were about one order of magnitude less than in the hypertrophic natural lake but are probably underestimated due to methodological problems. Bacterial activity in the shallow acidic mining lakes was high and comparable with that of hypertrophic hard water lakes. By application of microautoradiography, we checked whether these high thymidine uptake rates in acidic waters were caused by artefacts due to the complex chemistry. It was shown by this qualitative analysis that in addition to small cocci and rods, large filamentous bacteria in the shallow acidic lakes also contribute to the high thymidine uptake. We observed clearly lower bacterial activities in deep and dimictic acidic mining lakes. This phenomenon cannot be explained by the trophic state alone. It is assumed that shallowness in combination with the groundwater input, intense sediment–water interaction, the poor zooplankton colonization and photolytic processes favours the development of large bacterial cells with high specific activity in shallow acidic mining lakes.

Loss of Submerged Macrophytes in Shallow Lakes in North-Eastern Germany

During the 1950s, the submerged vegetation of shallow lakes in north-eastern Germany was dominated by nutrient tolerant species, with Ceratophyllum demersum and Myriophyllum sp. being most common. Almost one third of 300 investigated lakes had already lost their submerged macrophytes at that time. Very shallow lakes showed either high or low macrophyte abundance. Increasing depth resulted in medium macrophyte abundances, which may contribute to the stabilisation of local or temporary clearwater states. Forty years later, the percentage of lakes without macrophytes had dramatically increased. Between 55 and 85% of the investigated lakes showed a low abundance. The decline was most pronounced in very shallow lakes. The majority of the investigated lakes showed summer TP concentrations below 100 μg L–1, but no colonisation by submerged macrophytes, which indicates a resilience against re-colonisation.

Two-dimensional small-scale variability of pore water phosphate in freshwater lakes: results from a novel dialysis sampler.

Vertical concentration profiles of soluble reactive phosphorus (SRP) in the upper sedimentary zone of freshwater lakes are an important means for studying internal phosphorus (P) loading and to gain insight into early diagenetic processes. The interpretation of such pore water profiles generally neglects the occurrence of horizontal variability at a specific sampling site. To further examine this variability, we have designed a novel two-dimensional sampler (2D peeper) consisting of 2280 chambers at a spatial resolution of 9 mm providing a sampling area of 43 x 44 cm. This new device was deployed in three eutrophic lakes in north-eastern Germany. The resulting 2D images of the SRP concentrations, diffusive fluxes, and turnover rates revealed systematic vertical and horizontal structures with local niches of increased phosphorus release. Thus, the extrapolation of P flux calculations based on one-dimensional pore water profiles may lead to a considerable error. The observed small-scale horizontal heterogeneity, probably mainly caused by organisms, was larger in the biologically more active Lake Müllrose and Süsser See than in the deeper Arendsee where meio- and macrozoobenthos were missing. In all cases, the variability was highest at the sediment-water interface and diminished with sediment depth.